Addition of e–aq, H· and ·OH to acrylamide in aqueous solution and reactions of the adducts

Abstract

A detailed study has beeu niadc of the transient species produced by the reaction of eG, H and OH radicals with acrylamide (m,) in aqueous solution at natural pH (-6) and at pH = 11, using the technique of pulse radiolysis. The intense transient absorption spectrum which was observed at natural pH has been assigned to the protonated monomer radical anion, -mlH, and the products Rm,., of the reaction of R (= H, OH) with monomer. Their decays are second order and values of the extinction coefficients and rate constants have been determined. The yields of -mlH and Rm-' as a function of [ml] have been obtained and are compared with other solute systems which scavenge ea< in spurs. Thin layer chromatography has been used to identify adipamide and propionamide as two of the seven products obtained from pulse-irradiated solutions of acrylamide and an estimate of the total product yield has been made on the basis of these results.At pH = 11 the transient absorption spectrum has been assigned to the monomer radical anion, * m i and Rml. ; the decay of the former was first order whereas that of Rml * was complex and occurred with the concomitant growth of a permanent species. The extinction coefficients and rate constants for the decay of 'mi and Rml* have been determined. The yields of -mi and Rm19 as a function of [m,] have been obtained and compared with the corresponding yields of -mlH and Rml* at natural pH. Absolute rate constants (M-' s-I) have been obtained for the reaction of acrylamide with H atoms, ( 1 . 8 1 0 . 2 ) ~ lo'', CO;., -4x lo7, and *mlH, ( 2 . 5 k 0 . 4 ) ~ lo5, for reaction of *mlH with Ag+, (1.1 f 0 . 4 ) ~ lo8, and for reaction of ea& with propionamide, (3.0f0.5) x lo7, a-chloropropionamide, (5.8f0.5) x lo9, and P-chloropropionamide, (1.8f0.2) x lo9.E.s.r. spectra in a-methyl tetrahydrofuran glass at 77°K have been obtained for the radicals eH2CH2CONH2, CH36HCONH2 and the electron adduct of acrylamide. The yield and decay data presented in a previous publication ' for pulse radiolysed aqueous solutions of methacrylamide, N-t-butylacrylamide, acrylonitrile and acrylic acid have been recalculated in view of the yield dependence of (Gc);Y:H and (Gc)fG1. observed for acrylamide.

Photoiodocarboxylation of Activated C═C Double Bonds with CO2 and Lithium Iodide

“…Pulse radiolysis studies in aqueous medium have shown that the radical anion [CO 2 •– ] adds to acrylamide 1b (path b, Scheme ) with a second-order rate constant of (4 ± 1) × 10 7 M –1 s –1 without any significant competition of electron transfer (Scheme ). The addition of the radical anion [CO 2 •– ] to methyl acrylate ( 1a ) has also been demonstrated in hydrated clusters in the gas phase . This reaction proceeds with the rehybridization of only the β-carbon atom of substrate 1 as the radical anion [CO 2 •– ] already has a bent structure.…”

“…Substrates 1 and CO 2 are competitive scavengers of the photodetached electron from the iodide anion ( E ° red (aq/ e – aq ) = −3.11 V vs SCE) under our standard conditions, according to the data reported on the standard reduction potentials (Table ) − and the rate constants for the reaction with hydrated electrons (3.1 × 10 10 M –1 s –1 and 7.7 × 10 9 M –1 s –1 , for 1b and CO 2 , respectively). , The rate constants reported for selected reactions of acrylamide ( 1b ) from pulse radiolysis studies , are shown in Scheme . However, CO 2 has a singular competitive advantage over substrates 1 in acetonitrile solution as it actually resides in the solvation shell of the iodide anion.…”

Photosensitization by Phenylalanine of Carboxylic Acids, Amides, and Peptides in Frozen Aqueous Solution*

“…4) is the triplet corresponding to radical CH,-CONH,, already identified after irradiation with X rays131, and reaction with 6 H radicals in solution [7]. For propionamide, one recognizes the quintet of the similar radical CH,-cH-CONH,, already found after radiolysis of this amide [8] and of 2-chloropropionamide [9]. For isobutyramide, one also observes the same spectrum as after irradiation by electrons [8], i.e., the septet of (CH,),=C-CONH,.…”

Rate coefficient for the H atom reaction with acrylate monomers in aqueous solution

“…Most of the very high and very low values were determined in the early period of radiation chemical investigations when the technical possibilities and also the level of knowledge about the selection of proper experimental conditions were more limited than nowadays. 2,3,9,10 In principle the H atoms may add to the a-or to the b-carbon atom with respect to the CvO group, forming alkyl (Reaction (1)), or a-carboxyalkyl radicals (Reaction (2)), respectively. However, the H-atoms and also the OH radicals were shown react in the b-position of acrylic and methacrylic acid esters and acrylamides producing a-carboxyalkyl radicals.…”