CK-12-Chemistry Intermediate

http://www.ck12.org Chapter 25. Organic Chemistry

This reaction forms a molecule called a dipeptide, and the resulting carbon-nitrogen covalent bond is often called a

peptide bond. When repeated numerous times, a long molecule called a protein is eventually produced.

Esterification

Anesterificationis a reaction in which an ester is formed from an alcohol and a carboxylic acid. Esterification is

a subcategory of condensation reactions because a water molecule is produced in the reaction. The reaction can be

catalyzed by a strong acid, usually sulfuric acid. When the carboxylic acid, butanoic acid, is heated with an excess

of methanol and a few drops of sulfuric acid, the ester methyl butanoate is produced. Methyl butanoate has the scent

of pineapples. The reaction is shown below with both molecular and structural formulas.

CH 3 CH 2 CH 2 COOH+HOCH 3?

H 2 SO 4

−→ CH 3 CH 2 CH 2 COOCH 3 +H 2 O

Esterification reactions are reversible. When an ester is heated in the presence of a strong base such as sodium

hydroxide, the ester breaks down. The products are an alcohol and the conjugate base of the carboxylic acid.

CH 3 COOCH 2 CH 3
ethyl ethanoate

+NaOH→CH 3 COO−Na+

sodium acetate

+CH 3 CH 2 OH

ethanol

The sodium hydroxide is not acting as a catalyst; it is consumed in the reaction. Saponificationdescribes the

alkaline hydrolysis reaction of an ester. The term saponification originally described the hydrolysis of long-chain

esters called fatty acid esters to produce soap molecules, which are the salts of fatty acids. One such soap molecule

is sodium stearate, formed from the hydrolysis of ethyl stearate.

C 17 H 35 COOC 2 H 5
ethyl stearate

+NaOH→C 17 H 35 COO−Na+

sodium stearate(soa p)

+C 2 H 5 OH

Polymerization

Polymers are very different than the other kinds of organic molecules that you have seen so far. Whereas other

compounds are of relatively low molar mass, polymers are giant molecules of very high molar mass. Polymers are

the primary components of all sorts of plastics and related compounds. Apolymeris a large molecule formed of

many smaller molecules covalently bonded to one another in a repeating pattern. Thesmall molecules that make up

the polymer are calledmonomers. Polymers are generally formed by either addition or condensation reactions.