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Alcohols in Esterification: Structure & Products

Instructor: Sarah Pierce

Sarah has a doctorate in chemistry, and 12 years of experience teaching high school chemistry & biology, as well as college level chemistry.

This lesson is an introduction to alcohols, their role in ester synthesis, and the products they form after esterification. The structure of alcohols is also discussed, as well as how to name them.

Alcohols

Alcohols are most often known for their presence in drinks such as wine and beer. Did you know that the scientific name for the molecule in drinking alcohol is ethanol? Other important alcohol molecules are methanol, which is used as an antifreeze in some cars, and isopropyl alcohol, or more commonly known as rubbing alcohol, which is the liquid applied on your arm before a shot.

Ethanol (left) is the alcohol molecule in the cocktail people enjoy on the beach (right)
eth

An alcohol is also used in organic chemistry to describe an atom group on an organic molecule. When a molecule that is made of mostly carbon and hydrogen has an OH group, it belongs to the alcohol family or functional group. The reason why an alcohol is called a functional group in chemistry is because that part of the molecule (OH) can react with other molecules. As a matter of fact, alcohol molecules can react with another family of organic molecules called carboxylic acids to form another molecular family: esters! Let's learn a little bit more about alcohols and the esters that they form.

Naming Alcohols

Alcohols are named based on the number of carbons that are in the molecule. Each name has an ol suffix, which indicates the molecule has an alcohol functional group. The prefix tells us how many carbons the molecule has.

Number of
Carbon Atoms
Alcohol Name
1 Methanol
2 Ethanol
3 Propanol
4 Butanol
5 Pentanol
6 Hexanol
7 Heptanol
8 Octanol

Ester Synthesis

Alcohols can react with another family of organic compounds called carboxylic acids. Carboxylic acids are organic molecules that have a carbon with a double bond to an oxygen next to an OH molecule. The functional group of carboxylic acids is COOH. These react to form another functional group, called an ester. An ester is a molecule that has a carbon with double bonds to an oxygen and a single bond to another oxygen. Its functional group is R-COO-R'. R just stands for the other carbon atoms in the molecule. Wintergreen oil, also known as methyl salicylate, is an example of an ester that can be synthesized from methanol and salicylic acid.

Methyl salicylate is an ester made from methanol
wintergreen

Fischer Esterification

When an alcohol and carboxylic acid react to form an ester, the reaction that occurs is called Fischer esterification, named after the scientist Emil Fischer who discovered it. Let's look at the step-by-step process or mechanism for this reaction. In a mechanism, the arrows show how the electrons of the atoms or bonds move.

In the first step, the carboxylic acid is protonated by an acid. This means that a proton (H+) is added to the oxygen that has a double bond to the carbon.


Step 1: The carboxylic acid is protonated.
s1


In the second step, the electrons of the alcohol attack the doubly bonded carbon on the carboxylic acid. Once the bond forms, the hydrogen on the original alcohol group is removed by a base.


Step 2: The alcohol adds to the carboxylic acid.
step 2


In the third step, the alcohol group is protonated by an acid.


Step 3: An acid adds to the alcohol group.
3


In the fourth step, the electron from the alcohol reform a double bond to the carbon. The molecule loses water.


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