Vitamin isocyanates, reactions with

X5lenol is an important starting material for insecticides, xylenol—formaldehyde resins, disinfectants, wood preservatives, and for synthesis of a-tocopherol (vitamin E) (258) and i7/-a-tocopherol acetate (USP 34-50/kg, October 1994). The Bayer insecticide Methiocarb is manufactured by reaction of 3,5-x5lenol with methylsulfenyl chloride to yield 4-methylmercapto-3,5-xylenol, followed by reaction with methyl isocyanate (257). Disinfectants and preservatives are produced by chlorination to 4-chloro- and 2,4-dich1oro-3,5-dimethylpheno1 (251). 

Except for derivatives of lower alcohols, allophanates are usually high-melting, well crystalline derivatives suitable for characterization and isolation the alcohol can be regenerated by warming the allophanate with methanolic alkali. That the reaction is applicable even to a highly reactive, acid-sensitive alcohol is illustrated by the isolation of vitamin D, by Windaus and co-workers from a complex mixture resulting on irradiation of 7-dehydrocholesterol. Treatment of the crude, oily mixture with isocyanic acid afforded directly a solid product easily purified by... 

Dehydration with phenyl isocyanate afforded a more homogeneous product (still a mixture of isomers) of higher vitamin A activity. The reaction was carried out by treating a solution of 33 g. of (1) in 150 ml. of purified phenyl isocyanate with 2 ml. of 1.5M ethylmagnesium bromide as catalyst and stirring the mixture at 95° for 3 hrs., during which time diphenylurea continuously precipitated (in the absence of catalyst no significant amount of diphenylurea was observed). 

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