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In chemistry, the amino radical, , also known as the aminyl or azanyl, is the neutral form of the amide ion (). Aminyl radicals are highly reactive and consequently short-lived, like most radicals; however, they form an important part of nitrogen chemistry. In sufficiently high concentration, amino radicals dimerise to form hydrazine. While as a functional group is common in nature, forming a part of many compounds (e.g. the ), the radical cannot be isolated in its free form.
The rate constant ( k1) for this reaction was determined to be , while the parallel reaction of OH with was found to be much slower. This rate was redetermined by using two-pulse radiolysis competition methods with benzoate and thiocyanate ions at pH 11.4. A value of k1 = was obtained from both systems. While in acidic solution, the corresponding reaction of with is too slow to be observed by pulse radiolysis.
The reactivity of the amino radical in this reaction is expected to be pH dependent and should occur in the region of pH 3–7.
The more stable electronic state is 2B1, where the unpaired electron is in the p-orbital perpendicular to the plane of the molecule (π type radical). The high energy electronic state, 2A1, has the two electrons in the p-orbital and the unpaired electron in the sp2 orbital (σ type radical).
Nitrogen centered compounds, such as amines, are Nucleophile in nature. This character is also seen in amino radicals, which can be considered to be nucleophilic species.
When the amino radical is reacted with benzoate ions, the rate constant is very low and only a weak absorption in the UV spectra is observed, indicating that amino radicals do not react with benzene rapidly. Phenol, on the other hand, was found to react more rapidly with the amino radical. In experiments at pH 11.3 and 12, using 1.5 M NH3 and varying concentrations of phenol between 4 and 10 mM, the formation of the phenoxyl radical absorption was observed with a rate constant of . This reaction can produce phenoxyl radicals via two possible mechanisms:
While the amino radical is known to be weakly reactive, the recombination process of two amino radicals to form hydrazine appears to be one of the fastest. As a result, it often competes with other NH2 reactions.
At low pressures, this reaction is the fastest and therefore the principal mode of NH2 disappearance.
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