Reactions of 1,1-dialkoxyalkene radical cations in aqueous solution with OH–, HPO42–, and H2O. Electron spin resonance spectroscopic, pulse conductometric, and product analytical studies

Abstract

The reactions of H₂O, HPO₄^2–, and OH^– with eight, 1,1-dialkoxyalkene radical cations have been studied in aqueous solution by e.s.r. spectroscopy and in part by pulse conductometry and product analysis. Hydroxide ion reacts with the radical cations with rate constants ranging from k 2 × 10⁸ for species (5) to 6 × 10⁹ l mol^–1 s^–1 for (6), producing mainly alkoxycarbonylalkyl radicals. With (1) and with (6), in addition, the formation of 1,1-dialkoxy-2-hydroxyethyl radicals was observed and e.s.r. parameters are given. The HPO₄^2– anion was found to react with four of the radical cations to form phosphato-dianion-substituted radicals, (RO)₂(PO₄^2–)C–ĊH₂(e.s.r. parameters are given), with k values ranging from 2 × 10⁶ for (1) to 3 × 10⁸ l mol^–1 s^–1 for (6). Water reacted analogously with rate constants ranging from k 3 × 10² for (1) to 10⁴ s^–1 for (27) at 20 °C, the reaction yielding 2,2-dialkoxy-2-hydroxyethyl radicals (e.s.r. parameters are given) and protons. Attack of water occurs virtually only at the dioxygen-substituted carbon as is shown in one example. Product analysis by g.l.c.–m.s. of the higher boiling material from ⁶⁰Co γ-irradiation of N₂O-saturated aqueous solutions of (CH₃O)₂CH–CH₂Cl gave evidence for the formation of dimers and cross-dimers of the radicals ĊH₂OCH(OCH₃)CH₂Cl, CH₃OCOĊH₂, (CH₃O)₂CHĊHCl, (CH₃O)₂ĊHCH₂, and (CH₃O)₂ĊH₂OH. Structures and yields of the products agree with the conclusions drawn from e.s.r. spectroscopic and conductometric measurements.