Hydroxylamine, redox reactions

The base was being prepared by distilling a mixture of hydroxylamine hydrochloride and sodium hydroxide in methanol under reduced pressure, and a violent explosion occurred towards the end of distillation [1], probably owing to an increase in pressure above 53 mbar. It explodes when heated under atmospheric pressure [2], Traces of hydroxylamine remaining after reaction with acetonitrile to form acetamide oxime caused an explosion during evaporation of solvent. Traces can be removed by treatment with diacetyl monoxime and ammoniacal nickel sulfate, forming nickel dimethylglyoxime [3], An account of an extremely violent explosion towards the end of vacuum distillation had been published previously [4], Anhydrous hydroxylamine is usually stored at 10°C to prevent internal oxidation-reduction reactions which occur at ambient temperature [5], See other REDOX REACTIONS... 

Picryl chloride (87) reacts with hydroxylamine hydrochloride to yield 2,4,6-trinitroaniline (53) (picramide) and not the expected At-hydroxy-2,4,6-trinitroaniline. In contrast, the same reaction in the presence of sodium ethoxide is reported to yield 4,6-dinitrobenzofuroxan (94) via substitution of the halogen by hydroxylamine, followed by an internal redox reaction between the hydroxyamino group and one of the adjacent o-nitro groups. ... 

Elemental composition H 9.15%, N 42.41%, O 48.44%. Hydroxylamine may be measured by coulometric titration to a potentiometric end point using a coulometric titration cell. A standard solution of bromine may be used as oxidizer in the redox reaction. (Skoog, D. A., D. M. West, and F. J. HoUer. 1992. Fundamentals of Analytical Chemistry, 6th ed. pp. 467, Orlando Saunders College Publishing)... 

With hydroxylamine, the stability constant (log Xi) with silver(I) ions was determined to be 1.85. Attempts to measure the formation constants of higher complexes were thwarted due to the rate of the redox reaction being too high. An estimate of log /32 < 3 was made, however.120... 

The reaction employed to synthesize hydroxylamine, which produces die inteimediate N(0HKS03)2, probably involves the attack of HSOj (acting as a Lewis base) on N02 (acting as a Lewis acid), although, because the formal oxidation state of the N atom changes from +3 in N02 to +1 in N(0HXS03)2, this can also be seen as a redox reaction. Whether one considers reactions such as these to be redox reactions or nucleophilic substitutions may depend on the context in which the reactions being discussed. It is easy to see that these reactions do not involve simple electron transfer, such as in 2 Cu (aq) — Cu (s) + Cu (aq). 

Forster and Junge on the basis of the measured proton-release pattern (see Section II below), suggested a different model. In this model two hydroxylamine molecules bind cooperatively to the OEC only in the Spstate, and a redox reaction with NH2OH occurs only after the first flash, as shown in Fig. 4. As noted, in this model only the Spstate forms a stable complex withNH20H. 

When freshwater lake sediments were treated with hydroxylamine hydrochloride or sodium acetate, which are effective extractants for the removal of Mn (Oscarson et al., 1981b), the oxidation of As(III) to As(V) by the treated sediments was greatly decreased relative to untreated samples of the sediments (Table 8-2). Although the hydroxylamine hydrochloride treatment also removes Fe oxide, the evidence obtained from colorimetry and x-ray photoelectron spectroscopy shows that a redox reaction between Fe oxide and As(ni) does not occur within 72 h, indicating that the kinetics of the redox reaction between As(ni) and Fe(IIl) is relatively slow. This supports evidence that Mn oxide is a primary sediment component responsible for the oxidation of As(ni). 

Amide formation. Redox reaction between aldehydes and hydroxylamine leads to carboxamides. The reaction, catalyzed by Rh(OH)n in water at 160°, perhaps proceeds via oxime formation, dehydration and rehydration. 

