The effect of the exchangeable cation on the condensation of glycine and alanine was investigated using a series of homoinic bentonites. A cycling procedure of drying, warming and wetting was employed. Peptide bond formation was observed, and the effectiveness of metal ions to catalyze the condensation was Cu2+ greater than Ni2+ approximately Zn2+ greater than Na+. Glycine showed 6% of the monomer incorporated into oligomers with the largest detected being the pentamer. Alanine showed less peptide bond formation (a maximum of 2%) and only the dimer was observed.
The photodecarboxylation of a series of benzyl and naphthylmethyl phenylacetates (1, 2, 3, and 4) and 3,5-diphenyl--butyrolactones (5 and 6) was examined in detail by three labeling studies. Cage effects on the product forming step from 2naphthylmethyl phenylacetate (3) were readily established by deuterium labeling studies as well as by low temperature irradiations. The calculated cage combination ratio for product distribution and for deuterium label distribution provide evidence for coupling of the generated arylmethyl radicals in a manner dictated by ordinary diffusion-controlled processes. The scrambling of the carboxy oxygen atoms was shown to occur very efficiently for the 1-and 2-naphthylmethyl phenylacetates ^scramble = o.04 and 3scrambie = 0.16); in fact, this was found to be the most efficient reaction for these esters. Less efficiently, benzyl phenylacetate (1, <$>,scrambic = q.02) and 1 -phenylethy 1 phenylacetate (4) undergo the same scrambling process. Optically active 1-phenylethyl phenylacetate did not racemize with extended irradiation, providing evidence for a stereospecific oxygen interchange. Irradiation did not interconvert cisand tra/is-, -diphenyl--butyrolactones (5 and 6) nor scramble a carbonyl-l80 labeled sample of 5, indicating that 180 scrambling occurs in the flexible esters capable of a one-step X2S + "2S migration, a transformation unavailable to the lactones.
A modified pH 1.0 liquid redox sulfur recovery (LRSR) process, based on reactive absorption of H(2)S((g)) in an acidic (pH 1.0) iron solution ([Fe(III)] = 9-8 g L(-1), [Fe(II)] = 1-2 g L(-1)) and electrochemical regeneration of the Fe(III)/Fe(II) catalyst couple, is introduced. Fe(II) was oxidized in a flow-through electrolytic cell by Cl(2(aq)) formed on a Ti/RuO(2) anode. pH 1.0 was applied to retard the potential precipitation of predominantly jarosite group Fe(III) species. At pH 1.0, the presence of chloride ions at [Cl(-)] = 30 g L(-1) allows for both efficient (indirect) electrochemical oxidation of Fe(II) and efficient H(2)S((g)) reactive absorption. The latter observation was hypothesized to be associated with higher concentrations of Fe(III)-Cl complexes that are more highly reactive toward H(2)S((aq)) than are free Fe(III) ions and Fe-SO(4) complexes that otherwise dominate pH 1.0 Fe(III) solutions in the absence of a significant Cl(-) concentration. At the described operational conditions the rate of Fe(II) oxidation in the experimental system was 0.793 kg Fe h(-1) per m(2) anode surface area, at a current efficiency of 58%. Electricity cost within the electrochemical step was approximated at $0.9 per kg H(2)S((g)) removed.
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