Elsevier

Chinese Chemical Letters

Volume 21, Issue 11, November 2010, Pages 1303-1306
Chinese Chemical Letters

Novel cobalt(II) complexes of amino acids–Schiff bases catalyzed aerobic oxidation of various alcohols to ketones and aldehyde

https://doi.org/10.1016/j.cclet.2010.06.009Get rights and content

Abstract

Two cobalt(II) complexes 1 and 2 of Schiff bases derived from amino acids were synthesized and used for oxidation of benzyl alcohol with molecular oxygen at different conditions of pH, solvent, temperature and complex/alcohol molar ratio to optimize reaction conditions and to evaluate the catalytic efficiency of new cobalt Schiff base complexes. Under obtained optimum conditions, various alcohols were oxidized to corresponding aldehydes and ketones.

Section snippets

Experimental

All the materials were supplied by Merk Chemical Co. (Darmstadt, Germany) and Fluka Co. and were used as received. The 1H NMR measurements were carried out on an Inova 500 MHz high-resolution liquid nuclear magnetic resonance spectrometer. IR spectra were obtained with Nicolet Magna-IR 560 SXB and expressed in cm−1. Elemental analyses were performed with a Vanio-EL analyzer and VISTA-MPS.

Sodium hydroxide (10 mmol) and amino acid (10 mmol) were stirred in ethanol (100 mL). When the amino acid and

Results and discussion

Complexes 1 and 2 were used as catalysts for the oxygen activation in the oxidation of benzyl alcohol in basic aqueous conditions. Oxidation reaction of benzyl alcohol using the complexes 1 and 2 at pH 11.5 and at 80 °C was considered as a standard reaction to compare the catalytic activity. Generally, complex 1 showed higher activity than complex 2 (Table 1).

The activity of the both studied complexes was very low at room temperature and practically no product was obtained even after 4 h. The

Conclusion

In summary, we have demonstrated the successful examples of cobalt Schiff base complexes that have catalyzed oxidation of various alcohols to the corresponding ketones and aldehydes in excellent yields without further oxidation of aldehydes to their corresponding acids using molecular oxygen as the sole oxidant in aqueous media. Furthermore, performance of process in aqueous media makes these catalysts environmentally interesting. Easy procedure, broad substrate applicability, high yields

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