Chemical Reactions and Uses of Carboxylic Acids...Carboxylic acids undergo decomposition reaction...

Chemical Reactions and Uses of Carboxylic Acids

All of us have come across the word fatty acids. What are those? They

are members of the group carboxylic acids. Fatty acids are the higher

members, from C12-C18, of aliphatic carboxylic acids found in

natural fats in the form of esters of glycerol. A carboxylic group is

nothing but a carbon compound containing a carbonyl group along

with a carboxyl group, hence the name carboxylic acids. Carboxylic

are widespread in nature. Moreover, it is the precursor for many

essential organic compounds such as acid chlorides, esters,

anhydrides, amides, etc.

Carboxyl Group

A carboxyl group (COOH) comprises a carbonyl group (>C=O) and a

hydroxyl group (−OH). Carboxylic acids can easily release protons

and thus, demonstrate the acidic behaviour. Carboxyl group acts as the

functional group part of carboxylic acids. Carboxylic acids can be

either aliphatic or aromatic in nature depending on alkyl or aryl group

present with the carboxylic carbon.

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Browse more Topics Under Aldehydes Ketones Carboxylic Acids

● Chemical Reactions and Uses of Carboxylic Acids

● Methods of Preparation of Carboxylic Acids

● Nomenclature and Structure of Carbonyl Group

● Nomenclature and Structure of Carboxyl Group

● Nucleophilic Addition Reaction

● Oxidation

● Physical properties of Aldehydes, Ketones and Carboxylic

Acids

● Preparation of Aldehydes

● Preparation of Aldehydes and Ketones

● Preparation of Ketones

● Reactions due to Alpha-Hydrogen

● Reduction

● Uses of Aldehydes and Ketones

Acidic Property of Carboxylic Acids

Carboxylic Acids are weaker than sulphonic acids and mineral acids.

Mineral acids include H2SO4, HNO3, HCl. However, carboxylic acids

are stronger in comparison to phenols and alcohols.

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Comparison of Strength of Carboxylic acids with Alcohols

Carboxylic Acids are stronger acids in comparison to alcohols. The

reason for such a behaviour is the conjugate base of the carboxylic

acids achieves stabilization by resonance. In this case, the conjugate

base, the product remaining after hydrogen removal from the

conjugate base, will be carboxylate ion.

However, carboxylate ion stabilization is possible by resonance.

Therefore, it becomes easy for carboxylic acids to release a proton

thereby readily forming a carboxylate ion.

However, in case of alcohols, the alkoxide ion (conjugate base of

alcohol group) cannot readily achieve a resonance stabilized structure.

Thus, it is less stable. Therefore, we can say that alkoxide ion cannot

easily release proton for forming a less stable conjugate base. Hence,

alcohol is less acidic.

Comparisons of Acidic Behavior of Carboxylic Acids and Phenols

Carboxylic Acids are more acidic than phenol. In case of phenols,

phenoxide ion or C6H5O− act as the conjugate base of phenol. The

resonance structure of a phenoxide ion will be

From the third, fourth and fifth resonance structure, we can notice that

the less electronegative carbon atom bears the negative charge. Hence,

it does not help in resonance stabilization of phenoxide ion. Thus, the

contribution of these structures can be neglected.

Therefore, if we compare the first and second structure of phenoxide

ion with a carboxylate ion, the negative charge present on the oxygen

atom of the phenoxide ion undergoes localization, that is it remains in

the same oxygen atom. However, the carboxylate ion undergoes

delocalization of the negative charge. Hence, the carboxylate ion

becomes more resonance stabilized. Therefore, carboxylic acids are

stronger in nature than phenols.

Substitution Effect on the Acidic Property of Carboxylic Acids

The “I groups” or the electron attracting groups is responsible for

increasing the acidity of carboxylic acids. The increasing order of

electron attracting group with respect to −I-effect are

+I Group or Electron Releasing Group is responsible for decreasing

the acidity of carboxylic acids. The increasing order with respect to +I

Effect is

Ortho Effect on Carboxylic Acids

The benzoic acids with ortho substitution demonstrate more acidic

property than the normal benzoic acid regardless of the nature of the

substituent group, whether the substituent is electron withdrawing or

electron donating group. For instance, o-toluic acid exhibit more

acidic property in comparison to benzoic acid. Let us study the

ortho-effect in one such compound.

Ortho-Effect in the Compound “Aminobenzoic Acid”

An amino group exhibit weaker –I effect but it demonstrates a

stronger +R effect. This is the reason amino acids exhibit less acidic

property than benzoic acids. In fact, o-aminobenzoic acid has lesser

acidic property in comparison to benzoic acid. Now we have to

understand the reason behind such a behaviour.

We know that –COOH group exhibit acidic nature whereas –NH2

exhibit basic nature. Therefore, the nitrogen present in the amino

group will develop a bond with hydrogen present in the carboxyl

group. This, in turn, will lead to the formation of a zwitterion. A

zwitterion is a neutral molecule which contains both positive as well

as negative charges.

Therefore, the ortho-effect will gradually be reduced to an extent

where the compound will become weaker than a benzoic acid.

Chemical Reactions of Carboxylic Acid

The carboxylic acid (carbon compound containing carboxyl group)

will undergo a number of chemical reactions. Let us study one by one.

Reaction with Metals

The reaction of carboxylic acids with metals such as K, Na, Mg, Ca

leads to the formation of the corresponding salts. In the reaction

process, a proton will be released from the carboxyl group of the

carboxylic acid where the metal substation will occur. The reaction

liberates H2 gas.

Reaction with Alkalies

The reaction of carboxylic acids with alkalies will lead to the

formation of corresponding salts and water.

Reaction with Carbonates and Bicarbonates

Carboxylic acids undergo decomposition reaction with carbonates and

bicarbonates leading to the formation of respective salts, water, and

carbon dioxide gas.

This reaction can also help in testing the presence of carboxyl group.

Carboxylic acids undergo reaction with a saturated solution of sodium

bicarbonate produce effervescence due to the release of CO2 gas.

However, most phenols do not release effervescence with an aqueous

NaHCO3 solution. Thus the reaction of bicarbonate with carboxylic

acids helps in distinguishing between phenols and carboxylic acids.

Acid Chlorides Formation

Carboxylic Acids react with thionyl chloride (SOCl2), Phosphorus

pentachloride (PCl5), or Phosphorus pentachloride to form the

respective acid chlorides. Refer below to understand the reaction.

Formation of Esters (Esterification)

Warming carboxylic acids with alcohols in the presence of a

concentrated sulphuric acid or dry hydrochloric acid produces esters

having a fruity smell.

In this reaction concentrated sulphuric acid act as the dehydrating

agent. The reaction is an example of an equilibrium reaction. Hence,

the ester is distilled to continue shifting the reaction in the forward

direction.

Formation of Amide Compounds

Treatment of carboxylic acids with ammonia thereby forming

ammonium salts. Ammonium salts further upon heating lose a water

molecule leading to the formation of amides.

Decarboxylation

Distillation of soda lime (NaOH + CaO) with sodium salts of

carboxylic acids result in decarboxylation reaction thereby forming

alkanes.

