Organic Reactions

The rate of hydrolysis of an ester can be increased by hydroxide ion. Like an acid catalyst, hydroxide ion increases the rates of the two slow steps of the reaction—namely, formation of the tetrahedral intermediate and collapse of the tetrahedral intermediate.

MECHANISM FOR THE HYDROXIDE-ION-PROMOTED HYDROLYSIS OF AN ESTER

Hydrolysis of An Ester with a Tertiary Alkyl Group

The hydrolysis of an ester with a tertiary alkyl group is an SN1 reaction rather than a nucleophilic addition–elimination reaction, because the carboxylic acid leaves behind a relatively stable tertiary carbocation.

MECHANISM FOR THE HYDROLYSIS OF AN ESTER WITH A TERTIARY ALKYL GROUP

Hydrolysis of An Ester with a Primary or Secondary Alkyl Group

When an acid is added to a reaction, the first thing that happens is the acid protonates the atom in the reactant that has the greatest electron density. Therefore, when an acid is added to an ester, the acid protonates the carbonyl oxygen.

Acyl chlorides react with alcohols to form esters, with water to form carboxylic acids, and with amines to form amides because, in each case, the incoming nucleophile is a stronger base than the departing halide ion.

An alkene can be converted to an epoxide by a peroxyacid.An epoxide is an ether in which the oxygen is incorporated into a three-membered ring, and a peroxyacid is a carboxylic acid with an extra oxygen.

Another way to convert an alkene to an alcohol is by two successive reactions known as hydroboration–oxidation.

As the following reactions show, the alcohol formed from hydroboration–oxidation of an alkene has the H and OH groups switched compared to the alcohol formed from the acid-catalyzed addition of water.

When an alkene is treated with ozone (O3) at a low temperature, both the s and p bonds of the double bond break and the carbons that were doubly bonded to each other are now doubly bonded to oxygens instead. This is an oxidation reaction—called ozonolysis — because the number of C— O bonds increases.