PHENOL-FORMALDEHYDE RESINS AND PLASTICS Presented before the Division of Paint, Varnish, and Plastics Chemistry at the lOlst Meeting of the American Chemical Society, St. Louis, Mo.
Synthetic Phenols for Resin Manufacture E. C. BRITTON Dow Chemical Company, Midland, Mich.
OR many years following the discovery of Bakelite, the only phenols available for resin manufacture were coal tar phenols-namely, phenol and the cresols. For thermoset resin use these seemed to satisfy the demand. In recent years several phenols have been manufactured by synthetic processes and have found their places in the phenol resin industry, especially in the varnish resin field. Among these are p-tert-butylphenol, p-tert-aniylphenol, p-terl-octylphenol, p-phenylphenol, and p,p'-dihydroxydiphenylpropane. The purpose of this paper is to discuss the availability of these phenols for future expansion and the availability of other phenols by new synthetic processes which have not yet reached commercial development. Of the phenols named above, p-phenylphenol is the only one not derived from phenol but is synthesized from diphenyl. Accordingly, the production of phenol is the prime consideration in discussing the question of the availability of phenols. At present and so far as can be foreseen, sufficient benzene is available for the synthesis of the aromatic part of phenol and no shortage is likely. The hydroxyl group of phenol is introduced into the benzene ring by three different processes: (1) the classic process, involving the sulfonation of benzene to benzene sulfonic acid and sodium hydroxide fusion of sodium benzene sulfonate at a temperature of about 300" C.; (2) the more recent process, involving the chlorination of benzene to form monochlorobenzene followed by hydrolysis under autogenous pressure by dilute sodium hydroxide solution a t about 360" C.; (3) the recent catalytic vapor-phase hydrolysis of chlorobenzene a t about 450" C. I n the sulfonation process the raw materials are sulfuric acid, benzene, sodium hydroxide, and fuel. None of the reaction product can be re-used in the synthesis. In the second process named, the raw materials are benzene, chlorine, and sodium hydroxide. Fundamentally it involves only benzene, salt, and fuel inasmuch as the salt is electrolyzed to sodium hydroxide and chlorine. After the hydrolysis reaction the sodium phenate is neutralized with hydrochloric acid and forms salt which can be re-electrolyzed. Any large expansion of production by this process will undoubtedly require more 'chlorine than is now available. The last synthesis demands chlorine, benzene, and fuel as raw materials. However, the proponents of this synthesis claim that the chlorine is furnished by a modified Deacon process from the hydrogen
chloride produced in the reaction, only a small make-up being necessary. This latter process has been installed only a short time, and its expansion must await the trial of the present plant. The demand for phenol can be met by these synthetic processes. I n the above-mentioned para-substituted phenols, the substituted group-namely, the tert-butyl, tert-amyl, and tertoctyl-are derived from petroleum. Consequently there should be no shortage of the raw material for these groups. The p,p'-dihydroxydiphenylpropane is prepared from acetone and phenol and perhaps may be influenced considerably by the demand for acetone. Other phenols for which processes have been well developed are p-cyclohexylphenol from cyclohexene and phenol, p-cuminylphenol from a-methylstyrene and phenol, p-sec-butylphenol from n-butylene and phenol, m-phenylphenol from hydrolysis of 0- or p-chlorodiphenyl, dialkyl phenols from hydrolysis of dialkyl chlorobenzenes, p,p'-dihydroxydiphenylbutane or pentane, and p-benzylphenol from benzyl chloride and phenol. Practically all of the substituted phenols which are used by the resin manufacturers a t the present time are para-substituted phenols, and all those proposed in the paragraph above are the same type. I n the case of mixed cresols a considerable portion of m-cresol is used but no synthetic meta-substituted phenols are produced. For various reasons known to the resin producer, the ortho-substituted phenols are not used at all in the manufacture of phenolic resins. This is probably due to the poor color and light stability of the resin produced. If, however, the resin manufacturer would attempt to solve the problem of using ortho- and meta-substituted phenols as well as para-, there should be considerable expansion in the resin market. It is well known that unsaturates such as ethylene, propylene, butylene, and amylene, which are cheap raw materials and available in large quantities, will react with phenols to give a mixture of ortho- and parasubstituted phenols except when the olefin can react to give a tertiary group. Consequently, a manufacturer of synthetic phenols is limited in his choice of low-cost materials when the customer will consume only a para-substituted phenol. Many of the phenols known to chemistry can be c o m e r cially synthesized, several of them at lower cost than the present substituted phenols, especially if the resin manufacturer will utilize a mixture of substituted phenols.
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