Nitriles, aromatic catalytic trimerization

Figure 1. Proposed PUSH-PULL mechanism for catalytic trimerization of aromatic nitriles.

Catalytic Trimerization of Aromatic Nitriles for Synthesis of Polyimide Matrix Resins... 

Aromatic nitriles may be trimerized at moderate temperature and pressure with p-toluenesulfonic acid as catalyst. Studies were conducted to establish the effect of the reaction temperature, pressure, time, and catalyst concentration on yield of the trimerized product. Trimerization studies were also conducted to establish the effect of substituting electron donating or withdrawing groups on benzonitrile. Preliminary results of using the catalytic trimerization approach to prepare s-triazine cross-linked polyimide/graphite fiber composites are presented. 

The purpose of the present investigation was to study the trimerization of aromatic nitriles under the conventional resin/fiber composite fabrication conditions using p-toluenesulfonic acid as a catalyst. Trimerization parameters investigated included reaction temperature, pressure, time, and concentration of catalyst. The influence of the nature of aromatic nitriles on trimerization was also studied. Also presented are preliminary results on the use of the catalytic trimerization of the nitrile-terminated imide oligomers to fabricate graphite fiber reinforced composites. 

Catalytic Trimerization. About 0.01 mole of the aromatic nitrile togethter with 0.5 to 5.0 mole percent of the p-toluenesulfonic acid (PTSA) catalyst was introduced into a <+5-milliliter stainless steel pressure vessel. The vessel was flushed with nitrogen gas and the initial 2 pressure in the vessel was varied from 0 to 2.76 MH/m (0 to 1400 psi). The vessel was then heated to temperatures in the range of 100 to 316°C. The selected temperature was maintained for 2i4 to 90 hours. The PTSA catalyst and unreacted nitrile were then removed from the product by washing with water followed by distillation under reduced pressure. The product was then recrystallized from xylene or glacial acetic acid. Melting point and infrared spectrum were determined for identification purposes. 

The pyrolysis gas chromatogram of ABS at 550°C changes considerably when the pyrolysis products are passed over zeolite catalysts. The specific activity towards certain reactions, e.g., cycliza-tion, aromatization, or chain cleavage is somewhat dependent on the nature of the individual zeolite. In general, enhanced benzene, toluene, ethylbenzene at the cost of dimer, trimer formation is observed. Nitrogen containing compounds do not appear in the pyrolysis oil after catalytic conversion. However, the product gas is rich in nitriles (132). 

Aromatic nitriles can be thermally selectively polymerized in pyrrolidin-2-one at temperatures above 200 C. Between 200 and 350 °C trimerization to 2,4,6-triaryl-l,3,5-triazines occurs, while at temperatures above 300 °C imidization occurs resulting in nonmelting, linear polyaryl-carbimine. Mixtures of trimers and polymeric imines are separable by sublimation or extraction with aromatic hydrocarbons.180 Since aryltriazines and polymeric aryltriazines have various industrial applications, several catalytic systems have been developed for the trimerization of aromatic nitriles and dinitriles, e.g. metal chlorides,181 iron(II) or iron(lll) cyanide,182 cop-per(II) carbonate,183 and molten zinc(II) chloride.184... 

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