CARBOXYLIC ACIDS

Introduction

• Compounds containing the carboxyl group (-COOH) are called

carboxylic acids.

• General formula or RCOOH or RCO2H

• R group can be aliphatic, aromatic or cyclic.

• Major organic acids found in fruits and vegetables.

1. Classification of Carboxylic Acids

1. According to the Number of Carboxyl Group

Monocarboxylic Acids

• Acids that contain only one carboxyl group.

Polycarboxylic Acids

• Acids that contain more than one carboxyl group.

2. According to the Functional Group

Hydroxy Acids

• Acids that contain hydroxyl group.

Amino Acids

• Acids that contain amino group.

Example 1

Classify the following acids as mono and poly carboxylic acid.

2. Nomenclature of Carboxylic Acids

1. Common Names

Simple carboxylic acids known by common names.

2. Using The IUPAC System

• Number the longest carbon atom chain containing carboxyl group

starting from carboxyl carbon.

• Replace –e at the end of corresponding alkane by suffix –oic and

the word “acid”.

If the carboxylic acid contains more than one carboxyl group -dioic

acid or -trioic acid suffixes are used.

Example 2

Name the following carboxylic acids.

Example 3

Write the structural formulae for the following compounds.

A. 4-amino hexanoic acid

B. 1,5-pentanedioic acid

C. 2-phenyl propanoic acid

D. 3-bromo-1,4-butanedioic acid

E. 3-aminocyclohexanoic acid

Physical Properties of

Carboxylic Acids

• The first members are colorless liquids with sharp or unpleasant

odors.

• The members with 4-9 carbon atoms smell like butter and almond

oil. The smell of spoiled butter and cheese, and unpleasant odor of

sweat are due to acid formation.

• The higher members-more then ten carbons-are wax like solids.

• The first four members are soluble in water. Their solubilities and

boiling points are higher than alcohols with the same number of

carbon.

• When carboxylic acids dissolve in water hydrogen ions are

formed and equilibrium is established.

• Both number and location of electro negative substituent affect

the acid strength.

• As the size of alkyl group increases, acidic property decreases.

4. Chemical Properties of Carboxylic Acids

1. Reactions Involving of Cleavage of O-H Bond

In –COOH group H+ ion leaves and a carboxylate salt is formed.

Salt Formation

Carboxylic acids react with active metals and form carboxylate salts

and hydrogen gas.

Example 4

44.8 L of H2 gas at STP is produced as a result of the reaction between

excess Mg and 296 g of a monocarboxylic acid. What is the formula of

the acid?

Neutralization Reaction

2. Reactions Involving of C-O Bond Breakage

group is called the acyl group. If a different functional group is

attached to the acyl group other than the – OH group the compound

is called an acid derivative.

Formation of Acid Anhydrades

• If a carboxylic acid is dehydrated acid anhyrades are formed.

• The functional group of an acid unhydrade is

Formation of Acid Anhydrades

• Formation of acid anhydrides from acids is similar to the formation

of ether from alcohols.

Esterification

Formation of Acid Chlorides

• The –OH group of carboxylic acid can be replaced by chloride, RCOX.

• Instead of hydrogen halides, PCl3, PCl5 or SOCl2 are used.

3. Addition of Halogens

In the presence of red phosphorus catalyst , chlorine and bromine

react with carboxylic acids to produce –halo acids

4. Reduction Reactions

• The reduction of carboxylic acids requires strong reducing agents

like LiAlH4 or NaBH4.

• –COOH group is reduced to –CH2OH.

Example 5

Complete the following transformations.

A. CH3COOH + CH3CH2OH →

B. CH3CH2COOH + PCl5 →

C. CH3COOH + Br2 →

D. HCOOH + NaOH →

E. CH3CH2COOH + H2SO4 →

F. CH3CH2COOH + LiAlH4 →

Example 6

When a 12 g sample of a mono carboxylic acid is neutralized

by 400 mL of 0.5 M sodium hydroxide solution, what is the

formula of acid? (C:12, H:1)

5. Preparation of Carboxylic Acids

1. Oxidation of Primary Alcohols

• Oxidation of primary alcohols produces aldehydes and when

aldehydes are oxidized carboxylic acids are produced.

• KMnO4 and K2Cr2O7 solutions in acidic medium are used.

2. Oxidation of Aromatic Compounds

3. Oxidation of Alkenes

4. Carbonation of Grignard Reagents

5. Hydrolysis of Carboxylic Acid Derivatives

6. Hydrolysis of Nitriles

7. Reaction of Carboxylate Salts

Example 6

Complete the following transformations below indicating conditions

and catalyst.

