Catalytic oxidations with molecular oxygen

Abstract

How to make spearmint from oranges? This was the original idea behind this research project. The flavors and fragrances industry has access to a large supply of limonene, which is extracted from citrus fruit skins. A valuable product for the industry is carvone, which is chemically similar to limonene. This oil smells of spearmint, and is used in toothpaste and chewing gum. The only difference between the two chemicals is an oxygen atom. Carvone can therefore be made from limonene by reacting it with oxygen. Until recently, oxygen from the air, which is clean, cheap and readily available, could not be used for this process. Instead, environmentally unfriendly oxygen-containing compounds were used. The aim of this project was to investigate the possibility of using air as an oxygen source for oxidation processes such as the reaction of limonene to carvone. Several steps are necessary to obtain carvone from limonene. The first step, the epoxidation, comprises the larger part of this thesis. The mechanism of the epoxidation, which is the way in which the chemicals react with each other, was not well-known. All components of the reaction, such as temperature, pressure and several additives, were investigated in detail to create a clearer picture of the process. Furthermore, a different chemical reaction with oxygen was investigated: the benzylic oxidation. This reaction is used in the production of herbicides and pesticides. It was investigated whether the method used for the epoxidation was applicable to the benzylic oxidation. After some minor changes, an efficient process was developed for benzylic oxidations with air. It is concluded that the application of oxidations processes with air for the manufacture of flavors, fragrances and other fine chemicals, is promising. In order to make the process economically feasible, cheaper additives need to be found. The chemical oxidation method using oxygen from the air has been shown to be convenient and selective