Production of Adipic Acid from Mixtures of Cyclohexanol-Cyclohexanone using Polyoxometalate Catalysts

Adipic acid production through catalytic conversion of cyclohexanol-cyclohexanone using polyoxometalate H_5[α-BW_12O_40] and H_4[α-SiW_12O_40] as catalysts was carried out systematically. Polyoxometalates H_5[α-BW_12O_40] and H_4[α-SiW_12O_40] were synthesized using an inorganic synthesis method and were characterized using Fourier transform infrared spectroscopy (FTIR). Adipic acid was formed from conversion of cyclohexanol-cyclohexanone and was characterized by using melting point measurement, identification of functional group using FTIR spectrophotometer, analysis of gas chromatography-mass spectrometry (GC-MS), and 1^H and 13^C NMR (nuclear magnetic resonance) spectrophotometer. This research investigated the influence of reaction time and temperature on conversion. The results showed that adipic acid was formed successfully with a yield of 68% by using H_5[α-BW_12O_40] as catalyst at the melting point of 150-152 °C after optimization. In contrast, using H_4[α-SiW_12O_40] as catalyst, formation of adipic acid was only 3.7%. Investigation of time and temperature showed 9 h as the optimum reaction time and 90 °C as the optimum temperature for conversion of up to 68% adipic acid. Identification using FTIR, 1^H, and 13^C NMR showed that the adipic acid from conversion of cyclohexanol-cyclohexanone was in agreement with the standard adipic acid data in the literatures. GC-MS analysis indicated that several by-products were formed in conversion of cyclohexanol-cyclohexanone using H_5[α-BW_12O_40] and H_4[α-SiW_12O_40] as catalysts.