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Wednesday, July 23, 2008

General Procedure of React Bisphenol A

The general procedure for conducting the reaction is as follows: 2,2-(4,4-dihydroxydiphenyl)-propane (bisphenol A) is heated with epichlorohydrin and aqueous sodium hydroxide at a temperature somewhat below the boiling point. The initial reaction is between the epoxide group of the epichlorohydrin and the hydroxyl group of the bisphenol A molecule with the resulting formation of a chlorohydrin. Form this, hydrogen chloride is split off and forms sodium chloride and water by reaction with the sodium hydroxide; a new epoxide ring is formed as part of a glycidil ether group. The kinetics of the reaction have been studied and described by Fisch. Variation of the broad preparative methods that have been patented include a number of continuous production processes.

In the preparation of the glycidyl ethers the amount of epichlorohydrin that actually combines with bisphenol A is less than the amount added, thus the monomeric diglycidyl ether cannot be made by reacting two moles of epichlorohydrin with one of the bisphenol. On the other hand the higher molecular weight resins, the solid can be made by adding further bisphenol A to the liquid glycidyl compounds.

In practice it is impossible to produce a resin with one hundred percent monomeric diglycidyl ether (n = 0), the reaction being that phenol not only reacts to form chlorohydrin as described, but also adds on the existing glycidyl ether groups through an ether linkage, and there is competition between glycidyl ether groups through and epichlorohydrin for the remaining free hydroxyl groups. Naturally, the higher the ratio of epichlorohydrin to bisphenol A the less the competition; but even with epichlorohydrin in large excess a product that is wholly diglycidyl ether cannot be obtained except by separating the fraction under high vacuum distillation. Perhaps this is all the good, because the really pure monomeric diglycidyl ether is a crystalline solid which would be inconvenient to use as an adhesive; fortunately, however, contamination with a small amount of higher polymer prevents crystallization.