Prodn. of opt. substd. thioxanthone(s), useful photoinitiators - by reacting ortho,ortho'-di:halo-benzophenone with sulphur in alkaline 2-phase medium in the presence of phase transfer catalyst

摘要

Process for the prodn. of opt. substd. thioxanthones (I) comprises reacting the corresponding o,o'-dihalobenzophenone (II) with sulphur in alkaline medium in a 2-phase system in the presence of a phase transfer catalyst (III). Pref. (I) and (II) have the formulae given (R1 and R2 opt. the same) are H, 1-4 C alkyl, 1-12 C alkoxy or halogen; R3 (opt. the same) are 1-4 C alkyl; R4 (same or different) are 1-4 C alkyl; and m and n (same or different) are 1, 2 or 3; and Hal= halogen. (III) is esp. an onium salt such as an ammonium or phosphonium salt, esp. a quat. ammonium salt such as triethylbenzylammonium chloride, methyltricaprylammonium chloride, methyltrioctylammonium chloride or hexadecyltributyl-phosphonium bromide. The alkali is e.g. a hydroxide, (bi)carbonate or alcoholate. The two phase system is e.g. benzene/water, toluene/ water, etc. (I) are useful photoinitiators.