Hydroxyl radical-induced oligomerization of ethylene in deoxygenated aqueous solution

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Abstract
Deoxygenated aqueous solutions of ethylene (4 × 10–3 M) and nitrous oxide (9 × 10–3 M) were irradiated with γ-60Co rays at dose rates of 2.6 × 1015 and 2.1 × 1016 eVg–1s–1. The most prominent among the 19 products determined are butane-1,4-diol, hexane-1,6-diol, and octane-1,8-diol. A satisfactory material balance with respect to primary water radicals was obtained. In the radiolysis of N2O-containing water the major part (ca. 90%) of the primary radicals are OH radicals which are scavenged by ethylene to give β-hydroxyethyl radicals. These radicals either combine, butane-1,4-diol being the product [reaction (i)], or add to ethylene [reaction (ii)]. The 2HO–CH2–ĊH2→ HO–CH2–(CH2)2–CH2OH (i), HO–CH2–ĊH2+ CH2 CH2→ HO–CH2–(CH2)2–ĊH2(ii) self-termination rate constant has been measured by pulse radiolysis [2k(i)=(5 ± 2)× 108 l mol–1s–1]. The propagation rate constant [k(ii)=(3 ± 2)× 104 l mol–1s–1] has been derived from the dose rate dependence of G(diols) by computer-aided fitting. The β-hydroxyethyl radicals are readily oxidized by copper(II) ions (5 × 10–3 M). The major product is ethylene oxide [reaction (iii)], and little (ca. 3%) ethylene glycol is formed [reaction (iv)]. HO–CH2–ĊH2+ Cu2+→ [graphic omitted] + Cu++ H+(iii), HO–CH2–ĊH2+ Cu2++ H2O → HO–CH2–CH2–OH + Cu++ H+(iv)

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