Question

(a) Propose a mechanism for the reaction of bisphenol A with phosgene.

(b) Diethyl carbonate serves as a less-toxic alternative to phosgene for making Lexan. Propose a mechanism for the transesterification of diethyl carbonate with bisphenol A, catalyzed by a trace of sodium ethoxide. What small molecule is given off in this condensation?

Short answer

Ethanol is given off in this condensation process.

Step-by-step solution

Bisphenol A (BPA)

It is a common intermediate in polyester and polyurethane synthesis. BPA is primarily used in the production of polycarbonate plastics. BPA enhances rigidity when added to plastic resins.

Condensation polymerization

In this process, a large number of monomer molecules combine together usually with the loss of simple molecules like water, alcohol, ammonia, carbon dioxide, hydrogen chloride etc., to form a polymer in which the molecular formula of the repeat unit is not the same as that of the monomer.

Mechanism

(a) In the first step, bisphenol A reacts with phosgene to form the initial product as 4-(2-(4-hydoxyphenyl)propan-2-yl)phenyl carbonochloridate.

In the second step, the initial product again reacts with another bisphenol A molecule to give the product as that is more commonly called Lexan carbonate.

In the third step, reacts with another phosgene molecule to give 4-(2-(4-(((4-(2-(4-hydroxyphenyl) propan-2-yl) phenoxy) carbonyl) oxy) phenyl) propan-2-yl) phenyl carbonochloridate.

complete mechanism for the reaction

(b) In the first step, bisphenol A reacts with diethyl carbonate to form the initial product as ethyl (4-(2-(4-hydroxyphenyl) propan-2-yl) phenyl) carbonate.

In the second step, the initial product formed reacts with another bisphenol A molecule to give the product as bis(4-(2-(4-hydroxyphenyl) propan-2-yl) phenyl) carbonate that is more commonly called Lexan carbonate.

complete mechanism for the reaction

Small molecules like ethanol is given off in this condensation polymerization process.