Decomposition of nitramide

Figure 7-3. Br nsted plot for the decomposition of nitramide catalyzed by substituted anilines.

Thermal decomposition of nitramide, H2NNO2, or hyponitrous acid H2N2O2 (both of which have the empirical formula N2O.H2O) have also been used. The mechanisms of these and other reactions involving simple inorganic compounds of N have been reviewed. 

Consider the following mechanism for the decomposition of nitramide (NH2N02) in aqueous solution ... 

Example the acid- and base-catalysed decomposition of nitramide... 

The base-catalysed decomposition of nitramide (3 in Scheme 1.4) is of special historical importance as it was the reaction used to establish the Bronsted catalysis law. The reaction has been studied over manyyears and considerable evidence indicates that the decomposition... 

Scheme 1.4 Decomposition of nitramide (3) in aqueous solution via its ac/-form (4) B, catalysed by bases A, catalysed by acids [9, 10].

Correspondingly, in the acid-catalysed decomposition of nitramide (Scheme 1.4A), protonation of 4 on the hydroxyl also leads to an ion (6) which spontaneously fragments, i.e. 6 does not correspond to an energy minimum, so the upper stepwise path in Scheme 1.4A is not viable. The acid-catalysed decomposition of 3 via 4, therefore, also involves concerted proton transfer and fragmentation (the lower path in Scheme 1.4A). 

For the spontaneous decomposition of nitramide (NH2N02) the transition state is assumed to have formula 8, on the supposition that the rate-limiting step is base-catalysed removal of a proton from the (less stable) aci-tautomer (NH N02H). This suggestion is made in the... 

Fia. XVI. 1. Bronsted plot for the base-catalyzed decomposition of nitramide. (Data from compilation by R. P. Bell, Acid-Base Catalysis, Oxford University Press, New York, 1941.) + Doubly charged bases, B++, mostly aquo-iona, [M(H20) (0I1)]++. o Doubly charged bases, B". o- Uncharged bases, B° all substituted anilines. 

The most numerous cases of homogeneous catalysis are by certain ions or metal coordination compounds in aqueous solution and in biochemistry, where enzymes function catalytically. Many ionic effects are known. The hydronium ion H3O and the hydroxyl ion OH catalyze hydrolyses such as those of esters ferrous ion catalyzes the decomposition of hydrogen peroxide decomposition of nitramide is catalyzed by acetate ion. Other instances are inversion of sucrose by HCl, halogenation of acetone by H and OH , hydration of isobutene by acids, hydrolysis of esters by acids, and others. 

Amines are weaker acids than alcohols. On the other hand, they are strong nucleophiles even if they are not deprotonated. One of the relatively few mechanisms known which involves proton abstraction from a NH bond is the decomposition of nitramide... 

In 1924 Bronsted and Pedersen [67] found that base catalytic coefficients (feB) which they had measured for a large number of bases in the decomposition of nitramide were related to the base strength of the catalysts by eqn. (46)... 

Since 1924, the Bronsted relation has been applied to many general acid and base catalysed reactions, such as those discussed in Sect. 2.2, as well as to proton transfer equilibria like (43)—(45). Over limited ranges of acid strength and for variation within a similar catalyst type, G and a or j3 are constant and the relation holds well. Different catalyst types in a reaction often do not fit on a single Bronsted plot, but give different Bronsted lines. This was observed for the decomposition of nitramide [68]. It has also been observed in proton transfer from l,4-dicyano-2-butene(51)... 

The work of Brpnsted and Pedersen (23) on the catalytic decomposition of nitramide and the kinetic studies of Lowry and Faulkner (24) on the mutarotation of tetramethylglucose led to the formulation of a more general viewpoint on acids and bases which logically showed that the hydrogen ion and hydroxyl ion were not the unique carriers of acid and basic properties. An acid was defined as any substance capable of donating a proton, and a base any substance capable of accepting a proton. In accordance with this definition (Lowry, 25 Brpnsted, 26), the following substances are typical acids and bases ... 

Where the second term in equation (4) is negligible but the water reaction is sufficiently large to be detected, the result is curve d. The important example is the decomposition of nitramide (Brpnsted and Pedersen, 23), and others are the hydrolysis of jS-lactones (Johansson, 29) and the halogenation of nitroparaffins (Pedersen, 30). 

Gi increases with increasing positive charge, and a recent detailed analysis of catalytic effects of uncharged bases in the decomposition of nitramide shows that there is a dependence on the structure of the base (Bell and Wilson, 40 Bell, 41). For the mutarotation of glucose at 18°, Ga = 33 X 10 and y = 0.40. For the more accurate results on the acid catalysis of the acetone-iodine reaction at 25°, Gi and x are 120 X lO" and 0.62, respectively, in the equation... 

Table 2 shows rate constants for the base-catalysed decomposition of nitramide at 25 Graph the data for logZ g versus pAL, with and without the statistical correction and comment briefly on your result. What would happen to the correlation if a shorter range of pA /" values (say between 8 and 11) were employed ... 

J.N. Bronsted and K. Pedersen, The Catalytic Decomposition of Nitramide and its Physico-Chemical Applications, Z. Physik. Chem., 1923,108, 185 see also A.J. Kresge, The Bronsted Relation - Recent Developments, Chem. Soc. Rev., 1973,2,475. 

When all the variant reagents have similar structures each will have identical p and q values (for example alkyl phosphate dianions all have p - and q = 3). The slope, (3, will be identical using both treatments but the intercepts will differ. The statistically uncorrected Bronsted graph is illustrated in Figure 17 for the base-catalysed decomposition of nitramide. 

Fig. 7.24 Plot of the logarithm of the rate constant for the decomposition of nitramide against the logarithm of the basicity constant for the base used as catalyst [45].

Bransted LFER. Bronsted and Pederson (1923) were the first to describe a relationship between rates and equilibria for a series of compounds. They found that log/cB for base-catalyzed decomposition of nitramide, H2N202, varies linearly with log/CHB+, the acidity constant of the conjugate acid of the catalyst. Rate constants for many other acid- or base-catalyzed reactions (including the hydrolysis of amides, esters, carbamates, and organophosphates, and dissociation of acids and metal-ion complexes) are log-log related to the acid (or base) dissociation constant of the catalyst and follow either of the equations... 

The term nucleophilicity refers to the relative rate of reaction of an electron donor with a given electrophile, as distinct from basicity, which refers to its relative affinity for a proton in an acid-base equilibrium. A quantitative relationship between rate and equilibrium constants was discovered by Brpnsted and Pedersen (1) in 1924. These authors found that the rate constants for the catalytic decomposition of nitramide by a family of bases, such as carboxylate ions (GCH2C02 ), could be linearly correlated with the acidities of their conjugate acids, pKHB. This observation led to the discovery of general base catalysis and the first linear free-energy relationship, which later became known as the Brpnsted equation ... 

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