Mixed acid

C) Mixed acids. A solution containing 10 mg. of each acid in 20 ml. of methanol. 

Nitrations are usually carried out at comparatively low temperatures at higher temperatures there may be loss of material because of the oxidising action of the nitric acid. For substances which do not nitrate readily with a mixture of concentrated nitric and sulphuric acids ( mixed acid ), the intensity of the reaction may be increased inler alia by the use of fuming sulphuric acid (containing up to 60 per cent, of sulphur trioxide) or by fuming nitric acid. Thus nitrobenzene is converted by a mixture of fuming nitric acid and concentrated sulphuric acid into about 90 per cent, of wi-dinitrobenzene and small amounts of the o- and p-isomers the latter are eliminated in the process of recrystallisation ... 

Nitration of bromobenzene with mixed acid yields largely p-bromo nitrobenzene accompanied by a little of the o-isomeride ... 

Add 25 g. of finely-powdered, dry acetanilide to 25 ml. of glacial acetic acid contained in a 500 ml. beaker introduce into the well-stirred mixture 92 g. (50 ml.) of concentrated sulphuric acid. The mixture becomes warm and a clear solution results. Surround the beaker with a freezing mixture of ice and salt, and stir the solution mechanically. Support a separatory funnel, containing a cold mixture of 15 -5 g. (11 ml.) of concentrated nitric acid and 12 -5 g. (7 ml.) of concentrated sulphuric acid, over the beaker. When the temperature of the solution falls to 0-2°, run in the acid mixture gradually while the temperature is maintained below 10°. After all the mixed acid has been added, remove the beaker from the freezing mixture, and allow it to stand at room temperature for 1 hour. Pour the reaction mixture on to 250 g. of crushed ice (or into 500 ml. of cold water), whereby the crude nitroacetanilide is at once precipitated. Allow to stand for 15 minutes, filter with suction on a Buchner funnel, wash it thoroughly with cold water until free from acids (test the wash water), and drain well. Recrystallise the pale yellow product from alcohol or methylated spirit (see Section IV,12 for experimental details), filter at the pump, wash with a httle cold alcohol, and dry in the air upon filter paper. [The yellow o-nitroacetanihde remains in the filtrate.] The yield of p-nitroacetanihde, a colourless crystalline sohd of m.p. 214°, is 20 g. 

During my Cleveland years, I also continued and extended my studies in nitration, which I started in the early 1950s in Hungary. Conventional nitration of aromatic compounds uses mixed acid (mixture of nitric acid and sulfuric acid). The water formed in the reaetion dilutes the acid, and spent aeid disposal is beeoming a serious environ-... 

To solve some of the environmental problems of mixed-acid nitration, we were able to replaee sulfuric acid with solid superacid catalysts. This allowed us to develop a novel, clean, azeotropic nitration of aromatics with nitric acid over solid perfluorinated sulfonic acid catalysts (Nafion-H). The water formed is continuously azeotroped off by an excess of aromatics, thus preventing dilution of acid. Because the disposal of spent acids of nitration represents a serious environmental problem, the use of solid aeid eatalysts is a significant improvement. 

The first nitration to be reported was that of beri2ene itself. Mitscher-lich in 1834 prepared nitrobenzene by treating benzene with fuming nitric acid. Not long afterwards the important method of effecting nitration with a mixture of nitric and sulphuric acids ( mixed acid ) was introduced, evidently in a patent by Mansfield the poor quality of early nitric acid was probably the reason why the method was developed. Since these beginnings, nitration has been the subject of continuous study. 

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). 

Using sulpholan and acetic acid as solvents competitive nitrations were performed with solutions containing 75% and 30% of mixed acid (table 4.1, columns h, i and /, g, respectively). In the former the concentration of nitronium ions was substantial [c. 5-7 % by weight), whereas in the latter the concentration was below the level of spectroscopic detection. 

Fig. 4.1. Variation of NO2+ ion concentration with the concentration of mixed acid (nitric sulphuric, i mole i mole) inorganic solvents (a) in sulpholan (6)in aceticacid (c) in nitromethane. Curves (a) and (6) were determined by Raman measurements using the 1400 cm band while curve (c) was derived from infra-red measurements on the 237s cm band. Unity on the NO2+ concentration scale was determined to be 5-6 molar ( 2S 8 weight %). (From Olah et...

