Photoinduced Reactivity of Red Phosphorus and Ethanol at High Pressure

Dissociation of ethanol by two-photon absorption of UVML laser emission centered at 350 nm was employed to trigger a chemical reaction at ambient temperature with red phosphorus for pressures ranging between 0.2 and 1.5 GPa. The reaction products, identified by infrared and Raman spectroscopy, indicate a quite selective reactivity ascribable to the two main dissociation channels involving the splitting of the O-H and C-O bonds of ethanol. The ethoxy radical, obtained through the splitting of the O-H bond, has been identified as the main responsible for the phosphorus reactivity, giving rise to triethylphosphate. The same dissociation channel is also responsible for the formation of a consistent amount of molecular hydrogen, phosphine, and diethyl ether, whereas ethane and ethylene, the latter observed only in traces, likely derive from the C-O dissociation. The reaction is accelerated by increasing pressure from 0.2 to 0.6 GPa but is not favored, as also observed in pure ethanol, by a further pressure increase. The reaction proceeds until ethanol is completely consumed, and further irradiation determines the decomposition of the products, especially of diethyl ether, leading to the formation of CO2, methane, and ethane.