Synthesis Of4-benzylidene-2,6-di-tert-Butylcyclohexa-2,5-dienones

2,6-Di-tert-butyl-7-substituted quinone methides (QMs) have great antipolymerant and antioxidant characteristics, they are widely used as inhibitors of styrenes and acrylic compounds. With more attention the government paid to the environment and the prohibition of toxic inhibitors, QMs have endured extensive research lately.4-benzylidene-2,6-di-tert-butylcyclohexa-2,5-dienone is one of the most important quinone methides which also has been reported to have the antipolymerant and antioxidant characteristics. In the present paper, we made some improvements on current synthetic method and finally got the optimized reaction condition. Subsequently, we made some innovation of the traditional method, in our new technology, the Mannich base produced in the reaction were removed of amine through vacuum distillation other than using acetic anhydride. The improved technology has the characteristics of easier operation, higher production efficiency and lower production cost.In traditional technology, there are emissions of ammonia and nitrogen compouds, the catalyst used was larger than raw material which increases reaction cost. Based on the reversibility of forming Mannich base and the thermal instability of Mannich base, we explored one-pot solvent-free stoichiometric reaction technology and catalytic reaction technology of this reaction. During the reaction, the water produced was removed, which greatly accelerated the removal of amine, improved the conversion and reduced the dosage of the catalyst. The optimized reaction condition is2,6-ditertbutylphenol:benzaldehyde=1:1.2, piperidine:2,6-ditertbutylphenol=0.5:1, piperidine was added slowly in3hours, the reaction was preferred to be carried out at145℃for8hours. In our technology, the yield was89.1%, higher than reported86.1%; the decline of catalyst dosage is more than50percentage.Based on the solvent-free technology, we did further research with some other substituted benzaldehyde. Seen from the results, 4-benzylidene-2,6-di-tert-butylcyclohexa-2,5-dienone and its derivatives can be prepared with the new technology, the results were relatively good, the yields are higher than75%. In this paper, we synthesized a lot compounds based on the new technology, some have not been reported. Some conclusions were obtained:1) among all the reagents, the yield of reactions using benzaldehyde with electron-donating group were the best, such as using o-hydroxybenzaldehyde, o-anisaldehyde,3,4-dimethoxybenzaldehyde,4-N,N-dimethylbenzaldehyde as raw materials, the yields were92.8%,92.4%,91.2%,90.6%; then goes the benzaldehyde,89.1%; the yield of benzaldehyde with electron-drawing group were the lowest, using m-nitrobenzaldehyde,p-nitrobenzaldehyde, o-trifluoromethylbenzaldehyde as raw materials, the yields were79.5%,85.2%,75.3%.1HNMR and13CNMR were used to verify the product.