Identifying an Unknown Alcohol – Fischer Esterification

Written by Zahava

In this experiment, an unknown alcohol underwent a Fischer Esterification reaction by reacting it with acetic acid as well as sulfuric acid catalyst.  The unknown product material was purified through distillation and characterized by analyzing the NMR and IR spectrum and determining the density of the product.  In addition, the boiling point, refractive index, and chemical tests were performed to test for an ester.  Lastly, the starting material, an unknown alcohol, was determined after finding out the product and examining the NMR spectrum for the reactant.

An acetate was synthesized by reacting an alcohol with acetic acid.  Since the acetic acid, a carboxylic acid, is less reactive than the acetate, an ester, the sulfuric acid catalyst was used to make the reaction more favorable.  Sulfuric acid easily donates a hydrogen ion to protonate the carbonyl oxygen in acetic acid, forming a stable intermediate with contributing resonance structures.  The nucleophilic alcohol compound then simply attacks the electrophilic carbon in the intermediate.  After, the intermediate undergoes tautomerism where a proton is shifted from the newly formed oxonium ion to the hydroxyl group, forming an activated complex.  Overall, the reaction results in the removal of water and deprotonation of the complex forming an acetate.

The identified peaks in the IR spectrum indicate that the compound is (acetate) because of the aliphatic ester and alkyl groups.  The very strong narrow peak at about 2960 cm-1 indicates a C-H stretch and is in agreement with the literature value of 2960 cm-1 for a C-H antisymmetric stretch in an alkyl group.  The very weak narrow peak at 2870cm is due to a C-H stretch and is diagnostic of a C-H symmetric stretch for an alkyl group with the expected value of 2870 cm.  The very strong peak at 1750 cm-1 represents a C=O stretch and is in agreement with the literature range value of 1755 cm – 1735 cm for a c=o stretch in an aliphatic ester group.  The medium/strong narrow peak at 1360 is a ch3 bend and is in good agreement with the expected range value of 1370-1360 cm for a CH3 symmetric bend alpha to ester c=o in an aliphatic ester group.  The very strong wide peak at 1260 cm is due to a c-co-c stretch for an ester group and is in agreement with the expected range of 1260-1230 cm for a c-co-c antisymmetric stretch in acetates.  The very strong peak at 1060 cm is due to a o-ch2-c stretch and is diagnostic of a o-ch2-c antisymmetric stretch for primary acetates with the literature value of 1060-1030 cm.  The additional weak narrow peak at 3450 cm is implicit of a C=O overtone stretch and is in agreement with the literature range value of 3430-3410 cm for a carbonyl overtone stretch in an aliphatic ester group.