Isomerization of turpentine using various heterogeneous and homogeneous acid catalysts

Abstract

Turpentine oil and its derivatives are major monoterpene compounds widely used as organic solvent, fragrance, flavoring agent, disinfectant, pesticides, and pharmaceutical applications. Isomerization of turpentine (mostly composed of α-pinene) can results important products such as camphene and limonene. Unfortunately, the synthesis occurred in a very complex reaction pathway, which can produce several side-products such as terpinene, terpinolene, polymers, and hydrates. The aim of this study is to conduct isomerization reaction of turpentine by using heterogeneous and homogeneous catalysts in the optimum operation conditions. The reaction was carried out under acidic solution as it needs protons (H+) to attack the double bond of α-pinene and produce carbocation named pinanyl cation. Then it would be rearranged into more stable isomers that we desired. The procedures of the synthesis were divided into four steps i.e. preparation of catalyst, reaction of turpentine and the catalyst in an acidic solution, separation of water-oil phase by decantation, and analysis of the oil phase product by using Gas Chromatography-Mass Spectrophotometry (GC-MS) method. Titanium dioxide (TiO2), silicon dioxide (SiO2), and zeolite (treated and mixed by either HCl or p-toluenesulfonic acid) are the solid or heterogeneous catalysts used in this experiment while sulfuric acid and formic acid are the homogeneous ones. Other variations were conducted for obtaining the best operation condition i.e. reaction temperature, amount of the catalyst, and value of pH. It was found in heterogeneous acid catalysts; the highest limonene yield is 24.3% from zeolite catalyst with composition of 0.8 gram catalyst per 10 mL turpentine mixed with HCl 1 M at 85°C and agitation time of 6 hours. For homogeneous acid catalysts, the highest limonene yield is 48.2% by using combined sulfuric acid and formic acid at pH of 0.37 under the same temperature and reaction time as heterogeneous condition.