(+)-Limonene → P-Cymene

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When it was sought to isomerize limonene to terpinolene using orthotitanic acid as a catalyst in undiluted limonene, it was found that the reaction was wildly exothermic to 215 degrees C. yielding principally p-cymene. The use of a hydrocarbon solvent, e.g., heptane was found to hold the temperature to 105 degrees C. However, after a few hours, few diene components were found, with mostly dimers and higher polymers being obtained. It was then decided to utilize a material normally regarded as a buffer in effort to moderate the reaction. This proved to be successful in that it allowed control of the reaction easily at 100 degrees C. without exotherm. No solvent was necessary. Sodium acetate as a reaction control agent was found to be especially effective at concentrations of from 0.1% to 1.0% by weight of the limonene charge, and more particularly from 0.2% to 0.5% by weight. Higher amounts of the control agent or buffer appear not to improve the conversion or selectivity and thus, the upper limit of concentration is not critical. The lower limit appears to be about 0.05% by weight of the limonene charge. At levels of 0.2% and 0.5% sodium acetate buffer, excellent results were obtained at 100 degrees C. With 0.5%, after 4 hours, 55% conversion gave 70% selectivity of terpinolene. At 0.2%, after 4 hours 55% conversion gave 69% selectivity. The catalyst was solid orthotitanic acid. The foregoing conversions and selectivities are commercially acceptable.

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