Formation of Anhydrides

Two molecules of carboxylic Acids undergo heating with a

dehydrating agent like phosphorus pentoxide leading to the formation

of acid anhydrides.

HVZ Reaction or Hell-Volhard Zelinsky Reaction

Carboxylic Acids react with chlorine molecule (Cl2) or bromine

molecule (Br2) to form α-substituted carboxylic acids. The reaction

takes place in the presence of red phosphorus. This reaction refers to

as H.V.Z reaction or Hell-Volhard Zelinsky Reaction.

Formic Acid does not undergo this reaction because it does not

contain alkyl group. It is important to note that bromination will only

take place at the α-position. Moreover, the reaction will cease after

replacement of all the α-hydrogens by the bromine atoms. However,

chlorination will occur initially at the α-position and the replacement

will occur in hydrogen atom by chlorine atoms then the replacement

will move further along the chain.

Electrophilic Substitution Reactions

Aromatic carboxylic acids undergo different types of electrophilic

substitution reaction like nitration, sulphonation, and halogenation.

Carboxyl group (-COOH) is electron withdrawing group. Thus, the

reaction will occur at the meta-position. The carboxyl group

deactivates. Therefore, the reaction will only occur under vigorous

conditions.

Friedel Crafts Reactions

This group will not undergo Friedel-Crafts Reactions because the

carboxyl group is strong electron attracting group. Thus, benzene ring

will be deactivated. Hence, it will not undergo alkylation and

acylation.

Uses of Carboxylic Acids

● Carboxylic acid acts as a disinfectant.

● Simplest carboxylic acid “formic acid” acts as reducing agent

in textile treatments.

● Acetic acid, member of the carboxylic acid group, helps in the

production of esters and cellulose plastics.

● Acetic acid acts as the precursor for the formation of an ester of

salicylic acid which is used for aspirin production.

● Palmitic acid and stearic acid finds its use in the manufacturing

of soaps, pharmaceuticals, candles, cosmetics, protective

coating, etc.

● Stearic acid also helps in rubber manufacturing processes.

● Acrylic acid acts as an ester and helps in the production of

polymers or acrylates. Similarly, methacrylic acid undergoes

polymerization to form Lucite.

● Moreover, oleic acid, a type of carboxylic acids, helps in

manufacturing soaps and detergents. Additionally, it is also

used in textiles.

Solved Examples for You

Question: Identify the carboxylic acid having the highest boiling

point.

1. Hexanoic Acid

2. Heptanoic Acid

3. Nonanoic Acid

4. Decanoic Acid

Solution: Option 4 (Decanoic Acid). Intermolecular forces of

molecules affect the boiling point of a solution. Thus, the ability of

remain together increases with the increase in the intermolecular

forces. Therefore, more energy is needed to break the compounds. In

the above question, every option contains carboxyl functional group.

Thus, every option has hydrogen bonds. However, the major

difference is in the number of carbons present in the chain. With the

increase in the number of carbons, the molecular weight increases

thereby increasing the Van Der Walls molecular forces. Therefore,

this will further increase the heat energy required for breaking the

bond.

Among all the options, decanoic acid has longest carbon chain. Hence,

it will require more energy to break the bond and separate the

molecules. Thus, the decanoic acid will have the highest boiling point.

Methods of Preparation of Carboxylic Acids

Carboxylic Acids are one of the imperative organic compounds found

in a wide variety of living things. The Carboxylic Acid is part of the

amino acids and amino acids are the building block of proteins. We all

have heard about vinegar. Do you know that acetic acid, one of the

type carboxylic acids, is responsible for the formation of vinegar?

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● Oxidation


Acids




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● Reduction


Thus, carboxylic acid occurs in metabolism. Few examples which

contain carboxylic acid include coconut oil, butter, peanut oil, citrus

fruits, etc. Now, how this group of organic compounds is prepared?

Let us study the preparation method of carboxylic acid in detail in this

topic.

Carboxylic Acids

It is a group of an organic compound containing a carboxylic group

(C(=O)OH). Carboxylic acid contains a carbonyl group to which the

hydroxyl is attached. The general formula of the group is R-COOH. In

the formula, R denotes the rest of the group attached to the functional

group. The structure of carboxylic acid is

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Structure of Carboxylic Acid (Source Credit: Wikipedia)

Methods of Preparation of Carboxylic Acids

The primary preparation technique involves oxidation of different

types of functional groups. Let us go through the important

preparation technique.

Preparation from Primary Alcohols

Primary alcohols, as well as aldehydes, can undergo oxidation reaction

to form corresponding carboxylic acids with the help of oxidizing

agents such as potassium permanganate (KMnO4 for neutral or acidic

or alkaline media), chromium trioxide (CrO3– H2SO4– Jones reagent),

and potassium dichromate (K2Cr2O7– acidic media).

Primary alcohol undergoes oxidation to produce carboxylic acid on

the addition of the oxidizing agents. Therefore, the oxidation of

primary alcohols produces aldehydes which further repeat the

oxidation to produce carboxylic acids. The strong oxidizing agents

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including potassium dichromate, potassium permanganate, and

chromium trioxide can readily oxidize the aldehyde to form carboxylic

acids.

However, mild oxidizing agents can only undergo one step and

convert the primary alcohols into aldehydes. Example of mild

oxidizing agents includes manganese dioxide (MnO2) and Tollen’s

reagent [Ag(NH3)2+ OH−]. Hence, they are not strong enough to

undergo oxidation twice. Therefore, the mild oxidizing agents are used

for converting aldehydes into carboxylic acids.

It is important to remember that acidified oxidizing agents like

potassium dichromate and Jones reagent lead to the formation of

esters in a small amount. Therefore, it is preferable to use neutral or

alkaline agents such as potassium permanganate for this preparation

method.

Preparation from Aldehydes

As discussed in the above topic, Preparation of carboxylic acid is

possible from the usual strong oxidizing agents. Carboxylic acids

formation is possible with mild oxidizing agents such as Tollen’s

reagents [Ag(NH 3) 2 +OH −] and manganese dioxide (MnO2).

Preparation from Alkylbenzenes

Aromatic carboxylic acid preparation is possible through the oxidation

of alkylbenzenes. Vigorous oxidation of alkyl benzene compound with

acidic or alkaline potassium permanganate or chromic acid can lead to

the formation of aromatic carboxylic acid compounds. The oxidation

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of complete side chain of the carboxyl group takes place regardless of

the side chain length.

The resulting side products of the reaction vary depending on the

primary or secondary alkyl groups. However, the tertiary alkyl group

is not affected. Moreover, properly substituted alkenes can also

undergo oxidation process to form carboxylic acids with the help of

these oxidizing agents. Refer to the example below for the reactions

under this preparation technique.

Preparation from Nitriles

Nitriles undergo hydrolysis to form amides. The amides further

undergo reaction in the presence of a catalyst which then to form

carboxylic acids. The catalyst for this reaction is H+ or OH–.

Furthermore, application of mild reaction condition helps in ceasing

the reaction in the amide stage

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Preparation from Amides

Amide undergoes hydrolysis in the presence of catalyst H+ or OH– to

form carboxylic acids.

