Catalytic Synthesis of 2-Methyl-1,4-Naphthoquinone (Vitamin K₃) Over Silica-Supported Aminomethyl Phosphine-Ru(II), Pd(II), and Co(II) Complexes

Abstract

Ru(II), Pd(II), and Co(II) complexes of the free ditertiary aminomethylphosphine ligand, N,N-bis(diphenylphosphinomethyl)aminopropyltriethoxysilane [(EtO)₃Si(CH₂)₃ N(CH₂PPh₂)₂] (DIPAPTES), and its SiO₂-DIPAPES have been synthesized under a nitrogen atmosphere using Schlenk techniques. All the complexes were used as catalysts for the oxidation of 2-methyl naphthalene (2MN) to give 2-methyl-1,4-naphthoquinone (vitamin K₃, menadione, 2MNQ) in the presence of hydrogen peroxide as a clean and cheap oxidant. The catalytic synthesis of vitamin K₃ was investigated using both homogeneous catalysis with free complexes and heterogeneous catalysis with silica-supported complexes. [(DIPAPTES)PdCl₂] and its silica-supported form showed the best catalytic activity for the selective oxidation of 2-methyl naphthalene to 2-methyl-1,4-naphtoquinone compared to the other metal complexes. 2MNQ yield reached 52.26% with the 2MN conversion of 90.52% using complex [(DIPAPTES)PdCl₂] and 58.59% with the 2MN conversion of 99.56% using the silica supported [SiO₂(DIPAPES)PdCl₂] complex for 1 h. Recycling was investigated for the silica-supported Pd(II) complex and compared with the classical production of vitamin K₃.

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Keywords:

• Catalyst design
• menadione
• oxidation
• phosphines
• quinones
• vitamin K₃

Acknowledgments

We would like to thank to Mr. Nafiz Usta, Mr. Latif Çayhan, and Mrs. Serap Gökmen of Oxyvit Kimya San.Tic.A.Ş. for their all support. The authors also thank Çukurova University for financial support (Project No: FEF2007D007).