Mequinol Crystal, also known as hydroquinone monomethyl ether, p-methoxyphenol, p-hydroxyanisole, is an important chemical raw material for synthesizing aryl ester liquid crystals, and can also be used as dye intermediates. It can be used as a high-efficiency polymerization inhibitor in the production of olefin monomers such as acrylonitrile, acrylic acid, methacrylic acid and its esters, and can also be used as a stabilizer for unsaturated resins and ultraviolet inhibitors. The starting material, this compound has a variety of synthetic methods. P-Hydroxyanisole is an important organic synthesis raw material for fine chemical products such as medicines, pesticides and fragrances.
Synthetic research
The synthetic research of p-Hydroxyanisole has been reported in the literature, and at present, the following two processes are mostly used in the country to produce:
(1) The dimethyl sulfate method is prepared by reacting dimethyl sulfate with hydroquinone under alkaline conditions using dimethyl sulfate as a methylating reagent.
(2) Methanol method: Under the action of a catalyst, it is produced by the two processes of hydroquinone and the above-mentioned methanol. The price of the main raw material hydroquinone is high, which leads to high manufacturing costs; The ether mixture is not easy to separate and the product quality is poor.
The Chinese invention patent application of "Method for preparing p-hydroxyanisole with p-aminoanisole" discloses a method for preparing p-hydroxyanisole with p-aminoanisole through diazotization and hydrolysis reaction, and its shortcoming is that The hydrolysis of the diazonium salt must be carried out in a high acid solution and a relatively high temperature, which easily leads to the decomposition of the diazonium salt, and the method produces more waste water and lower yield, which is not suitable for industrial application. At present, the synthesis of p-hydroxyanisole at home and abroad mainly takes hydroquinone as raw material, and adopts dimethyl sulfate method or methanol catalytic method to synthesize p-hydroxyanisole, wherein, the shortcoming of dimethyl sulfate method It is because dimethyl sulfate itself is a highly toxic, expensive and strict reaction requirements. Due to its relatively active chemical properties, it has poor selectivity in the reaction. In addition to producing about 30% of p-xylylene ether, it is also very easy to produce other tars. As by-products, it is difficult to handle in production, and affects the quality and yield of the product; methanol catalysis method avoids the toxicity of dimethyl sulfate, and the highest yield can reach about 82%, but its disadvantage is that the commonly used toxicity is higher than that of dimethyl sulfate. Large benzene is used as a solvent, or crown ethers with high toxicity and high price are commonly used as catalysts. The reaction solution needs to be subjected to complex follow-up processes such as extraction, neutralization, washing, concentration, vacuum distillation, and recrystallization to obtain products with stable quality. .
Synthesis of p-Hydroxyanisole: Using p-aminoanisole as the starting material, the target compound was synthesized through two steps of diazotization and hydrolysis. Through the optimization of process conditions, the best process conditions were obtained, namely, p-aminoanisole (mol):sulfuric acid (mol) was 1:2.0, the diazotization temperature was -5℃, and the hydrolysis temperature was 60℃. As a result, the total yield of two steps calculated with p-aminoanisole was 71.2%.
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