Chapter-1 Chapter-1 ALCOHOLSALCOHOLS

ContentsContents

IntroductionIntroduction

Nomenclature Nomenclature

PreparationPreparation

ReactionsReactions

IntroductionIntroduction Introduction, classification, nomenclature and Introduction, classification, nomenclature and

isomerism of alcoholsisomerism of alcohols : : The hydroxy derivatives of aliphatic hydrocarbons (compounds having The hydroxy derivatives of aliphatic hydrocarbons (compounds having

their carbon atoms in chains and not in the form of rings) are called their carbon atoms in chains and not in the form of rings) are called alcohols. When one, two or more hydrogen atoms of a hydrocarbon are alcohols. When one, two or more hydrogen atoms of a hydrocarbon are replaced by a corresponding number of hydroxyl groups (-OH), alcohols replaced by a corresponding number of hydroxyl groups (-OH), alcohols can be obtained.can be obtained.

Classification of AlcoholsClassification of Alcohols

They can be classified as:They can be classified as: Alcohols with one hydroxyl group - Monohydric alcoholAlcohols with one hydroxyl group - Monohydric alcohol Alcohols with two hydroxyl groups - Dihydric alcoholAlcohols with two hydroxyl groups - Dihydric alcohol Alcohols with three hydroxyl groups - Trihydric alcoholsAlcohols with three hydroxyl groups - Trihydric alcohols Alcohols with four or more hydroxyl groups - Polyhydric alcoholsAlcohols with four or more hydroxyl groups - Polyhydric alcohols

Secondary AlcoholSecondary Alcohol Here the carbon atom bearing the hydroxyl group is attached Here the carbon atom bearing the hydroxyl group is attached

to two other carbon atoms.to two other carbon atoms.

Tertiary AlcoholTertiary Alcohol Here the carbon atom bearing the hydroxyl group is attached Here the carbon atom bearing the hydroxyl group is attached

to three other carbon atoms to three other carbon atoms

Nomenclature of alcoholsNomenclature of alcohols

In the IUPAC system, the names of saturated alcohols are In the IUPAC system, the names of saturated alcohols are derived from corresponding alkenes by replacing 'e' of alkenes derived from corresponding alkenes by replacing 'e' of alkenes by 'ol'by 'ol'

Some examples are shown belowSome examples are shown below

The numbering is done such that the carbon atom attached to the,-The numbering is done such that the carbon atom attached to the,-

OH group gets the lowest numberOH group gets the lowest number..

For naming polyhydric alcohols, the name of the alkane is retained For naming polyhydric alcohols, the name of the alkane is retained and the ending -e is not dropped. Thus dihydric alcohols are named and the ending -e is not dropped. Thus dihydric alcohols are named as alkane diols and trihydric alcohols are named as alkene triolsas alkane diols and trihydric alcohols are named as alkene triols

Isomerism Of AlcoholsIsomerism Of Alcohols Alcohols exhibit following types of isomerism:Alcohols exhibit following types of isomerism:

1. Chain isomerism1. Chain isomerism Alcohols with four or more carbon atoms exhibit this type of Alcohols with four or more carbon atoms exhibit this type of

isomerism in which the carbon skeleton is different.isomerism in which the carbon skeleton is different.

2. Position isomerism2. Position isomerism Alcohols with three or more carbon atoms can exhibit position Alcohols with three or more carbon atoms can exhibit position

isomerism. isomerism.

3. 3. Functional isomerismFunctional isomerism Alcohols with two or more carbon atoms can exhibit functional Alcohols with two or more carbon atoms can exhibit functional

isomerism with ethers. isomerism with ethers.

4. 4. Optical isomerismOptical isomerism Alcohols containing chiral centrescen exhibit enantiomerismor Alcohols containing chiral centrescen exhibit enantiomerismor

optical isomerism. optical isomerism.

PreparationPreparation

A common source for producing alcohols is from A common source for producing alcohols is from carbonyl compounds. The choice of carbonyl type carbonyl compounds. The choice of carbonyl type (ketone, aldehyde, ester, etc) and the type of (ketone, aldehyde, ester, etc) and the type of reaction (Grignard addition or Reduction), will reaction (Grignard addition or Reduction), will determine the product(s) you will get.determine the product(s) you will get.

