Reactivity of the charge transfer excited state of sodium decatungstate at the nanosecond time scale

Heterogeneous Photooxidation of Alcohols in Water by Photocatalytic Membranes Incorporating Decatungstate

“…This reactivity behaviour is known for photooxidations promoted by POMs in water, and may be related to an efficient flow of hydroxyl radicals generated from the solvent (Scheme 1). [2,20,24,27,36] The kinetic traces, determined by following the substrate conversion over time ( Figure 5), highlight the superior velocity of the homogeneous photocatalyst, nevertheless both membrane-based systems show a good performance (cf. entries 1, 2, and 8 in Table 1).…”

“…[2,24,26,27] Its UV-VIS spectrum ( Figure 1) shows a maximum absorption band at 324 nm, which overlaps with the UV solar emission, so opening the potential for environmentally benign solar-photoassisted applications. [24] While it is clear that the excited charge-transfer state of decatungstate (W 10 O 32 4± *) decays in less than 30 ps to an extremely reactive transient which is the competent photoreactant, [25] the formation of hydroxyl radicals during photoirradiation in water is still a matter of debate. [2,20,24,27] Furthermore, the solvent effect on the lifetime of the photoactive transient and on the oxidation rates of different substrates appears complicated, which hampers a direct comparison of the kinetic results obtained in different media.…”

“…[24] While it is clear that the excited charge-transfer state of decatungstate (W 10 O 32 4± *) decays in less than 30 ps to an extremely reactive transient which is the competent photoreactant, [25] the formation of hydroxyl radicals during photoirradiation in water is still a matter of debate. [2,20,24,27] Furthermore, the solvent effect on the lifetime of the photoactive transient and on the oxidation rates of different substrates appears complicated, which hampers a direct comparison of the kinetic results obtained in different media. [23,24] Basically, two main drawbacks dictate the method×s limitation especially for practical organic synthesis: these are (i) low quantum yields, which are generally found in the range 0.1 ± 0.5, [22,23] (ii) poor selectivity, due to fast over-oxidation processes leading eventually to substrate mineralisation.…”

“…[2,20,24,27] Furthermore, the solvent effect on the lifetime of the photoactive transient and on the oxidation rates of different substrates appears complicated, which hampers a direct comparison of the kinetic results obtained in different media. [23,24] Basically, two main drawbacks dictate the method×s limitation especially for practical organic synthesis: these are (i) low quantum yields, which are generally found in the range 0.1 ± 0.5, [22,23] (ii) poor selectivity, due to fast over-oxidation processes leading eventually to substrate mineralisation. [2,3] Both issues can be addressed through the heterogenisation of the photocatalyst, which may allow a significant increase of the total turnover number (TON) by catalyst recycling and a selectivity tuning as a function of the substrate affinity towards the heterogeneous support.…”

Tetrabutylammonium Decatungstate (Chemo)selective Photocatalyzed, Radical CH Functionalization in Amides

“…The diethylamino carbamate 1g likewise gave an alkylation product with dimethyl maleate in a medium yield as a ca. 1 to 1 diastereoisomeric mixture (16). The alkylation of methyl vinyl ketone, on the other hand, gave only a modest yield of carbamate 17.…”