Role of Lewis Acids in Preventing the Degradation of Dithioester-Dormant Species in the RAFT Polymerization of Acrylamides in Methanol to Enable the Successful Dual Control of Molecular Weight and Tacticity

Reversible addition-fragmentation chain transfer (RAFT) polymerization of acrylamide in methanol using dithioester RAFT chain-transfer agents was unsuccessful due to degradation of the end group. However, this degradation was completely suppressed by the addition of rare-earth metal triflates (RMTs). As RMTs are effective for the stereoselective polymerization of acrylamides, RAFT polymerization in the presence of RMTs afforded the corresponding poly(acrylamide)s with controlled molecular weight and tacticity. The conditions allowed the synthesis of high-molecular-weight polyacrylamides with molecular weights up to 168,000, low dispersity (<1.5) and high tacticity (90% <i>meso</i> diad selectivity). The degradation mechanism initiated by nucleophilic attack of acrylamide on the dithioester group was experimentally clarified for the first time. As RMT is a Lewis acid, its coordination to the amide group of acrylamide reduces its nucleophilicity.

Role of Lewis Acids in Preventing the Degradation of Dithioester-Dormant Species in the RAFT Polymerization of Acrylamides in Methanol to Enable the Successful Dual Control of Molecular Weight and Tacticity

Reversible addition-fragmentation chain transfer (RAFT) polymerization of acrylamide in methanol using dithioester RAFT chain-transfer agents was unsuccessful due to degradation of the end group. However, this degradation was completely suppressed by the addition of rare-earth metal triflates (RMTs). As RMTs are effective for the stereoselective polymerization of acrylamides, RAFT polymerization in the presence of RMTs afforded the corresponding poly(acrylamide)s with controlled molecular weight and tacticity. The conditions allowed the synthesis of high-molecular-weight polyacrylamides with molecular weights up to 168,000, low dispersity (<1.5) and high tacticity (90% <i>meso</i> diad selectivity). The degradation mechanism initiated by nucleophilic attack of acrylamide on the dithioester group was experimentally clarified for the first time. As RMT is a Lewis acid, its coordination to the amide group of acrylamide reduces its nucleophilicity.

Metal triflates formation of C12-C22 phenolic compounds by simultaneous C-O breaking and C-C coupling of lignin-derived benzyl phenyl ether

The production of fuels and chemicals from lignin can mitigate greenhouse gas emissions generated by fossil fuel processing. Current upgrading pathways for converting lignin into useful chemicals require multiple steps...

A comparative study of metal-catalyzed three-component synthesis of α-aminophosphonates

Different metal catalysts have been tested for the one-pot transformation of carbonyl compounds, amines and phosphites to α-aminophosphonates. The influence of catalyst type, amount, solvent and the substrate electronic factor have been investigated. The results revealed that the carbonyl compounds could be smoothly converted into α-aminophosphonates at room temperature in good to excellent yields, with or without solvent in a reasonable reaction time. These results suggested that among others, lithium perchlorate and metal triflates were proven to be effective catalysts in 10 moles % catalysts. Polar aprotic solvents proved to be the best for the synthesis of α-aminophosphonates. The synthesized compounds' structure characterizations were elucidated by different spectroscopic tools and showed results consistent with the expected structures.

The Baeyer–Villiger rearrangement with metal triflates: new developments toward mechanism

New insight into the mechanism of Baeyer–Villiger oxidation with H2O2 and metal triflates was presented.