4-methyl cinnamic acid methyl ester is a pharmaceutical intermediate. It is mainly used for the synthesis of methyl bromomethylcinnamate, the upstream raw material of the antithrombotic drug Ozagrel sodium. Methyl p-methylcinnamate is brominated by N-bromosuccinimide to obtain methyl p-bromomethylcinnamate, methyl p-bromomethylcinnamate in ionic liquid N-n-butylpyridine tetrafluoroboron The acid salt was lyophilized with imidazole at room temperature and then hydrolyzed to obtain an antithrombotic drug, ozagrel sodium, with a total yield of 67%. Methyl p-methylcinnamate is first reacted with p-methylbenzaldehyde and malonic acid to form p-methylcinnamic acid, which is then esterified with p-methylcinnamic acid and methanol to form methyl p-methylcinnamate.
The process for preparing cinnamate by condensation of benzoquinone with acetate is known as the Claisen-Schmidt condensation reaction. The main methods for preparing cinnamate by Claisen-Schmidt reaction are as follows:
1. Prepared with anhydrous ethanol as solvent and 10% NaOH as catalyst, but the method has long reaction time and side reaction.
Should be more, product yield is low, production efficiency is poor.
2. The acetic acid ester is used as a solvent and the sodium alkoxide is used as a catalyst to condense. This method improves the product yield, but the post-treatment is complicated and the purification is difficult. In the preparation, a large excess of the raw material ratio of the acetate is used, and the excess acetate is prone to ester condensation reaction under a strong basic catalyst, and a large amount of by-products are formed, which leads to difficulty in product purification.
In addition, methyl cinnamate is mostly obtained by reacting p-methylbenzaldehyde with acetic anhydride or malonic acid to obtain p-methylcinnamic acid, followed by esterification with methanol to obtain methyl p-methylcinnamate. Because of the existing process steps, poor production conditions, low product yield, high cost and serious pollution, it does not meet the requirements of green production.
Now, A new method for preparing 4-methyl cinnamic acid methyl ester comprises the following steps:
1) stirring and mixing with ethylene glycol dimethyl ether as a solvent and lithium diisopropylamide as a catalyst, and then stirring slowly Add p-methylbenzaldehyde dropwise, keep the temperature below 5 degrees Celsius
2) After the dropwise addition, keep the reaction at 0 degrees Celsius- 10 degrees Celsius for 3-6h, slowly add 10% by mass of sulfuric acid to make The PH of the reaction solution is adjusted between 6.8 and 7.2
3) The above solution is separated into an organic layer, and the solvent and excess p-methylbenzaldehyde are recovered under reduced pressure to obtain a white solid, which is washed with water and dried to give a crude product. Recrystallization from absolute ethanol gave 4-methyl cinnamic acid methyl ester.
The invention has the advantages of low raw material cost, mild reaction condition, and methyl p-methylcinnamate obtained by one-step reaction, and the method is simple, easy to operate, high in yield, stable and reliable in product quality, and non-polluting to the environment, is a kind of green The method of synthesizing fragrance.