Other methods, among which thermolysis or photolysis of tetrazene [59], photolysis of nitrosoamines in acidic solution [60], photolysis of nitrosoamides in neutral medium [61], anodic oxidation of lithium amides [62], tributylstannane-mediated homolysis of O-benzoyl hydroxamic derivatives [63, 64], and spontaneous homolysis of a transient hydroxamic acid sulfinate ester [65] could have specific advantages. The redox reaction of hydroxylamine with titanium trichloride in aqueous acidic solution results in the formation of the simplest protonated aminyl radical [66] similarly, oxaziridines react with various metals, notably iron and copper, to generate a nitrogen-centered radical/oxygen-centered anion pair [67, 68]. The development of thiocarbazone derivatives by Zard [5, 69] has provided complementary useful method able to sustain, under favorable conditions, a chain reaction where stannyl radicals act simply as initiators and allow transfer of a sulfur-containing... 

TEMPO and other organic nitroxyls have been used as catalysts in combination with numerous stoichiometric oxidants, such as sodium hypochlorite [24], PhI(OAc)2 [25], and sodium chlorite [26]. A number of recent studies have shown that NO -based redox cocatalysts enable these reactions to be conducted with O2 as the terminal oxidant [27]. The general catalytic cycle for these aerobic nitroxyl/NO -catalyzed alcohol oxidation reactions is depicted in Scheme 15.6a. A variation of this approach features halides as additives, in which the X2/HX redox couple is believed to mediate the NO2/NO and oxoammonium/hydroxylamine redox couples (Scheme 15.6b). 

Accordingly, the test involves a redox reaction analogous to that in the tests for hydrazine, hydroxylamine, sodium hydrosulfite, Rongalite, which function as hydrogen donors in alkaline solution. 

In aqueous solutions NH2 radicals are produced by the redox reaction between Ti ions [1] or ions [5] and hydroxylamine in acid media... 

Perhaps the most important application of redox chemicals in the modern laboratory is in oxidation or reduction reactions that are required as part of a preparation scheme. Such preoxidation or prereduction is also frequently required for certain instrumental procedures for which a specific oxidation state is essential in order to measure whatever property is measured by the instrument. An example in this textbook can be found in Experiment 19 (the hydroxylamine hydrochloride keeps the iron in the +2 state). Also in wastewater treatment plants, it is important to measure dissolved oxygen (DO). In this procedure, Mn(OH)2 reacts with the oxygen in basic solution to form Mn(OH)3. When acidified and in the presence of KI, iodine is liberated and titrated. This method is called the Winkler method. 

From the discussion of the Marcus theory above and equations (20) and (21), we see that the experimental data needed to judge the feasibility of ET steps involving spin traps and spin adducts are the redox potentials and A values of the ST +/ST and ST/ST - couples, as well as those for hydroxylamine derivatives related to the operation of reactions (4) or (5). The electroactivity of the spin adducts themselves is also of interest since it must somehow be related to their lifetimes in a redox-active environment. Moreover, the excited-state redox potentials (of ST /ST and ST,+/ST ) are also necessary for the understanding of photo-ET processes of spin traps. 

This review describes electrochemical reactions of hydroxylamines, oximes and hydroxamic acids. In addition, utilization of hydroxylamines and hydroxamic acids as redox mediators are shown. Since the electroorganic chemistry of hydroxylamines, oximes and hydroxamic acids is rather a minor area in the electrochemistry of organic compounds, the reader is advised to refer to texts which are written for organic chemists unfamiliar with the electroorganic chemistry. 

The reductive NO chemistry will cover some new developments on the electrophilic reactions of bound nitrosyl with different nucleophiles, particularly the nitrogen hydrides (hydrazine, hydroxylamine, ammonia, azide) and trioxodinitrate, along with new density functional theoretical (DFT) calculations which have allowed to better understand the detailed mechanistic features of these long-studied addition reactions, including the one with OH-. The redox chemistry of other molecules relevant to biochemistry, such as O2, H2O2 and the thiolates (SR-) will also be presented. 

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