Zifei Yan,Grace Dai Zhen Lee,Jian Deng,Guangsheng Luo
The synthesis of terminal epoxides, which are vital components in pharmaceuticals and resins, often involves dehydrochlorination of β-chlorohydrins. Although intrinsic kinetics indicate that the dehydrochlorination reaction in the presence of sodium hydroxide could be very rapid, the practical implementation could always be hindered by long reaction time and low conversion rate. Extended contact between the product and the alkaline solution can lead to hydrolysis of the epoxy group, thus necessitating the process intensification to realize higher production efficiency and selectivity. Here, by characterizing thermodynamic equilibrium data and in-situ recording of the reaction that proceeded in a constant interphase reactor, the heterogeneous dehydrochlorination is demonstrated to occur primarily in the organic phase, and the overall reaction rate depends on the equilibrium concentration of sodium alkoxides. This finding, which is fundamentally different from the traditional view that chlorohydrin is first dissolved in the aqueous phase and then reacts with NaOH, leads us to use inert alcohols to assist in the extraction of NaOH. Based on this method, the reaction time can be reduced over 80 % both in batch and continuous reactors. Besides, the method is demonstrated to be effective in the dehydrochlorination of five different long-chain β-chlorohydrins.
Polyvinylidene chloride (PVDC) is widely employed in packaging and construction materials due to its high chemical stability and excellent barrier performance. However, its persistent nature results in significant environmental accumulation, posing ecological risks. Conventional treatment methods often generate highly toxic byproducts, leading to the waste of chlorine resources. To address these challenges, this study introduces a novel electrochemical approach for the resource recovery of PVDC. Using PVDC as a chlorine source and di(2-ethylhexyl)phthalate (DEHP) as an electron mediator, we achieved the coupling of electrochemical dechlorination of PVDC with the synthesis of β-chloroalcohols. The halogenated alcohol derivatives were obtained in yields up to 76%, with good substrate versatility encompassing styrene derivatives bearing various functional groups as well as certain cyclic olefins. Moreover, the methodology was successfully applied to commercially available PVDC products, affording the target compounds in approximately 50% yield. This work offers a novel strategy for the sustainable recycling and valorization of plastic waste.
Grace Dai Zhen Lee,Zifei Yan,Jing Song,Jian Deng,Guangsheng Luo
Terminal epoxides are important monomers and modifiers that are widely used in the polymer and coating industries. Apart from direct oxidation of alkenes to produce ethylene oxide or propylene oxide, many terminal epoxides are still synthesized through the chlorohydrin method. Due to the limited mass transfer performance and complex thermodynamics and kinetics in this heterogeneous reaction system, the dehydrochlorination reaction still suffers from low reaction efficiency, large amounts of solid precipitation waste, and highly excessive use of alkali. Herein, the dehydrochlorination process of 3-chloro-2-hydroxypropyl neodecanoate (CHPDA), selected as a typical β-chlorohydrin with extremely poor solubility in water, was intensified using phase transfer catalysts (PTCs). The structure–function relationship of PTCs was elucidated and it was demonstrated that tetrabutylammonium chloride (TBACl) is one of the most effective catalysts for heterogeneous dehydrochlorination. Due to the significant promotion of mass transfer by applying a catalytic amount of TBACl, the reaction time was shortened from several hours to just 3 min, and the usage of the reactant sodium hydroxide can be reduced from multiple equivalents to nearly stoichiometric with β-chlorohydrin, while the selectivities of the side products, neodecanoic acid (NDA) and diester, were only 0.4 and 1 mol%, respectively. Compared to existing works, this study could be very helpful for the development of continuous and green synthesis technology for epoxides.
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