α-Pinene Conversion to Terpineol and Other Derivatives: Molecular Modeling and Infrared Mechanistic Study

A method to control terpineol production from turpentine by acid catalysts mixing

“…Similar to the previous work [ 7 ], that conducted the experiment with a mixture of phosphoric acid and formic acid as catalysts, the optimum reaction time of this study was found around 6–8 h. Proper reaction time is required to avoid over-dehydration reaction that could result limonene which has almost similar reaction energy level compared to terpineol [ 14 ]. This result is also supported by previous work [ 8 ] that conducted the reaction in the range between 8 and 12 h. Although the hydrolysis of turpentine requires stoichiometry balance of 1 mol of water per 1 mol of reactant following the mechanism of pinene + H 2 O → terpineol, more water was required to ensure the reaction completion.…”

“…In this work some reaction parameters, i.e . reaction temperature, reaction time, and water to reactant ratio, are optimized by using PTSA as the selected catalyst following the result of previous work [ 14 ]. Thus, optimum reaction condition was determined based on the highest yield of terpineol using PTSA as catalyst and catalyst to reactant ratio of 1–10.…”

“…This reaction begins with the transformation of one double-bond into single-bond of C–C to form carbocation with the help of an acid catalyst [ 13 ]. There are five carbocation species, pinanyl, p-menthenyl, isobornyl, fenchyl, and terpinene, have been identified with relatively different in term of reaction activation energy [ 14 ]. These carbocations will be attacked by water molecules (as a nucleophile) forming a hydroxyl bond and become terpineol.…”

“…However, this reaction tends to form by-products such as fenchol, borneol, cineol, and others. By-products formation has been reported as the effect of isomerization reaction via terpinene carbocation formation [ 14 ]. Previous works have been conducted in order to synthesise pure α-pinene to terpineol focusing on the acid catalyst selection [ 14 ].…”

“…By-products formation has been reported as the effect of isomerization reaction via terpinene carbocation formation [ 14 ]. Previous works have been conducted in order to synthesise pure α-pinene to terpineol focusing on the acid catalyst selection [ 14 ]. Studies on the type of acid catalysts were done by applying: (1) sulfuric acid and resulting 47% of terpineol yield [ 10 ]; (2) Heteropolyacid and producing 90% of α-pinene conversion with 30% of terpineol selectivity [ 15 ]; (3) mixed hydrochloric acid, acetic acid, oxalic acid and chloroacetic acid and resulting 91.2% of α-pinene conversion with 49.2% of terpineol selectivity [ 3 ].…”