Copper based macromolecular catalysts for the hydroxylation of phenols

Abstract

Copper containing macromolecules, viz., Copper-meso-tetrakis-(4-carboxyphenyl)porphyrin (CuTCPP) and Copper-meso-tetra-phenylporphyrin (CuTPP) complexes were synthesized and heterogenized on the surface of aminated SBA-15 molecular sieves. The 1H NMR, mass spectral and elemental (CHN) analyses were performed to confirm the formation of these copper complexes (CuTCPP and CuTPP). The absence of 1H NMR signal, characteristic of NH bond (-2.79 ppm in TCPP and -2.74 ppm in TPP) in CuTCPP and CuTPP clearly confirms the incorporation of copper ion in to the cavities of the TCPP and TPP ligands. In addition, the decreased intensity of the soret band and the reduction of the number of Q bands also supports the formation of copper complexes. Further the homogeneous CuTCPP and CuTPP were grafted on the amino functionalized SBA-15. The grafting of copper complexes on amino functionalised SBA-15 was evident from the surface area analysis, powder XRD and N2 sorption isotherm. In the powder XRD, the shift in 2θ value compared to parent SBA-15 materials, and the broadening of the signal supports the grafting of copper complexes in to the amino functionalized SBA-15. Both homogeneous and heterogeneous copper macromolecular complexes were used as catalysts for the hydroxylation of phenolic compounds. The catalysts showed comparable conversion (72%) with the formation of ortho- and para- substituted products which have industrial importance. The hydroxylation reaction using the copper based macromolecular catalyst was found to be first order with an activation energy of 26.03 KJ/mol. Subsequently various substituted phenolic compounds, anisole and benzene also yielded the corresponding hydroxylated product with comparable conversion.