The Hydrazyl Radical

Other names Hydrazinyl, diazyl CAS Registry Number [13598-46-4] 

Decomposition of Hydrazine. N2H3 radicals were generated by a MW discharge [1, 2] and by photoionization [3, 4] of hydrazine as shown by mass spectrometry. 

The formation of N2H3 radicals during the low-pressure Hg( Pi)-photosensitized decomposition of gaseous hydrazine was demonstrated by adding dimethyl mercury to give mono-methylhydrazine [12]. 

N2H3 radicals were mass-spectrometrically detected during the decomposition of hydrazine on a heated platinum surface between 773 and 973 K [22]. The formation of N2H3 via a secondary reaction (N2H4 + H, see below) during the thermolytic decomposition of 

The rate law given in [31] was recommended in a critical evaluation of kinetic data on high-temperature reactions [33]. A reevaluation led to a 50% higher rate constant at 

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The hydrazyl radicals either dimerize to form tetrazane, which then decomposes to form dinitrogen and ammonia (62), or are oxidized further to diazene, which disproportionates to dinitrogen and hydrazine, thus yielding (64). 

Hydrazyl radicals derived from 1,2 diaryl- and 1,2-dialkyldiazenes have been postulated [186] and identified in homogeneous solution by ESR [187]. The observation that the product 15a, obtained from l-/er/-butyl-2-phenyldiazene, consists of only one isomer is in agreement with the expectation that the hydrazyl radical should be more stable when the unpaired electron is localized rather on the PhN than on the /BuN group. The oxidative IFET is assumed to proceed as described for the pho-todehydrodimerization. Heterocoupling of the hydrazyl and allyl radicals affords the allylhydrazine. Thus, formation of the addition product is a le lh+ process, whereas the by-products are formed via a 2e 2h+ process, irrespective whether the hydrazobenzene derivative is formed by subsequent reduction or disproportionation of the hydrazyl radical (Eqs. 34 and 35) ... 

A linear relation exists between entropies and enthalpies for the equilibria and it was concluded that differences in enthalpies reflect relative potential energies. The rates of first order dissociation of the substituted tetrazanes in acetone were determined, and the rates of recombination of the hydrazyl radicals could therefore be calculated from a knowledge of the equilibrium constants. 

In addition the hydrazyl radical 6a reacts with BSD to produce trisilyl-amine (5), nitrogen, and the bis(trimethylsilyl)amine radical 7a [Eq. (30)]. 

Y -[2,4,6-tns(tnfluoromethylsulfonyl)phenyl]-A, A -diphenylhydrazineis oxidized to the stable hydrazyl radical by lead dioxide [84] (equation 76). 

Catechin-immobilizing polymer particles were prepared by laccase-catalyzed oxidation of catechin in the presence of amine-containing porous polymer particles. The resulting particles showed good scavenging activity toward stable free l,l-diphenyl-2-picryl-hydrazyl radical and 2,2 -azinobis(3-ethylbenzothiazoline-6-sulfonate) radical cation. These particles may be applied for packed column systems to remove radical species such as reactive oxygen closely related to various diseases. 

The adducts of azodicarboxylate with EtsSi or PhsSi radicals [79], have been identified as hydrazyl radicals (Reaction 5.41). The addition of RsSi radical to alkyl azides takes place at the terminal nitrogen (Reaction 5.42) affording the triazenyl o-type radical in which the SOMO is in the NNN plane (only one canonical structure is shown) [80,81]. 

Radical scavenging activity. Green tea, evaluated using the l,l-diphenyl-2-picryl-hydrazyl radical, indicated that the galloyl... 

Xanthosoma violaceum, Araceae, widely distributed in Dominican Republic, Puerto Rico, Guatemala, and Equator, was investigated for in vitro antioxidant and free-radical scavenger activities. The fraction rich in C-glycosylflavones showed with l,l-diphenyl-2-picryl-hydrazyl radical (DPPH) test an EC50 of 11.6 pg/ml, compared with quercetin (2.3 pg/ml) and a-tocopherol (10.1 pg/ml). 

Saturated Hydronitrogens (Type formula NnHn+2)- Ammonia NH3 Hydrazine (diamide) H2N.NH2 Triazane (prozane) H2 N.NH.NH2 Tetrazane(buzane, hydrotetrazane) H2N.NH.NH. NH2. Ammonia and Hydrazine are known in the free state the Triazanes are rather poorly defined as a class, whereas Tetrazanes exhibit a tendency towards instability by undergoing dissociation in solution to yield hydrazyl radicals... 

