The invention discloses a method by which the
gallic acid in high-temperature
liquid water medium is non-catalystically decarboxylated to prepare pyrogallic acid. The method includes three steps; firstly, deionized water and
gallic acid are added into a high-pressure reaction kettle, the
mass ratio between the deionized water and the
gallic acid is 2 : 1 to 6 : 1, stiring is started, temperature under the normal pressure is raised until boiling, and an
exhaust valve is opened for two to five minutes; secondly, the
exhaust valve is closed, the temperature is continuously raised to 180 DEG C to 250 DEG C, and reaction lasts half to four hours; thirdly, after being cooled down until
room temperature, a
reaction product is extracted by
organic solvent, crude pyrogallic acid is produced after the
organic solvent is evaporated from extract, and after the crude pyrogallic acid resolved in deionized water is decoloured, recrystallized and undergoes
vacuum drying, the pyrogallic acid product is produced. The invention has the advantages of simple reaction process, high utilization ratio of materials, high product yield, environment-friendly production procedure and high quality of pyrogallic acid product, and as a result, the invention resolves the major problem that the current preparation of pyrogallic acid by catalyzing acid and alkali pollutes envrionment.