Thiourea dioxides decompose in air-saturated alkaline solutions to give dithionite, S2O42−. Kinetics of decomposition of aminoiminomethanesulfinic acid (AIMSA), methylaminoiminomethanesulfinic acid (MAIMSA) and dimethylaminoiminomethanesulfinic acid (DMAIMSA) were studied in alkaline solutions under aerobic and anaerobic conditions. No dithionite was formed in strictly anaerobic conditions. Dithionite, however, was formed in the presence of KO2 and H2O2 under anaerobic conditions. The rate of decomposition was fastest for DMAIMSA and slowest for MAIMSA. The proposed mechanism involves the initial formation of the dioxosulfate(2−) ion, SO22−, through the heterolytic cleavage of the C–S bond. The dioxosulfate(2−) ion then reacts with dioxygen to give a series of reactive oxygen species: superoxide, peroxide and the hydroxyl radical. The expected dismutation of superoxide is important only in weakly alkaline solutions of pH less than 10. It is suggested, for the first time, that the reactive oxygen species and the sulfur leaving groups may be responsible for the toxicity observed in most thioureas.
二氧
硫脲在空气饱和的碱性溶液中分解生成二
亚硫酸盐 S2O42-。在有氧和无氧条件下,研究了
氨基亚
氨基
甲烷亚
磺酸(AIM
SA)、甲基
氨基亚
氨基
甲烷亚
磺酸(MAIM
SA)和二甲基
氨基亚
氨基
甲烷亚
磺酸(
DMAIM
SA)在碱性溶液中的分解动力学。在严格的厌氧条件下,没有形成二
亚硫酸盐。但在厌氧条件下,有
KO2 和
H2O2 存在时,会形成
连二亚硫酸盐。
DMAIM
SA 的分解速度最快,而 MAIM
SA 的分解速度最慢。所提出的机理包括通过异性裂解 C-S 键初步形成二氧
硫酸盐(2-)离子 SO22-。然后,二氧
硫酸盐(2-)离子与二氧反应,产生一系列活性氧物种:超氧化物、过氧化物和羟基自由基。只有在 pH 值小于 10 的弱碱性溶液中,超氧化物才会发生预期的歧化反应。研究首次提出,活性氧和
硫离去基团可能是大多数
硫脲类化合物毒性的原因。