α-pinene is a naturally occurring organic compound that belongs to the terpene group of chemicals. It is a colorless liquid with a strong pine odor and is commonly found in the essential oils of various plants, especially conifers such as pine, fir, and cedar.
α-pinene is the main component of turpentine, a renewable natural resource. Through catalytic isomerization and subsequent reaction with maleic anhydride, α-pinene can undergo a Diels-Alder reaction to form 1-isopropyl-4-methylbicyclo[2,2,2]-5-octene-2,3-dianhydride, which is commonly referred to as α-terpinene-maleic anhydride adduct (TMA).
Fig. 1 Synthetic route of TMA.
TMA has unique properties and applications as a precursor for the synthesis of novel functional derivatives based on turpentine. The reaction of TMA with isooctanol catalyzed by p-toluenesulfonic acid allows the synthesis of a novel plasticizer-like substance: di-2-ethylhey α-pinene-maleate.
Synthesis of TMA
Reagents and Equipment:
Maleic anhydride, α-pinene, DLB catalyst, N,N-dimethylaniline, 10% NaCl solution, Distilled water.
Four-necked flask, Electric stirrer, Thermocouple probe, Reflux condenser, Constant pressure-dropping funnel, Electric heating jacket.
Procedure:
(1) Add 40 g of maleic anhydride to a 250 mL four-necked flask equipped with an electric stirrer, thermocouple probe, reflux condenser, and constant pressure-dropping funnel. The flask is heated using an electric heating jacket until the maleic anhydride melted.
(2) After stirring and heating the molten maleic anhydride to 145°C, DLB catalyst is added. The amount of catalyst is 3% (by mass of α-pinene).
(3) An excess of α-pinene (molar ratio of α-pinene to maleic anhydride 1.4:1) is added slowly and dropwise over a period of 30-40 minutes, maintaining constant stirring. The progress of the reaction is monitored with N,N-dimethylaniline until no red color appeared, indicating completion of the reaction. (Reaction time is about 1.0 hours)
(4) The mixture is cooled, the catalyst is removed and the crude product is ished with 10% NaCl solution followed by distilled water 2-3 times.
(5) Distill the unreacted terpene under reduced pressure at 0.096-0.098 MPa and vacuum dry to obtain a light yellow transparent viscous liquid.
Synthesis of Di-2-ethylhey α-pinene-maleate
Reagents and Equipment:
TMA, Isooctyl alcohol, p-toluenesulfonic acid (catalyst), 3% NaOH solution.
Four-necked flask, Stirrer, Thermometer, Reflux condenser, Vacuum system, Oil bath.
Fig. 2 Synthetic route of di-2-ethylhey α-pinene-maleate.
Procedure:
(1) 20.0 g of TMA and the corresponding molar amount of isooctanol are added to a 250 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, and connected to a vacuum system (the ratio of TMA to isooctanol in substance is 1:3.5).
(2) After heating the flask to 130 °C using an oil bath, 1.0% p-toluenesulfonic acid (by mass of α-pinene) is added and a vacuum is initiated. The reaction mixture is stirred uniformly. the reaction is stopped after 180 min.
(3) The reaction product is cooled and neutralized with 3% NaOH solution. The product is ished 2-3 times and distilled at 10-11 kPa under reduced pressure to remove water and excess isooctanol to obtain the product, the appearance of light yellow transparent liquid.
Overall, α-Pinene is an important natural compound with a wide range of potential applications in various industries, as well as in the field of medicine and biology.