There are primarily two types of reactions used There are primarily two types of reactions used to create alcohols from carbonyls: Grignard to create alcohols from carbonyls: Grignard

Addition reactions and Reduction reactions.Addition reactions and Reduction reactions.

Grignard Addition Reactions :Grignard Addition Reactions :   Grignard reagents are created by reacting  are created by reacting

magnesium metal with an alkyl halide . The magnesium metal with an alkyl halide . The magnesium atom then gets between the alkyl magnesium atom then gets between the alkyl group and the halogen atom with the general group and the halogen atom with the general reaction:reaction:

R-X + Mg → R-Mg-XR-X + Mg → R-Mg-X

Mechanism of Grignard reagent reacting with a Mechanism of Grignard reagent reacting with a carbonyl:carbonyl:

The general mechanism of a Grignard reagent reacting The general mechanism of a Grignard reagent reacting with a carbonyl (except esters) involves the creation of with a carbonyl (except esters) involves the creation of a 6-membered ring transition state .a 6-membered ring transition state .

Synthesis from an Aldehyde / Synthesis from an Aldehyde / Ketone/EsterKetone/Ester

When a When a formaldehydeformaldehyde is the target of the Grignard's is the target of the Grignard's attack, the result is a primary alcohol. attack, the result is a primary alcohol.

When an When an aldehydealdehyde is the target of the Grignard's is the target of the Grignard's attack, the result is a secondary alcohol. attack, the result is a secondary alcohol.

When a When a ketoneketone is the target of the Grignard's attack, is the target of the Grignard's attack, the result is a tertiary alcohol . the result is a tertiary alcohol .

Synthesis of alcohol from an epoxide Synthesis of alcohol from an epoxide and Grignard reagentand Grignard reagent

The reaction of Grignard reagents with epoxides The reaction of Grignard reagents with epoxides is regioselective. The Grignard reagent attacks at is regioselective. The Grignard reagent attacks at the least substituted side of the carbon-oxygen the least substituted side of the carbon-oxygen

bonds, if there is one.bonds, if there is one.

Organolithium Alternative Organolithium Alternative

Organolithium reagents are slightly more Organolithium reagents are slightly more reactive, but produce the same general results as reactive, but produce the same general results as

Grignard reagentsGrignard reagents

ReductionReduction

From an Aldehyde From an Aldehyde

From KetoneFrom Ketone

From an EsterFrom an Ester

From carboxylic acidFrom carboxylic acid

AcidityAcidity In an O-H bond, the O steals the H's electron In an O-H bond, the O steals the H's electron

due to its electronegativity, and O can carry a due to its electronegativity, and O can carry a negative charge (R-O-). negative charge (R-O-).

. This makes the -OH group (and alcohols) . This makes the -OH group (and alcohols) Bronsted acids. Alcohols are weak acids, even Bronsted acids. Alcohols are weak acids, even weaker than water.weaker than water.

On the other hand, alcohols are also weakly On the other hand, alcohols are also weakly basic, As a Bronsted base, the oxygen atom in basic, As a Bronsted base, the oxygen atom in the -OH group can accept a proton (hydrogen the -OH group can accept a proton (hydrogen ion.) This results in a positively-charged ion.) This results in a positively-charged species known as an oxonium ion.species known as an oxonium ion.

ReactionsReactions

Conversion of alcohols to haloalkanesConversion of alcohols to haloalkanes : : This process can occur through SN2 (backside attack) This process can occur through SN2 (backside attack)

or SN1 (carbocation intermediate) mechanismsor SN1 (carbocation intermediate) mechanisms . . SN2 conversion of an alcohol to a haloalkane:SN2 conversion of an alcohol to a haloalkane:

R-O-H + H+ + X- → R-O+-H2 + X- → R-XR-O-H + H+ + X- → R-O+-H2 + X- → R-X + H2O + H2O SN1 conversion of an alcohol to a haloalkane:SN1 conversion of an alcohol to a haloalkane: R-O-H + H+ + X- → R-O+-H2 + X- → R+ + H2O + X- → R-O-H + H+ + X- → R-O+-H2 + X- → R+ + H2O + X- →

R-X + H2O R-X + H2O

OxidationOxidation With regards to alcohol, oxidizing reagents can be With regards to alcohol, oxidizing reagents can be

strong or weak. strong or weak. WeakWeak reagantsreagants are able to are able to oxidize a primary alcohol group into a oxidize a primary alcohol group into a aldehydealdehyde group and a secondary alcohol into a group and a secondary alcohol into a ketoneketone

