Thiol-ene coupling (TEC) reactions are considered “click” due to high reaction rates, yields and selectivities, and involve the addition of thiol to double bonds. Despite the numerous applications and the promising alternatives for the synthesis of polymer precursors, this concept has become controversial, mainly due to secondary reactions and to the poor reactivity of internal double bonds. The knowledge and mathematical modelling of reaction kinetics would allow to understand, predict and optimize the main system parameters.<br/>This work investigates the amine functionalization of simple molecules via TEC reaction. The work involved the study of simple and complete reactions between cysteamine hydrochloride (CAHC) and methyl oleate (MO), employing DMPA as photoinitiatior. The reactions considered different gas atmospheres (oxygen and nitrogen) and solvents (MeOH:EtOH or EtOH), and a CAHC/MO/DMPA = 3/1/0.1 molar ratio.<br/>The effect of solvent on the photoinitiator decomposition was evaluated by UV for Exp. 1, observing that the decomposition rate was higher in EtOH than MeOH:EtOH. The effect of atmosphere was evaluated by NMR for Exp. 2. In absence of thiol, no MO double bond isomerization was observed. In presence of air, double bonds react with oxygen, generating secondary products, yielding a 30% conversion. Thiol initiation was studied for Exp. 3, observing that the only product was cystamine hydrochloride. Exp. 4 was monitored by RMN and GC, yielding final conversions values of 59% for MeOH:EtOH and 83% for EtOH, and 68 and 85% selectivity, respectively. These results are in concordance with the decomposition rates observed for Exp. 1. The product was a mixture of isomers in a 60:40 molar ratio. A kinetic scheme that considers initiation, isomerization, propagation, secondary reactions, and termination was proposed. A mathematical model was developed that allows simulating reactions, determining kinetic parameters and process optimization. This study might be extended to more complex systems as the functionalization of vegetal oils.

Thiol-ene coupling reaction between methyl oleate and cysteamine hydrochloride: Reaction kinetics

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.