Sulphuric acid operation

Methyl nitrate is prepared by the effect of nitric acid on methanol in the presence of sulphuric acid. Operating conditions are critical, given the exothermicity of the reaction and the compound thermal instability (see previous table). Moreover, methyl nitrate is very sensitive to impact. It combusts spontaneously at 250-316°C when it is in the vapour state and even when the vapour is diluted by an inert gas. The flame temperature reaches 2600°C. 

Beckmann Rearrangement. Prepare the 85% sulphuric acid by adding 50 ml. of the concentrated acid cautiously to 10 ml. of water, stirring the mixture meanwhile, and then cool the diluted acid in ice-water. Place 16 ml. of the cold acid in a 500 ml. beaker, add 8 g, of the pure oxime, and warm the mixture cautiously until effervescence begins, and then at once remove the heat. A vigorous reaction occurs, and is soon complete. Repeat this operation with another 8 g. of the oxime in a second beaker the reaction is too vigorous to be carried out with larger quantities. 

Although these nitrations proceed smoothly, attempted nitration of an unidentified substance should always be carried out with extreme care, e.g., by working in a fume-cupboard and pointing the boiling-tube away from the operator. Many organic substances e.g., alcohols and phenols) react with great violence with a mixture of nitric and sulphuric acids. 

Concentrated solutions are here considered to be those containing > c. 89 % by weight of sulphuric acid. In these solutions nitric acid is completely ionised to the nitronium ion. This fact, and the notion that the nitronium ion is the most powerful electrophilic nitrating species, makes operation of this species in these media seem probable. Evidence on this point comes from the effect on the rate of added water ( 2.4.2)... 

Addition of water to solutions of nitric acid in 90% sulphuric acid reduces rates of nitration. Between 90% and 85% sulphuric acid the decrease in rate parallels the accompanying fall in the concentration of nitronium ions. This is good evidence for the operation of the nitronium ion as the nitrating agent, both in solutions more acidic than 90% and in weakly diluted solutions in which nitronium ion is still spectroscopically detectable. 

Nitration in sulphuric acid is a reaction for which the nature and concentrations of the electrophile, the nitronium ion, are well established. In these solutions compounds reacting one or two orders of magnitude faster than benzene do so at the rate of encounter of the aromatic molecules and the nitronium ion ( 2.5). If there were a connection between selectivity and reactivity in electrophilic aromatic substitutions, then electrophiles such as those operating in mercuration and Friedel-Crafts alkylation should be subject to control by encounter at a lower threshold of substrate reactivity than in nitration this does not appear to occur. 

Acid pickling This can be done under the following operating conditions, either with sulphuric acid (H2SO4), or hydrochloric acid (HCl). H2SO4 releases a lot of fumes and is ineffective under cold conditions. It forms iron sulphate, which forms a hard deposit at the bottom of the tank and is difficult to remove (see table on next page). 

To prepare sabinenic acid for the identification of the terpene, Wallach operates as follows 10 grams of the crude terpene are mixed with the theoretical amount of potassium permanganate in water at ice temperature. The oxide of manganese is filtered off, the liquid rendered acid and extracted with ether, and the ethereal solution shaken with caustic soda solution. The sodium salt is very sparingly soluble, and is precipitated, collected, and decomposed with dilute sulphuric acid and purified by a further solution in ether. It must be well dried in a desiccator before its melting-point is determined. Sabinene has the following constitution —... 

We add to the above-mentioned hydrocarbons, which during the operation should be kept thoroughly cool, a little more than the molecular quantity of fuming nitric acid or nitro-sulphuric acid. The acid should be gradually run in and the whole then allowed to stand undisturbed for from one to two hours, the resulting mass being then poured into water in order to get rid of the excess of acid. The well-washed substances thus obtained are then subjected to distillation by means of steam, whereupon simultaneously formed bodies, which smell like nitro-benzol and overpower the musk odour, readily distil over, whilst the pure substances remain behind. ... 

Kaesche considers that proton reduction may also play a role in polluted environments where the pH of the electrolyte is likely to be low. This would be particularly likely in the case of iron if the Schikorr mechanism, involving the presence of sulphuric acid, did in fact operate. However, Russian work" " has shown that oxygen depolarisation is many times more efficient in thin moisture films than in bulk solutions and therefore proton reduction may not be important in affecting corrosion rates. 

Reconcentration of sulphuric acid A very large amount of tantalum heater surface has been installed in plants for the reconcentration of diluted sulphuric acid arising from metal pickling, oil refinery operations and from petrochemical processes producing alcohols and ketones. Since reconcentration provides a means of overcoming a waste of disposal problem, the use of such plants is expanding ... 

Nitric acid must be absent, for this is reduced to hydroxylamine and other compounds which react with permanganate. If nitric acid is present, evaporate the solution just to dryness, wash the sides of the vessel with about 3 mL of water, carefully add 3-4 mL of concentrated sulphuric acid, and evaporate until fumes of the latter are evolved. Repeat this operation twice to ensure complete removal of the nitric acid, dilute to 100 mL with water, add 5 mL of concentrated sulphuric acid, and proceed with the reduction. 

The process can be adapted to handle all concentrations of bromide in the effluent, whether present as hydrobromic acid or salts. The controlling parameter is pH which must be maintained in the acidic region to enable the process to operate. This is most easily achieved using a mineral acid such as sulphuric acid to adjust the pH. 

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