Hydrolysis reaction paths and kinetics of cationic bleaching activators with different leaving groups based on LC-MS and HPLC

Abstract

Cationic bleaching activators can effectively achieve low-temperature bleaching in hydrogen peroxide system, but at the same time, self-hydrolysis reaction will occur to affect the low-temperature bleaching effect, and the complex hydrolysis pathways of cationic bleaching activators are still elusive. In this paper, the hydrolysis reaction pathways, mechanisms, rates and kinetics of cationic bleaching activators N-[4-(triethylaminomethyl)benzoyl]lactam chlorides (TBLCs) with different lactam leaving groups were investigated in depth by liquid chromatography-mass spectrometry (LC-MS) and high-performance liquid chromatography (HPLC). Specifically, we characterized the hydrolysis products by LC-MS and further quantified the hydrolysis products using HPLC, demonstrating that the hydrolysis can take place via two pathways, generating chain-breaking products and ring-opening products, and that both react at different rates depending on the different lactam leaving groups. Notably, the quantitative results showed that the chain-breaking products were always larger than the ring-opening products, and the chain-breaking products were ineffective for bleaching, which was the main reason for the decrease in the bleaching performance of TBLCs. The mechanism of hydrolysis is discussed and the reaction rate was determined to follow first-order kinetics using HPLC. We have successfully delineated the complete transformation pathway of the hydrolysis reaction using this method, providing valuable information for the future preparation of novel bleaching activators and the reduction of this reaction.