P-toluic Acid

1. It is prepared by catalytic oxidation of p-xylene with air. When the atmospheric pressure method is used, xylene and cobalt naphthenate can be added into the reaction pot, and air is introduced when heating to 90 ℃. The reaction temperature is controlled at 110-115 ℃ for about 24 hours, and about 5% of p-xylene is converted to p-methylbenzoic acid. Cool to room temperature, filter, wash the filter cake with p-xylene, and dry to obtain p-methylbenzoic acid. P-xylene is recycled. The yield is 30-40%. When the pressure oxidation method is used, the reaction temperature is 125 ℃, the pressure is 0.25MPa, the gas flow rate is 250L in 1H, and the reaction time is 6h. Then, the unreacted xylene was distilled by steam, the oxygen chemical book material was acidified with concentrated hydrochloric acid to pH 2, stirred and cooled, and filtered. The filter cake was soaked in p-xylene, then filtered and dried to obtain p-methylbenzoic acid. The content of p-methylbenzoic acid was more than 96%. The one-way conversion rate of p-xylene was 40%, and the yield was 60-70%.

2.It was prepared by oxidation of p-isopropyltoluene with nitric acid. 20% nitric acid and p-isopropyltoluene were mixed, stirred and heated to 80-90 ℃ for 4h, then heated to 90-95 ℃ for 6h. Cooling, filtration, recrystallization of filter cake with toluene to give p-methylbenzoic acid in 50-53% yield. In addition, p-xylene was oxidized by concentrated nitric acid for 30 h, and the yield was 58%.