Facile Peroxidation of Cyclohexane Catalysed by In Situ Generated Triazole-Functionalised Schiff Base Copper Complexes

A set of facile room temperature catalytic systems for the oxidation of cyclohexane C-H bonds was developed from in situ generated triazole-functionalised Schiff base copper complexes. The combination of a new triazolium-functionalised Schiff base, [(E)-3-methyl-1-propyl-4-(2-(((2-(pyridin-2-yl)ethyl)imino)methyl)phenyl)-1H-1,2,3-triazol-3-ium hexafluorophosphate(V), 2] with a range of bench-top Cu(I) and Cu(II) salts (Cu2O, CuO, Cu(CH3CN)(4)PF6, CuSO4 center dot 5H(2)O, Cu-2(OAc)(4)center dot 2H(2)O, CuCl2, Cu(NO3)(2)center dot 3H(2)O) as catalysts were screened under varying reaction conditions for the peroxidation of cyclohexane using hydrogen peroxide as a green source of oxygen. High conversions to oxidised products were obtained with up to 80% in 6 h for the 2/CuSO4 center dot 5H(2)O system at 1 mol% catalyst concentration under optimised reaction conditions. All the copper salts yielded the ketone-alcohol (K-A) oil containing varying ratios of cyclohexanol and cyclohexanone. The results also showed that at room temperature, the various in situ generated copper catalysts exclusively yielded only the K-A oil. Furthermore, by changing the reaction temperature to reflux in acetonitrile and depending on the starting substrate (cyclohexane, cyclohexanol or cyclohexanone), 23-100% of adipic acid was also obtained. The kinetics study for the peroxidation reaction reveals activation energy of 12.29 +/- 2 kJ/mol following a copper initiated radical mechanism. [GRAPHICS] .

Automated summary

A set of facile room temperature catalytic systems were developed for the oxidation of cyclohexane C-H bonds using triazole-functionalised Schiff base copper complexes. The copper catalysts yielded high conversions to oxidised products with varying ratios of cyclohexanol and cyclohexanone. The kinetics study revealed an activation energy of 12.29 +/- 2 kJ/mol following a copper initiated radical mechanism.