Hydroxylamines anodic oxidation

An anodic azacyclization, producing tropane-related 11-substituted dibenzo[a,d]cycloheptimines 123, was recently developed by Karady et al. [136, 137]. This two-electron process is initiated by anodic oxidation of the O-substituted hydroxylamine 119 in nucleophilic solvent. It is proposed that the first one-electron oxidation leads to the aminium radical cation 120 which adds rapidly to the double bond. The electron-rich carbon radical 121 is readily oxidized to the carbocation 122. Selective nucleophilic attack on 122 from the less hindered exo-side yields the 11- substituted product 123. Depending on the... 

E. C. Szarvasky found that the electrolysis of hydroxylamine was accompanied by the spontaneous transformation of hydroxylamine into ammonia. Secondary reactions always occur—the base being reduced to ammonia at the cathode and at the anode oxidized to nitrogen oxides. F. Balia found that with various electrodes the percentage current yield of NaN02 NaN03 in the electrolytic oxidation of hydroxylamine with anodes of different metals was as follows ... 

When heated with solid potassium nitrite, ammonium sulphate reacts very energetically, sufficient heat being generated to raise the temperature of the mass to incandescence.7 When heated in solution, the two substances decompose, all the nitrogen being evolved in the free state.8 Electrolytic oxidation of a dilute-acid solution of ammonium sulphate at a lead-peroxide anode produces hydroxylamine and hypo-nitrous acid, these substances decomposing with liberation of nitrogen and nitrous oxide 9... 

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... 

Alkylhydroxylamines give a well-defined anodic wave in alkaline solution [6,76]. Anodic oxidation of hexafluorodimethylhydroxylamine to the stable free radical, hexa-fluorodimethyl nitroxide, is a convenient way of preparing this radical [77]. Dialkyl-hydroxylamines may be oxidized to nitrones by electrogenerated in methanol... 

The action of hydroxylamine on the dibromo-ketone (327) unexpectedly resulted in the isoxazoline (328)." The spiro-isoxazoline (330) is formed by anodic oxidation of the phenolic oxime (329)." Three novel reactiom leading to isoxazolines have been reported the nitrone PhCH=CHCPh=N-(CH2SMe)-0 undergoes 1,5-dipolar cyclization and elimination on heating, to yield compound (331)," silylation of secondary nitro-alkanes gives silyl-nitronates, which, in the presence of triethylamine, undergo 1,3-cyclo-addition to olefins thus sequential treatment of MejCHNOa with trimethyl-... 

Triaza-Compounds. 2-(Ethoxymethyleneamino)pyridine is converted into the triazolopyridine (564) by the action of hydroxylamine-O-sulphonic acid. Anodic oxidation of the hydrazone Ar NHN=CHAr (Ar =p-NO2C6H4, Ar = /7-MeC6H4) in the presence of pyridine and tetraethyl-ammonium perchlorate affords the salt (565). Oxidative cyclization of the pyridylhydrazone PyCH=NNHPy (Py = 2-pyridyl) by means of mercury(II) acetate yields compound (566). 2,4,6-Triphenylpyrylium fluoroborate reacts with amidrazones ArC(NH2)=NNH2 in the presence of triethylamine to give the pyrazolopyrimidines (567). The tricyclic compound (568) is... 

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... 

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). 

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... 

Since paired electrosynthesis of nitrones from Af-hydroxylamines can proceed by both anodic and cathodic oxidation, the current efficiencies are very high . 

A cathodic depolarizer is reduced in preference to solvent. For oxidation reoctions. anodic depolarizers include N2H4 (hydrazine) and NH2OH (hydroxylamine)... 

J. Tafel found that while nitric acid is reduced only to hydroxylamine q.v.) by mercury or well-amalgamated electrodes, a copper cathode reduces it to ammonia and at the same time has no action on hydroxylamine. A. Brochet and J. Petit studied the electro-reduction of nitric acid by an alternating current. T. H. Jeffery described the electrolysis of nitric acid with a gold anode, and obtained from the anode liquor crystals of aurinitric acid, HAu(N03)4.3H20. R. Ihle s observations on the oxidation-potential of nitric acid have been discussed in connection with nitrous acid (q.v.). He found that if the cone, of the nitric acid be expressed by... 

Similarly, the anode potential can be controlled by adding a suitable reducing agent. For example, if deposition of metallic lead at the cathode is desired, the anodic deposition of lead dioxide can be prevented by use of hydroxylamine or hydrazine in dilute hydrochloric acid. Lingane and Jones found hydrazine to be superior in keeping the anode potential at a lower value and in forming simpler oxidation products (nitrogen instead of mixtures of nitrous oxide, nitrate, and nitrite). 

The anodic peak at B arises from the oxidation of the hydroxylamine to a nitroso derivative during the reverse scan. The electrode reaction is... 

For other irreversible processes it is possible to reverse the electrode reaction but only at much increased potentials. Hydroxylamines undergo irreversible reduction to amines. At the potential of the reduction wave, the rate of the back reaction (reoxidation of the amine) is negligible. However at much more anodic (positive) potentials a solution of the amine can undergo oxidation. This oxidation is also an irreversible process and at these more anodic potentials rereduction of the hydroxylamine back to amine has become negligible. Thus the cathodic wave (reduction of hydroxylamine to amine) and anodic wave (reoxidation of the amine) occur at widely separated potentials. At each wave the appropriate back reaction rate is negligible. In both cases the potential of the wave is determined by the initial species only and not by the electrode product. (The oxidation of the amine in fact usually occurs at potentials too anodic to be achieved at a dropping mercury electrode and requires a graphite electrode to be seen.)... 

A small anodic peak (ai) is observed in the reverse scan in cyclic voltammetry in acidic and neutral media ( i.e., 2.00 < pH < 8.00). In the second scan, another small cathodic peak (C2) is observed at more positive potential than Ci. The anodic peak may be due to the oxidation of reduced product and the peak C2 may be due to the back reduction of oxidized nitroso to hydroxylamine as also observed by Morales et al. in the case of nitrosubstituted furans. The redox couple is noticed to be irreversible as evidenced from the separation of the Ep values. 

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