Decomposition of Five Phenolic Compounds in High Temperature Water

In this work, the stability of five phenolic compounds (catechol, protocatechualdehyde, salvianic acid A, protocatechuic acid, and ferulaic acid) under high temperature water was investigated. The effects of two main factors on the stability experiments, such as temperature and time, were investigated. The decomposition of three phenolic acid compounds (salvianic A, protocatechuic, and ferulaic acids) increased with rising temperature and the acids became less stable with longer heating time. The three phenolic acid compounds showed very minor decomposition at 200 degrees C and their complete decomposition was observed at 300-350 degrees C. The decomposition products of salvianic acid A, protocatechuic acid, and ferulaic acid were characterized and quantified by high performance liquid chromatography (HPLC) and further confirmed by high performance liquid chromatography/mass spectrometry (HPLC/MS). Salvianic acid A, protocatechuic acid, and ferulaic acid in high temperature water mainly underwent decarboxylation reaction to form 4-ethylcatechol, catechol, and 2-methoxy-4-vinylphenol, respectively. However, catechol and protocatechualdehyde almost remained stable even at temperatures up to 350 degrees C. Reaction temperature and time showed relatively little effect on the decomposition of catechol and protocatechualdehyde. These results demonstrated that through adjusting the temperature or time, the extraction of phenolic compounds can be controlled.