Nitrogen -1 Hydroxylamine, NH2OH

Many different nitrogen-containing nucleophiles can attack a carbonyl group. In this section you consider primary amines (RNH2), secondary amines (R2NH), hydroxylamine (NH2OH), and hydrazine (NH2NH2). 

A very good picture of some of the properties of hydrogen compounds can be obtained with the aid of an electrostatic model, but we must be careful not to conclude that all the hydrogen compounds are therefore ionic in character. In addition to NHS, there are two other nitrogen compounds, hydrazine H2NNH2 and hydroxylamine NH2OH, which have properties not fundamentally dissimilar to those of ammonia. It is not possible to devise a plausible electrostatic model for these compounds because of the bond between like atoms. In addition to water there is also the compound hydrogen... 

The biomedical research on nitrogen oxides has nearly exclusively involved NO and its oxidative metabolites. Reduced species, such as nitroxyl (HNO) and hydroxylamine (NH2OH), have been largely unexplored in mammalian systems until recently. The initial interest in the biochemistry of HNO arose following observation of nitrous oxide (N20) during bacterial reduction of nitrite to NH3. Dehydrative dimerization of HNO to form N20 (77, 78) was well documented in the gas phase,... 

Hydroxylamine (NH2OH) and some of its derivatives have been used for example in the reduction of mercury species, nitrogen oxides, aqueous chlorine... 

The redox relationship of NO with other nitrogen oxides is shown in Fig. 3. As indicated, NO occupies a central and unique position in this redox scheme. The two-electron oxidation of ammonia (NH3) generates hydroxylamine (NH2OH) and a further two-electron oxidation of hydroxyl-amine generates nitroxyl (HNO). NO can then be generated by a single-... 

In the process of ammonification, hydroxylamine (NH2OH) is an important intermediate in two directions, denitrification direct to ammonium as well as the oxidation of ammonium to nitrate (nitrification). As long as nitrogen remains in its reduced form (NH4), it remains in the local environment because of its affinity for soil absorption and its rapid uptake by biota. NH4 is in equilibrium with NH3, which can escape to the atmosphere, depending on pH, temperature, soil moisture, soil type and atmospheric NH3 partial pressure. The equilibrium between emission and deposition (gas uptake) is called the compensation point, similar factors control the emission/dry deposition of NO. 

If a molecular compound is not an acid, you must then consider whether or not it is a weak base. Many weak bases are related to ammonia in that they consist of a nitrogen atom bonded to hydrogen and/or carbon atoms. Examples include methylamine (CH3NH2), pyridine (C5H5N), and hydroxylamine (NH2OH). Weak bases are weak electrolytes. 

Hydroxylamine, NH2OH, the thermodynamically strongest nitrogen reductant, going to N2, is unstable, decomposing slowly at ambient T. An aqueous solution reacts alkaline and soon decomposes ... 

Comparative studies have been made in the oxidation of N2H4 and NH2OH by Co(III) complexes. The reactions of [Co(edta)(OH2)] with the substrates in acid media are considered to proceed via an inner-sphere mechanism with a proton bridge between the cobalt(III) species and (a filled orbital on) the nitrogen of the reductant. The rates are greater than for [Co(ox)3] or [Co(acac)3] despite the fact that all three species have similar redox potentials. Reactions with cationic cobalt(III) species appear to be much slower. The stoichiometry of the reaction between NH2OH and V(V) in HCIO4 media is dependent on the reaction conditions.In the presence of excess reductant, however, the reaction is first order with respect to [VO ] and the dependence on hydroxylamine concentration... 

---