Complexes, in nitration

The ion exchange reaction of anionic complexes in nitrate media is generally expressed as following equation [7],... 

VII.3.3.2 Spedation model for Th(IV) hydroxide complexes in nitrate media... 

In a two-cycle Purex procedure, the recoveries of both Pu and U are on the order of 99.9% the Pu/U separation factor is 10 . The literature reports that plutonium decontamination factors from the fission products are 10 , and that the only long-lived impurities detected in the final product are Zr, Tc, and ° Ru. However, the authors experience has been that the light rare earths (mainly La and Ce), thorium, neptunium, and the trivalent actinides (Am and Cm), which exhibit some degree of complexation in nitrate media (Guseva and Tikhomirova 1979), are present in a gram-sized plutonium sample at concentrations that are detectable by radiochemical means. 

There is evidence for the existence of structures of this kind, and for their importance in electrophilic substitution in general, and in nitration in particular. Because of the way in which the electrophile is attached to the ring they are called cr-complexes. 

Numerous explosives are based on hydrazine and its derivatives, including the simple azide, nitrate, perchlorate, and diperchlorate salts. These are sometimes dissolved in anhydrous hydrazine for propeUant appUcations or in mixtures with other explosives (207). Hydrazine transition-metal complexes of nitrates, azides, and perchlorates are primary explosives (208). 

Complexation of bromine with iron(III) bromide makes bromine more electrophilic, and it attacks benzene to give a cyclohexadienyl intennediate as shown in step 1 of the mechanism (Figure 12.6). In step 2, as in nitration and sulfonation, loss of a proton from the cyclohexadienyl cation is rapid and gives the product of electrophilic aromatic substitution. 

There are a Tew compounds of alkalies, nitrate, and acetate thai have low solubilities, but most of them are quite complex in composition. For example, sodium uranyl acetate, NaUQifCHjCOOh has low solubility. Silver acetate is an exception but its solubility is moderate. 

Tri-n-butyl phosphate, ( -C4H9)3P04. This solvent is useful for the extraction of metal thiocyanate complexes, of nitrates from nitric acid solution (e.g. cerium, thallium, and uranium), of chloride complexes, and of acetic acid from aqueous solution. In the analysis of steel, iron(III) may be removed as the soluble iron(III) thiocyanate . The solvent is non-volatile, non-flammable, and rapid in its action. 

Note that all the zero-order rate constants are essentially equivalent except those for the poly-hydric alcohols which are exactly half the value of the others. Ingold et al (Ref 49a) interpret this to mean that the rate of attack of nitronium is the same for both OH groups of the glycol molecule. Since there are two such groups the overall rate constant k0 is Vi that for monohydric alcohols. The explanation for the observed k0 for glycerol is more complex. In essence it consists of postulating that the two outside OH s are readily nitrated, ie, the 1-OH is nitrated at the same rate as the 3-OH, but the middle OH is nitrated much more slowly... 

The mechanism of the reaction has not been elucidated. Presumably several reactions occur simultaneously. Thiocyanates react with iron(III) salts with the formation of red-colored complexes. In sulfuric acid medium nitrate or nitrite coddize diphenylamine to... 

The ferrocene moiety is not just an innocent steric element to create a three-dimensional chiral catalyst environment. Instead, the Fe center can influence a catalytic asymmetric process by electronic interaction with the catalytic site, if the latter is directly coimected to the sandwich core. This interaction is often comparable to the stabilization of a-ferrocenylcarbocations 3 (see Sect. 1) making use of the electron-donating character of the Cp2Fe moiety, but can also be reversed by the formation of feirocenium systems thereby increasing the acidity of a directly attached Lewis acid. Alternative applications in asymmetric catalysis, for which the interaction of the Fe center and the catalytic center is less distinct, have recently been summarized in excellent extensive reviews and are outside the scope of this chapter [48, 49], Moreover, related complexes in which one Cp ring has been replaced with an ri -arene ligand, and which have, for example, been utilized as catalysts for nitrate or nitrite reduction in water [50], are not covered in this chapter. 

