Nitrates solvents

Bonnesen, P. V., Sloop, F. V., Jr., and Engle, N. L. Stability of the Caustic-Side Solvent Extraction (CSSX) Process Solvent, Effect of High Nitrite on Solvent Nitration, ORNL Report ORNL/TM-2002/115, Oak Ridge National Laboratory, Oak Ridge, TN, July 2002. 

Hybrid poplars Chlorinated solvents/nitrates Groundwater... 

The existence of the nitronium ion in sulfiiric-nitric acid mixtures can be demonstrated by both cryoscopic measurements and spectroscopy. An increase in the strong acid concentration increases the rate of reaction by shifting the equilibrium of Step 1 to the right. Addition of a nitrate salt has the opposite effect by suppressing the preequilibrium dissociation of nitric acid. It is possible to prepare crystalline salts of nitronium ions such as nitronium tetrafluoroborate. Solutions of these salts in organic solvents nitrate aromatic compounds rapidly. ... 

CH3CH(0H)C(0)0Et. A colourless liquid with a pleasant odour, b.p. 154 C. Manufactured by distilling a mixture of ( )-lactic acid, ethanol and benzene in the presence of a little sulphuric or benzenesulphonic acid. It is a solvent for cellulose nitrate and acetate and also for various resins. Used as a lacquer solvent. 

Glycerol ct-dichlorohydrin, sym-dichloroiso-propyl alcohol, 1,3-dichloro-2-hydroxypropane, CH2CI-CHOH-CH2C1. Colourless liquid with an ethereal odour b.p. 174-175" C. Prepared by passing dry HCl into glycerin containing 2% elhanoic acid at 100-1 lO C. Converted to x-epichlorohydrin by K.OH, Used as a solvent for cellulose nitrate and resins. 

C5H10O2, CHjCOOPr. Colourless liquid with a fragrant odour b.p. 88 C. Manufactured by leading propene into hot ethanoic acid containing sulphuric acid, or by heating isopropyl alcohol with ethanoic and sulphuric acids. Used as a solvent for cellulose nitrate and various gums. 

Me2C = CHCOCH= CMca- Yellow liquid having a camphor-like odour m.p. 28 C, b.p. 198-5°C. It is formed when propanone is saturated with HCl and allowed to stand. Resembles camphor in many of its properties and is a solvent for cellulose nitrate. Used to prepare diisobutyl ketone (reduction). 

Obtained by the catalytic hydrogenation of naphthalene. Owing to the presence of one aromatic ring it can be nitrated and sulphon-ated. It is non-toxic and is used as a solvent for fats, oils and resins. 

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 rate of the uncatalysed reaction in all four solvents is rather slow. (The half-life at [2.5] = 1.00 mM is at least 28 hours). However, upon complexation of Cu ion to 2.4a-g the rate of the Diels-Alder reaction between these compounds and 2.5 increases dramatically. Figure 2.2 shows the apparent rate of the Diels-Alder reaction of 2.4a with 2.5 in water as a lunction of the concentration of copper(II)nitrate. At higher catalyst concentrations the rate of the reaction clearly levels off, most likely due to complete binding of the dienophile to the catalyst. Note that in the kinetic experiments... 

Nitronium salts in solution in inert organie solvents have been used in reeent years to nitrate a wide range of aromatic compounds. Yields are generally good, but in preparative work the method is advantageous only in speeial cases, notably where the aromatie contains a hydrolysable substituent ( 4.4). 

Nitric acid being the solvent, terms involving its concentration cannot enter the rate equation. This form of the rate equation is consistent with reaction via molecular nitric acid, or any species whose concentration throughout the reaction bears a constant ratio to the stoichiometric concentration of nitric acid. In the latter case the nitrating agent may account for any fraction of the total concentration of acid, provided that it is formed quickly relative to the speed of nitration. More detailed information about the mechanism was obtained from the effects of certain added species on the rate of reaction. 

Sulphuric acid catalysed nitration in concentrated nitric acid, but the effect was much weaker than that observed in nitration in organic solvents ( 3.2.3). The concentration of sulphuric acid required to double the rate of nitration of i-nitroanthraquinone was about 0-23 mol 1, whereas typically, a concentration of io mol 1 will effect the same change in nitration in mixtures of nitric acid and organic solvents. The acceleration in the rate was not linear in the concentration of catalyst, for the sensitivity to catalysis was small with low concentrations of sulphuric acid, but increased with the progressive addition of more catalyst and eventually approached a linear acceleration. 

Potassium nitrate anticatalysed nitration in nitric acid (the solutions used also contained 2-5 mol 1 of water) but the effect was small in comparison with the corresponding effect in nitration in organic solvents ( 3.2.3 4), for the rate was only halved by the addition of 0-31 mol 1 of the salt. As in the case of the addition of sulphuric acid, the effect was not linear in the concentration of the additive, and the variation of k j with [KNOgj/mol 1 " was similar to that of with [H2SO4]/ mol 1. ... 

Nitration at a rate independent of the concentration of the compound being nitrated had previously been observed in reactions in organic solvents ( 3.2.1). Such kinetics would be observed if the bulk reactivity of the aromatic towards the nitrating species exceeded that of water, and the measured rate would then be the rate of production of the nitrating species. The identification of the slow reaction with the formation of the nitronium ion followed from the fact that the initial rate under zeroth-order conditions was the same, to within experimental error, as the rate of 0-exchange in a similar solution. It was inferred that the exchange of oxygen occurred via heterolysis to the nitronium ion, and that it was the rate of this heterolysis which limited the rates of nitration of reactive aromatic compounds. 

