Illustrated Guide to Home Chemistry Experiments

374 DIY Science: Illustrated Guide to Home Chemistry Experiments

LABORATORY 21.1:

SyNTHESIzE mETHyL SALICyLATE fRom ASpIRIN

Esters are a class of organic compounds.

An ester comprises an organic or inorganic

acid in which one or more hydroxy (OH) groups

has been replaced by an alkoxy (O-alkyl)

group. For example, the simplest ester, methyl

formate (CHO-OCH 3 ), is made up of formic

acid (CHO-OH) in which the hydroxy group has

been replaced by a methoxy group (-OCH 3 ).

Similarly, ethyl acetate (CH 3 CO-OCH 2 CH 3 ) is

made up of acetic acid (CH 3 CO-OH) in which

the hydroxy group has been replaced by an

ethoxy group (-OCH 2 CH 3 ).

Although esters can be produced by many mechanisms, the
most commonly used method is called esterification, which is a
condensation reaction between an alcohol and an acid, typically
in the presence of a strong acid catalyst, such as sulfuric acid.
For example, ethyl acetate can be produced by reacting ethanol
(ethyl alcohol) with acetic acid and isopropyl butyrate by reacting
isopropanol (isopropyl alcohol) with butyric acid.

Esters were traditionally named by combining the name of
the alcohol with the root name of the acid and adding “ate”

EvRdE y Ay SyNTHESES

With the exception of natural materials such as wood, metals, and raw food products, nearly

every material with which you come into daily contact exists because a chemist synthesized

it. As a thought experiment, I began looking around my office as I wrote this section, counting

objects made from or that contain synthetic materials. I stopped when I reached 100, and I was

still counting objects on my desk. (Yes, I have a very cluttered desk.)

All of us are utterly dependent on artificial materials synthesized by chemists. Life without

synthetic materials is difficult to imagine.

as a postfix. Traditional names are still widely used by most

chemists, particularly for the simpler esters. The IUPAC

naming system uses the systematic names for the alcohol

and root name of the acid, followed by “oate.” For example,

the traditional name n-amyl acetate (n-amyl alcohol with

acetic acid) is represented in IUPAC nomenclature as 1-pentyl

ethanoate (1-pentyl alcohol, the systematic name for n-amyl

alcohol, with ethanoic acid, the systematic name for acetic

acid).

Esters typically have strong, often pleasant, scents and tastes,

so many esters are used as flavoring and perfume agents,

either individually or in combination. For example, the scent

and taste of strawberries is due to the presence of (among

others) methyl cinnamate, ethyl formate, ethyl butyrate, ethyl

caproate, isobutyl acetate, and benzyl acetate.

In this lab session, we’ll synthesize methyl salicylate, whose

common name is oil of wintergreen. You might expect that

we’d synthesize this compound by reacting methyl alcohol

(methanol) with salicylic acid, and that is indeed one possible

method. Instead, however, we’ll synthesize methyl salicylate by

reacting methanol with aspirin, which is much easier to come

by than salicylic acid. Aspirin is actually a substituted salicylic

acid, called acetylsalicylic acid, which is itself both an acid and

an ester.

FIGURE 21-1: Conversion of aspirin to salicylic acid to methyl salicylate (image courtesy Dr. Paul B. Jones)

aspirin fast salicylic acid slow

methyl salicylate

(oil of wintergreen)