In nitrate media ( 6 Af), fluoride ion has a catalytic effect on the exchange reaction between Ce(IV) and Ce(III). Hornig and Libby have made a detailed study of this effect, over the range of added KF, 0 to 8.4 x 10 M, and have concluded that a pathway involving a monofluoro complex occurs, possibly involving a fluoride-bridged activated complex. 

It has been demonstrated spectroscopically that Ce(IV) - and V(V) perchlorates and Ce(IV) nitrate form complexes with alcohols of composition [ROH Ce(IV)] and [ROH V(OH)3]. The agreement between the determined formation constant and the Michaelis-Menten constant for Ce(IV) oxidation is good evidence for the role of these complexes in the oxidation process. The oxidations by Co(iri) and V(V) perchlorates have kinetics... 

Treatment of the complex with further amine produced the violet dyes. The importance of this complex in the mechanism is suggested by the inability of cupric acetate, nitrate or sulphate to achieve the oxidation. 

A particular feature of the whole process is the trade-off between the key intermediates of both mechanistic cycles. While the N—N bond formation (controlled by thermal stability of the mononitrosyl intermediate) is favored by lower temperatures, the 0-0 bond formation step (constrained by endothermic decomposition of the nitrate intermediate) is favored by higher temperatures. Indeed, as revealed by operando IR studies (Figure 2.24), at low temperatures nitrates accumulate on the surface, whereas at high temperatures the surfaces is essentially depleted of the mononitrosyl complexes. The optimal reaction temperature corresponds, therefore, to a subtle balance between the rate of formation of the Cu NO Z surface complex in the early stages, and the rate of decomposition of the CuN03 Z complex in the late stages of the reaction. 

Cavrini et al. [32] reported the development of a colorimetric method for the determination of miconazole nitrate in pharmaceutical preparation. The method is based on the formation of a yellow complex between the drug and bromocresol green. The absorption peak of this complex, extracted by chloroform over the pH 2—4 range, was at 424 nm, and linear response was obtained from 3—13 pg/mL. The molar absorptivity of the complex in chloroform was 1.845 x 104. This procedure is suitable for the analysis of miconazole nitrate in commercial dosage forms. 

The latter authors demonstrate in their latest paper101) that bluelight (under physiological conditions stimulating conidiation and LIAC) will depress nitrate reductase activity and increase the activity of the smaller subunit of the enzyme complex in Neurospora. It is therefore suggested to be a key enzyme for physiological bluelight action. 

Comments on the thermal nitration of enol silyl ethers with TNM. The strikingly similar color changes that accompany the photochemical and thermal nitration of various enol silyl ethers in Table 2 indicates that the preequilibrium [D, A] complex in equation (15) is common to both processes. Moreover, the formation of the same a-nitroketones from the thermal and photochemical nitrations suggests that intermediates leading to thermal nitration are similar to those derived from photochemical nitration. Accordingly, the differences in the qualitative rates of thermal nitrations are best reconciled on the basis of the donor strengths of various ESEs toward TNM as a weak oxidant in the rate-limiting dissociative thermal electron transfer (kET), as described in Scheme 4.40... 

Tolerance to nitrates is defined as the reduction in hemodynamic effect or the requirement for higher doses to achieve a persistent effect with continuous use in the face of constant plasma concentrations [15]. Nitrate tolerance was first described for nitroglycerin in 1888 [36] it occurs with all organic nitrates, albeit to different extents. For reasons that are not understood, PETN appears to be the least susceptible to the development of tolerance. No, or much less, tolerance is observed with nitrite esters, such as amyl nitrite [37], molsidomine, and sodium nitroprusside. Earlier investigations suggested that a depletion of intracellular thiols is involved in tolerance development [17], but this has not been substantiated in later studies [38, 39]. As with organic nitrate bioactivation, the precise mechanism(s) involved in nitrate tolerance remain(s) unknown, but it is likely to be complex and multifactorial. Two principal... 

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