Hydroxyl radical-induced oligomerization of ethylene in deoxygenated aqueous solution

Abstract

Deoxygenated aqueous solutions of ethylene (4 × 10^–3M) and nitrous oxide (9 × 10^–3M) 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+ CH₂CH₂→ 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^–3M). 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)