Preparation from Grignard Reagents

The carboxylic acid formation is possible by Grignard reagents

reaction. The reaction of Grignard reagents with crushed dry ice or

solid carbon dioxide leads to the formation of salts of carboxylic

acids. Further, the acidification of the salts of a carboxylic acid with

mineral acids leads to the formation of corresponding carboxylic

acids.

Thus, preparation of Grignard reagents and nitriles is possible from

alkyl halides. The preparation techniques help in the conversion of

alkyl halides into the respective carboxylic acids. The resultant

carboxylic acid will always have one carbon atom more than the

corresponding alkyl halides.f

Preparation from Acyl Halides and Anhydrides

Hydrolysis of acid chlorides with water produces carboxylic acids.

Additionally, acid chlorides can easily undergo hydrolysis with

aqueous base to produce carboxylate ions which undergo further

acidification to provide respective carboxylic acids. On the other hand,

anhydrides undergo hydrolysis with water to produce respective acid.

Thus, we can summarize

● Hydrolysis of acid chlorides with water to produce carboxylic

acids

● Acid chlorides undergo reaction with a base and further

acidification leads to carboxylic acid

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● Hydrolysis of acid anhydrides leads to carboxylic acids.

Carboxylic Acids from Esters

Acidic hydrolysis of esters leads to the formation of carboxylic acids.

However, hydrolysis of the base produces carboxylates followed by

acidification leads to the formation of corresponding carboxylic acids.

Furthermore, hydrolysis of esters is carried out with mineral acids or

alkali in order to produce a carboxylic acid.

Solved Example for You

Question: Explain Koch Reaction and its application.

Solution: Koch Reaction is used for the production of fatty acids. In

this process, heating of olefin takes place with CO and steam at the

temperature of 300-400 ° C and under pressure. The reaction occurs in

the presence of phosphoric acid that behaves as a catalyst during the

production of fatty acid. The reaction for this process is

CH2 = CH2 + CO + H2O → CH3 – CH2 – COOH

Nomenclature and Structure of Carbonyl Group

Do you know that the Carbonyl group is present in all type of organic

compounds such as carbohydrates, nucleic acids, fats, proteins,

vitamins, and hormones? These organic compounds are essential to

every living organism. Structure of aldehydes and ketones are

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responsible for the smell and taste of many different aromatic

compounds found in nature.

But do you know what is a carbonyl group, to begin with? If you

don’t, let us help you out. We will learn about the carbonyl group and

its nomenclature and structure below. Let’s start.







● Oxidation


Acids





● Reduction

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What is Carbonyl Group?

Aldehydes and Ketones fall into the category of simplest compounds

containing the carbonyl group. They are also essential types of

carbonyl compounds. A carbonyl group consists of carbon and oxygen

joined together by a double bond. The joining of carbonyl carbon is

with hydrogen on one side in aldehydes whereas the joining of two

carbon atoms on both the side of carbonyl carbon in the case of

ketones.

In a carbonyl group, the carbon and oxygen have sp2 hybridization

and is planar. Carbonyl group structure is “C=O” and members of this

group are carbonyl compounds (X-C=O).

Carbonyl Compound (Source: Wikipedia)

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The joining of the same carbonyl group to an oxygen atom on one side

forms carboxylic acid compounds. The derivatives of this class are

anhydrides, esters, etc. If the attachment of the carbonyl group is to

nitrogen then the class of compounds is amides. Similarly, the joining

of the carbonyl group to the members of halogen group forms acyl

halide compounds. Refer to the table below to study the structure and

general formula of different members of the carbonyl groups.

Members of Carbonyl Group (Source: Wikipedia)

Nomenclature of Aldehydes and Ketones

Common Name

Common names are often used for referring to an aldehyde or ketone

instead of their respective IUPAC names. The common names of

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many aldehydes are taken from the common names of the respective

carboxylic acids by exchanging the end letters “–ic” with an aldehyde.

Mostly these names reflect corresponding Latin or Greek term of the

original source of the aldehyde compound or an acid compound.

We use letters such as α, β, γ, and δ, and so on to indicate the location

of the substituent present in the carbon chain. The α-carbon is the one

to which the aldehyde group is attached. β- carbon is the carbon next

to the α-carbon, and so on.

The proper common naming of the ketone requires the naming of the

two alkyl or the aryl groups joined to the carbonyl group. Again, we

use α α′, β β′, etc to indicate the substituents location. The naming of

α α′ begins with the carbon atoms present next to the carbonyl group.

However, there are certain ketones that have historical common

names. These common names are in use to date such as we call the

simplest ketone “dimethyl ketone” as acetone. We name the Alkyl

phenyl ketones by the addition of acyl group as the prefix to the word

“phenone”.

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Examples of Ketones

IUPAC Names

The IUPAC naming of aliphatic aldehydes and aliphatic ketones is

comparatively easy. It is derived by taking the corresponding alkane

and replacing the end letter –e of the alkane with either –al or –one. In

case of aldehyde –al is written whereas in case of ketone –one is

written.

The numbering of the longest carbon chain in the case of aldehyde

begins from the carbon-containing the aldehyde group. However, in

case of ketones, the numbering starts from the side of

carbon-containing the carbonyl group.

Adding prefix in alphabetical order along with the numerals help in

indicating the positions of the substituents in the carbon chain. This is

same for cyclic ketones as well. In the case of cyclic ketones, the

numbering begins with the carbonyl carbon.

We have to add the suffix carbaldehyde after the complete name of the

cycloalkane in case the attachment is between an aldehyde group and

a ring. The numbering of the ring begins from the carbon atom that is

attached to the aldehyde group.

The nomenclature of the simplest aromatic aldehyde containing a

benzene ring along with an aldehyde group is benzenecarbaldehyde.

Moreover, IUPAC has also accepted the common name benzaldehyde.

Additionally, the naming of aromatic aldehyde is done as substituted

benzaldehydes.

Examples of Aldehydes

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Examples of Ketones

Structure of Carbonyl Group

The carbon atom present in the carbonyl group has an sp2

hybridization and it develops three sigma(σ) bonds. However, the

fourth valence electron of the carbon atom remains in the p-orbital.

Thus, it develops π-bond by overlapping with the oxygen from the

p-orbital of the oxygen atom. Additionally, the oxygen atom also

contains two non-bonded pairs of electrons.

Therefore, the carbonyl carbon along with its three attached atom lies

in the same plane. The cloud of π-electron is present below and above

the plane. The structure is a trigonal coplanar structure and the bond

angles are nearly 120°.

Polarization occurs in the carbon-oxygen bond due to the higher

electronegativity of the oxygen atom in comparison to the carbon

atom. Thus, the carbonyl carbon demonstrates the electrophilic

property of a Lewis acid whereas the carbonyl oxygen demonstrates

the electrophilic property of a Lewis base.

Carbonyl compounds contain significant dipole moments. Therefore,

it demonstrates more polarity than ethers. The high polarity of the

carbonyl group is mainly due to the resonance with respect to neutral

and dipolar structures.

Orbital Diagram for the Formation of Carbonyl Group

A Solved Question for You

Q. Give the structures of the compounds given below.

1. 3-Hydroxybutanal

2. α-Methoxypropionaldehyde

3. 2-Hydroxycyclopentane carbaldehyde

4. Di-sec-butyl ketone

5. 4-Oxopentanal

6. 4-Fluoroacetophenone

Solution:

1.