This h)rpothesis has, however, been supported. The o p-ratio in chlorobenzene was found to be lower when acetic anhydride was the solvent, than when nitric acid or mixed acids were used. The ratio was still further reduced by the introduction into the solution of an even less polar solvent such as carbon tetrachloride, and was increased by the addition of a polar solvent such as acetonitrile. The orientation of substitution in toluene in which the substituent does not posses a strong dipole was found to be independent of the conditions used. The author... 

In a later paper Knowles and Norman compared more fully nitrations of benzylic compounds in acetyl nitrate and in mixed acid (table 5.9), and interpreted the results in terms of three factors nitronium ion nitration in both media some degree of protonation of the oxygen... 

Evidence for the influence of protonation was convincingly adduced from the trend of the quantity m p (mixed acid)/ M p (acetyl nitrate) in the series Ph.CH2.OMe, Ph.(CH2)2 OMe, Ph.(CH2)3.0Me, hut it was argued that protonation in mixed acid cannot explain the change... 

Melander first sought for a kinetic isotope effect in aromatic nitration he nitrated tritiobenzene, and several other compounds, in mixed acid and found the tritium to be replaced at the same rate as protium (table 6.1). Whilst the result shows only that the hydrogen is not appreciably loosened in the transition state of the rate-determining step, it is most easily understood in terms of the S 2 mechanism with... 

That some modification to the position so far described might be necessary was indicated by some experiments of Nesmeyanov and his co-workers. Amongst other compounds they nitrated phenyl trimethyl ammonium and triphenyloxonium tetrafluoroborates with mixed acid the former gave 96 % of m- and 4 % of -nitro compound (88 % total yield), whilst the latter gave 80% of the tri-(p-nitrophenyl)oxonium salt. Ridd and his co-workers have made a quantitative study of the phenyl trimethyl ammonium ion. Their results, and those of other recent workers on the nitration of several cations, are collected in table 9.3. 

Biphenylene is nitrated with nitric acid in acetic acid at C(2), and further nitration with mixed acid gives 2,6-dinitrobiphenylene. The relative rate was not determined. 

The preparative nitration of quinoline in mixed acid has been described several times, and has usually been carried out under unnecessarily severe conditions good yields of 5- and 8-nitroquinoline in roughly... 

Phenylbenzimidazole is nitrated first at the 5-position with mixed acid, and subsequent reaction produces 5-nitro-2-(4-nitrophenyl)-and 5-nitro-2-(3-nitrophenyl)-benzimidazole. 2-Phenyl-, 2-(4-nitro-phenyl)- and 5-nitro-2-phenyl-benzimidazole are nitrated as their conjugate acids. ... 

Nitration of aromatic rings is possible by use of Pd(N03)2[356], Pd(OAc)2-NaN02[357], Pd(0Ac)2-N02[358], and Pd(0)-NO2[359], The nitration can be carried out fully catalytically by Pd(0Ac)2-N02 and oxygen. This reaction offers a promising new method of nitration without using mixed acids of HNO3 and H2SO4. 

Glucose Hot mixed acid (sulfuric plus nitric acids). 

Other Glycol Nitrates. Other Hquid nitrates have been used as explosive plasticizers for nitroceUulose (Table 8). These may be made by mixed-acid nitration using procedures similar to those used for nitroglycerin. 

Nitroglycol maybe made by nitration of ethylene glycol [107-21-1] with mixed acid with a yield of ca 93%. The demand for both NG and nitroglycol has been gready decreased (115,116). 

Cotton linters or wood pulp are nitrated using mixed acid followed by treatment with hot acidified water, pulping, neutralization, and washing. The finished product is blended for uniformity to a required nitrogen content. The controlling factors in the nitration process are the rates of diffusion of the acid into the fibers and of water out of the fibers, the composition of mixed acid, and the temperature (see Cellulose esters, inorganic esters). 

THP—Amide Process. THP has also been made directly from phosphine [7803-5-27] and formaldehyde. The THP so generated contains one less mole of formaldehyde than either THPC or THPOH. It can be used in a THP—amide flame-retardant finish. The pad formulation contains THP, TMM, methylol urea, and a mixed acid catalyst (93—95). 

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