1H chemically induced dynamic nuclear polarization in the photodecomposition of uranyl carboxylates

Abstract

Chemically induced dynamic nuclear polarization (¹H CIDNP) has been observed during photolysis of uranyl salts of pivalic, propionic, and acetic acids in D₂O solution, [²H₆]acetone, [²H₄]methanol or in some other solvent. The multiplet polarization of isobutene and isobutane protons has beei found under photolysis of deoxygenated pivalate solution. The polarized compounds are formed ii the triplet pairs of tert-butyl free radicals. ¹H Emission of the tert-butylperoxyl group and emissioi of ¹H from isobutene have been recorded under photolysis of air-saturated pivalate solutions. The CIDNP of butane protons stays as a multiplet. Such changes in the presence of air/oxygen have arisen apparently because of the formation of tert-butylperoxyl free radical and its reaction with ten butyl radical products, i.e. hydroperoxide (peroxide) and isobutene. Isobutene probably forms a complex with molecular oxygen which has a very short proton relaxation time.

During the photolysis of uranyl pivalate in the presence of p-benzoquinone (5 × 10^–2–0.1 mol dm^–3) we have not observed any CIDNP, whereas under p-benzoquinone concentrations of 10^–3-10^–2 mol dm^–3 the CIDNP from both hydroquinone and p-benzoquinone has been followed.

Photolysis of uranyl propionate has led to CIDNP from butane protons. An emission from methyl group protons of a compound with an ethylperoxyl fragment in the presence of air/oxygen has been observed. The same polarization picture has arisen under interaction of photoexcited uranyl with propionic acid.

During the photolysis of uranyl acetate at relatively low concentrations (10^–2 mol dm^–3) a CIDNP very similar to that registered for uranyl propionate was recorded. The ethyl fragment is probably obtained in reactions for two methyl radicals formed from acetate with the parent uranyl acetate, namely hydrogen-atom abstraction and addition reactions.