Nitroso compounds electrochemical oxidation

It will be helpful at this point to review a few well-known features of the electrochemical behavior of nitro and nitroso compounds. The reader is referred to a previous review in this series for more detail on this point1. The primary fact of which one must be aware of is that the electrochemistry of nitro compounds is exclusively cathodic the high oxidation level of nitrogen in the nitro group means that while they are easily reduced, they generally cannot be oxidized. As a matter of fact, nitrobenzene and nitromethane have been used as solvents for electrochemical oxidations because of their stability under anodic conditions2. Nitroso compounds are readily both oxidized and reduced, although the literature on these substances is much more sparse. 

Electrochemical reduction of benzylic nitro compounds (27) in an ethanolic aqueous acetic acid buffer (35 65) affords a mixture of the corresponding oxime and hydroxylamine (equation 6)48. The hydroxylamine can subsequently be oxidized back to the oxime (28) (via the intermediate nitroso compound) conversions as high as 90% can be obtained. 

As can be seen from the preceding discussion, the existence of nitroso compounds as intermediates in the electrochemical reduction of nitro compounds is mostly inferential nitroso compounds are easier to reduce than nitro compounds. Hence, they should be reduced as quickly as they are formed and would not be expected to be isolable. However, nitroso compounds have occasionally been isolated in unusual structural cases54 and the nitrosobenzene radical anion has been identified by ESR spectroscopy in at least one instance64. It is possible to prepare nitroso compounds by a two-step sequence one reduces the nitro compound electrochemically to the hydroxylamine, then electrochemi-cally oxidizes the hydroxylamine to the nitroso compound65. 

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... 

Although electrochemical oxidation of Al-cyclohexyl-Al-hydroxylamine in the presence of pyridine afforded the corresponding dimeric nitroso compound with a low yield, A-hydroxy t-alkylamines were transformed into the corresponding nitroso compounds (equation 8) . Similarly, A-phenylhydroxylamine was transformed into nitrosobenzene under similar reaction conditions. ... 

Electrochemically inactive organic compounds can be converted into an electrochemically active state by nitration, nitrosation, oxidation, hydrolysis, or some other preliminary chemical reaction, and can then be determined polarographically or voltammetrically. Examples of this are polarographic determinations of alkylbenzenesulfonates in natural water samples after extraction and nitration of the aromatic ring [77] and determinations of beta-receptor blocking agents in tablets after conversion to the corresponding V-nitroso derivatives [78]. 

Nitroaromatic compounds. By using an in series-LC-DED in the redox mode, it is possible to electrochemically reduce aromatic nitro compounds to their corresponding hydro)q lamine. This species can then be readily measured at the subsequent downstream detector electrode via oxidation to the nitroso. This is attractive analytically this latter species can be measured at potentials close to that of 0 V, away from many possible interfering compounds. This approach has been used by us for the determination of nitro aromatic drug, nitrazepam (iv) in bovine and human serum. ... 

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