相转移催化反应的研究——Ⅱ.聚乙二醇催化合成硝基苯烷醚的动力学和机理

Studies of Phase Transfer Catalysis Ⅱ. Kinetics and Mechanism of Alkoxylation of Nitrochlorobenzene with Polyethylene Glycol as Catalyst

用不同分子量的聚乙二醇(PEG)及其单醚类化合物,作为相转移催化剂(PTC),研究了由硝基氯苯(Ⅰ)合成硝基苯烷醚的反应动力学和机理。结果表明,在一定浓度的催化剂存在下,合成反应遵循假一级动力学关系:-d[Ⅰ]=k[Ⅰ],反应活化能为E_2=71.43 kJ/mol,求得了该反应的活化参数△H~≠、△G~≠和△S~≠,并与季铵盐作为PTC的反应结果做了比较。在本反应体系中,PEG和相应的单醚类PTC,其催化活性大体一致,主要取决于分子链中的有效(?)CH_2CH_1O(?)单元数。此外,还初步研究了反应机理,认为相转移催化反应过程中形成一反应中间体络合物[PEG-Na]^+OH^-。

The kinetics and mechanism of the alkoxylation of nitrochlorobenzene(Ⅰ)with polyethylene glycol (Ⅱ) of different molecular weights as catalyst were studied. The results indicate that the reaction in a constant concentration of catalyst obeys the pseudo-first-order kinetically with Ⅰ, that is-d[Ⅰ]/dt=k[Ⅰ]; and the activation energy is 71.43kJ/mol; the activation parameters(activation entropy △H^(?), activation enthalph △S^(?) and activation free energy △G^(?))were calculated based on the absolute rate theory, and were compared with the results of quaternary ammonium salts as catalyst. In this reaction system, Ⅱ and their single ethers exhibit similar phase transfer catalysis activity, which mainly depends on the effective unit number of(—CH_2CH_2O—)of Ⅱ. The catalysis mechanism of Ⅱ was studied, the reaction intermediate complex is [PEG-Na] ^+OH^-.