Preparation method of 3,5-dimethyl-4-chlorophenol

The invention discloses a preparation method of 3,5-dimethyl-4-chlorophenol, which takes tetrachloroethylene as a solvent, benzyl thiophenol and aluminium chloride as cocatalysts, sulfuric chloride as a chloridizing agent, orientation chlorination is carried out through two phases of low-temperature chlorination and high-temperature chlorination, the mass ratio of tetrachloroethylene to MX is 0.5-4: 1; the mass ratio of the cocatalyst to MX is 2.5-6.5:1000; at low temperature chlorination phase, the mass ratio of sulfuric chloride dropping amount to MX is 0.9-1.2: 1; at high temperature chlorination phase, the mass ratio of sulfuric chloride dropping amount to MX is 0.1-0.2: 1; the temperature at the low temperature chlorination phase is controlled at 30-45 DEG C, chlorination is carried out for 4-6 hours; the temperature at high temperature chlorination phase is controlled at 50-65 DEG C, and chlorination is carried out for 1-2 hours, insulation reaction is carried out after the dropping process of sulfuric chloride is completed, tail gas is removed for 1-2 hours, and steps of water-washing layering, cooling and crystallizing, centrifuging and washing, and drying to obtain the product. According to the method, the conversion rate can reach more than 95%, finished product PCMX yield is increased, and the by-product can be effectively reduced.