THE STATE OF NITRIC ACID IN INERT ORGANIC SOLVENTS The absence of ions in mixtures of acetic acid and nitric acid is shown by their poor electrical conductivity and the Raman spectra of solutions in acetic acid, nitromethane, and chloroform show only the absorptions of the solvent and molecular nitric acid the bands corresponding to the nitronium and nitrate ions cannot be detected. -... 

TABLE 3.1 Zeroth-order rate constants for nitrations in organic solvents... 

Data for zeroth-order nitration in these various solvents are given in table 3.1. Fig. 3.1 shows how zeroth-order rate constants depend on the concentration of nitric acid, and table 3.2 shows how the kinetic forms of nitration in organic solvents depend on the reactivities of the compounds being nitrated. 

TABLE 3.2 Comparison of organic solvents as media for nitration... 

Accepting, for the moment without further evidence, that the nitro-nium ion formed by heterolysis of nitric acid is the active reagent in the solutions imder discussion, it remains to consider briefly why nitration in such solutions depends on the concentrations of nitric acid to such high powers (fig. 3.1), and why different solvents behave so differently (table 3.2). 

The zeroth-order rates of nitration depend on a process, the heterolysis of nitric acid, which, whatever its details, must generate ions from neutral molecules. Such a process will be accelerated by an increase in the polarity of the medium such as would be produced by an increase in the concentration of nitric acid. In the case of nitration in carbon tetrachloride, where the concentration of nitric acid used was very much smaller than in the other solvents (table 3.1), the zeroth-order rate of nitration depended on the concentrationof nitric acid approximately to the fifth power. It is argued therefore that five molecules of nitric acid are associated with a pre-equilibrium step or are present in the transition state. Since nitric acid is evidently not much associated in carbon tetrachloride a scheme for nitronium ion formation might be as follows ... 

The more strongly acidic a solution of nitric acid at a given concentration is in a particular organic solvent, the more readily should that solvent support zeroth-order nitration. The values of for solutions of sulphuric acid in nitromethane, sulpholan, and acetic acid show clearly the superiority of nitromethane in this respect. ... 

The relative abilities of nitromethane, sulpholan, and acetic acid to support the ionisation of nitric acid to nitronium ions are closely similar to their efficiencies as solvents in nitration. Raman spectroscopy showed that for a given concentration of mixed acid (i i nitric and sulphuric acids) the concentration of nitronium ions in these three solvents varied in the order nitromethane > sulpholan > acetic acid. The concentration of mixed acid needed to permit the spectroscopic detection of nitronimn ions was 25 %, 50 % and 60 % in the three solvents, respectively (see 4.4.3). 

The influence of added species upon the rates and kinetic forms of nitration in organic solvents were of the greatest importance in elucidating details of the processes involved, particularly of the steps leading to the nitronium ion. These influences will first be described, and then in the following section explained. The species to be considered are sulphuric acid, nitrate ions, urea and water. The effect of nitrous acid is considered later ( 4.3). 

Nitration in organic solvents is strongly catalysed by small concentrations of strong acids typically a concentration of io mol 1 of sulphuric acid doubles the rate of reaction. Reaction under zeroth-order conditions is accelerated without disturbing the kinetic form, even under the influence of very strong catalysis. The effect of sulphuric acid on the nitration of benzene in nitromethane is tabulated in table 3.3. The catalysis is linear in the concentration of sulphuric acid. 

The outcome of the studies discussed, of nitrations in inert organic solvents, is then the mechanistic scheme formulated below ... 

NITRATION AT THE ENCOUNTER RATE IN INERT ORGANIC SOLVENTS... 

A similar circumstance is detectable for nitrations in organic solvents, and has been established for sulpholan, nitromethane, 7-5 % aqueous sulpholan, and 15 % aqueous nitromethane. Nitrations in the two organic solvents are, in some instances, zeroth order in the concentration of the aromatic compound (table 3.2). In these circumstances comparisons with benzene can only be made by the competitive method. In the aqueous organic solvents the reactions are first order in the concentration of the aromatic ( 3.2.3) and comparisons could be made either competitively or by directly measuring the second-order rate constants. Data are given in table 3.6, and compared there with data for nitration in perchloric and sulphuric acids (see table 2.6). Nitration at the encounter rate has been demonstrated in carbon tetrachloride, but less fully explored. ... 

NITRATION WITH DINITROGEN PENTOXIDE 4.3.1 The State of dinitrogen pentoxide in various solvents... 

Kinetic studies of nitration using dilute solutions of dinitrogen pentoxide in organic solvents, chiefly carbon tetrachloride, have provided evidence for the operation, under certain circumstances of the molecular species as the electrophile. The reactions of benzene and toluene were inconveniently fast, and therefore a series of halogenobenzenes and aromatic esters was examined. 

This reaction showed certain characteristics which distinguish it from nitrations in solutions of nitric acid in organic solvents. Thus, in changing the solvent from carbon tetrachloride to nitromethane, the rate increased by a factor of only 6, whereas nitration involving the nitronium ion was accelerated by a factor of about 30 when the solvent was changed from acetic acid to nitromethane. It was held that the... 

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