2.

3.

4.

5.

6.

Carboxyl Group: Carboxylic Acid, Definition, and Structure

Carboxyl group is defined as carbonyl and hydroxyl attached to a

carbon atom, which means carbon atom is double bonded with oxygen

and single bonded with the hydroxyl. And Carboxylic acid is organic

compound which consists of a carboxyl group. In this topic, we are

going to learn about the carboxyl group and carboxylic acid structure.

Let’s begin.

Carboxylic Acid

It is one of the very important classes of organic compounds. The

general formula of the class is R-C(O)OH. In this formula, R is the

alkyl or aryl group. Carboxylic acids occur widely in nature. However,

the majority of the members of this group is manufactured

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synthetically. The double bond presents in the structure of carboxylic

acids play a very important role in properties of the different

compounds of carboxylic acids. Refer to the diagram below.

Diagram of Carboxylic Acid (Source: Wikipedia)

When a carbon compound is attached to the functional group –COOH

(carboxyl group) then the compound refers to as carboxylic acids.

However, the formation of a carboxyl group is possible by the

attachment of a hydroxyl group to a carbonyl group, thus the name

“carboxyl group.” Carboxylic acids can be either aliphatic or aromatic

on the basis of the group present. If an alkyl group is present

(RCOOH) and if an aryl group is present (ArCOOH).

The higher members of the aliphatic carboxylic acids, from C12-C18,

are known as fatty acids. They are found in nature as natural fats or

esters of glycerol. Moreover, this group is the starting material for

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many essential organic compounds like esters, acid chlorides,

anhydrides, amides etc.

There are many natural compounds containing carboxylic acid. For

instance formic acid is present in insect sting, butyric acid is present in

butter, carbonic acid is present in the bicarbonate system of blood and

tissues, lauric acid is present in coconut oil, palmitic acid is present in

palm oil, arachidic acid is present in peanut oil, and stearic acid is

present in chocolate, waxes, soaps, and oils. In this topic, we will

discuss how the properties and structure of the carboxyl group affect

the properties of the compounds in the carboxylic acid group.

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● Oxidation


Acids


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● Reduction


Carboxylic acid structure

Carboxyl group is a functional organic compound. In this structure of

a carboxyl group, a carbon atom is attached to an oxygen atom with

the help of a double bond. It also has a single bond to a hydroxyl

group. Carboxylic acids are compound containing carboxyl structure.

There are many members in this class of organic acids such as acetic

acid and amino acid.

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Carboxyl group is generally present on the sides of the molecules. The

carboxyl group ionizes and releases the H atom present in the

hydroxyl group part as a free H+ ion or a proton. However, the rest of

part, this is O, convey a negative charge. The charge moves in

between the two oxygen molecules forward and backward thereby

making the state of ionization relatively steady.

3-D structure of Carboxyl Group (Source: Wikipedia)

Resonance Structure of Carboxylic Group

The bonds present in the carboxyl carbon lie in one plane in

carboxylic acids. The bonds angles of carboxyl carbon are

approximately 120°. The resonance structure of the carboxyl carbon

makes it less electrophilic in comparison to a carbonyl carbon.

Learn more about the Structure of Carbonyl Group.

Nomenclature of Carboxylic Acids

This class is among one of the earliest organic compounds that were

isolated from nature. This is the reason many of the compounds of this

class of compounds have common names more in use.

Common Names

The origin of the common names of many members of the carboxylic

acids group is from their respective Latin or Greek names of the

natural sources. The common names generally end with the suffix –ic

acid. For instance, HCOOH is formic acid. The origin of the name is

from the Latin word “formica” which means ant. The source of formic

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acid is red ants. Vinegar is the source of acetic acid (CH3COOH) and

the Latin word for vinegar is “acetum.” Similarly, rancid butter is the

source of butyric acid which in Latin refers to butyrum.

IUPAC Name

According to the IUPAC system, it is easy to name aliphatic

carboxylic acids by replacing the “e” of the respective alkane with

–oic acid. The numbering of the carbon atom chain in a carboxylic

acid starts with the carboxylic carbon. This means carboxylic carbon

will always be the first carbon in the parent chain.

It is important to number the alkyl chain if more than one carboxyl

group is present in a compound. You can indicate the number of

carboxylic acids present in the compound by addition of the

multiplicative prefix to the name of the parent alkyl chain such as

dicarboxylic acid, tricarboxylic acid, and so on. Additionally, it is

necessary to write the Arabic numerals prior to the multiplicative

prefix to indicate the position of –COOH groups in a particular

compound.

The simple members of this class of compound have names such as

methanoic acid, next is ethanoic acid, propanoic acid, butanoic acid

and so on. However, the nomenclature of aromatic carboxylic acids is

not usually is in the standard form. In fact, they have the special

IUPAC-approved special name such as benzoic acid.

Nomenclature of Carboxylic Acid

We can also name the compounds on the basis of the position and

alphabetical order to the subject compound.


If a particular compound contains more than one functional group, the

nomenclature is on the basis of carboxyl group instead of other

functional groups. Importance is given to Carboxylic group over other

functional groups. In the below example the name of the molecule is

carboxylic acid instead of alcohol.


By now we know that the carboxyl carbon atom will always be the

carbon-1 during the naming of a compound. Therefore, we do not

require to use a locant while naming the carboxyl group.

Learn more about the Nomenclature of Carbonyl Group.

Solved Question for You

Q. Name the common name and IUPAC name of the following

structures:

1. CH3(CH2)2COOH

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2. CH3(CH2)8 COOH

Solution:

1. The common name of CH3(CH2)2COOH is Butyric acid and

the IUPAC name is Butanoic Acid.

2. The common name of CH3(CH2)8COOH is Capric acid and the

IUPAC name is Decanoic Acid.

Nucleophilic addition reaction

The different reactions we learn in organic chemistry are not just

limited to books. If you delve a little you will get to know these

reactions happen in our common day to day life or it may be a part of

the processes living organisms undergoes. Similarly, different

nucleophile and the corresponding reactions help in the biological

synthesis of compounds in metabolic processes of living organisms.

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● Oxidation


Acids




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● Reduction


The reactions also form part of the pharmaceutical preparation

processes in industries and academia. The reaction helps in the

formation of new complex organic chemicals. Therefore, nucleophilic

addition reactions are central to organic chemistry.

Nucleophilic Addition Reactions

We will be able to convert multiple bonds into different functional

groups with the help of addition reactions. The reaction will help to

convert the unsaturated compounds to saturated and more functional

species. In this topic, we will go through a series of very important

reactions occurring due to nucleophilic addition reactions. Usually,

electrophilic addition reactions take place in an alkene. Contrary to

this, aldehydes and ketones undergo nucleophilic addition reaction.

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Mechanism of Nucleophilic Addition Reaction

We know that carbonyl carbon demonstrates sp2 hybridization and

together the structure is coplanar. A nucleophile acts on the polar

carbonyl’s electrophilic carbon atom perpendicular to the orbital

demonstration sp2 hybridization of the carbonyl carbon structure.

