The development of reaction kinetics for CO2 absorption into novel solvent systems: Frustrated Lewis pairs (FLPs)

Abstract

Frustrated Lewis Pairs (FLPs) comprising sterically hindered Lewis acids and bases were developed and kinetic parameters for the homogenous reaction between CO2 and FLP dissolved in bromobenzene were obtained by using the stopped-flow method for the first time in the scope of this work. As a sterically hindered Lewis acid chlorobis(pentafluorophenyl)borane, B(C6F5)2Cl and as a sterically hindered Lewis base tri-tert-butylphosphine, tBu3P were analyzed. Experiments were performed by varying FLP concentration in bromobenzene medium over the range of 0.02–0.035 M and for a temperature range of 298–313 K. Modified termolecular reaction mechanism was used to analyse the experimental kinetic data. Then, the relatively low reaction rate of FLP: bromobenzene system was enhanced significantly by blending constant amounts of promoters, such as amino ethyl piperazine (AEPZ), carbonic anhydrase (CA) and 1-ethyl-3-methyl imidazolium bis (trifluoromethyl sulfonyl) imide ([emim][Tf2N]). The intrinsic reaction rates of promoted solvents were measured in a stopped-flow technique over a temperature range of 293–323 K. The empirical power law reaction orders with respect to FLP concentration were found to be between 1.0 and 2.0 at various temperatures. Additionally, at these operating conditions, the promoting effects of AEPZ, CA, and [emim][Tf2N] results in a higher reaction rate and lower activation energy values.