Electrolytic reduction hydroxylamines

Hydroxylamine is derived from ammonia by replacing one hydrogen atom by a hydroxyl group. It is prepared by the electrolytic reduction of nitric acid, using a lead cathode ... 

Electrolytic reductions generally caimot compete economically with chemical reductions of nitro compounds to amines, but they have been appHed in some specific reactions, such as the preparation of aminophenols (qv) from aromatic nitro compounds. For example, in the presence of sulfuric acid, cathodic reduction of aromatic nitro compounds with a free para-position leads to -aminophenol [123-30-8] hy rearrangement of the intermediate N-phenyl-hydroxylamine [100-65-2] (61). 

Dimethylaminobenzaldehyde has been made by the condensation of chloral with dimethylaniline, and subsequent hydrolysis 1 by the hydrolysis of tetramethyldiaminobenzhydrol with acetic acid 2 by the condensation of dimethylaniline, formaldehyde and m-sulfo-/>-tolyI hydroxylamine followed by hydrolysis 3 by the electrolytic reduction of a mixture of sodium nitrobenzene sulfonate, dimethylaniline and formaldehyde, and subsequent hydrolysis 4 by the reduction of a mixture of dimethylaniline, formaldehyde and sodium nitrobenzene sulfonate with iron and hydrochloric acid, followed by hydrolysis 5 by the condensation of alloxan with dimethylaniline followed by hydrolysis 6 by the condensation of dimethylaniline, formaldehyde and sodium -toluidine sulfonate in the presence of hydrochloric acid and potassium dichromate followed by hydrolysis.7 The most satisfactory method, however, is the condensation of dimethylaniline, formaldehyde and nitroso dimethylaniline, followed by hydrolysis,8 a method which was first described by E. Noelting and later perfected in detail by L. Baumann. 

Hydroxylamine is unstable as a free base. It is prepared from hydroxylamine hydrochloride, NH20H HC1, which is obtained by electrolytic reduction of ammonium chloride solution. The hydrochloride undergoes alkaline decomposition to hydroxylamine, which is collected by vacuum distdlation. 

Hydroxylamine hydrochloride is prepared by electrolytic reduction of ammonium chloride. 

The field of reductive preparations for the formation of nitroso compounds has not yet been adequately explored. For example, only indirect evidence exists that the electrolytic reduction of f-nitroalkanes to tertiary alkyl-hydroxylamines proceeds by way of nitroso compounds. 

It is natural to presuppose that the reduction of nitro compounds should lead to the nitroso compounds, at least as an intermediate stage. Until quite recently, no reductive processes for the formation of nitrosoalkanes were known [3], More recently, some indirect evidence is said to show that, on electrolytic reduction of tertiary aliphatic nitro compounds, the final t-alkyl-hydroxylamines are produced by the intermediate formation of nitroso compounds which were not isolated [99]. 

Sodium hypnnitrite Na N 0 is formed (I) by reaction of sodium nitrate or nitrite solution with sodium amalgam (sodium dissolved in incrcuryl, alter which acetic acid is added to neutralize the alkali. Sodium stannite ferrous hydroxide, or electrolytic reduction w ith mercury cathode may also be utilized. (2) by reaclion of hydroxylamine sulfonic acid and sodium hydroxide. Silver hyponitrite is formed by reaclion of silver nitrate solution and sodium hyponitrite. 

The catalytic effect of copper is shown in the reduction of nitrobenzene, which at a copper cathode is reduced to aniline, but while copper sponge under ordinary chemical conditions will reduce phenyl-hydroxylamine to aniline it has no effect upon nitrobenzene, and the inference is that in electrolytic reduction phenylhydroxylamine may be first formed by electrolysis, and this substance is then converted to aniline largely by the catalytic effect of the copper cathode. 

