CHAPTER 14: CARBOXYLIC ACIDS

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INTRODUCTION The functional group of carboxylic acids

consists of a C=O with -OH bonded to the same carbon.

Carboxyl group is usually written -COOH. Aliphatic acids have an alkyl group bonded

to -COOH. Fatty acids are long-chain aliphatic acids

Aromatic acids have an aryl group bonded to -COOH.

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COMMON NAMES Many aliphatic acids have historical names. Positions of substituents on the chain are labeled

with Greek letters.

CH3CH2CHC

Cl

OH

O

-chlorobutyric acid

CH3CH2CH2CHCH2COOH

Ph

-phenylcaproic acid

NOMENCLATURE

Common names you need to know: Formic acid (methanoic acid)

Acetic Acid (ethanoic acid)

Benzoic Acid

O

OH

O

OH

O

OH

H

Propionic Acid (propanoic acid) Butyric acid (butanoic acid) Valeric acid (pentanoic acid)

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IUPAC NAMES

Remove -e from alkane (or alkene) name, add -oic acid.

The carbon of the carboxyl group is #1.

CH3CH2CHC

Cl

OH

O

2-chlorobutanoic acid

PhC

HC

H

COOH

trans-3-phenyl-2-propenoic acid

Nomenclature

• For acyclic acid chlorides: change the suffix –ic acid of the parent carboxylic acid to the suffix –yl chloride; or

• When the –COCl group is bonded to a ring: change the suffix –carboxylic acid to –carbonyl chloride.

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NAMING CYCLIC ACIDS Cycloalkanes bonded to -COOH are named as

cycloalkanecarboxylic acids. Aromatic acids are named as benzoic acids.

COOH

CH(CH3)2

2-isopropylcyclopentanecarboxylic acid

COOH

OH

o-hydroxybenzoic acid

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DICARBOXYLIC ACIDS Aliphatic diacids are usually called by their

common names. For IUPAC name, number the chain from the end

closest to a substituent. Two carboxyl groups on a benzene ring indicate a

phthalic acid.

HOOCCH2CHCH2CH2COOH

Br

3-bromohexanedioic acid -bromoadipic acid (common)

STRUCTURE OF CARBOXYL Carbon is sp2 hybridized. Bond angles are close to 120. O-H eclipsed with C=O, to get overlap of orbital

with orbital of lone pair on oxygen.

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BOILING POINTSHigher boiling points than similar alcohols, due

to dimer formation.

Acetic acid, b.p. 118C

PHYSICAL PROPERTIES

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MELTING POINTS

Aliphatic acids with more than 8 carbons are solids at room temperature.

Double bonds (especially cis) lower the melting point. Note these 18-C acids: Stearic acid (saturated): 72C Oleic acid (one cis double bond): 16C Linoleic acid (two cis double bonds): -5C

SOLUBILITY

Water solubility decreases with the length of the carbon chain.

Up to 4 carbons, acid is miscible in water. More soluble in alcohol. Also soluble in relatively nonpolar solvents

like chloroform because it dissolves as a dimer.

ACIDITY

They are weak acids. The Ka value for most unsubsituted aliphatic and aromatic carboxylic acids fall within the range from 10-4 to 10-5.

Recall small pKa stronger acid large pKa waker acid

Ka are related as such pKa= -log(Ka) pka+pKb=14

ACIDITY

Substitution of the alpha-carbon of an atom or a group of atoms of higher electronegativity than carbon increases the acidity of carboxylic acid.

The inductive effect of an electronegative atom

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SUBSTITUENT EFFECTS ON ACIDITY

=>

Ch

ap

ter 2

0

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SALTS OF CARBOXYLIC ACIDS

Sodium hydroxide removes a proton to form the salt.

Adding a strong acid, like HCl, regenerates the carboxylic acid.

CH3 C

O

OHNaOH

CH3 C

O

O_

Na+

HCl=>

SALTS

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NAMING ACID SALTS

Name the cation. Then name the anion by replacing the

-ic acid with -ate.

CH3CH2CHCH2COO- K

+

Cl

potassium -chlorovalerate (common)potassium 3-chloropentanoate (IUPAC)

COMPLETE REACTIONS AND NAME THE SALTS

A) Butanoic Acid + Sodium HydroxideB) 2-hydroxypropanoic (lactic acid) acid +

sodium bicarbonate

A)

B)

COOH + NaOH COONa +H2O

Butanoic Sodium Sodium WaterAcid Hydroxide Butanoate

COOH + NaHCO3 + H2O +CO2

OHOH

COONa

2-Hydroxypropanoic Sodium Sodium 2-hydroxypropanoateAcid Bicarbonate (sodium lactate, common)

(Lactic Acid COMMON)

REDUCTION OF CARBOXYL GROUP TO1 ALCOHOLS Use strong reducing agent, LiAlH4 (Lithium

Aluminum Hydride) And either diethyl ether or Tetrahydrofuran (THF) as

solvents; it reduces carboxylic acid to alcohol, but does not reduce it to a ketone.

FISCHER ESTERIFICATION

After the German Chemist Emil Fischer Carboxylic Acid (strong acid as a catalyst) +

alcohol yields ester + water. All steps are reversible. Reaction reaches equilibrium.

COOH

+ CH3CH2OHH+ COCH2CH3

O

+ HOH

ACID CHLORIDES The functional group of an acid halide is a

carbonyl bonded to a halogen atom Acid chlorides are the most frequently used in

lab and in industrial organic chemistry. The most common way to synthesize acid

chlorides is to treat a carboxylic acid with thionyl chloride (SOCl2) or oxalyl chloride with the acid.

C

O

OHC

O

C

O

Cl Cl+

C

O

Cl+ + +HCl CO CO2

(Oxalyl Chloride)