Synthesis Of 2,6-Di-tert-Butyl-7-Substituted Quinone Methides

2,6-Di-tert-butyl-7-substituted Quinone Methides(QMs for short)has excellent antioxidation and inhibition properties and can be applied to inhibit the polymerization of Styrene and Acrylates.The use of toxic polymerization inhibitors has been gradually banned,especially the use of 4,6-dinitro-2-sec-butylphenol(DNBP).QMs as the best alternatives to DNBP are receiving increasing attention with environmental protection in the future.2,6-Di-tert-butyl-4-phenylmethylene-2,5-cyclohexadien-1-one(QM-ph for short)is one of the most important QMs and has a very good inhibitory effect.In this paper,a novel synthesis method has improved through Mannich reaction.Mannich base can be decomposed by inorganic acid and the secondary amine can be recovered by neutralization of caustic alkali in this method.Low cost and high yield is advantages of this method,compared with the traditional method of deamination by acetic anhydride.QM-ph was synthesized by Mannich reaction using 2,6-di-tert-butylphenol and benzaldehyde as starting materials.The reaction was tracked by thin layer chromatography(TLC)and high performance liquid chromatography(HPLC).The optimum reaction conditions were as follows: toluene as solvent,2,6-di-tert-butylphenol:benzaldehyde=1:1.15,2,6-di-tert-butylphenol:piperidine=1:1.4,piperidine:sulfuric acid=1:0.5,reaction at 125?,piperidine was added dropwise for 3 h,the reaction was continued for 8 h,sulfuric acid was added at 110? for 1 h,with the yield of 86.5% and 90% of piperidine recovery.The yield was 86.2% using recovered piperidine with the same condition.The pilot test was completed,the yield was 89.6%,and the yield was 85.9% using recovered piperidine with the same condition.The progress of the reaction and the target product were monitored by HPLC.By-product was separated,and the structure of by-product was determined by Nuclear Magnetic Resonance spectroscopy and Mass spectrometry.The target product was verified by NMR and High Resolution Mass spectrometry and the structure was correct.