Improved production of unsaturated ethers, especially isopropenylmethylether, by ketalization and ketal pyrolysis with combined extraction of the product streams

摘要

Production of unsaturated ethers (1) by pyrolysis of acetals or ketals (2) is such that the ketalization product stream is combined with the product stream of the ketal pyrolysis. Production of unsaturated ethers of formula (1) by pyrolysis of acetals or ketals of formula (2) is such that: (a) the acetals or ketals (2) are produced from an alcohol of formula (3) and an aldehyde or ketal of formula (IV) in presence of an acid catalyst; (b) the product stream (I) from the ketalization, consisting of a mixture of (2), (3) and (4) and water, is combined with the product stream (VI) of the ketal (or acetal) pyrolysis, consisting of ketal (or acetal), the desired ether (1) and alcohol (3); (c) the combined product streams (II) are extracted with an aqueous alkaline solution, the organic product stream (III) of this extraction consisting of a mixture of the corresponding acetal or ketal, the desired ether (1) and residual amounts of the aldehyde or ketone (4); (d) the desired ether (1) is isolated from this largely alcohol-free organic heteroazeotrope product stream (V) by distillation; and (e) the distillation residue (product stream (IV)) which contains the acetal of formula (2) and the corresponding carbonyl compound of formula (4), is pyrolyzed at 80-300 deg C in a high boiling point organic carboxylic acid and the thus-formed product stream (VI), which contains not only the desired ether (1) but also unreacted ketal or acetal and the corresponding alcohol, is fed to the extraction stage (b) and combined with the organic product stream (I) from the ketalization. R1 = H or 1-8C alkyl; R2 = H, Me, Et or Cl; R3 = 1-8C alkyl; and R4 = H or 1-3C alkyl or can form a 5-7-membered ring together with R1.