Sulfuric Acid → 2,4'-Diphenylmethane diisocyanate

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0.3 g. of an ethyl ester of 2-[(ethoxycarbonyl)-phenylaminomethyl]phenylcarbamic acid (N-benzyl compound), prepared as in Example 1, along with 1.0 g. of 96.4 weight percent concentrated sulfuric acid was charged to a 300 ml reaction flask. The mixture was heated to 100° C. on a constant temperature bath for 60 minutes. High speed liquid chromatographic analysis showed conversion of the ethyl ester of 2-[(ethoxycarbonyl)phenylaminomethyl]phenylcarbamic acid to the diethyl ester of 2,4'-methylenebis(phenylcarbamic) acid and higher homologs to be 99+ percent with minor amounts of ethylphenylcarbamate. After acid extraction with water, the resulting 2,4'-methylenebis(phenylcarbamic) acid, diethyl ester (diurethane) was subjected to thermal decomposition by the method described in U.S. Pat. No. 3,962,302 to produce the diphenylmethane-2,4'-diisocyanate in good yield.

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