The Stability of Carboquone in Aqueous Solution. I. Kinetics and Mechanisms of Degradation of 2,5-Diethylenimino-1,4-benzoquinone in Aqueous Solution

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The kinetics and mechanisms of the degradation of 2,5-diethylenimino-1,4-benzoquinone (EB) in aqueous solution were investigated as a function of pH (4-11), temperature (20-50℃), buffer concentration (0.01-0.1M) and ionic strength (0.1-0.5) by means of high pressure liquid chromatography. The reaction followed pseudo first-order kinetics. The pH-rate profile showed slopes of -1 at pH below 7.5 and +1 at pH over 7.5. Thus, the degradation of EB is subjected to specific acid-base catalysis. No effect of buffer concentration on the degradation rate of EB was apparent in the range of pH 4-11,though some effect of ionic strength on it was observed below pH 7. The apparent activation energies for the degradation of EB at pH 4 or 5 and pH 10 or 11 were 14 and 19 kcal/mol, respectively. In the range of pH 4-6,EB was degraded to 2,5-diethanolamino-1,4-benzoquinone with sequential hydrolytic cleavage of two ethylenimine rings. In the range of pH 10-11,EB was degraded to 2,5-dihydroxy-1,4-benzoquinone with sequential substitution of the two ethylenimine rings by hydroxyl ion (radical). In the range of pH 7-9,EB was degraded to 2,5-diethanolamino-1,4-benzoquinone, 2,5-dihydroxy-1,4-benzoquinone and 2-ethanol-amino-5-hydroxy-1,4-benzoquinone by the two mechanisms described above.
公益社団法人日本薬学会の論文
1981-12-25