Review on heterogeneous catalysts for the synthesis of perfumery chemicals via isomerization, acetalization and hydrogenation

Abstract

Synthetic fragrance has dominated the perfumery industry in recent decades due to the ability to produce perfumery ingredients on a large scale at a low cost. Extensive research in the field of synthetic perfumery chemical involved the utilization of catalysts to improve the productivity. This review will discuss recent advances of heterogeneous catalysts for the synthesis of perfumery chemicals as fragrance ingredients. Transition from homogeneous to heterogeneous catalysts will be included in order to provide insight into the benefits of heterogeneous catalysts to overcome the limitation of homogeneous reaction. Isomerization, acetalization and hydrogenation were identified as three main reactions for the synthesis of perfumery chemicals based on the number of reported work since 2000. This review will focus on α-pinene and α-pinene oxide as the main molecular substrates, however, different molecules, for example, linalool, citronellal and cinnamaldehyde will also be included. The synthesis, modification and possible mechanisms for the reactions involving zeolite, aluminosilicate, metal oxides, metal organic framework, monometallic and bimetallic nanoparticles as heterogeneous catalysts will be discussed. Discussion on isomerization and acetalization reactions will focus on the acidity and the porosity of the catalysts as the two main factors that determine the conversion and selectivity. For perfumery chemicals produced via hydrogenation reaction, the role of monometallic and bimetallic nanoparticles catalysts will be discussed in the chemoselective reduction of cinnamaldehyde and citronellal.