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

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Balancing the transesterification reactivity of isosorbide with diphenyl carbonate: preferential activation of exo-OH
Polymer Chemistry ( IF 4.1 ) Pub Date : 2020-07-23 , DOI: 10.1039/d0py00764a
Ming Zhang _{1,

2,

3,

4,

5} , Yifei Tu _{1,

2,

3,

4,

5} , Zibo Zhou _{1,

2,

3,

4,

5} , Guozhang Wu _{1,

2,

3,

4,

5}

Affiliation

The exo-hydroxyl group (exo-OH) on isosorbide (ISB) has long been asserted as a highly reactive moiety compared with the endo-hydroxyl group (endo-OH). In this study, calculations based on density functional theory and experiments without adding catalysts reveal that endo-OH has strong nucleophilic ability, and in the case of transesterification with diphenyl carbonate, the nucleophilic attack surmounts steric hindrance in rendering endo-OH more reactive than exo-OH. The kinetics of transesterification with different catalysts is investigated to determine the catalytic reactivity and molecular structure evolution. The results show that preferential activation of exo-OH moieties can be achieved either by reducing the coordination ability of catalytic cations (lg β₁) or by enhancing the alkalinity of catalytic anions. Despite the low reactivity of exo-OH on ISB monomers, terminal exo-OH on carbonate oligomers exhibits higher reactivity than terminal endo-OH, justifying the experimental fact that ISB-based polycarbonates (ISB-PCs) are mostly terminated by endo-OH. Balancing the reactivity between endo-OH and exo-OH can be promoted by increasing the reaction temperature, thus accelerating transesterification to a high equilibrium constant. These findings help to clarify the mechanism of ISB transesterification and provide new strategies for the synthesis of high-molecular-weight ISB-PCs.

中文翻译：

平衡异山梨醇与碳酸二苯酯的酯交换反应性：exo-OH的优先活化

长期以来，异山梨醇（ISB）上的exo-羟基（exo -OH）一直被认为是与内羟基（endo -OH）相比具有高反应性的部分。在这项研究中，根据密度泛函理论和不添加催化剂的实验进行的计算表明，内-OH具有很强的亲核能力，在与碳酸二苯酯进行酯交换反应的情况下，亲核的攻击要克服位阻，从而使内-OH的反应性比外源性的要高。-哦。研究了用不同催化剂进行酯交换反应的动力学，以确定催化反应性和分子结构的演变。结果表明的那优先激活外可以通过降低催化阳离子的配位能力（LG任一实现-OH结构部分 β ₁）或通过增强催化阴离子的碱度。尽管低反应性外切于ISB单体，末端-OH外-OH上碳酸酯低聚物的反应性显示出高于终端内切-OH，证明实验事实，即基于ISB的聚碳酸酯（ISB-PC）的主要是由封端的内切-OH。平衡的反应性内切-OH和外-OH可通过提高反应温度来促进，从而将酯交换反应加速至高平衡常数。这些发现有助于阐明ISB酯交换的机理，并为合成高分子量ISB-PCs提供了新的策略。

更新日期：2020-09-01

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