Photoactivated and photopassivated benzylic oxidation catalyzed by pristine and oxidized carbons

Selective and Clean Cyclohexene-Promoted Oxidation and Photooxidation by Air

“…As we reported earlier [13], graphite nanofibers (GNF) belong to the group of carbonaceous materials activated by ambient light. In the presence of cyclohexene, GNF kept their photocatalitic properties toward oxidation of p-xylene ( Table 1, Entries 7, 8) and produced acid 2 with high conversion and selectivity similar to that we observed in the absence of cyclohexene [13].…”

“…Interestingly, the presence of cyclohexene does not affect the relationship between photosensitivity of carbonaceous materials toward oxidation of p-xylene, and their structure, discussed in detail earlier [13]. Employing cyclohexene as an activator led us to the most practical procedures for preparation of hydroperoxide 1 partially due to the complete suppression of formation of unidentified phenolic products.…”

“…Addition of cyclohexene did not change the unique ability of Multi Wall Carbon Nanotubes (MWCNT) to catalyze formation of "coupled" products: di(4-methylbenzyl) ether 10 and 1,4-dimethyl-2-(4-methylbenzyl)benzene 11. However, both the increased conversion and complete suppression of unidentified phenolic products [13] make MWCNT a promising material for the design of new carbonaceous catalysts for organic synthesis.…”

“…The methyl groups of the hydroperoxide 15 [26] and alcohol 4 [27] show up in the 1 H NMR as singlets at 1.55 -1.60 ppm. We determined the molar ratio of 15 and 4 by integration of the inverse-gated broad band decoupled 13 C NMR spectrum as we described earlier [14]. The molar ratios of products are presented in Tables 2 and 3.…”

“…Recently we reported [13] that oxidation of p-xylene 6 by air on carbonaceous materials can be significantly affected by ambient light that may lead to either activation or passivation of the catalyst along with significant shifts in the product composition. Due to the adsorption of the key intermediate 1 (Figure 1), carbonaceous ma-terials with the elevated defects-to-basal plane ratio and highly sorptive surface (carbon black (CB) and oxidized graphite (OG)), provided higher yields of the hydroperoxide 1 comparing with graphite [13]. However, noticeable loss of their catalytic activity upon exposure to light significantly curtailed application of these materials for organic synthesis.…”