Balancing the transesterification reactivity of isosorbide with diphenyl carbonate: preferential activation of exo-OH

Abstract

Exo-OH on ISB has long been asserted as a highly reactive moiety compared with endo-OH. Herein, we report that the nucleophilic attack surmounts steric hindrance in rendering endo-OH more reactive than exo-OH in case of transesterification with DPC.

Short-process synthetic strategies of sustainable isohexide-based polyesters towards higher molecular weight and commercial applicability

“…The nucleophilicities of different hydroxyls are in the order: endo -OH (IM) > endo -OH (IS) > exo -OH (II) > exo -OH (IS), corresponding to the atomic charge distribution of −0.752, −0.747, −0.744, and −0.742, respectively. 70 The authors did not explain why the nucleophilicity of endo -OH or exo -OH differs in different IM and IS. We assume it may be that the formation of intramolecular hydrogen bonds affects a longer range of the charge density, resulting in a difference in charge distribution.…”

“…3). 70 With the assistance of natural bond orbital (NBO) calculation, it was found that the endo -OH is more negatively charged than exo -OH and is thus more nucleophilic. The nucleophilicities of different hydroxyls are in the order: endo -OH (IM) > endo -OH (IS) > exo -OH (II) > exo -OH (IS), corresponding to the atomic charge distribution of −0.752, −0.747, −0.744, and −0.742, respectively.…”

The future of isosorbide as a fundamental constituent for polycarbonates and polyurethanes

“…IBPC can be obtained by reacting isosorbide with toxic molecules as diphenyl carbonate (Scheme 1) or phenyl chloroformate using pyridine as a catalyst (13). Zang et al (14) studied the reactivity of the endo and exo hydroxyl groups of isosorbide in the reaction with diphenyl carbonate (DPC) using basic catalysts as alkaline hydroxides, temperatures of 160°C or higher, and high vacuum to promote the elimination of toxic phenol. The transesterification reaction can be speed up by increasing the temperature, but also oligomers of different Mw were formed leading to a monomer of poor quality which must be purified by a costly and time-consuming procedure.…”

Acylamido-based anion-functionalized ionic liquids for efficient synthesis of poly(isosorbide carbonate)

“…Previously, Zhang et al screened some metal-based catalysts for balancing the reactivity of endo-OH and exo-OH with DPC. 43 Additionally, Tundo et al reported that potassium carbonate and cesium carbonate showed good selectivity for the carboxymethylation of DMC. 44 However, metal-based catalysts have potential environmental issues due to their toxicity and corrosiveness.…”