ESTERS[1]

ESTERS

The general formula of esters

CnH2n + 1COOCmH2m+1 where n =0,1,2,3… and m = 1,2,3…

The values of m and n in both the alkyl groups may be the same or different.

When n=1, and m =2, the formula of ester is CH3

COOC2H5 ( ethyl ethanoate )

Esters are formed by the reaction between carboxylic acids and alcohols.

Hence, the general formula of esters is obtained by combining the general formulae of carboxylic acid and alcohol.

O

CnH2n+1 — C—OH + CmH2m+1 —OH

O

CnH2n+1 — C—O—CmH2m+1 + H2O

Removal of water molecule

Carboxylic acid

Alcohol

In and ester, the H in the carboxyl group is replaced with an alkyl group

O

CH3 — C—O —CH3 = CH3—COO —CH3

ester group

The functional group of ester

Is the carboxylate group

O

CnH2n+1 — C— O— CmH2m+1

The molecular formula of esters can be written as CnH2nO2.

The molecular formula of carboxylic acid is also CnH2nO2.

This means that the esters and carboxylic acids that have the same number of carbon atoms are isomers.

Example :

Methyl methanoate (CH3COOCH3) is the isomer of propanoic acid (CH3CH2COOH) because both of the compounds have the same molecular formula that is C3H6O2.

C3H6O2

CH3COOCH3

Methyl ethanoate(ester)

CH3CH2COOHPropanoic acid(carboxylic acid)

isomers

Ester are also isometric with other esters. Example: Ethyl ethanoate (CH3COOCH2CH3) and

methyl propanoate (CH3CH2COOCH3) are isomers.

Both of these esters have the same molecular formula that is C4H8O2.

Derived from the alcohol and the carboxylic acid used to prepare it.

Consists of two parts.

Naming Esters

First part

The name of the ester is taken from the alkyl group of alcohol.

Example : a. methanol methylb. ethanol ethylc. propanol propyl

Second part

Is obtained by changing the –oic on the name of carboxylic acid to –oate.

Example :a. methanoic acid methanoateb. ethanoic acid ethanoatec. propanoic acid propanoate

Hence, the ester prepared from ethanol and ethanoic acid is called ethyl ethanoate.

Naming Esters

Name the alkyl from the alcohol –O- Name the acid with the C=O with –ate

acid alcohol

O

methyl

CH3 — C—O —CH3

Ethanoate methyl ethanoate (IUPAC)

(acetate) methyl acetate (common)

Some Esters and Their Names

Flavor/Odor

Raspberries

HCOOCH2CH3 ethyl methanoate

(IUPAC)

ethyl formate (common)

Pineapples

CH3CH2CH2 COOCH2CH3

ethyl butanoate (IUPAC)

ethyl butyrate (common)

Isopentyl acetate Ethyl butyrate

banana pineapple

Isobutyl propionate Octyl acetaterum orange

Propyl acetate Methyl butyratepear apple

CH3 C O CH2 CH2 CH3

O

CH3 CH2 C O CH2 CH CH3

O

CH3

CH3 C O CH2 CH2 CH2

O

CH2 CH2 CH2 CH2 CH3

CH3 CH2 CH2 C O CH2 CH3

O

CH3 C O CH2 CH2 CH

O

CH3

CH3

CH3 CH2 CH2 C O CH3

O

Learning Check

Give the IUPAC and common names of the following compound, which is responsible for the flavor and odor of pears.

O

CH3 — C—O —CH2CH2CH3

Solution

O propyl

CH3 — C—O —CH2CH2CH3

propyl ethanoate (IUPAC)

propyl acetate (common)

Learning Check

Draw the structure of the following compounds:

A. 3-bromobutanoic acid

B. Ethyl propionoate

Solution

A. 3-bromobutanoic acid

Br

|

CH3CHCH2COOH

B. Ethyl propionoate O

CH3 CH2 COCH2CH3 CH3CH2COOCH2CH3

Name of some common esters together with the carboxylic acid and alcohol used to prepare them.

Name of ester Formula of ester Prepared from

Ethyl methanoate

HCOOCH2CH3 Ethanol + Methanoic acid

C2H5OH + HCOOH

Methyl ethanoate

CH3COOCH3 Methanol + Ethanoic acid

CH3OH + CH3COOH

Propyl ethanoate

CH3COOCH2CH2CH2 Propanol + ethanoic acid

CH3CH2CH2OH + CH3COOH

Ethyl propanoate

CH3CH2COOCH2CH3 Ethanol + propanoic acid

C2H5OH + CH3CH2COOH

Butyl methanoate

HCOOCH3CH2CH2CH3 Butanol + methanoic acid

CH3CH2CH2CH2OH + HCOOH

Methyl butanoate

CH3CH2CH2COOCH3 Methanol + butanoic acid

CH3OH + CH3CH2CH2COOH

hydration

Alkene

Ester

Carboxylic acidAlcohol

Alkanehydrogenation

cracking

dehydration

Oxidation

esterification

The flow chart shows the interconversions of alkane, alkene, alcohol,Carboxylic acid and ester.

Preparation of ethyl ethanoate

Esterification

Reaction of a carboxylic acid and alcohol Acid catalyst

O H+

CH3 — C—OH + HO—CH2CH3

O

CH3 — C—O—CH2CH3 + H2O

Hydrolysis

Esters react with water and acid catalyst Split into carboxylic acid and alcohol

O H+

H — C—O—CH2CH3 + H2O

O

H — C—OH + HO—CH2CH3

Saponification

Esters react with a bases Produce the salt of the carboxylic acid and

alcohol O

CH3C—OCH2CH3 + NaOH

O CH3C—O– Na+ + HOCH2CH3

salt of carboxylic acid

Learning Check

Write the equation for the reaction of propionic acid and methyl alcohol in the presence of an acid catalyst.

Solution

O H+

CH3CH2COH + HOCH3

O

CH3CH2COCH3 + H2O

Learning Check

What are the organic products when methylacetate reacts with

A. Water and an acid catalyst?B. KOH?

Solution

A.

O

CH3COH + HOCH3

O

B. CH3CO– K+ + HOCH3