Tetroxide

Dichlorine tetroxide, CIOCIO3, chlorine perchlorate (CSCIO4 plus chlorine fluorosul-phate, CIOSO2F) diehlorine hexoxide, CliO, oily red liquid (ozone plus CIO2). Both unstable. 

Trilead tetroxide, Pb304, red lead and other intermediate phases, e.g. Pb70i, and Pb203 are formed by heating PbO or Pb02- Uses... 

Other liquid inorganic compounds show the auto-dissociation characteristic of water and liquid ammonia for example, dinitrogen tetroxide (p. 231), as well as undergoing the more familiar homolytic dissociation... 

Unlike nitrogen monoxide, nitrogen dioxide has properties more typical of an odd electron molecule. It is a coloured (brown), reactive gas which dimerises to the diamagnetic colourless gas dinitrogen tetroxide, N2O4. in which the odd electron is paired. The structure of dinitrogen tetroxide can be represented as a resonance hybrid of ... 

Dinitrogen tetroxide, N2O4, as a liquid, has some power as a solvent, and appears to dissociate slightly to give nitrosyl nitrate, thus ... 

Hence dinitrogen tetroxide (sometimes mixed with an organic solvent) can be used to prepare anhydrous metal nitrates (many heavy metal nitrates are hydrated when prepared in aqueous solution, and they cannot be dehydrated without decomposition). 

The second equilibrium is the more important, giving rise to the nitronium ion, NOj, already mentioned as a product of the dis sociation of dinitrogen tetroxide. Several nitronium salts have been identified, for example nitronium chlorate(VII), (N02) (C104) . If pure nitric acid is dissolved in concentrated sulphuric acid, the freezing point of the latter is depressed to an extent suggesting the formation of four ions, thus ... 

Outline the laboratory preparation of a sample of dinitrogen tetroxide. Describe and explain what happens when it is heated from 290 K to 900 K. Suggest electronic structures for dinitrogen tetroxide and the other nitrogen-containing molecules formed from it on heating to 900 K. Point out any unusual structural features. 

The mixed oxide Fc304 (tri-iron tetroxide) is a black solid, which occurs naturally as magnetite it is formed when iron(III) oxide is strongly heated, and its structure is effectively made up of oxide (O ) and iron(II) and iron(III) ions. 

If copper is treated with a solution of dinitrogen tetroxide in ethyl ethanoate (acetate), a blue solution is obtained, which on evapora-... 

Another method for the hydroxylation of the etliylenic linkage consists in treatment of the alkene with osmium tetroxide in an inert solvent (ether or dioxan) at room temperature for several days an osmic ester is formed which either precipitates from the reaction mixture or may be isolated by evaporation of the solvent. Hydrolysis of the osmic ester in a reducing medium (in the presence of alkaline formaldehyde or of aqueous-alcoholic sodium sulphite) gives the 1 2-glycol and osmium. The glycol has the cis structure it is probably derived from the cyclic osmic ester ... 

The reagent Is expensive and poisonous, consequently the hydroxylation procedure is employed only for the conversion of rare or expensive alkenes (e.g., in the steroid field) into the glycols. Another method for hydroxylation utilises catalytic amounts of osmium tetroxide rather than the stoichiometric quantity the reagent is hydrogen peroxide in tert.-butyl alcohol This reagent converts, for example, cyc/ohexene into cis 1 2- t/ohexanedlol. 

Free cydohexene from peroxides by treating it with a saturated solution of sodium bisulphite, separate, dry and distil collect the fraction, b.p. 81-83°. Mix 8 -2 g. of cycZohexene with 55 ml. of the reagent, add a solution of 15 mg. of osmium tetroxide in anhydrous butyl alcohol and cool the mixture to 0°. Allow to stand overnight, by which time the initial orange colouration will have disappeared. Remove the solvent and unused cydohexene by distillation at atmospheric pressure and fractionate the residue under reduced pressure. Collect the fraction of b.p. 120-140°/15 mm. this solidifies almost immediately. Recrystallise from ethyl acetate The yield of pure cis-l 2 cydohexanediol, m.p. 96°, is 5 0 g. 

Concentrations in air as low as IO7 g/ms can cause lung congestion, skin damage, or eye damage. Exposure to osmium tetroxide should not exceed 0.0016 mg/ms (8-hour time weighted average - 40-hour work week). 

The tetroxide has been used to detect fingerprints and to stain fatty tissue for miscroscope slides. The metal is almost entirely used to produce very hard alloys, with other metals of the platinum group, for fountain pen tips, instrument pivots, phonograph needles, and electrical contacts. 

Solutions of dinitrogen tetroxide (the mixed anhydride of nitric and nitrous acids) in sulphuric acid are nitrating agents ( 4.3.2), and there is no doubt that the effective reagent is the nitronium ion. Its formation has been demonstrated by Raman spectroscopy and by cryoscopy ... 

