SELECTIVE DEHYDROGENATION OF DIPENTENE (R-(-LIMONENE) INTO PARACYMENEON SILICA-SUPPORTED PALLADIUM ASSISTED BY ALPHA-OLEFINS AS HYDROGEN ACCEPTOR())

Paracymene is a well known material used in polymers and perfume chemi stry. It can be obtained by the dehydrogenation and the aromatization of dipentene (R-(+)-limonene). To be useful, this reaction must be ful ly selective to avoid further purification processes. Dipentene is rea dily dehydrogenated with a palladium catalyst, but hydrogenation simul taneously takes place leading to cis and trans paramenthanes which dra stically decreases the yield in paracymene. To avoid this hydrogenatio n which occurs by hydrogen transfer, alpha-olefin has been used as hyd rogen acceptor. Using silica supported palladium and a hydrogen accept or(e.g. 1-decene) paracymene is obtained from dipentene with a very hi gh yield (95%) at a moderate temperature (145 degrees C).