- Reduction of the carbamate pesticides oxamyl and methomyl by dissolved FeII and CuI
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The degradation of two oxime carbamate pesticides, oxamyl and methomyl, was investigated in anoxic solutions containing various metal ions and reducing agents. In reagent-free solutions, these carbamates degrade slowly via base-catalyzed elimination. Rates of carbamate degradation are accelerated by FeII, CuI, and CuII, but not by several other metal ions and reducing agents. In the presence of FeII, carbamates undergo a net two-electron reduction that is coupled to the sequential one-electron oxidation of two FeII ions. The observed products are a substituted nitrile, methanethiol, and methylamine. A radical intermediate is inferred by polymerization of the radical scavenger acrylonitrile. Redox kinetics (i) vary with carbamate identity, (ii) exhibit first-order dependence on both FeII and carbamate concentration, (iii) are relatively independent of pH, (iv) follow Arrhenius temperature dependence, and (v) are only indirectly influenced by the presence of O2. Coordinatively saturated FeII complexes (FeIIEDTA2- and FeII(CN)64-) react with oxamyl at rates equal to and greater than hexaquo FeII, respectively, indicating that an inner-sphere FeII-carbamate coordination complex is not required for electron transfer. Experimental results indicate that CuI reduces the carbamates by the same mechanism as FeII but at much higher rates. In contrast, CuII acts as a catalyst for both elimination and reduction reactions.
- Strathmann, Timothy J.,Stone, Alan T.
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- Cleavage of 1,3-dicarbonyls through oxidative amidation
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A mild and convenient protocol for the oxidative cleavage of 1,3-diketone compounds is described. Under metal-free conditions, the method converts the 1,3-dicarbonyls into amides when treated with (nBu4N)N3 and iodine in the presence of an amine at room temperature. Using this method, a range of 1,3-dicarbonyls with various structural motifs including sterically demanding substituents and ordinary functional groups were easily fragmented, and it is demonstrated that cyclic 1,3-dicarbonyls can be directly transformed into acyclic diamides through ring-opening. Initial mechanistic studies show that diazidation of the enol form is followed by nucleophilic substitution with the amine.
- Biallas, Phillip,H?ring, Andreas P.,Kirsch, Stefan F.
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supporting information
p. 3184 - 3187
(2017/04/21)
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- Pathways in the Degradation of Geminal Diazides
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The degradation of geminal diazides is described. We show that diazido acetates are converted into tetrazoles through the treatment with bases. The reaction of dichloro ketones with azide anions provides acyl azides, through in situ formation of diazido ketones. We present experimental and theoretical evidence that both fragmentations may involve the generation of acyl cyanide intermediates. The controlled degradation of terminal alkynes into amides (by loss of one carbon) or ureas (by loss of two carbons) is also shown.
- Holzschneider, Kristina,H?ring, Andreas P.,Haack, Alexander,Corey, Daniel J.,Benter, Thorsten,Kirsch, Stefan F.
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p. 8242 - 8250
(2017/08/14)
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