However, on the attack of the nucleophile, the hybridization of the

carbon atom changes from sp2 hybridization of sp3 hybridization

thereby forming tetrahedral alkoxide intermediate complex. This

intermediate complex will take a proton from reaction medium to

produce an electrically neutral compound. Hence, the reaction results

in the addition of nucleophile and hydrogen in the carbon-oxygen

double bond.

Aldehyde and ketones demonstrate polar nature. Moreover, these

compounds have a higher boiling point in comparison to

hydrocarbons. However, aldehydes and ketones have lower boiling

points in comparison to alcohols. The many reactions involving

aldehydes and ketones are sufficient for different synthesis reactions.

However, the majority of characteristics reactions of aldehydes and

ketones involve a nucleophilic addition to the carbonyl group. The

general equation of the aldehyde and ketone are

Reactivity of Aldehydes and Ketones

Aldehydes are more reactive and readily undergo nucleophilic

addition reactions in comparison to ketones. Aldehydes demonstrate

more favourable equilibrium constants for addition reactions than

ketones because of electronic and steric effect. In the case of ketones,

two large substituents are present in the structure of ketones which

causes steric hindrance when the nucleophile approaches the carbonyl

carbon.

However, aldehydes contain one substituent and thus the steric

hindrance to the approaching nucleophile is less. Moreover,

electronically aldehydes demonstrate better reactivity than ketone.

This is because ketones contain two alkyl groups which decrease the

electrophilicity of carbonyl carbon atom more than aldehydes.

The rate determining step with respect to base-catalyzed nucleophilic

addition reaction and acid-catalyzed nucleophilic addition reaction is

the step in which the nucleophile acts on the carbonyl carbon.

However, protonation process occurs in the carbonyl oxygen after

nucleophilic addition step in case of acid catalysis conditions. The

carbocation character of carbonyl structure increases due to

protonation and thus makes it more electrophilic. Various nucleophilic

addition and nucleophilic addition-elimination reactions are

Addition of Hydrogen Cyanide (HCN)

Aldehydes and ketones undergo reaction with HCN to produce

cyanohydrins. The reaction progresses very slowly by using pure

hydrogen cyanide. Hence, base as a catalyst helps to speed up the

reaction. This is because catalysis helps in the generation of cyanide

ion (CN) which acts as a stronger nucleophile and adds to carbonyl

compounds to produce the corresponding cyanohydrin. Cyanohydrins

are important synthetic intermediates.

Mechanism of the Reaction

Due to the electronegativity difference in carbon atoms and oxygen

atoms, the C=O bond demonstrates a polar behaviour. This, in turn,

results in gaining of partial negative charge on the oxygen atom and

partial positive charge on the carbon atom. The partial positive charge

of the carbon atom will attract the cyanide ion of H+CN−. The double

bond of C=O will break and a new C-CN bond development occurs.

Furthermore, the unstable oxygen will attract the H+ of Hydrogen

cyanide.

Addition of Sodium Hydrogen Sulphite

Addition of Sodium Hydrogen Sulphite to aldehydes and ketones will

result in the formation of the addition of products. The equilibrium

position of the reaction for aldehydes will be on the right-hand side

but the equilibrium position of the reaction for will be on the left-hand

side because of the steric effect.

The hydrogen sulphite compound form from the sodium hydrogen

sulphite addition is water soluble. Therefore, it can be converted back

to parent carbonyl compound by treatment of the compound with

dilute mineral acid or alkali. The reaction is also useful for the

purification and separation processes of aldehydes.

Addition of Alcohols

Aldehydes undergo reaction with the monohydric alcohol to produce

hemiacetals or alkoxyalcohol intermediate. The hemiacetal will

further undergo reaction with an alcohol to produce gem-dialkoxy

compound or acetal. The reaction is carried out in the presence of dry

hydrogen chloride. On application of similar conditions, ketone

undergoes reaction with ethylene glycol to produce cyclic compounds

or ethylene glycol ketals.

The dry hydrogen chloride present in the reaction protonates the

oxygen atom present in the carbonyl structure thereby increasing the

electrophilicity of the carbonyl carbon. Thus, it helps in the

nucleophilic attack of ethylene glycol. Further hydrolysis of acetals

and ketals with mineral acids (aqueous) will help in retrieval of

respective aldehydes and ketones.

Let’s see few examples of aldehydes and ketones and the resulting

acetals and ketals. Aldehyde reacts with dihydric alcohols

(ethane-1,2-diol) to produce cyclic acetals.

Similarly, ketones react with dihydric alcohols to produce cyclic

ketals. Dry HCl gas helps in shifting the equilibrium of the reaction to

the right-hand side. Furthermore, hydrolysis of acetals and ketals and

aqueous mineral acids help in retrieving the aldehydes and ketones.

Addition of Grignard Reagents

Grignard Reagents or R-MgX demonstrates polar nature. In this

compound, the carbon atom is electronegative in nature and the Mg

atom is electropositive in nature. The polar nature of the Grignard

Reagents helps the compound reacts with aldehydes and ketone to

produce additional products. The addition products undergo

decomposition reaction to give alcohol with water or dilute sulphuric

acid.

Necessary Points to Note in this Reaction

If Grignard Reagent reacts with formaldehyde (HCHO), the reaction

will form primary alcohol as the product.

If the reagent reacts with aldehydes other than HCHO, the reaction

will produce secondary alcohols.

Ketone reaction with the reagent will produce tertiary alcohols.

Addition of Ammonia and Derivatives

Many nucleophiles like ammonia and derivatives of ammonia

(H2N-Z) can also be added to the carbonyl group of aldehydes and

ketones. The reaction of ammonia and its derivatives is reversible and

the reaction happens in the presence of acid to form addition products.

The reaction equilibrium will help the product formation because of

fast dehydration of the intermediate complex. Thus, the reaction

finally forms the compound >C=N-Z. In the structure >C=N-Z, Z can

be alkyl, OH, aryl, NH2, NHCONH2, C6H5NH, etc.

Acid catalysts

Generally, we use weak acids as catalysts in the addition reaction of

aldehydes and ketones with ammonia and its derivatives. The carbonyl

group in aldehydes or ketone contains lone pair which reacts with

weak acids. Refer to the example below. The product formed in the

reaction will show resonance.

The resonance of the product will increase the positive charge on

carbonyl carbon. This makes the carbon prone to a nucleophile attack

thus favouring the reaction. However, the reaction is possible pH 4 to

5 only. Hence, the reaction is pH dependent.

The reason for a restricted pH is because if the pH is very low then the

ammonia derivative will form their respective salts due to their basic

nature and at the same time will lose their nucleophilic nature. If the

pH is high then the carbonyl group will not be able to undergo

sufficient protonation.

Few reactions with different derivatives of ammonia are given below

● NH2OH (hydroxylamine)

● NH2-NH2 (hydrazine)

● C6H5NHNH2 (phenylhydrazine)

● NH2CONH2 (Semicarbazide)

Hydroxylamine

Aldehydes and ketones undergo reaction with hydroxylamine

(NH2OH) and lead to the formation of oximes.

