A new procedure for the transesterification of alkyl acetates and formates with model glycerol acetals (GAs: Solketal and glycerol formal) was explored in the absence of any catalysts at 180–275 °C. Highly selective transformations occurred in both batch and continuous-flow (CF) modes; particularly, the enol derivative isopropenyl acetate (iPAc) was the best performing reactant by which quantitative acetylation reactions were achieved with yields on GAs acetates >95%. An excess acylating agent was necessary (2–20 molar equivs), but the unconverted ester was fully recovered and could be reused. The reaction plausibly involved multiple mechanisms where either the electrophilic and the nucleophilic activation of reagents took place through both traces of acetic acid (formed in situ by the hydrolysis of esters) and the autoprotolysis of GAs. iPAc confirmed a superior performance than other esters also for the high-temperature conversion of glycerol; in this case, although acylation and acetalization processes were simultaneously possible, conditions were optimized to achieve the exhaustive transesterification of glycerol to triacetin, in both batch and CF modes. Triacetin was isolated in 99% yield.

中文翻译：

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甘油和乙缩醛衍生物对烷基和烯醇酯的高温间歇连续流酯交换反应

在没有催化剂存在的情况下，在180–275°C的条件下，探索了一种用乙酸甘油缩醛与乙酸烷基酯和甲酸酯进行酯交换的新方法（GA：Solketal和甘油缩甲醛）。批处理和连续流（CF）模式都发生了高度选择性的转化；尤其是，烯醇衍生物乙酸异丙烯酯（iPAc）是性能最好的反应物，通过该反应物可以实现定量乙酰化反应，乙酸乙酸甘油酯的收率> 95％。过量的酰化剂是必要的（2-20摩尔当量），但是未转化的酯已被完全回收，可以重复使用。该反应似乎涉及多种机理，其中试剂的亲电和亲核活化都是通过痕量的乙酸（由酯水解原位形成）和GA的自质分解发生的。iPAc在甘油的高温转化方面也证实了优于其他酯的性能。在这种情况下，尽管可以同时进行酰化和乙缩醛化工艺，但可以优化条件，以分批和CF模式实现甘油向三醋精的彻底酯交换。分离出三醋精的产率为99％。