Application Of Heteropolytungstate Catalyst In The Photo-oxygenation Of Aromatic 1,3-diketones

Carboxylic acids and their derivatives are widely used as industrial sources of various organic substances, such as cosmetics, pharmaceuticals, agrochemicals, and food additives. Thus, many useful methods have been developed for the preparation of carboxylic acids, among them; the oxidative conversion of β-diketones has been paid much attention by chemists. We report a green, efficient and mild procedure for the synthesis of carboxylic acids.Polyoxometalate is a kind of photocatalyst with strong oxidizing, and apply in olefin epoxidation, alcohol oxidation and other organic synthesis systems successfully. In this paper, the Keggin anion can produce active intermediates, promote the reaction. However, polyoxometalate has its drawbacks, such as deactivate rapidly and recycling difficulty.In our study, we have synthesized high-activity polyoxometalates by modifying with [TEAH]+ or [NBu4]+.They are immobilized on SBA-15 in order to increase its service life. In addition, we also examine the photocatalytic activity of titanium doping polyoxometalate.First section:We synthesized samples [TEAH]nH3-nPW12O40(n=1,2,3) and [NBu4]3PW12O40] through simple acid-base reaction and double decomposition reaction. DRS, XRD and FTIR results indicated that the structure of Keggin-anion didn’t change. [TEAH]H2PW12O40(n=1) showed the highest activity for the oxidation of 1-phenyl-1,3-butanedione.Besides, we have researched reactive conditions in order to find the optimum, such as different catalyst quantity, various reactant concentrations and kind of solvent.Second section:We use the classic method synthesized carrier SBA-15, then [TEAH]H2PW12O40 and [NBu4]3[PW12O40] were immobilized on it using hydrothermal method. The result of XRD indicated that [TEAH]H2PW12O40 and [NBu4]3[PW12O40] were homodispersed on SBA-15 very well. The two immobilized polyoxometalates showed great photocatalytic activity for the oxidation of 1-phenyl-1,3-butanedione and other typical β-diketones, and showed better catalytic effect and stability in recirculation. Furthermore, [NBu4]3[PW12O40]/SBA-15 inactivated faster than [TEAH]H2PW12O40.Third section:[NBu4]5[PTiW11O40], which prepared through degradation and substitution, was immobilized on SBA-15 using hydrothermal method. DRS,XRD and FTIR results indicated that the structure of Keggin-anion didn’t change, and [NBu4]5[PTiW11O40] was homodispersed on SBA-15 very well. We examined the photocatalytic activity of polyoxometalates, before and after titanium doping and immobilization, for the oxidation of 1-phenyl-1,3-butanedione.The results showed that [NBu4]5[PTiW11O40]/SBA-15 has better photocatalytic activity for the oxidation of typical β-diketones in recirculation.