Hydrazine

Aldehydes and ketones undergo reaction with hydrazine (NH2−NH2)

thereby forming hydrazones. Additionally, aldehydes and ketones can

also undergo reaction with phenylhydrazines (C6H5NHNH2) to

produce phenylhydrazones.

2,4-DNP Test

This test can produce different precipitate depending on the basis of

compounds. Aldehydes and ketones can undergo reaction with

2,4-dinitrophenylhydrazine to form a yellow, orange or red precipitate.

This reaction helps to differentiate and identify aldehydes and ketones

from other compounds. The reaction is also known as 2,4-DNP test or

Brady’s test.

Aliphatic aldehydes and ketones produce yellow precipitate upon

reaction with 2,4-dinitrophenylhydrazine. We obtain red precipitate on

the reaction of aromatic aldehydes and ketones.

Semicarbazides

Aldehydes and ketones undergo reaction with semicarbazide

(NH2CONH2) to produce semicarbazones.


Question: Formaldehyde reacts with ammonia to give a white solid,

Hexamethylenetetramine (methenamine). Identify the correct formula

of Hexamethylenetetramine

1. (CH2)6N4

2. (CH2)3N3(NO2)3

3. NH2OH

4. N2H4

Solution: Option 1 (CH2)6N4

Oxidation

Do you know it is possible to generate one organic compound from

others by certain processes? One such process is oxidation. It helps to

generate one compound from the other. For instance, alcohol

oxidations lead to the generation of aldehydes under particular

conditions.

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● Oxidation


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● Reduction

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Formaldehyde is an organic compound that is produced on a very

large scale by methanol oxidation. Similarly, oxidation of aldehydes

and ketones can give rise to different products. For example, oxidation

of aldehydes leads to the formation of carboxylic acid. Let us

understand oxidation reactions with respect to aldehydes and ketones.

Oxidation of Aldehydes and Ketones

Aldehydes and ketone vary in their oxidation reactions but aldehydes

can easily undergo this process to form carboxylic acids with known

oxidizing agents such as potassium dichromate, potassium

permanganate, and nitric acid, etc. Moreover, the oxidizing agents

with a mild property such as Tollen’s reagents and Fehling’s reagent

are also capable of oxidizing aldehydes.

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This type of organic compounds can only oxidize under extreme or

vigorous conditions. It requires strong oxidizing agents and high

temperatures to carry out this process. Oxidation of ketones requires

carbon-carbon bond cleavage so that the reaction can produce

carboxylic acid containing a lesser number of bonds with respect to

the parent ketone.

Learn more about Methods of Preparation of Carboxylic Acid here in

detail.

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What happens when Aldehydes are Oxidized under an Acidic and Alkaline condition?

Separate products are formed under different conditions (acidic or

alkaline). Acidic conditions during oxidation reaction give rise to a

carboxylic acid. However, alkaline conditions give rise to salt because

the carboxylic acid would react with alkali thereby producing the salt

of carboxylic acids.

We have discussed previously it is easy to oxidize aldehydes in

comparison to ketones. Therefore, oxidation of aldehydes is possible

by either mild or strong oxidizing agents. However, ketone requires

strong oxidizing reagents in order to undergo this process.

Learn more about the Preparation of Aldehydes and Ketones here in

detail.

Few examples of oxidizing agents for aldehyde include potassium

permanganate and potassium dichromate in acid solution. Other

oxidizing agents include Tollen’s reagent, peroxy acids etc. Ketone

oxidation is possible by Peroxy benzoic. Refer to the examples below

to observe few examples of oxidation of aldehydes and ketones using

different reagents.

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Mild Oxidizing agents

Mild oxidizing agents can be used for distinguishing between

aldehydes and ketones. Now, we will discuss the mild oxidizing

agents in detail and how it is used for distinguishing between the

aldehydes and ketones.

Tollen’s Reagents & Tollen’s Test

It is a very common qualitative laboratory test help in differentiating

between aldehydes and ketones. We know that aldehydes readily

undergo oxidation whereas ketones are not. Tollen’s test also refers to

as silver mirror test. Tollen’s reagent is a colourless, basic

ammoniacal silver nitrate solution. It is a two-step procedure in which

the resultant reagent is an aqueous solution containing silver ions in

coordination with ammonia [Ag (NH3)2+].

When aldehyde undergoes oxidation with the fresh preparation of

Tollen’s reagent resulting in the formation of the bright silver mirror.

This occurs due to the formation of silver metal during the reaction.

Finally, the aldehydes undergo oxidation to produce carboxylate

anion. The reaction happens in an alkaline medium.

Procedure for Preparation of Tollen’s Reagent

● Step 1: Mixing of aqueous silver nitrate with aqueous sodium

hydroxide

● Step 2: Drop-wise addition of aqueous ammonia so that the

precipitation of silver oxide entirely dissolves in the solution

The reagent will oxidize an aldehyde compound to its corresponding

carboxylic acid. The reaction also reduces the silver ions present in the

Tollen’s Reagent to metallic silver. Therefore, one should always use

a clean glass tube to carry out this reaction to properly observe the

mirror formation. However, ketones will not be able to oxidize

Tollen’s reagent and hence it will not produce a silver mirror in the

test tube. Hence, we can distinguish aldehydes and ketone with the

help of this test.

Fehling’s Test & Fehling’s Reagent

Fehling’s Reagent consists of a mixture of two solutions (Fehling

Solution A & B). Fehling solution A is made up of aqueous copper

sulfate and Fehling solution B is made up of Rochelle salt or alkaline

sodium potassium tartrate. Prior to the test equal quantity of both the

solutions are mixed together.

The reaction requires heating of aldehyde with Fehling’s Reagent

which will result in the formation of a reddish-brown colour

precipitate. Hence, the reaction results in the formation of carboxylate

anion. However, aromatic aldehydes do not react to Fehling’s Test.

Moreover, ketones do not undergo this reaction. Thus, we can

differentiate between aldehydes and ketones.

Methyl Ketone Oxidation by Haloform Reaction

There will always be at least one methyl group accompanying

carbonyl carbon atom in case of aldehydes and ketones, hence the

name methyl ketones. The compounds undergo oxidation with the

help of sodium hypohalite thereby forming sodium salts of the

respective carboxylic acids.

However, the product formed will always have one carbon atom less

than the parent carbonyl compound. In the reaction, methyl group

conversion to haloform occurs. The oxidation reaction does not cause

any change in the double bond of the carbon-carbon atom.

Haloform reaction is one of the particular types of alpha halogenation

reaction. The reaction occurs in the methyl ketone and converts the

methyl group into a strong haloform leaving the group. The reaction

can include chloroform, bromoform, and iodoform solid precipitate.

This reaction helps to detect the presence of methyl ketone in the

laboratories.

For instance, iodoform reaction and sodium hypoiodite reaction helps

to detect the CH3CO group or CH3CH(OH) group that results in the

formation of CH3CO group upon oxidation.

Baeyer-Villiger Oxidation

It is another example of ketone oxidation. We know that ketone

requires a strong oxidizing agent such as peroxybenzoic acid. For

instance, phenyl methyl ketone undergoes oxidation by peroxybenzoic

acid to produce phenylacetate.


Question: What is the reason for the difference in behaviour of

aldehydes and ketones?

