Advanced Synthesis and Catalysis p. 1877 - 1889 (2009)
Update date:2022-07-30
Topics:
Kholdeeva, Oxana A.
Ivanchikova, Irina D.
Guidotti, Matteo
Pirovano, Claudio
Ravasio, Nicoletta
Barmatova, Marina V.
Chesalov, Yurii A.
Titanium-silica catalysts have been prepared by supporting titanium(IV) precursors with different nuclearity {mononuclear titanocene dichloride Ti(Cp)2Cl2, dinuclear titanium diethyl tartrate and the tetranuclear titanium peroxo complex (NH4)8[Ti 4(C6H4O7)4(O 2)4].8H2O} onto the surface of silica materials with different textural characteristics. The supported catalysts have been explored as highly active and reusable catalysts for the oxidation of 2,3,6-trimethylphenol (TMP) and 2,6-dimethylphenol (DMP) to 2,3,5-trimethyl-l,4- benzoquinone (TMBQ, vitamin E key intermediate) and 2,6-dimethyl-l,4- benzoquinone (DMBQ), respectively, using aqueous hydrogen peroxide as green oxidant. Catalysts prepared by grafting mononuclear Ti(Cp)2Cl 2 revealed a strong dependence of the product selectivity on the surface concentration of titanium active centers. Mesoporous materials with titanium surface concentration in the range of 0.61.0 Ti/nm2 were identified as optimal catalysts for the transformation of alkylphenols to benzoquinones. Catalysts having <0.6Ti/nm2 produced a mixture of benzoquinones and dimeric by-products. Conversely, when di-/tetranuclear titanium precursors were employed for the catalyst preparation, a diminution of the titanium surface concentration had no impact on the benzoquinone selectivity, which was typically as high as 96-99%. DR-UV spectroscopic studies revealed that the catalysts capable of producing alkylbenzoquinones with nearly quantitative yields possess titanium dimers and/or subnanometer-size clusters homogeneously distributed on a silica surface. On the contrary, catalysts with isolated titanium sites give a considerable amount of dimeric by-products. This is the first example which clearly demonstrates the advantages of titanium cluster-site catalysts over titanium single-site catalysts in hydrogen peroxidebased selective oxidation reaction.
View MoreShanghai Mokai Pharmaceutical Co.,Ltd
Contact:021-60257269
Address:Rm506,No.915,Zhenbei Road,Shanghai,200333,China
Henan Techway Chemical Co.,Ltd.
website:http://www.techwaychem.com
Contact:+86-371-66380080
Address:No.27 Shunhe Road,
Anhui Sholon New Material Technology Co., Ltd.
website:http://www.sholonchem.com
Contact:+86-550-5261666
Address:4/F Block B, Beijing Chemical Building.No.520 Tianrun Road ,Science & Education Town Wujin District, Changzhou City Jiangsu Province
Yangling Ciyuan biotech Co., Ltd.
Contact:86-15802970736
Address:2-1804, International Park Mansion, No.2, South Fengdeng Road, Lianhu District
Huangshi Meifeng Chemical Co.,ltd.
Contact:+86-714-6516706
Address:1941-4-3#,Hubin Avenue,Huangshi,Hubei,China
Doi:10.1111/j.1399-3011.1977.tb02776.x
(1977)Doi:10.1021/ja01176a536
()Doi:10.1248/cpb.24.1331
(1976)Doi:10.1107/S0108768183002566
(1983)Doi:10.1039/c39760000293
(1976)Doi:10.1016/S0040-4039(00)97989-9
(1990)