Epoxidation of the Commercially Relevant Divinylbenzene with [tetrakis-(Pentafluorophenyl)porphyrinato]iron(III) Chloride and Its Derivatives

Fluorinated Fe-porphyrins, especially [tetrakis(pentafluorophenyl)porphyrinato]iron(III) chloride (tetrakis(pentafluorophenyl)porphyrinato = TPFPP) (TPFPP)FeCl (Fepor-2a), were found to be highly efficient for catalyzing the double epoxidation of divinylbenzene (DVB) to divinylbenzene dioxide (DVBDO), a novel component of epoxy resin formulation. The electronic properties of the catalysts are highly dependent on the substituents on the phenyl groups of these metalloporphyrins. The electron-rich fluorinated Fe-porphyrins are more selective toward epoxidation but are more vulnerable toward decomposition in H2O2. On the other hand, the electron deficient Fe-porphyrins are more stable, yet more Lewis acidic, which facilitates the formation of byproducts such as epoxide ring opening and overoxidation. E resins are materials of great industrial importance, as they are commonly used in paintings, coatings and electronic packagings. Conventional epoxy resin formulation usually involves diglycidyl ether of bisphenol A or bisphenol F, with this synthesis resulting in high viscosity and large coefficients for thermal expansion (CTEs), as well as high chlorine content. For some applications, however, these characteristics are undesirable. For example, high viscosity results in low heat resistance for epoxy thermosets, which is disadvantageous in applications like modeling or electronic coating. High thermal expansion (represented by the coefficient of thermal expansion (CTE)) is not desirable for electronic laminates to have good resistance to thermal fatigue. The chlorine content arising from the coupling of bisphenol A and epichlorohydrin renders the epoxy resins corrosive, a problematic property for applications involving electronic devices. Thus, new types of epoxy resin formulations that circumvent these problems are desirable. Epoxy resin formulation using divinylbenzene dioxide (DVBDO in Figure 1) results in a material possessing low viscosity (20 cP), high heat resistance, low CTE loading, high filler loading, high glass transition (Tg) values, and very low to no extractable ionic contamination. These properties contribute to the application of DVBDO in various products such as electronic packaging materials, composites, or other industrial materials. Therefore, developing a highly efficient process to synthesize DVBDO is of substantial industrial value. Epoxidation of divinylbenzene (DVB) is the key step for the synthesis of divinylbenzene dioxide (DVBDO). However, to date, there are only limited examples that provide DVBDO with both high yield and high turnover number. For approaches that use environmentally benign oxidants such as H2O2, to the best of our knowledge, only two peer-reviewed reports are available, both of which suffered from low yield and low selectivity. Dow Chemical Company patented several processes for the double epoxidation of DVB: they have demonstrated that catalysts like methyltrioxorhenium, phosphotungstic acid, and the Fe(III)-pyridinedicarboxylate complex are efficient for the double epoxidation of DVB, and that oxidants like peroxyacetimidic acid show very good selectivity for the formation of DVBDO. However, some of these catalysts have drawbacks such as low selectivity, low turnover number, using high cost noble metal, and stoichiometric formation of organic byproducts. Other oxidant such as m-CPBA and tertbutylhydroperoxide have also been studied; however, these oxidants generate stoichiometric amount of organic byproduct. We have recently discovered that a Mn-porphyrincontaining porous organic polymer (Mn-PPOP) is a very selective heterogeneous catalyst for the double-epoxidation of DVB to DVBDO us ing 2 ( t e r t bu t y l s u l f ony l ) iodosylbenzene. Unfortunately, 2-(tert-butylsulfonyl)iodosylbenzene is synthesized from a highly toxic starting material thiophenol via a route entailing several steps. Most importantly, the epoxidation reaction generates 2-(tertbutylsulfonyl)iodobenzene as a stoichiometric byproduct, making the process unsuitable at an industrial scale. Clearly desirable for large-scale production of DVBDO would be a Received: November 19, 2014 Revised: December 22, 2014 Accepted: December 29, 2014 Published: December 29, 2014 Article