Nitration has also been effected with the complexes from dinitrogen tetroxide and Lewis acidsin the case of boron trifluoride the complex appears to be a mixture of nitronium and nitrosonium tetrafluoroborates. ... 

In an excess of nitric acid, nitrous acid exists essentially as dinitrogen tetroxide which, in anhydrous nitric acid, is almost completely ionised. This is shown by measurements of electrical conductivity, and Raman and infra-red spectroscopy identify the ionic species... 

In mixtures of nitric acid and organic solvents, nitrous acid exists mainly as un-ionised dinitrogen tetroxide. The heterolysis of dinitrogen tetroxide is thus complete in sulphuric acid ( 4 i), considerable in nitric acid, and very small in organic solvents. 

If we consider the effect of nitrous acid upon zeroth-order nitration in organic solvents we must bear in mind that in these circumstances dinitrogen tetroxide is not much ionised, so the measured concentration of nitrous acid gives to a close approximation the concentration of dinitrogen tetroxide. Further, the negligible self-ionisation of nitric acid ensures that the total concentration of nitrate ions is effectively that formed from dinitrogen tetroxide. Consequently as we can see from the equation for the ionisation of dinitrogen tetroxide ( 4.3.1),... 

The catalysed nitration of phenol gives chiefly 0- and />-nitrophenol, (< 0-1% of w-nitrophenol is formed), with small quantities of dinitrated compound and condensed products. The ortho para ratio is very dependent on the conditions of reaction and the concentration of nitrous acid. Thus, in aqueous solution containing sulphuric acid (i 75 mol 1 ) and nitric acid (0-5 mol 1 ), the proportion of oriha-substitution decreases from 73 % to 9 % as the concentration of nitrous acid is varied from o-i mol l i. However, when acetic acid is the solvent the proportion of ortAo-substitution changes from 44 % to 74 % on the introduction of dinitrogen tetroxide (4-5 mol 1 ). 

It was estimated from an analysis of the results that the nitrosonium ion was at least ten times more effective than dinitrogen tetroxide this is a lower limit, and the ion is likely to be much more reactive than the latter species. 

It has been considered that nitric acid was responsible for the oxidation of the nitroso compoimd, but there is recent evidence from the catalysed nitration of p-dimethoxybenzene in carbon tetrachloride that dinitrogen tetroxide is involved ... 

In solutions of acetyl nitrate in acetic anhydride, prepared from purified nitric acid, the 0 -ratio increases slightly with increasing concentrations of acetyl nitrate (table 5.7, expts. 11,13,16). The use of fuming nitric acid in the preparation of the acetyl nitrate considerably accelerates the rates of reaction and also increases the proportion of o-substitution (table 5.7, expts. 12, 15, 18). These effects resemble, but are much stronger than the corresponding effects in nitrations with solutions of nitric acid in acetic acid contaimng dinitrogen tetroxide. 

Ridd - has reinterpreted the results concerning the anticatalysis of the first-order nitration of nitrobenzene in pure and in partly aqueous nitric acid brought about by the addition of dinitrogen tetroxide. In these media this solute is almost fully ionised to nitrosonium ion and nitrate ion. The latter is responsible for the anticatalysis, because it reduces the concentration of nitronium ion formed in the following equilibrium ... 

Considering first pure nitric acid as the solvent, if the concentrations of nitronium ion in the absence and presence of a stoichiometric concentration x of dinitrogen tetroxide are yo and y respectively, these will also represent the concentrations of water in the two solutions, and the concentrations of nitrate ion will be y and x- y respectively. The equilibrium law, assuming that the variation of activity coefficients is negligible, then requires that ... 

Since the first-order rate constant for nitration is proportional to y, the equilibrium concentration of nitronium ion, the above equations show the way in which the rate constant will vary with x, the stoichiometric concentration of dinitrogen tetroxide, in the two media. An adequate fit between theory and experiment was thus obtained. A significant feature of this analysis is that the weak anticatalysis in pure nitric acid, and the substantially stronger anticatalysis in partly aqueous nitric acid, do not require separate interpretations, as have been given for the similar observations concerning nitration in organic solvents. 

A catalytic enantio- and diastereoselective dihydroxylation procedure without the assistance of a directing functional group (like the allylic alcohol group in the Sharpless epox-idation) has also been developed by K.B. Sharpless (E.N. Jacobsen, 1988 H.-L. Kwong, 1990 B.M. Kim, 1990 H. Waldmann, 1992). It uses osmium tetroxide as a catalytic oxidant (as little as 20 ppm to date) and two readily available cinchona alkaloid diastereomeis, namely the 4-chlorobenzoate esters or bulky aryl ethers of dihydroquinine and dihydroquinidine (cf. p. 290% as stereosteering reagents (structures of the Os complexes see R.M. Pearlstein, 1990). The transformation lacks the high asymmetric inductions of the Sharpless epoxidation, but it is broadly applicable and insensitive to air and water. Further improvements are to be expected. 

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