Strong reagentsStrong reagents will further oxidize the will further oxidize the aldehyde into a carboxylic acid (COOH). Tertiary aldehyde into a carboxylic acid (COOH). Tertiary alcohols cannot be oxidizedalcohols cannot be oxidized

An example of a strong oxidizing reagent is An example of a strong oxidizing reagent is chromic acid (H2CrO4). An example of a weak chromic acid (H2CrO4). An example of a weak oxidizing reagent is pyridinium chlorochromateoxidizing reagent is pyridinium chlorochromate (PCC) (C5H6NCrO3Cl)(PCC) (C5H6NCrO3Cl)

GlycolGlycol

Ethylene glycolEthylene glycol IUPAC name:Ethan-1,2-diol:Ethan-1,2-diol Other names:Other names:1,2Ethanediol1,2Ethanediol

Ethylene Alcohol,Ethylene Alcohol,

Hypodicarbonous acid ,Hypodicarbonous acid ,

Monoethylene glycolMonoethylene glycol

Ethylene glycolEthylene glycol  ((IUPAC name: ethane-1,2-diol) is an : ethane-1,2-diol) is an organic compound widely used as an widely used as anautomotive  antifreeze and a precursor to polymers. In its pure form, it is an  and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid. Ethylene odorless, colorless, syrupy, sweet-tasting liquid. Ethylene glycol is toxic, and ingestion can result in death.glycol is toxic, and ingestion can result in death.

Ethylene glycol was first prepared in 1859 by the Ethylene glycol was first prepared in 1859 by the French chemist  chemist Charles-Adolphe Wurtzfrom from ethylene glycol diacetate via ethylene glycol diacetate via saponification with  with potassium hydroxide and, in 1860, from the  and, in 1860, from the hydration of  of ethylene oxide..

Current methodCurrent method Ethylene glycol is produced from Ethylene glycol is produced from ethylene

 (ethene), via the intermediate  (ethene), via the intermediate ethylene oxide. . Ethylene oxide reacts with Ethylene oxide reacts with water to produce  to produce ethylene glycol according to the ethylene glycol according to the chemical equation--

C2H4O + H2O → HOCH2CH2OHC2H4O + H2O → HOCH2CH2OH This This reaction can be  can be catalyzed by  by

either  either acids or  or bases

ReactionsReactions Ethylene glycol is used as a Ethylene glycol is used as a protecting group for  for 

carbonyl groups in  in organic synthesis. Treating a . Treating a ketone or aldehyde with ethylene glycol in the ketone or aldehyde with ethylene glycol in the presence of an acid catalyst (e.g., presence of an acid catalyst (e.g., p-toluenesulfonic acid; ; BF3•Et2O) gives the ) gives the corresponding a 1,3-dioxolane, which is resistant corresponding a 1,3-dioxolane, which is resistant to bases and other nucleophiles. The 1,3-to bases and other nucleophiles. The 1,3-dioxolane protecting group can thereafter be dioxolane protecting group can thereafter be

removed by further acid removed by further acid hydrolysis..

Uses:Uses: The major use of ethylene glycol is as a The major use of ethylene glycol is as a

medium for medium for convective heat transfer in, for  in, for example, automobiles and liquid cooled example, automobiles and liquid cooled computers. Ethylene glycol is also computers. Ethylene glycol is also commonly used in chilled water commonly used in chilled water air conditioning systems  systems

In the plastics industry, ethylene glycol is In the plastics industry, ethylene glycol is important precursor to polyester fibers important precursor to polyester fibers and resins. and resins. 

Niche ApplicationsNiche Applications Minor uses of ethylene glycol include the manufacture Minor uses of ethylene glycol include the manufacture

of capacitors, as a chemical intermediate in the of capacitors, as a chemical intermediate in the manufacture of 1,4-dioxane manufacture of 1,4-dioxane

. Ethylene glycol is also used in the manufacture of . Ethylene glycol is also used in the manufacture of some vaccines.some vaccines.

Ethylene glycol is commonly used as apreservative for Ethylene glycol is commonly used as apreservative for biological specimens, especially in secondary schools biological specimens, especially in secondary schools

during dissection as a safer alternative to formaldehydeduring dissection as a safer alternative to formaldehyde