Synthesis of macrocyclic poly(alpha-hydroxyl acids) via DABCO-mediated ROP of O-carboxylanhydrides derived from l-phenylalanine even in the presence of an alcohol
Authors: Liang, Jinpeng; Yin, Ting; Han, Song; Yang, Jing
Cyclic polyesters with very interesting topologies and unique properties have great potential. However, the synthesis of cyclic polyesters via ring-opening polymerization (ROP) of O-carboxyanhydrides (OCAs) has been hardly reported to date. Herein, a simple combination of triethylboron (TEB) and 1,4-diazabicyclo-[2.2.2]octane (DABCO) in the presence of benzyl alcohol (BnOH) was explored to promote the ROP of l-phenyl O-carboxyanhydride (l-PheOCA) for the synthesis of well-defined cyclic poly(alpha-hydroxy acid)s (PAHAs). Such a ternary catalytic system was found to exhibit well-controlled and living catalytic activities for l-PheOCA, and the polymerization produced cyclic PAHAs with a narrow molecular weight distribution (M-w/M-n < 1.2) and the isotacticity of P-m = 0.83. Careful analysis of the catalytic system showed the interaction of DABCO, TEB, and BnOH. Combined with the kinetic experiments, it was deduced that DABCO with preferable nucleophilicity played a predominant role in the polymerization process, and BnOH acted as a cocatalyst, not as an initiator during the polymerization. The zwitterionic active species with DABCO at one end and an alkyloxide at the other end of the propagation chain was involved in the synthesis of cyclic PAHAs. The thermal properties of the resulting polymers were analyzed by DSC and TGA, respectively. The degradation temperature of cyclic PAHAs was 30 degrees C higher than that of the corresponding linear polymers, exhibiting much better thermal stability. This is the first work on cyclic PAHAs fabricated via ROP of OCAs, which provides one new way to synthesize cyclic PAHAs and has significant potential to enrich the diversity of cyclic PAHAs.
Steric hindrance effect and kinetic investigation for ionic liquid catalyzed synthesis of 4-hydroxy-2-butanone via aldol reaction
CHEMICAL ENGINEERING SCIENCE
Authors: Wang, Gang; Cai, Guangming
4-Hydroxy-2-butanone as important chemical intermediate in the field of both pharmaceutical and food industries is traditionally synthesized from formaldehyde and acetone via aldol reaction with relatively low selectivity due to the heavy side reactions. Herein, series of basic ionic liquids with different sterically hindered cations were prepared for this reaction process. The catalytic performance evaluation results revealed the selectivity of 4-hydroxy-2-butanone could be enhanced with the extension of alkyl chain length substituted in the cation of ionic liquid and increasing number of substituted alkyl group. And the tetraoctyl ammonium hydroxide ([N8,8,8,8]OH) was identified as the optimal ionic liquid catalyst with selectivity of 91.1% toward 4-hydroxy-2-butanone at 40 degrees C. The kinetic studies indicated the forma-tion of 4-hydroxy-2-butanone was first-order dependent on both acetone and formaldehyde concentrations, with the lowest activation barrier of 49.8 kJ/mol among all steps. (c) 2020 Elsevier Ltd. All rights reserved.