Solution: The major difference between aldehyde and ketone is in the

structure. Aldehyde contains an extra hydrogen atom in the

carbon-oxygen double bond in comparison to a ketone. It lacks

hydrogen atom.

The presence of the hydrogen atom in case of aldehydes makes it easy

to oxidize. Hence, it acts as a strong reducing agent. However, ketones

lack that particular hydrogen atom oxidation process becomes

difficult. Hence, it will require very strong oxidizing agents to

undergo the process. Moreover, oxidation of ketone happens in a very

destructive manner and breaks the carbon-carbon bonds. This is the

reason aldehydes react with all sorts of oxidizing agents but ketones

are very selective and require strong oxidizing agents.

Physical Properties of Aldehydes, Ketones and Carboxylic Acids

All of us have had a vanilla cake or vanilla flavoured ice-cream at

some point in our life. How many of us have thought how the

particular flavour and fragrance is found in vanilla beans. Aldehydes

and ketones help in addition of flavour and fragrance to nature.

Few examples include cinnamaldehyde that adds flavour and

fragrance to cinnamon, vanillin adds flavour and fragrance to vanilla

beans, salicylaldehyde adds flavour and fragrance meadowsweet.

Aldehydes and ketones are an essential component of many industrial

processes such as solvent, polymer precursors, food, perfumes, and

pharmaceuticals.

They form an essential part of biochemical processes such as

photosynthesis and Krebs cycle. Do you know medical conditions

such as “inborn errors of metabolism” requires consumption of ketone

associated foods? Moreover, most sugars are aldehyde derivatives.

Even few sugars are the ketone. All of us have heard about fructose.

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Let us study about aldehydes and ketones which form an integral part

of many industrial as well as natural processes.







● Oxidation


Acids





● Reduction


Aldehydes and Ketones

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Aldehydes and ketones are one of the classes of organic compounds.

They have carbonyl group, a double bond between carbon-oxygen

(-C=O), attached to them. They are simple compounds as they lack

any other reactive groups such as –OH or -Cl in their structure.

Presence of carbonyl group highly influences the chemistry of

aldehydes and ketones.

Physical Properties of Aldehydes & Ketones

1) Boiling Point

At room temperature, methanol behaves as a gas whereas ethanol is in

liquid form that is volatile in nature. The boiling point of methanol

and ethanol is -19o C and +21o C. Thus, the boiling point of ethanol is

nearly at room temperature. Moreover, all other aldehydes and ketones

are either liquid or solid at room temperature.

The boiling point of these compounds increases with increase in

molecular weight. Additionally, the strength of intermolecular forces

is also responsible for the boiling point of aldehydes and ketones.

However, the boiling points of these organic compounds are higher in

comparison to hydrocarbons or ethers having nearly similar molecular

masses.

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The reason for such behaviour is the weak molecular association of

these compounds occurring due to dipole-dipole interactions.

Similarly, the boiling of aldehydes and ketones are lower than alcohol

of nearly same molecular masses. The reason is lack of intermolecular

hydrogen bonding.

Vander Waals Dispersion Force

The boiling point of aldehydes and ketones depends on the numbers of

the carbon atom. It increases with increase in the number of atoms of

carbon. The longer the molecules become and with the increase in the

number of electrons, the attraction between the compounds increases.

Vander Waals Dipole-Dipole Attraction

Aldehydes and ketones are polar in nature due to the presence of the

carbon-oxygen double bond. This creates an attraction between the

permanent dipoles and with the nearby present molecules. Hence, the

reason why this compound has a higher boiling point in comparison to

the hydrocarbons of similar size.

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Refer to the table below to note the arrangement of boiling points in

the increasing order of the compounds having molecular masses from

58 to 60.

Name of the Compound Molecular mass Boiling Point

n-Butane 58 273

Methoxymethane 60 281

Propanal 58 322

Acetone 58 329

Propan-1-ol 60 370

2) The Solubility of Aldehydes and Ketones

Generally, these aldehydes and ketones are soluble in nature with

respect to water. However, the solubility gradually decreases with the

increase in the alkyl chain length. Therefore, lower members such as

methanal, ethanal, and propanone demonstrate miscible nature with all

proportions of water.

This happens due to the ability of the lower members of the aldehydes

and ketones to develop hydrogen bong with water. However, these

compounds are unable to form hydrogen bonds with themselves. The

reason for such behaviour is dispersion forces and dipole-dipole

interaction.

Usually, all aldehydes and ketones are relatively soluble in organic

solvents such as ether, methanol, benzene, chloroform, etc. The lower

members of these classes of compounds demonstrate the characteristic

sharp pungent odours but the odour converts to more fragrant smell

with an increase in the size of molecules.

Hence, aldehydes and ketones are used in different industrial

applications. In fact, there are certain naturally occurring aldehydes

and ketones that help in the blending of perfumes and also act as

flavouring agents.

Physical Properties of Carboxylic Acids

Aliphatic carboxylic acids which consist of nine carbon atoms or less

are colourless liquids at room temperature. They are characterized by

very unpleasant smell/ odour. The higher members of this class of

compounds are odourless and are present in the form of wax-like

solids because of their low volatile nature.

The boiling points of carboxylic acids are higher than the comparable

molecular masses of aldehydes, ketones, and alcohols. The reason for

such behaviour is the ability of carboxylic acids molecules to

extensively associate with each other through intermolecular hydrogen

bonding. As a result of which, the hydrogen bonds are not broken

entirely and remain intact even during the vapour state. Most of this

class of compounds are present as dimers during the vapour stage or in

the aprotic solvents.

The simple aliphatic members of this class having up to four carbon

atoms can dissolve in water because of the ability of these members to

develop hydrogen bonds with water. However, the solubility gradually

decreases with the increase in the increase in the numbers of atoms of

carboxylic acids.

The reason behind the insolubility of higher members of carboxylic

acids is the hydrophobic interaction in the hydrocarbon part of the

carboxylic acid. Therefore, higher carboxylic acids are insoluble in

water. However, they are soluble in less polar organic solvents such as

alcohol, benzene, chloroform, ether, etc. Even the simplest aromatic

carboxylic acid “Benzoic acid” is almost insoluble in cold water.

Dimer of Carboxylic Acid (Source: Wikipedia)

A Solved Question for You

Q. Arrange the given compounds according to the increasing order of

their boiling points.

CH3CH2CH2CHO, CH3CH2CH2CH2OH, H5C2-O-C2H5,

CH3CH2CH2CH3

Solution: The arrangement orders of the compounds according to the

boiling points are CH3CH2CH2CH3 < H5C2-O-C2H5 <

CH3CH2CH2CHO < CH3CH2CH2CH2OH

Explanation: The molecular mass of all the compounds is in between

the range 72 to 74. However, the only compound having an extensive

intermolecular hydrogen bonding is butan-1-ol will be the highest. We

know that Butanal is more polar in nature in comparison to

ethoxyethane.

