Carvone prepn. - by thermal dehydration of 1-methyl-1-hydroxy-4-isopropenyl-2-cyclohexanone

摘要

Prepn. of carvone (I) is carried out by thermal dehydration of 1-methyl-1-hydroxy-4-isopropenyl-2-cyclohexanone (II) at 150-350 degrees C (200-300 degrees C, esp. 250-280 degrees C). Dehydration is pref. effected by passing a mixt. of (II) and an inert diluent through a heated tube. (II) is pref. prepd. by reacting d-limonene with nitrosylsulphuric acid (III) in 50-90 wt.% H2SO4 at -20 to +10 degrees C, opt. in the presence of H3PO4; hydrolysing the resulting limonene nitrosylsulphate with H2O mto form 1-methyl-1-hydroxy-2-hydroxzyimino-4-isopropenylcyclohexane (IV); and treating the product with an alkali metal bisulphite at 40-70 degrees C in anhydrous MeOH or EtOH. The process gives high yields of (I) with high purity; e.g. dehydration of (II) prepd. from d-limonene gives 1-carvone with a specific rotation of >=-60 degrees.