原位还原的FeCl2催化合成1,1,1,3-四氯丙烷

Synthesis of 1,1,1,3-tetrachloropropane catalyzed by FeCl2 in situ

摘要:

基于Fe(Ⅱ)与Fe(Ⅲ)之间自旋态的可逆转换特性，以还原Fe粉对FeCl3原位还原生成的FeCl2为催化剂、磷酸三丁酯（TBP）为配位剂，搭建Fe/FeCl3/TBP催化剂体系，催化CCl4与乙烯经原子转移自由基加成（ATRA）反应，合成1,1,1,3-四氯丙烷（TCP），考察了CCl4投料量0.4 kg的反应中，Fe/FeCl3/TBP催化剂体系成分组成、反应条件等工艺参数对CCl4的转化率、TCP的选择性和收率的影响，并在最优条件下进行20 kg级放大实验。结合密度泛函理论（DFT）计算，研究了FeCl2催化反应过程中各物种结构、相互作用及能量变化，采用基于Hirshfeld独立梯度模型（IGMH）法分析了配合物各片段之间的相互作用。结果表明，CCl4投料量0.4 kg的反应中，优化条件为：n(CCl4)∶n(Fe)∶n(FeCl3)∶n(TBP)＝520∶3∶2∶6，乙烯压力1.0 MPa，反应温度110 ℃，反应时间6 h，TCP的收率可达96.4%；CCl4的投料量20 kg时，反应时间延长至10 h时，TCP选择性99.7%，收率高于92.4%。反应中间体1,1,1-三氯丙烯自由基淬灭生成TCP的过程因具有+22.2 kcal/mol的能垒而成为反应的决速步骤；乙烯的活化主要是通过C==C的π电子窜迁至FeCl2中Fe原子反键轨道而实现有效配位；自然键轨道分析进一步证实了FeCl2对CCl4及乙烯的活化过程是协同进行的。经计算，FeCl2活化CCl4及乙烯前后的二阶微扰稳定能变化分别为+9.97和+9.41 kcal/mol。Fe/FeCl3/TBP催化CCl4与乙烯经ATRA反应合成TCP为链式氧化-还原反应循环催化机制。

Abstract:

Based on the reversible spin state transition characteristics between Fe(Ⅱ) and Fe(Ⅲ), FeCl2 in situ reduced by Fe and FeCl3 was used as main catalyst, and tributyl-phosphate was used as cocatalyst. High yield synthesis of 1,1,1,3-tetrachloropropane (TCP) was achieved through atom transfer radical addition(ATRA) reaction using CCl4 and ethylene as raw materials. The influence of process parameters such as the composition and reaction conditions of the Fe/FeCl3/tributyl-phosphate catalytic system under the CCl4 feed amount of 0.4 kg was investigated, and the 20 kg scale amplification experiment was performed. The structures, interactions, and energy changes of various species in the FeCl2 catalytic reaction process were studied by the method of density functional theory(DFT) calculations, and the interaction of the complexes were analyzed by Hirshfeld independent gradient model (IGMH). The results show that in the CCl4 feeding amount of 0.4 kg, the best reaction conditions are: n(CCl4): n(Fe): n(FeCl3): n(TBP) =520:3:2:6, ethylene pressure 1.0 MPa, reaction temperature 110℃, reaction time of 6 hours, TCP yield can reach 96.4%; when the feeding amount of CCl4 increases to 20 kg, the reaction time is extended to 10 hours, TCP selectivity is 99.7%, the yield is higher than 92.4%. The DFT calculation results indicate that the quenching of the intermediate 1,1,1-trichloropropene radical to generate TCP is the rate determining step of the reaction due to its energy barrier of +22.2 kcal/mol. The natural bond orbital analysis confirms that the activation process of FeCl2 to CCl4 and ethylene is coordinated. The calculations showed that the second-order perturbation stabilization energy changes before and after FeCl2 activated CCl4 and ethylene were +9.97 and +9.41 kcal/mol, respectively. Experiments and DFT calculations revealed the cyclic catalytic mechanism of FeCl2 catalyzed atomic transfer radical addition chain oxidation-reduction reactions.