Was to Prepare Variety of Esters and Try to Identify the Smell of Esters Formed

Aim

Was to prepare variety of esters and try to identify the smell of esters formed.

Introduction

Everything that has scent is made up of molecules. Their scent is determined by the functional group each molecule contains, which is connected to an organic compound, a carbon-based molecule. These functional groups can determine whether a molecule is an alcohol, if it smells putrid (a carboxylic acid), or if it smells sweet (an ester). However, there are more than just three functional groups (Williamson, 2011). When different functional groups react with one another, a new functional group is formed. For example, if an alcohol reacts with a carboxylic acid, an ester is formed. For this experiment, this is exactly what we had to do. The class was assigned to prepare certain esters and to combine alcohols and carboxylic acids in order to create different type of esters. If reacted correctly, the different properties of the different alcohols and carboxylic acids could make scents such as apple, strawberry, and banana.

The compounds you will be making are also naturally occurring compounds; the chemical structure of these compounds is already known from other investigations.

Esters are organic molecules of the general form:

[pic 1]

Where R and R’ are any carbon chain.  Esters are unique in that they often have strong, pleasant odors.  As such, they are often used in fragrances, and many artificial flavorings are in fact esters. Naming esters systematically requires naming the functional groups on both sides of the bridging oxygen.  Deriving the names of the side from the carboxylic acid merely requires replacing the suffix –ic with –ate. The process of making esters is called esterification (Rainsford, 2004). The reaction is catalyzed by the presence of H+ ions. Sulphuric acid is used as a catalyst for this experiment. In the past decade, esters of long chain fatty acids and alcohols have earned a special interest. There are several industrial possibilities for industrial use of fatty acid esters as natural compounds (Banyai et al, 2011). In the esterification process of vegetable oils, there is usually a reaction of oleic acid and other long chain fatty acids (12-20 carbon atoms) with selected alcohols. The chain length of the alcohol substrate determinates the use of the ester product. Short-chain alcohols with low molecular weights can be used for production of biodiesel and biofuels (Metzger, 2004). Long-chain alcohols (5 to 12 carbon atoms) in the esterification process make lubricants (Banyai et al, 2011). Fatty acid esters with high molecular weight alcohols (C16-C30) are waxes.

Apparatus

Test tubes

Test tube rack

Spatula

Beaker

Dropper

Water bath

Methanol

1-propanol

Stearic acid

Ethanoic acid

Glycerol

Sulphuric acid (conc.)

Oxalate

Method

Esters were prepared accordingly, test tube A, methyl ethanoate was prepared by adding 2.00ml methanol and 2.00ml Ethanoic acid and for test tube B, propyl stearate 2.00ml of 1-propanol was added with powder of stearic acid and for test tube C, diethyl oxalate 2.00ml ethanol was mixed with powder oxalate, and for test tube D, glyceryl tristerate 2.00ml glycerol was mixed with powder stearic acid. Then for all these reactions 10 drops of concentrated sulphuric acid was added and the reactions were heated at water bath for 2 minutes and were cooled by cold running water.

Results and discussion

1. (i) prepare methyl ethanoate

(ii) Provide names of the reactants used to prepare this ester.

Smell: nail polish remover

Provide a balanced equation for reaction (a):

1. (i) Prepare the ester obtained when propan-1-ol reacts with stearic acid.

Name of ester: propyl stearate

Smell: oil

Provide a balanced equation for reaction (b):

1. (i) prepare the ester diethyl oxalate

Provide the names of the reactants used to prepare this ester.

Ethanol and oxalate

Smell: aromatic odor (sweet smell)

Provide a balanced equation for reaction (c):

1. (i) prepare the tri-ester, glyceryl tristerate.

Provide the names of the reactants used to prepare this ester.

Glycerol and stearic acid

Provide a balanced equation for reaction (d):