The pure, anhydrous nitrite is not hygroscopic, but as usually prepared the substance is a very deliquescent, crystalline solid, its aqueous solution having a slight alkaline reaction. At 15-5° C. the solubility is 300 grams per 100 grams of water.11 The heat of formation in aqueous solution from the elements is 88-9 Cal.12 The products of electrolytic reduction are hyponitrite, ammonia, and hydroxylamine. 

Non-Reversible Processes. —Reactions of the non-reversible type, i.e., with systems which do not give reversible equilibrium potentials, occur most frequently with un-ionized organic compounds the cathodic reduction of nitrobenzene to aniline and the anodic oxidation of alcohol to acetic acid are instances of this type of process. A number of inorganic reactions, such as the electrolytic reduction of nitric acid and nitrates to hydroxylamine and ammonia, and the anodic oxidation of chromic ions to chromate, are also probably irreversible in character. Although the problems of electrolytic oxidation and reduction have been the subject of much experimental investigation, the exact mechanisms of the reactions involved are still in dispute. For example, the electrolytic reduction of the compound RO to R may be represented by... 

The nature of the electrolyte sometimes has an important influence on the products of electrolytic reduction. The alkalinity or acidity, for example, plays an essential part in determining the nature of the substance obtained in the reduction of nitrobenzene in this case the effect is mainly due to the influence of the hydrogen ion concentration on various possible side reactions. The formation of azoxybenzene, for example, in an alkaline electrolyte is due to the reaction between phenyl-hydroxylamine and nitrosobenzene, viz.,... 

The reduction of nitroalkanes to A -monosubstituted hydroxylamines has not been extensively explored. The classical approach involves electrolytic reduction of primary and secondary nitroalkanes. Catalytic hydrogenation and hydride reductions of nitroalkenes also yield hydroxylamine derivatives. 

If the reaction path shown is as general as the available evidence suggests, attempts to reduce protonated oximes electrolytically to hydroxylamines are not likely to succeed. Some unprotonated oximes, such as benzaldoxime and benzophenone oxime, are reducible in not too strongly alkaline solution the oxime anion is not reducible. An investigation of the reduction of benzaldoxime in alkaline solution [79] showed that some benzylhy-droxylamine is formed under these conditions. 

When reduced with lithium aluminum hydride, both lycorenine and homolycorine yield tetrahydrohomolycorine (LXXXVa). When warmed with dilute acid, LXXXVa formed the cyclic ether (LXXXVI) which was identical with deoxylycorenine, the product of the electrolytic reduction of lycorenine. Acetylation of LXXXVI with acetic anhydride and sulfuric acid gave the so-called acetyldeoxylycorenine of Kondo and Ikeda which was identical with tetrahydrohomolycorine diacetate. Acetylation of homolycorine was reported by Kondo and Tomimura (120a) to yield a diacetyl derivative, m.p. 173°. In view of the absence of OH or NH groups in homolycorine, it must be presumed that these workers had merely recovered homolycorine, m.p. 175°. Acetylation of lycorenine produced only one acetyl derivative, m.p. 179-180°. Upon further purification (116), the so-called monoacetyl (m.p. 185-187°) and diacetyl (m.p. 175-176°) derivatives (120b) of lycorenine were found to be identical with it. Acetyllycorenine gave lycorenine on saponification and an oxime hydrochloride with hydroxylamine hydrochloride. Because the ultraviolet spectrum of acetyllycorenine resembled that of veratraldehyde, it was represented as LXXXVII rather than as the acetyl derivative of the hemiacetal form (LXXXIV). 

Hydroxylamine is used for plutonium reduction instead of cathodic reduction as in the Barnwell flow sheet Fig. 10.11, because the plutonium/uranium ratio in this LMFBR fuel is 10 times that in LWR fuel and because electrolytic reduction has not been demonstrated for this high plutonium content. 

