title: Photochemical decomposition of phenazone derivatives. Part 7: Mechanism of decomposition in aqueous solutions.
abstract: Kinetic studies, supplemented by the isolation and identification of the products of decomposition, have proved the process of photochemical decomposition of phenazone derivatives to be a complex reaction, involving several successive parallel reactions, one of which is predominant depending on the concentration of the solution and the atmosphere above it. In an oxygen-free atmosphere and at low concentrations (10(-4) mol/dm3) decomposition is almost wholly the result of second photolysis of zero order to aziridine derivative----aniline----isonitrile. At higher concentrations (10(-3)-10(-2) mol/dm3), the contribution from the reaction of water photoaddition to the double bond C3-C4 increases. Whereas at concentrations of order greater than or equal to 10(-2) mol/dm3, photoisomerization to imidazole derivatives is predominant. In air, one onserves additionally a second reaction of photooxidation to 4-hydroxy-phenazone----1-acetylo-1-methyl-2-phenyl-hydrazine, a reaction of photodemethylation at N2 with simultaneous oxidation to the 4-ketoderivative, and reactions of hydrolysis characteristic for the individual derivatives. The principal primary photolytic reaction for the group of compounds studied consists in cleavage of the N1-N2 bond of the pyrazoline ring.
mesh_terms: D000983:Antipyrine / Q000031:analogs & derivatives* / Q000032:analysis; D055598:Chemical Phenomena; D002621:Chemistry; D004355:Drug Stability; D008401:Gas Chromatography-Mass Spectrometry; D007700:Kinetics; D010100:Oxygen; D010777:Photochemistry; D012996:Solutions
chemical_list: D012996:Solutions; D010100:Oxygen; D000983:Antipyrine