Esterification

A condensation between a carboxylic acid and an alcohol O O + H + H OH CH3 C OH + CH3 OH CH3 C OCH3

The carboxylic acid condenses with the alcohol; water is formed in the process.

The alkoxy group (from the alcohol) becomes the OR group in the product ester.

The OH group (from the acid) and the H atom from the alcohol produce the by-product, water. Esterification The carbonyl bond does not change

O O H+ CH3 C OH + CH3 OH CH3 C OCH3 + H OH

The alkyl group (R group) does not change

The only change is a substitution of OH by OR

O O

CH3 C O H OCH3 CH3 C O + H OH H CH3

A proton (H) from the alcohol attaches to the OH group to form water Esterification

Different alcohols produce different esters … O O + CH C OCH CH + H OH 1 CH3 C OH CH3CH2O H 3 2 3 Acetic acid Ethanol ethyl ester of acetic acid

O O

2 CH3 C OH + CH3CH2CH2O H CH3 C OCH2CH2CH3 + H OH Propanol propyl ester of acetic acid

… but only the alkoxy groups are different.

The alkyl group (CH3) remains the same. Esterification Two more alcohols produce two more esters; again, only the alkoxy groups are different. O O H O CH CH 3 + H OH CH3 C OH + CH3 C OCH-CH3 3 CH3 CH3 same structure! isopropyl ester Isopropanol same structure! O O H CH3 CH3CHCH3 CH3 C OCH CH3

O 4 O + OH CH C O + H OH CH3 C OH 3 Cyclopentanol cyclopentyl ester

All four esters are acetic acid esters, also called acetate esters. Esterification Different acids (different alkyl groups) all give ethyl esters if ethanol is used for each reaction: O O + CH C OCH CH + H OH 1 CH3 C OH CH3CH2O H 3 2 3

O O + CH CH CH C OCH CH 2 CH3CH2CH2 C OH CH3CH2O H 3 2 2 2 3

O O + CH CHCH C OCH CH 3 CH3CHCH2 C OH CH3CH2O H 3 2 2 3 CH CH3 3 (Water by-product is not shown in these examples.) Esterification Two more examples of ethyl esters O O C OCH CH 4 C OH + CH3CH2O H 2 3

O OH O OCH CH C C 2 3

5 + CH3CH2O H

C C HO O CH3CH2O O Notice the last example: both carboxylic acid groups undergo esterification; two equivalents of water are formed.

Each reaction contains an excess of the alcohol to drive the reactions to completion. Esterification Where does the variety of esters come from?

The alkyl group (R1) O The alkoxy group can be changed (R2) can be changed R1 C OR2 O O R C OCH CH3 C OR2 1 3

O Notice that either the O CH3 alkyl group (R1) or the OCH CH3CH2 C OR2 alkoxy group (R2) may R1 C be branched groups or CH3 CH3 O contain other O functional groups. CH3 C OR 2 R1 C O CH2 CH C CH3 CH CH2 Esterification Draw the major organic product (the ester product) from each reaction. O Ignore the by- product (water) 1 CH3 C OH + CH3CH2OH

O OH

2 CH3 C OH + CH3 C CH3 CH3 O OH

3 CH3 C OH + CH3 C CH2 CH2 CH3 CH3 O See next slide for answers OH 4 CH3 C OH + CH3 Esterification O O

1 CH3 C OH + CH3CH2OH CH3 C OCH2CH3

O O OH CH3 CH C OH + CH C CH 2 3 3 3 CH3 C O C CH3 CH 3 CH3 O O OH CH3 3 + CH3 C OH CH3 C CH2 CH2 CH3 C OC CH2 CH2 CH CH3 3 CH3 CH3 O O CH3 4 OH CH3 C OH + CH3 C O CH3 Esterification

Using a diol as the alcohol produces a diester. Diols are also called glycols. O

O CH3 C O CH + O 2 2 CH3 C OH H O CH2CH2 O H + 2 HOH CH Ethane diol CH3 C 2 (ethylene glycol) O diester One molecule of water is formed for each ester bond formed. Two equivalents of ester condense with one equivalent of the diol. However, excess diol is used to drive the reaction to completion. Esterification Using a triol as the alcohol produces a triester. Triols are also called glycols.

O 3 esters bonds C O produces 3 H O molecules of CH CH O CH2 3 2 water O O CH CH 3 CH3 C OH + H + 3 HOH CH3 C CH CH2 O 2 H O O CH C Propane triol3 triester O Three equivalents of ester condense with one equivalent of the triol. However, excess triol is used to drive the reaction to completion. Esterification O OH + Draw the major 1 CH3 C OH O organic product. CH C OH + Assume acid 2 3 Cl OH catalysis for O each reaction. 3 + C OH OH Ignore water. O C OH + 4 OH OH OH HO + C 5 (assume excess acid is present) OH OH O O C OH HO O

6 + O C OH OH HO C HO Esterification problem # 1

O O

CH3 C OH CH3 C O + OH

Verify that you have 12 carbon atoms in both the alcohol and the alkoxy group Esterification problem # 2

O O + Cl CH3 C OH Cl OH CH3 C O

Verify that you have 7 carbon atoms in both the alcohol and the alkoxy group Esterification problem # 3

O O + C O C OH OH

Verify that you have 7 carbon atoms in the alkyl group and 5 carbons in the alkoxy group Esterification problem # 4

O C OH + O O OH OH O O

Remember there is free rotation around single bonds: the alkene functional group is rotated “up” in the product Esterification problem # 5

OH HO + C OH OH O O C O O C O O C O

Including the carbonyl carbon, there are 12 carbon atoms in each alkyl group Esterification problem # 6 O C OH HO O

+ O C OH OH HO C HO O Including the carbonyl C carbons, there are 12 O O carbons in each alkyl group. All double C bonds are cis. O O C O