Esterification Reactions of Vanillin: The Use of Nmr to Determine a Structure

[pic 1]

Experiment 3

 Esterification Reactions of Vanillin:

The Use of NMR to Determine a Structure

Objective

To investigate the reactions between vanillin and acetic anhydride under two conditions, basic and acidic conditions, melting point of the product and it’s percentage yield.

Introduction

        Esters came from the reaction of carboxylic acid and alcohol and contains the –COOH group. Esterification is a process to produce an ester as its final product. The OH group of carboxylic acid where substituted with the alkyl group of the alcohol and dehydration process occur (removal of water). This process is acid-catalyzed by a Lewis acid where it is in equilibrium in products and reactants. Fischer esterification proceed very slowly without the presence of strong acid but can achieve equilibrium when reflux with small amount of concentrated sulphuric acid and sodium hydroxide.

[pic 2]

Carboxylic group

[pic 3]

        In this experiment, esterification of vanillin will be carry out and the final product will produce vanillin (4-hydroxy-3-methoxybenzaldehyde). Vanillin is a food flavouring agent that is use in the culinary industry. The experiment will be carry out under two condition; acid and base. Sulphuric acid will be use under acidic condition while sodium hydroxide will be use under basic condition

[pic 4]

Structure of Vanillin

Apparatus/Reagents

Apparatus

1. Erlenmeyer Flask
2. Rubber stopper
3. Hirsch funnel
4. Beaker
5. Conical flask
6. Glass rod

Reagents

1. Vanillin
2. 10% sodium hydroxide
3. Acetic anhydride
4. Ice-cold water
5. Hot bath
6. 1.0M sulphuric acid
7. Crushed ice

Procedure

Preparation of 4-Acetoxy-3-Methoxybenzaldehyde (Vanillyl Acetate)

1.50g of vanillin were dissolved in 25mL of 10% sodium hydroxide in a 250mL Erlenmeyer flask. 30 g of crushed ice and 4 mL of acetic anhydride were added. The flask were stoppered with a clean rubber stopper and shaken over 20 minutes period. The precipitate were filtered and washed with 3 5mL portions of ice-cold water. The solid were recrystallized from 95% ethyl alcohol. The mixture were heated in hot water bath at 60℃. The dried crystal were weighed and the percentage yield was calculated. The melting point were obtained. The infared spectrum of product were determined using dry-film method. The proton NMR spectrum of the product in CDCl3 solution.

Esterification of Vanillin in the presence of acid

        1.5g of vanillin were dissolved in 10mL of acetic anhydride in a 125-mL Erlenmeyer flask. A magnetic stir bar were placed in the flask and the mixture were stirred at room temperature. 10 drops of 1.0 M sulphuric acid were added. The flask were stoppered and stired for 1 hour. The flask then were cooled in an ice-water bath for 5 minutes. 35mL of ice-cold water were added to the mixture. The flask were stoppered tightly and shaken vigorously. Then the flask were cooled and shaken. The product were filtered and washed with three 5mL portions of ice-cold water. The crude product were recrystallized from hot 95% ethanol. The crystal were dried and weighed. The percentage yield were calculated and the melting point were determined. The infared spectrum of product were determined using dry-film method. The proton NMR spectrum of the product in CDCl3 solution.

Results/Calculation

A. Preparation of 4-Acetoxy-3-Methoxybenzaldehyde (Vanillyl Acetate)

Mass of acetic anhydride

= 4mL x 1.08g/mL

= 4.32g

Mole of acetic anhydride

= [pic 5]

= 0.042 mol

Mass of vanillin= 1.5g

Mole of vanillin

[pic 6]

= 0.0098587 mol

1 mol vanillin = 1 mole vanillyl acetate

0.0098587 mol vanillin = 0.0098587 mol vanillyl acetate

Mass of vanillyl acetate

= 0.0098587 mol x 196.2 g/mol

= 1.9343g

Limitting reactant: Vanillin

Percentage yield of product

=  x 100%[pic 7]

= 78.09%

B. Esterification of Vanillin in the presence of Acid

Mass of acetic anhydride

= 10mL x 1.08 g/mL

= 10.8 g

Mole of acetic anhydride

= [pic 8]

= 0.1508 mol

Mass of vanillin

= 1.5 g

Mole of vanillin