PREPARATION OF ISOPRENE

PURPOSE:To prepare isoprene, in high yield, by the liquid-phase reaction of an isobutylene source with a formaldehyde source in the presence of an acidic catalyst, wherein the reaction is carried out in the presence of a large amount of water in the reaction system in two steps at low temperature and high temperature under specific conditions. CONSTITUTION:Isoprene is prepared by the liquid-phase reaction of an isobutylene source with a formaldehyde source in the presence of water and an acidic catalyst. The amount of charged water is adjusted to >=4pts.wt., preferably 5- 100pts.wt., especially 10-50pts.wt. per 1pt.wt. of formaldehyde generated from the aldehyde source, and the temperature is changed in two steps; i.e. an isoprene precursor is synthesized at =150 deg.C, preferably 150-230 deg.C to decompose the precursor to isoprene. Isoprene can be prepared in high selectivity and yield by the one-step liquid-phase reaction, suppressing the production of hardly handleable by-products.