P. Lesage et al., SELECTIVE DEHYDROGENATION OF DIPENTENE (R-(-LIMONENE) INTO PARACYMENEON SILICA-SUPPORTED PALLADIUM ASSISTED BY ALPHA-OLEFINS AS HYDROGEN ACCEPTOR()), Journal of molecular catalysis. A, Chemical, 112(3), 1996, pp. 431-435
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).