Sunlight Induced Oxidative Photoactivation of N‐Hydroxyphthalimide Mediated by Naphthalene Imides

We report the aerobic photoactivation of N‐hydroxyphthlimide (NHPI) to the phthalimido‐N‐oxyl (PINO) radical mediated by naphthalene monoimides (NI) for promoting the selective oxidation of alkylaromatics and allylic compounds to the corresponding hydroperoxides. In the absence of either NI or NHPI no oxidation was observed, meaning that the two molecules operate in a synergistic way. Sunlight as well as artificial UV‐light irradiation was necessary in order to perform the process at low temperature (30–35 °C). EPR spectroscopy confirmed the role of NI and oxygen in promoting the formation of the superoxide radicals O₂^.− which, in turn, increased the concentration of PINO radicals during the UV light irradiation of NI/NHPI mixtures in MeCN. The investigation was extended to NI bearing different substituents on the naphthalene moiety. Finally, the synthesis and application of a unique photocatalyst including the NI and NHPI moieties linked by a suitable spacer was also considered. In this case the photocatalyst showed a substrate‐dependent behaviour with some peculiarities in comparison to the system where NI and NHPI are independent units in the same reacting system. This photocatalytic system paves the way to a non‐thermal, metal‐free approach for C H bond activation towards aerobic oxidation under very mild conditions.

     

Development of Composite Wicks for Heat Pipe Performance Enhancement

This study examines the enhancement of heat pipe thermal performance through the employment of composite wicks. Wicks were fabricated from a biporous structure comprised of fine nickel metal powders sintered onto layers of coarse pore copper mesh. Wick structures were designed to explore the effects of both enhanced evaporation heat transfer at the liquid/vapor interface and the extension of the capillary limit. A number of composite wick heat pipe configurations were fabricated and tested to assess performance improvements in comparison to conventional designs. Horizontal, gravity-assisted, and against-gravity tests were conducted to determine whether these designs were orientation-dependent. At various heat inputs, some configurations achieved thermal performance levels greater than three times higher than those of conventional heat pipes. During against-gravity tests, virtually all composite designs exhibited improved performance over the conventional heat pipe at all heat inputs. These results clearly demonstrated that significant improvements in heat pipe performance were achieved through composite wick design.