Redox hydroxylamine

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... 

But in this case spin trapping with hydroxylamine may artificially enhance superoxide production through redox cycling. On the other hand, hydroxylamines are probably able to react directly with perhydroxyl HOO ... 

To undertake oxidation of both cyclic and acyclic hydroxylamines to nitrones, an electrochemical oxidative system has been developed, where WC>42-/WC>52-are used as cathodic redox mediators and Br /Br2 or I—/I2 as anodic redox mediators (129-131). 

C-Nitroso compounds, oximes, N-hydroxyguanidines and N-hydroxyureas each contain an N-O bond and release nitric oxide (NO) or one of its redox forms under some conditions. The nitrogen atom of a C-nitroso compound formally exists in the +1 oxidation state, the same oxidation state as nitroxyl (HNO), the one-electron reduced form of N O. The nitrogen atoms of oximes, N-hydroxyguanidines, and N-hydroxyureas each formally exist in the -1 oxidation state, the same oxidation state as hydroxylamine. Consequently, the direct formation of NO (formal oxidation state = +2) from any of these species requires oxidation, one electron for a C-nitroso compound and three electrons for an oxime, N-hydroxyguanidine or N-hydroxyurea. This chapter summarizes the syntheses and properties, NO-releasing mechanisms and the known structure-activity relationships of these compounds. 

Some metabolites, most commonly aromatic hydroxylamines and quinone-type metabolites, can undergo redox cycling and generate reactive oxygen species, especially... 

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. 

However, an improved electrochemical redox methodology using a flow cell fitted with two consecutive porous electrodes of opposite polarities (cathode then anode), allows a rapid and total oxidation at the anode of the hydroxylamine intermediate produced at the cathode. Various nitroso compounds may be obtained in high yields without... 

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. ... 

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. 

IV. HYDROXYLAMINES AND HYDROXAMIC ACIDS AS REDOX CATALYSTS A. Hydroxylamines... 

Persistent or moderately stable aminoxyl radicals (1, in Scheme 6) lend themselves to one-electron oxidation to yield an oxoammonium ion (4) at a redox potential that depends on the structure of the hydroxylamine precursor Calculation methods have... 

We have seen that the generation of an aminoxyi radical from the hydroxylamine precursor (cf. Scheme 2) is viable through the use of a monoelectronic oxidant having appropriate redox potential, such as CAN (i.e. Ce" +) or by the use of the inner-sphere Pb(OAc)4 oxidant the case of PINO and BTNO from HPI and HBT, respectively, has been underpinned above. It is of no wonder, then, that the generation of PINO and BTNO, and of additional aminoxyi radicals as well has been achieved through... 

SCHEME 13. Redox generation of an aminoxyi radical from the hydroxylamine by an enzyme... 

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)... 

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. 

In a similar way it is possible to perform the amination of aromatics by indirect electrochemical reduction of hydroxylamine using a combination of the Cu /Cu and redox pairs Thus, aniline and toluidine are formed from benzene... 

Tertiary amine oxides and hydroxy la mines are also reduced by cytochromes P-450. Hydroxylamines, as well as being reduced by cytochromes P-450, are also reduced by a flavoprotein, which is part of a system, which requires NADH and includes NADH cytochrome b5 reductase and cytochrome b5. Quinones, such as the anticancer drug adriamycin (doxorubicin) and menadione, can undergo one-electron reduction catalyzed by NADPH cytochrome P-450 reductase. The semiquinone product may be oxidized back to the quinone with the concomitant production of superoxide anion radical, giving rise to redox cycling and potential cytotoxicity. This underlies the cardiac toxicity of adriamycin (see chap. 6). 

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... 

In the course of redox pyrrolization of the oxime 39 with X = OH, the hydroxyl group in position 5 is vinylated to a slight extent to form 1-vinyl-5-vinyloxy-4,4,6,6-tetramethyl-4,5,6,7-tetrahydro-5-azaindole (40, X = OCH=CH2). This was the first example of nucleophilic addition of hydroxylamine to a triple bond not activated by strong electron-withdrawing substituents. x... 

---