Preparation method of 5-methylpyrazine-2-carboxylic acid

The invention discloses a preparation method of 5-methylpyrazine-2-carboxylic acid. The preparation method comprises the following step: (1) preparing an inorganic base, reducing the temperature to be0-25 DEG C, controlling the temperature of the system to be maintained at a room temperature, and adding 2,5-dimethylpyrazine in batches to ensure that the temperature of the system is stabilized at5-30 DEG C; (2) adding solid potassium permanganate in batches at an interval of 0.5-1h each time, keeping the temperature in the system at 10-30 DEG C for reaction in a feeding process and after feeding until the reaction is finished; (3) after the reaction is finished, carrying out filtering, retaining a filtrate, extracting and washing unreacted raw materials in the filtrate by using an organicsolvent, reserving an organic phase for later use, carrying out stirring, retesting the pH value, carrying out stirring and suction filtering, and retaining the filtrate; (4) extracting the product with butanone, and then dist