Cyclohexanone Oxidation to C4, C5 and C6 Dicarboxilic Acids Over P/Mo/W Dawson-Type Polyoxometalates

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Polyoxometalates (POMs) are a valuable class of inorganic compounds. The consistency of size and charge of a polyoxometalate structure, together with the inclusion of a variety of transition metals and/or functional groups, has made them very attractive in catalysis and materials science. Dawson and Keggin type POMs are known to be active in the oxidation of cyclohexanone(-One) to C6 dicarboxylic acid, namely adipic acid (AA). In this work, we are interested not only in AA (C6) but also in glutaric GA (C5) and succenic SA(C4) acids. For this purpose, we tested a series of Dawson-type POMs in the oxidation of (-One) at 90°C in the presence of hydrogen peroxide as green oxidant. The catalytic tests were monitored by HPLC during 20 hours of reaction. K6P2W12Mo6O62, K8P2W12Mo5SnO61 and Cs4SnP2W12Mo6O62 were synthesised, characterised then tested in the oxidation of cyclohexanone to dicarboxylic acids (C4, C5 and C6). The obtained results show that the formation of these products depends not only on the reaction time but also on the chemical composition of the catalyst. So, GA is favoured after 4 hours of reaction in the presence of K8P2W12Mo5SnO61 with 59.11 10-4 mol. The highest amount of SA was obtained after 4 hours of reaction over 26.32 10-4 mol of Cs4SnP2W12Mo6O62 as catalytic system. In addition, using the same catalyst, the progression of the reaction over time led to an increase in the amount of AA. Since, after 20 hours, 30.47 10-4 moles of AA were obtained compared to 1.07 and 1.19 10-4 moles of C5 and C4 diacids respectively. At the last we can concluted that the P/Mo/W Dawson POMs catalyst is a promising alternative for the synthesis of dicarboxylic acids from cyclohexanone in the presence of hydrogen peroxide.