Bisphenol A

Bisphenol A (BPA) is the commercial name used in the United States for 4,4'-isopropylidenediphenol. In Europe I.U.P.A.C. nomenclature and other unsystematic names are still used. Its commercial name indicates the preparation from two molecules of phenol and one of acetone. The molecule of BPA cm be described as two phenolic rings joined together by a bridging isopropylidene group (Chernical Abstract now calls the radical 1 –methylethylidene

Preparation of Bisphenol A

This subsection describes the chemistry of BPA formation including mechanisms, possible reactions, by-products, and order of reaction.

Primary Reaction

The acid catalyzed condensation of acetone with 2 moles of phenol is the oldest process for producing BPA.

The heat of reaction, for reactants and products in their natural physical state at 25°C, is calculated from heats of formation as + 18.4 kcal/mol. Severe conditions are not required; a 1:2 molar ratio mixture of acetone and phenol, in the presence of concentrated hydrochloric acid or sulfuric acid 70% at room temperature deposits a mass of crude BPA crystals. The reaction conditions predominantly favour the formation of the products.

Some sources claim that the presence of 10% water in the reaction mixture greatly increases the rate of the reaction catalyzed by hydrochloric acid (Scheibel, 1974). Other sources claim that processes catalyzed by sulfonic acid ion exchange resins modified with alkyl-SH groups are also improved by the presence of 0.6 to 5% by weight water in the initial reaction mixture On the other hand, since water is a product of the desired reaction, its presence decreases the yield of BPA. To counterbalance this effect, dehydration by various water-binding agents (such as calcium chloride or phenyl acetate) or by azeotropic distillation have been suggested.

By - Products Formation

For reactions involving the substitution of a proton in an aromatic ring, both the rate of reaction and the equilibrium distribution of products are influenced by the density of electrons at the centre of reaction. This only applies if there are no steric effects. Thus the p,p-isorner (BPA) is the most likely to form since the density of electrons in the para position of the phenol is higher than in the ortho position. Also, the p,p-isomer formation is favoured from the thermodynamic point of view.

Still, o,p-isomer and some o,o-isomer are observed.

It was observed that the o,o-isormer is produced in negligible amounts. Another possible product that can result from the reaction of the already formed BPA with the tertiary carbonium ion @-phenyl isopropylidene is the so called "triphenol 1" (4,4'-(4-Hydroxy-m-phenyIenediisopropylidene)diphenol):

Resin - Catalyzed Process II

The resin catalyzed process for obtaining bisphenol A from a post-reaction mixture resulting from the step

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