The second part of Table 10.22 gives equations for the concentration ratio of tetravalent to pentavalent neptunium calculated for the three reductants listed there. In the older Purex plants the ferrous sulfamate used to reduce plutonium to inextractable Pu reduced neptunium partly to inextractable Np(V) and partly to extractable Np(IV). The reductants now preferred, tetravalent uranium (possibly made electrolytically) or hydroxylamine, are sufficiently strong, in sufficient time, to make neptunium almost completely tetravalent, but the reactions are much slower than reduction of tetravalent plutonium, because of slow deoxidation of the NpOj radical. Kinetics of these reductions are also discussed in Sec. 7.5. 

Hydroxylamine may be prepared by the reduction of nitric oxide, nitrous add, ethyl nitrate etc., using nascent hydrogen, SO ete. It is also obtained by the electrolytic reduction of HNO3. 

Coin-cyclam322-324 and Nin-cyclam322 catalyze the electroreduction of nitrate in aqueous electrolytes with good current efficiencies and turnover numbers, giving mixtures of ammonia, nitrite, and hydroxylamine at a variety of electrode materials. Mechanistic investigations suggested the adsorption of electroreduced Co1- and Ni1 cyclam onto the electrode surface,322 and the formation of an oxo-metal bond via reduction of coordinated nitrate.323... 

Thus, copper and platinum give similar results the nitrite formation is greater with iron, nickel, and cobalt, and the nitrate formation less. The gases were mainly nitrous oxide and nitrogen with a small proportion of oxygen. N. D. Zelinsky and S. G. Krapiwin showed that the decomposition of hydroxylamine into acid and base does not occur in soln. with methyl alcohol as solvent. J. Tafel showed that an aq. soln. of hydroxylamine sulphate in presence of 20-50 per cent, of sulphuric acid is not reduced at a copper cathode. O. Flaschner observed some reduction in dil. sulphuric acid soln. J. Tafel and H. Hahl found that reduction always takes place when the sulphuric acid cone, in the layer of electrolyte in contact with the cathode is reduced beyond a certain point, and when there is no excess of acid in other words, when hydroxylamine sulphate itself is electrolyzed, the reduction is quantitative. These results are most readily accounted for on the view that only free hydroxylamine (produced in this case by partial hydrolysis of the sulphate), but not the hydroxylammonium ion, NH3OH, is reduced at a copper... 

Nitrosobenzene.—It is natural that so good a depolarizer as nitrosobenzene is at the cathode cannot be separated as such under the conditions of a continuous reduction. Haber,5, by adding a-naphthol and hydroxylamine to the electrolyte in alkaline solution, could, however, prove the presence of nitrosobenzene in the form of its characteristic condensation product,... 

The influence of the cathode metal is much more manifest when acid electrolytes are employed than in alkaline reduction. In alkaline solution at copper electrodes, if we except the last-mentioned process, the rapidly occurring condensation of the first reduction phases—of the nitroso- and hydroxylamine body—always leads immediately to the azoxy-body and makes this appear to be the typical product of the alkaline reduction, which can in turn be further reduced. In acid solution this condensation takes place so slowly that the molecular rearrangement of the hydroxylamine and its further reduction to amine has time to take place alongside the formation of the azoxy-body and the reduction of the latter to the hydrozo-compound or benzidine.4... 

Hydroxylamine can be made by reduction of NO in dilute solution by H2 using platinized charcoal as catalyst or by reduction of nitrates electrolytically or with S02. The solid (mp 33°C) decomposes above ca. 0°C and the amine is normally encountered as stable, water soluble salts of NH3OH+. 

Often, from the point of view of electrolysis, the choice of electrolyte or solvent is free within certain limits, and the workup may then be facilitated considerably by a suitable selection of experimental conditions. For example, the reduction of a nitroalkane [50] to a hydroxylamine requires an aqueous acid medium sulfuric acid is just as good as hydrochloride acid for the electrolysis, but whereas hydrochloric acid may be removed in vacuo at a low temperature, leaving an alkylhydroxylamine hydrochloride, the sulfuric acid must be neutralized and the free, less stable base extracted. 

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