Therefore, the dipole-dipole interaction between the molecules will be

greater in case of butanal. N-pentane molecules are having just the

weak Vander Waals forces. Therefore, the arrangement of the

compounds in increasing order will be CH3CH2CH2CH3 <

H5C2-O-C2H5 < CH3CH2CH2CHO < CH3CH2CH2CH2OH

Preparation of Aldehydes

Do you know aldehyde play a major role in human vision? Also, it is

important in many physiological processes. Vitamin A contains

aldehyde found in the retina which is necessary for eyesight. It is also

found in many natural and synthetic hormones. Aldehyde

condensation polymers find its use in many industrial processes such

as Bakelite during plastic production, Formica for the formation of

laminate tabletop material. By now, we also know that aldehydes are

important in the synthesis of solvents, perfumes, pharmaceutical, and

dyes. Therefore, in this topic, it is very crucial to understand the

preparation of aldehydes.

Preparation of Aldehydes from Acid Chloride or Acyl Chloride

Acyl chloride/acid chloride undergoes hydrogenation in the presence

of a catalyst such as barium sulfate (BaSO4) or Palladium (Pd) to

form aldehydes. Aldehyde formation with this process is possible after

the partial poisoning of the reaction by the addition of compounds

such as sulfur or quinolone. This is an important step for the formation

of aldehydes. This is also known as Rosenmund’s Reaction.

Points to Remember in Rosenmund’s Reaction

In this reaction, Sulphur or quinolone behaves as poison for catalysts

and causes partial poisoning to stop further reduction of aldehydes

into alcohols. However, it is not possible to prepare formaldehyde

from this reaction because the acyl chloride form, formyl chloride, is

not stable at room temperature. It is not possible to prepare Ketones by

this reaction.

Preparation of Aldehydes from Nitriles and Esters

Preparation of Aldehydes is possible with the help of nitriles.

Reduction of nitriles with the compound Stannous Chloride (SnCl2) in

the presence of HCl leads to the formation of the nitrile compound’s

corresponding imine form. The imine compound undergoes hydrolysis

to yield the corresponding aldehydes. The reaction is known as

Stephen’s Reduction.

Moreover, nitriles can undergo reduction by the compound DIBAL-H

or di-isobutyl aluminium hydride for the formation of imines. The

imines further undergo hydrolysis thereby forming aldehyde

compounds.

Similarly, esters can also undergo reduction with DIBAL-H to form

aldehydes.

Videos on Aldehydes, Ketones & Carboxylic Acids

Preparation of Aromatic Aldehydes from Hydrocarbons

Formation of Aromatic Aldehyde, benzaldehydes and the derivatives

of benzaldehyde, is possible with the help of aromatic hydrocarbons

primarily by methods mentioned below.

● Oxidation of methylbenzene

● Side chain chlorination

● Gatterman – Koch reaction

Preparation of Aromatic Aldehydes by Oxidation of Methylbenzene

Toluene and the derivatives of toluene undergo oxidation with the

help of a strong oxidizing agent to form benzoic acids. However, it is

possible to stop the reaction at the aldehyde stage with the help of

proper reagents. The reagents can convert the methyl group to an

intermediate that cannot undergo further oxidation easily. Oxidation of

methylbenzene or toluene falls under two categories on the basis of

reagents used in the reaction

● Use of chromyl chloride

● Use of chromic oxide

● Side chain halogenation

Oxidation of Methylbenzene or Toluene Using Chromyl Chloride

Oxidising agent chromyl chloride can oxidize and convert methyl

group to a chromium complex. The chromium complex undergoes

hydrolysis to produce benzaldehyde. We refer to this reaction as Etard

Reaction. In this reaction, methylbenzene/toluene undergo oxidation

process with the reagent of chromyl chloride (CrO2Cl2) present in

solution form in CCl4 or in CS2 thereby forming chromium complex.

Oxidation of Methylbenzene or Toluene Using Chromic Oxide

It is possible to oxidize toluene or substituted toluene to aldehydes on

treatment with reagents such as Chromium oxide, chromium trioxide,

with acetic anhydride. This reaction leads to the formation of

benzylidene diacetate. The intermediate or in this case benzylidene

diacetate can undergo further hydrolysis to corresponding

benzaldehyde with aqueous acid.

Side Chain Halogenation

Preparation of aldehydes is possible by side chain halogenation, more

specifically side chain chlorination, followed by hydrolysis. Side

chain chlorination of toluene yields benzal chloride which undergoes

hydrolysis leads to the formation of benzaldehyde. The preparation

technique is also the commercial way of benzaldehyde manufacture.

By Gatterman – Koch Reaction

When benzene and its derivatives undergo treatment with carbon

monoxide and HCl in the presence of a Lewis acid such as cuprous

chloride/ anhydrous aluminium chloride leads to the formation of

benzaldehyde or substitution of benzaldehyde compounds. This

reaction method refers to as Gatterman-Koch Reaction


Question: Complete the reactions

Solution:

Preparation of Aldehydes and Ketones

We know that organic compounds (Ketones and aldehydes)

production is possible in industrial scale and laboratory scale.

However, do you know that ketone, as well as aldehyde production,

occurs naturally in many living organisms? Ketone generation in the

form of ribulose-1,5-bisphosphate is one of the steps of photosynthesis

and help in the formation of the necessary organic compounds during

photosynthesis.

Ketones are present as sugars and are called ketoses. It is also present

in most vertebrates including humans as ketone bodies. Now, that you

know how organisms produce ketone, try finding how living

organisms generate aldehydes. In this topic, we will learn how the

preparation of Aldehydes and Ketones is possible by various chemical

reactions.

Aldehydes and Ketones

Aldehydes and Ketones are simple organic compounds containing a

carbonyl group. Carbonyl group contains carbon-oxygen double bond.

These organic compounds are simple because the carbon atom

presents in the carbonyl group lack reactive groups such as OH or Cl.

Aldehydes

An aldehyde is one of the classes of carbonyl group-containing alkyl

group on one end and hydrogen on the other end. The R and Ar denote

alkyl or aryl member respectively. In the condensed form, the

aldehyde is written as –CHO.

Structure of Aldehyde (SourceCredit: Wikipedia)

Ketones

Ketone is a member of the carbonyl group-containing alkyl or aryl

group on both the end of the carbonyl group. The compound formula

is RC(=O)R’. In this case, R and R’ are the different carbon

containing substituents.

Structures Of Ketones (SourceCredit: Wikipedia)

Method of Preparation of Aldehydes and Ketones

Aldehydes and Ketones can be prepared by a number of methods.

Let’s discuss the method one by one.

Formation by Oxidation of Alcohols

Oxidation of primary and secondary alcohols leads to the formation of

aldehydes and ketones. The oxidation is possible with the help of

common oxidizing agents are KMnO4, K2Cr2O7, and CrO3. Strong

oxidizing agents helps in the oxidation of the primary alcohol to

aldehyde then to a carboxylic acid.

Primary alcohols having low molecular weight can undergo oxidation

and form aldehydes. The reaction mixture after aldehyde formation

can avoid further oxidation if the reaction temperature is modulated so

that the boiling point of the aldehyde is lower than the alcohol which

helps in the distillation of aldehyde from the reaction mixture soon

after its formation. Hence, it is important to maintain the reaction

temperature slightly more than 349K. Refer to the reaction below

Aldehyd

Chemical Reactions and Uses of Carboxylic Acids...Carboxylic acids undergo decomposition reaction...

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