Alternative solvents in carvone hydrogenation

Dissertação para obtenção do Grau de Mestre em Engenharia Química e Bioquimica

Hydrogenation of monoterpenes, such as carvone, in high-density carbon dioxide over 0.5 wt.% Pd, or Rh, or Ru supported on alumina was investigated. Hydrogenation is generally faster in a single supercritical (sc) phase than in a biphasic system. The reaction catalysed by Pd produces full hydrogenated products (isomers of carvomenthone) and carvacrol while Rh catalyst is more selective and favours carvomenthone isomers with higher selectivity and carvotanacetone as secondary product. Additionally, the Rh catalysed reaction exhibited high >84% selectivity of carvotanacetone with the conversion of >25% after only 2 minutes of reaction. Ru catalyst gives significantly lower conversion of carvone and the product variety is greater as carvomenthone isomers, carvotanacetone and carvacrol are formed. The conversion and selectivity to carvomenthone within 2 hours course of the reaction followed the order: Pd > Rh > Ru and Rh > Pd > Ru, respectively. Efficient synthesis of carvacrol, an antimicrobial reagent, has been accomplished by using three “one-pot” sequences. After hydrogenation catalysed by palladium, carvacrol is separated from the post-reaction mixture using an ionic liquid at easily achievable temperature which could be later extracted with supercritical carbon dioxide.