Photolysis of phosphine in the presence of acetylene and propyne, gas mixtures of planetary interest

Abstract

Phosphine (PH 3) 1 has been observed in the atmospheres of Jupiter and Saturn. We have studied the photochemical reactions of this compound with acetylene (C 2H 2), an alkyne also detected in these atmospheres. The volatile products formed in these reactions were characterized by 1H, 31P and 13C NMR. The ethenylphosphine 2 is the first product formed in the photolysis of PH 3 in the presence of C 2H 2. Photolysis of PH 3 in the presence of propyne (C 3H 4) led to the formation of the Z- and E-prop-1-enylphosphines and traces of 1-methylethenylphosphine. A reaction pathway is proposed. The initial step is the dissociation of PH 3 to hydrogen and PH 2 radicals. Addition of the phosphinyl radical on alkyne occurs as the next step. Vinylphosphines are then formed by radical combination. This proposed reaction pathway takes into account the nature of the products and studies devoted to the photolysis of germane (GeH 4) or hydrogen sulfide (H 2S) in the presence of alkyne. Attempts to detect the methylidynephosphine HCP (the isoelectronic compound of HCN), in the photolysis products of PH 3C 2H 2 mixtures were unsuccessful. The application of these findings to Jovian and Saturn atmospheric chemistry is discussed.