Study On Decarboxylation Of Gallic Acid

The decarboxylation reaction is that the carboxylic acid molecule lose the carboxyl group to release carbon dioxide in certain conditions.Generally,The decarboxylation reaction include thermochemical decarboxylation,electrochemical decarboxylation,catalytic decarboxy-lation and so on,which have wide application in biological manufacturing,organic synthesis,medicine preparation,chemical industry and other fields.Pyrogallic acid,an important chemical intermediate,is widely used for food,pharmaceutical synthesis,fuel,polymer materials and other areas.The preparation of pyrogallic acid consist of total-synthesis and semi-synthetic: total-synthesis is that used kinds of simple,cheap and easy-obtained raw material via multi-step synthesis of organic reactions;semi-synthesis is that used gallnut,tara powder and gallic acid as raw material via decarboxylation reaction,pyrogallic acid can be obtained by one step reaction.This paper included three parts:(1)Investigation on the decarboxylation reaction of gallic acid to prepare pyrogallic acid in the condition of HTLW(high temperature liquid water)and no catalyst.The influence of water consumption,reaction time and reation temperature on the decarboxylation of gallic acid have been inspected through orthogonal experiments,we obtained the best condition of gallic acid decarboxylation reaction in HTLW: industrial gallic acid is 60 g,water is 240 mL,the temperature is 200 ℃and reaction time is 3 hours.The experimental result indicated that the conversion of gallic acid was 90.9%,the selectivity of decarboxylation was 97.9% and the content of pyrogallic acid was 89.0% in the decarboxylation products.(2)Methanol,ethanol,ethylene glycol,propylene glycol and other alcohol solvent was used to substitute of water as solvent on the decarboxylation of gallic acid.The experimental results indicated that the decarboxylation conversion and selectivity have improved in alcohol solvent compared with water.37.6 g gallic acid in 100 mL ethanol decarboxylatet at the temperature of 210℃ for 3 hours,we get a result what the conversion rate of industrial gallic acid is 95.5%,selectivity of pyrogallic acid is 100% nearly and the content of pyrogallic acid is beyond 95%.(3)Used gallic acid as raw materials,pyridine and its derivatives(4-methylpyridine and 2,6-dimethylpyridine)was used as catalyst to prepare pyrogallic acid by catalytic decarboxylation.At first,the thermal stability of gallic acid and the catalytic activity of 4-methylpyridine and 2,6-dimethylpyridine was investigated.The result showed that the catalytic activity of 4-methylpyridine is evidently higher than 2,6-dimethylpyridine.Then we inspected the influence of catalyst dosage,reaction time and reation temperature on the decarboxylation of gallic acid.We applied xylene as solvent to conduct recrystallization experiment,the result showed that the content of pyrogallic acid is 98% and the yield of pyrogallic acid is 84%.