Chapter 40Chapter 40Esterification. Synthesis of Esterification. Synthesis of nn-Butyl -Butyl

Ester of Unknown Acid by Ester of Unknown Acid by Azeotropic Distillation of WaterAzeotropic Distillation of Water

PurposePurpose

• In this experiment an Unknown carboxylic acid is In this experiment an Unknown carboxylic acid is esterified with butanol in the presence of an acid esterified with butanol in the presence of an acid catalyst in an azeotropic distillation mode.catalyst in an azeotropic distillation mode.

• The product is isolated by: The product is isolated by: 1)1) withdrawing the reaction mixture from reaction flask with withdrawing the reaction mixture from reaction flask with

a Pasteur pipette to leave the catalyst behind anda Pasteur pipette to leave the catalyst behind and

2)2) extraction with aqueous NaHCOextraction with aqueous NaHCO33 solution and ether. solution and ether.

R OH

O

HO+

R O

O

+ H2O

H+

SO3H

Unknown acid Butan-1-olMW 74.12bp 117.7

n-Butyl Ester

Reaction MechanismReaction Mechanism

• The mechanism involves initial protonation of COThe mechanism involves initial protonation of CO22H group, H group, attack of the nucleophilic OH, a proton transfer, and loss of Hattack of the nucleophilic OH, a proton transfer, and loss of H22O O followed by loss of the catalyzing proton to give an ester.followed by loss of the catalyzing proton to give an ester.

CommentsComments• Follow pp. 559-560 (microscale).Follow pp. 559-560 (microscale).• Follow the lab handout for all experimental Follow the lab handout for all experimental

procedures. procedures. • Unreacted acid should be removed by washing Unreacted acid should be removed by washing

reaction mixture with aqueous NaHCOreaction mixture with aqueous NaHCO33 with with following extraction.following extraction.

• Perform IR and GC/MS analysis of the product. Perform IR and GC/MS analysis of the product. Prepare sample for NMR.Prepare sample for NMR.

• Determine the structure of the Unknown acid Determine the structure of the Unknown acid from spectral data.from spectral data.

• Calculate yield. Calculate yield. High to moderate yields should be High to moderate yields should be achieved.achieved.

SafetySafety

• Flammable reagents are used in this experiment, Flammable reagents are used in this experiment, keep away from open flame.keep away from open flame.

• Acids are corrosive, avoid contact with skin and Acids are corrosive, avoid contact with skin and eyes. eyes.

• Caution: Note ‘fruity’ fragrance of the final product Caution: Note ‘fruity’ fragrance of the final product (use wafting, do not inhale!). (use wafting, do not inhale!). n-n-Butyl acetate can Butyl acetate can cause irritation of eyes, upper respiratory system cause irritation of eyes, upper respiratory system and skin.and skin. Potential symptoms of overexposure are Potential symptoms of overexposure are headache, drowsiness, narcosis. Do not inhale, avoid headache, drowsiness, narcosis. Do not inhale, avoid contact with skin and eyes. contact with skin and eyes.