Bromothymol Blue → di-N-Octyl Phthalate

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A standard esterification apparatus, consisting of a 1-liter, 3 neck flask fitted with heating mantle, thermometer, nitrogen inlet tube and modified Dean-Stark separator topped with a total reflux condenser connected to a vacuum system, was charged with 148 g (1 mol) of phthalic anhydride, 312 g (2.4 mol) of 2-ethyl hexyl alcohol and 0.2 g (0.135% of PA charge) of tetrabutyl titanate (Tyzor TBT) catalyst. Heat was applied at a standardized setting and water of esterification began to form at a kettle temperature of 165° C. Heating was continued to reflux at 220° C. while removing water of reaction as fast as it is formed by azeotrope with toluene. Progress of reaction was monitored by rate of water formation until about 98% conversion of acid, at which time the reaction was sampled and the acid number determined by titration with 0.05N alcoholic KOH using bromthymol blue indicator. After 3.0 hours reaction time, the AN was reduced to 0.1 mg KOH/g, at which time the excess alcohol was removed by reducing the pressure of the system and removing alcohol distillate through the modified separator. Vacuum distillation was continued to 20 torr/200° C. at which time conditions were adjusted to 75 torr/150° C. and removal of alcohol continued by steam distillation, accomplished by dropwise addition of water to the bottom of the flask at a rate of about 1 ml/minute while maintaining the kettle at 150°-160° C. The kettle became cloudy after about 10 minutes. Distillation was continued for 30 minutes, at which time heat was removed and the system dried at full vacuum (12 torr) for 10 minutes. After cooling to 90° C. the cloudy residue was filtered through a No. 1 Whatman paper with a Buchner vacuum filter. The filtrate is cloudy and plugs the filter quickly. Refiltering with filter aid gives low odor di-octyl phthalate with AN=0.14 and color of 20 APHA.

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