A. n-butanoic acid from n-butanol

B. 1, 6-hexanedioic acid from cyclohexene

C. benzoic acid from chlorobenzene

D. 1, 5-pentanedioic acid from 1,3-dichloropropane

E. acetic acid from ethyl acetate

6. Some Common Carboxylic Acids

1. Formic Acid, HCOOH

• First member and the simplest carboxylic acids.

• Was obtained by the distillation of ants.

• Soluble in water, colorless, pungent, fuming and corrosive liquid.

• In its structure there are both aldehyde and carboxyl group. It can

react with Fehling’s and Tollens’ reagents.

• It is a good disinfectant, exists in honey to prevent spoiling, used in

textile dying, leather tanning, is a starting substance in the production

of fertilizers, rubbers and plastics and its calcium salt is a good water

softener.

• Prepared by following method in industry,

• In laboratory,

2. Acetic, CH3COOH

• Principal ingredient of vinegar which has 4-6 % of acetic acid and

water.

• It is produced commercially by the oxidation of acetaldehyde, and

is also formed from the oxidation of ethyl alcohol.

• Soluble in water, and colorless.

It is an important substance for making textile fibers, vinyl plastics.

7. Dicarboxylic Acids

• They have two carboxyl groups.

• General formula is HOOC-(CH2)n-COOH

• All they have common names.

• Some of them are important monomers.

1. Oxalic Acid

• It occurs in beet leaves, sorrel, spinach, asparagus, tobacco, and

tomatoes.

• It is a white crystalline solid, its calcium salt precipitates in kidneys.

• It is used as bleach in wood cellulose, hay, and feathers, and in the

manufacture of ink.

• Free oxalic acid is toxic and is used to remove stain from fabrics and

porcelain ware.

• Tomatoes are vegetables that contain oxalic acid and its salts.

• Oxalic acid salts can be obtained from some plants, such as

asparagus.

2. Malonic Acid

• It was first obtained from malic acid (apple acid).

• It is colorless liquid, soluble in water and alcohol.

• It can be obtained from the hydrolysis of cyanoacetic acid.

3. Adipic Acid

• It was first obtained from oil.

• It is a solid, and produced from the oxidation of cyclohexanol with a

nitric acid catalyst.

• Adipic acid is used in making of nylon.

8. Fatty Acids

1. Saturated Fatty Acid

CH3-COONa + HCl CH3-COOH + NaClsodium acetate acetic acid

• They are long chained carboxylic acids.

• Simplest fatty acid is butyric acid, C3H7COOH

Palmitic Acid, C15H31COOH

It is a white crystalline solid, insoluble in water but soluble in alcohol

and ether.

• It occurs in palm oil, beeswax and other animal and vegetable fats

and oils.

Stearic Acid, C17H35COOH

• It is a crystalline solid, soluble in ether and hot alcohol.

• It occurs in the form of glycerides in most animal and vegetable fats.

• Candles are a mixture of stearic acid and palmitic acid.

2. Unsaturated Fatty Acid

• Fatty acids containing carbon-carbon double bond on the chain.

Oleic Acid, C17H33COOH

• It occurs in the form of glycerides in olive, almond, cotton, and

sunflower oils.

• It is colorless, tasteless, and odorless liquid.

• It is used in the production of lubricants, detergents, resins and

other products.

• Stearic acid is obtained by the addition of hydrogen to oleic acid.

Linoleic Acid, C17H31COOH and Linolenic Acid C17H29COOH

• They are found in the form of glycerides in vegetables oils such as

linseed, sesame and poppy oils.

• Linoleic acid has two and Linolenic acid has three double bonds in

alkyl chain.

9. Oxy Acids

• Organic acids with a hydroxyl group attached to alkyl group.

• Most oxyacids occur in plants.

• Since they have both carboxyl and hydroxyl groups they are highly

soluble in water.

Carbonic Acid, H2CO3

• It is the simplest member of hydroxyl acids.

• All fizzy drinks (cola, mineral water, etc.) contain carbonic acid.

10. Optical Isomerism

• Molecules having nonsuperimposible mirror images are called

chiral.

• A chiral molecule and its nonsuperimposible image are called

enantiomers.

• For molecules to have enantiomers, their structures must be

asymmetrical.

• The simplest asymmetric molecule is the tetrahedrally bonded

carbon atom with four different types of atom or atom groups

attached to it.

• Enantiomers can be represented by different letters. (D and L)

• If the rotation is to right the molecule

is D, if the rotation is to left the molecule

is L.

•

• If enantiomers (D and L) are equal amounts in a mixture it is

optically inactive and the mixture is called racemic mixture.

Example 7

How many asymmetric carbon atoms do the molecules below

contain?