Takuo Kawaguchi

New Industrial Synthesis of 6-Methyl-5-hepten-2-one by Phase Transfer Reaction

6-Methyl-5-hepten-2-one (1) had been synthesized from 1-chloro-3-methyl-2-butene (3) and acetone (5) in anhydrous systems by using flaky alkali hydroxide with troublesome handlings. Much improvement in handlings, such as recovery of the catalyst or separation of sodium hydroxide and sodium chloride, was obtained by using phase transfer catalysts in aqueous systems.Various amines, quaternary ammonium salts, quaternary phosphonium salts, and tertiary sulfonium salts were investigated as catalsyts. Quaternary ammonium salts of long alkyl or benzyl derivatives and tricyclohexyl phosphonium salts were effective for industrial usage.Effects of solvents or sodium iodide and application to other ketones were also studied. It was suggested that the affinity of the catalyst to both organic and aqueous phase was quite important to obtain monoalkylated ketones.The reaction of (3) and (5) with aqueous sodium hydroxide in the presence of trimethyl (n-octadecyl) ammonium chloride (7) was investigated under various conditions from the viewpoint of conversion-selectivity of (3) to obtain (1) in an optimum yield. The reaction was dependent upon the concentration of sodium hydroxide as depicted in Figs.-6A, 7B, and 6C.Reactions of (3) and (5) in anhydrous systems by using flaky sodium hydroxide were also examined to compare with aqueous systems. Industrial profits of phase transfer reactions were discussed in consideration of a continuous process.