| 摘要 |
PURPOSE:On the decomposition or dehydration of gem-diot, hemiacetal or hemiketal corresponding to the objective compound with concentrated sulfuric acid, the reaction is effected in two-staged process at an individually specified temperature respectively to enable the advantageous production of the titled compound which is useful as an intermediate of drugs and agricultural chemicals. CONSTITUTION:In the production of a compound of formula II by the decomposition or dehydration of a compound of formula I , the reaction is effected by means of a two-stage process where at the first stage 4, the decomposition and dehydration with sulfuric acid 3 is carried out at 90-140 deg.C, preferably 120- 130 deg.C and at the second stage, the reaction product at the first stage 11 is decomposed or dehydrated with conc. sulfuric acid at a temperature lower than 60 deg.C, preferably lower than 30 deg.C, thus giving the objective compound undergoing sufficient decomposition and dehydration with a very small amount of sulfuric acid employed. The concentration of the sulfuric acid at the first stage is preferably over 65 wt% and at the second stage, over 93wt% and the reaction is effected preferably as a continuous process.
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