Study On The Synthesis Of Methyl Cyclopentenol Ketone Based On On-line Infrared Spectroscopy

Methyl cyclopentenol ketone（MCP）,also known as 3-methyl-2-hydroxy-2-cyclopentene-1-one,is a natural flavor substance,which is popular because of its caramel and nut aroma.At present,the market demand of MCP is increasing because of its high economic value,but the final yield of MCP is only about 90%.The existing synthesis process of MCP mainly includes:Diethyl Oxalate method,dimethyl adipate method,2,5-hexanedione method,isoprene method,2-methylfuran method,etc.Among them,2-methylfuran method is widely used because of its cheap raw materials and mild reaction conditions,but the mechanism of the synthesis process is less studied.In this paper,the synthesis of MCP from 2-methylfuran was studied by on-line infrared spectroscopy,the main results are as follows:1.An infrared absorption peak(970 cm^-1)was found when the first Mannich reaction was monitored by on-line infrared technology.After enrichment and purification,the impurity was characterized by GC-MS and 1H-NMR,and the reaction mechanism was studied;Using the infrared quantitative model of N,N-dimethyl-5-methylfurfuramine,the effects of reaction temperature,feeding mode and other experimental conditions on the conversion were investigated.After optimizing the synthesis step,the conversion rate of raw materials≥99%,and the yield≥98%.2.The second step of ring opening reaction was monitored by on-line infrared spectroscopy.It was found that the reaction lasted for 3 h and belonged to an infrared characteristic absorption peak of ring opening product(1732.5 cm^-1,vC=o stretching vibration)decreased with reaction time;The other characteristic infrared absorption peak is 1705.7 cm^-1（vC=o stretching vibration）red shift to 1709 cm^-1,accompanied by the appearance of other infrared absorption peaks（δC-O、δO-H and VC=C）,it is concluded that aldol condensation may occur after 3 h.By optimizing the reaction process,the conversion of ring opening product can reach 92%.3.The third step closed-loop rearrangement reaction and the fourth step hydrolysis reaction were monitored by on-line infrared technology.It was found that the trend of infrared absorption peak reached the platform after 0.5 h of closed-loop rearrangement reaction,that is,the reaction reached equilibrium,after optimization,the product yield of the closed-loop rearrangement reaction can reach 80%;When the hydrolysis reaction was monitored on-line,it was found that the infrared characteristic absorption peaks of closed-loop rearrangement products shifted to low frequency after adding hydrochloric acid solution;After 3 h of reaction,the characteristic absorption peak intensity of hydrolysate tended to be stable,that is,the reaction reached equilibrium.4.After the end of the reaction,the mother liquor was concentrated to remove part of the water.The dimethylamine hydrochloride in the mother liquor was quantitatively analyzed by on-line infrared spectroscopy,and the corresponding molar amounts of dimethylfuran and formaldehyde were determined for Mannich reaction.By repeating the experimental process,the recovery of dimethylamine hydrochloride can reach 97%,the conversion of Mannich product（N,N-dimethyl-5-methylfurfuramine）is more than 98%,and the yield is more than 96%;The results show that the recovered dimethylamine hydrochloride can be recycled for MCP synthesis process,which not only effectively reduces the process cost,improves the economic benefit of the whole synthesis process,but also reduces the environmental pollution.In this paper,on-line monitoring of MCP synthesis process was carried out by infrared spectroscopy for the first time.The real-time information of raw materials,products and by-products in the reaction were obtained by the change of absorption peak of infrared spectrum and the establishment of infrared quantitative model,which guided the real-time optimization of reaction process conditions.In order to improve the conversion of raw materials and the yield of products,the reaction mechanism was further studied by using on-line infrared data,nuclear magnetic resonance spectroscopy,gas chromatography and high performance liquid chromatography.In addition,the infrared quantitative model of dimethylamine hydrochloride was used to analyze the crystallization mother liquor quantitatively,so that the mother liquor could be recyclily used for the first step Mannich reaction.The process not only reduces the cost of raw material purchase and waste water post-treatment,but also reduces the environmental pollution and improves the yield of MCP.Under the guidance of on-line infrared spectroscopy technology,an economic,feasible,green and efficient industrial route for MCP synthesis was optimized.