Although platinum(IV) is a stable oxidation state of platinum, the complex PtCl2 will oxidize hydrazinium ion. Hydrogen ion does not affect the rate. The reaction proceeds via a platinum(III) intermediate and a protonated hydrazyl radical which decomposes to N2 and... 

The scavenging approach is to add a substance that reacts very rapidly with radicals. Some typical scavengers are the stabilized free radicals such as gal-vinoxyl (3, p. 464), the Koelch radical (4, p. 464), and diphenylpicryl hydrazyl (33).102 These radicals will not undergo self-recombination, but nevertheless... 

It can be seen that as the proportion of 1 in the monomer mixture increases, the rate of polymerization decreases sharply. Additionally, the azo monomer, in this case, is preferentially incorporated into the copolymer and the molar mass of the product is inversely proportional to the amount of azo monomer present. It has been suggested that the formation of hydrazyl radicals are responsible for these retarding effects since such radicals would probably not be capable of initiating a new chain... 

It should be noted that 2 shows the same retarding effect on the rate of polymerization and on the molar mass of the products as does 1. Again the explanation lies in the ability of the azo function to react with the chain propagating alkyl radicals to yield hydrazyl radicals. Indeed, that these effects are also observed for 2 tends to corroborate this explanation. 

At the reaction temperature prevailing, 3 is partially thermolised and acts as an initiator. This might explain that the rate of copolymerization increases with the proportion of 3 in the monomer mixture. The simultaneous decrease in M can be explained in terms of the intervention of hydrazyl radicals, or simply by the well-known relation Mn 1/[I] /2. 

A retarding effect of monomers similar to 3 on the overall rate of the polymerization and on the molecular masses of the products was explained by evoking the reaction of the azo compounds with the chain propagating radicals to yield the stabilized hydrazyl radicals. The results of the terpolymerization with 4-6 are given in Table 3.11 52). 

The concentration of trapped radicals and the degree of occlusion (how deeply they are buried) have been studied extensively by Bamford and Jenkins (9). They determined the approximate radical concentration by swelling or dissolving polymer in solutions of diphenylpicryl hydrazyl (DPPH), a violet substance that becomes colorless on reaction with radicals. Nitrobenzene was generally used as the medium to dissolve the hydrazyl and to swell the polymer /3-propiolactone, a solvent for the polymer, was used also. 

One of the earliest studies addressing the antioxidant activity of various procyanidins in vitro reported strong scavenging activity against free radicals such as the stable radical 1,1-diphenyl-2-picryl-hydrazyl (DPPH) and the oxygen free radicals O-2 and HO, as assessed by ESR spectroscopy. 

ESR spectroscopy can generally be used to study the multiplicity of the radicals formed by photolysis of azo compounds. Very few studies of this type have however been reported. Photolysis of the azo compounds 16, 17 and 18 in isopentane/ methylcyclohexane in a matrix did not give rise to the radical pair but instead hydrazyl radicals 19 were detected 34>. These were formed by attack of the initially produced radicals on solvent, which then adds as a radical to the azo compound to give 19. 

The method described by Benington involves the reaction of the free radicals produced in a gas stream with a thin film of organic solution containing triphcnyl methyl radicals. The stream impinges upon the solution-covered surface, and the products of the reaction are measured spectroscopically. The work of Bartlett is more directly concerned with free radicals in solution. A fairly stable but nonetheless reactive free radical l,l-diphenyl-2-picryl hydrazyl (DPPH), 2-N-N-C6H2(N02)3, is capa-... 

Reactions (63) and (65) often occm simultaneously. For example, iodate or iodine in acidic conditions and cyano-ferrate(III) in alkaline solutions prefer reaction (62), while iron(III) or manganate prefer reaction (64). The oxidation to dinitrogen either takes place directly or stepwise in a one-electron oxidation with hydrazyl radicals N2H3-(A/ff = 231 kJmol ) as intermediates. 

Triazene HN=N-NH2 is formed in the pulse radiolysis of aqueous solutions of hydrazine. In the radiolysis, hydrazyl radicals N2H3- are formed that dimerize to tetrazane, which decomposes under elimination of ammonia to form triazene. ... 

From the discussion at the end of Section 6.3.2 and the experimental results presented above, a simplified reaction scheme can be constructed (Figure 23). Since the presence of the diazene completely inhibits hydrogen evolution and the reaction proceeds only in protic solvents or in the presence of water, it is very likely that the reductive IFET is a proton-coupled reduction of the diazene to a hydrazyl radical (Eq. 33) ... 

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