Behaviour with Concentrated Sulphuric Acid

An iodate does not react with concentrated sulphuric acid in the cold or upon gentle heating. A solution of an iodate gives with silver nitrate solution a white precipitate of silver iodate, insoluble in m nitric acid but soluble in dilute ammonia solution, thus simulating the behaviour of a chloride towards these reagents. Iodates, however, give a white precipitate of barium iodate, Ba(I03)2, with barium chloride solution the precipitate is sparingly soluble in dilute nitric acid. 

BEHAVIOUR WHEN TREATED WITH CONCENTRATED SULPHURIC ACID BY MOISTENING OR BY IMMERSION... 

These elements are generally unaffected by non-oxidising acids (behaviour expected for non-metallic elements) but they do react when heated with concentrated sulphuric and nitric acids, both powerful oxidising agents. Sulphur is oxidised to sulphur dioxide by hot concentrated sulphuric acid,... 

Group II. The classes 1 to 5 are usually soluble in dilute alkali and acid. Useful information may, however, be obtained by examining the behaviour of Sails to alkaline or acidic solvents. With a salt of a water-soluble base, the characteristic odour of an amine is usually apparent when it is treated with dilute alkali likewise, the salt of a water soluble, weak acid is decomposed by dilute hydrochloric acid or by concentrated sulphuric acid. The water-soluble salt of a water-insoluble acid or base will give a precipitate of either the free acid or the free base when treated with dilute acid or dilute alkali. The salts of sulphonic acids and of quaternary bases (R4NOH) are unaflFected by dilute sodium hydroxide or hydrochloric acid. 

Hydrolysis of a nitrile to an amide. Warm a solution of 1 g. of the nitrile benzyl cyanide) in 4 ml. of concentrated sulphuric acid to 80-90°, and allow the solution to stand for 5 minutes. Cool and pour the solution cautiously into 40 ml. of cold water. Filter oflT the precipitate stir it with 20 ml. of cold 5 per cent, sodium hydroxide solution and filter again. RecrystaUise the amide from dilute alcohol, and determine its m.p. Examine the solubility behaviour and also the action of warm sodium hydroxide solution upon the amide. 

The state of aqueous solutions of nitric acid In strongly acidic solutions water is a weaker base than its behaviour in dilute solutions would predict, for it is almost unprotonated in concentrated nitric acid, and only partially protonated in concentrated sulphuric acid. The addition of water to nitric acid affects the equilibrium leading to the formation of the nitronium and nitrate ions ( 2.2.1). The intensity of the peak in the Raman spectrum associated with the nitronium ion decreases with the progressive addition of water, and the peak is absent from the spectrum of solutions containing more than about 5% of water a similar effect has been observed in the infra-red spectrum. ... 

For deactivated compounds this limitation does not exist, and nitration in sulphuric acid is an excellent method for comparing the reactivities of such compounds. For these, however, there remains the practical difficulty of following slow reactions and the possibility that with such reactions secondary processes might become important. With deactivated compounds, comparisons of reactivities can be made using nitration in concentrated sulphuric acid such comparisons are not accurate because of the behaviour of rate profiles at high acidities ( 2.3.2 figs. 2.1, 2.3). 

Ultraviolet spectra of benzoic acid in sulphuric acid solutions, published by Hosoya and Nagakura (1961), show a considerable medium effect on the spectrum of the unprotonated acid, but a much smaller one in concentrated acid. The former is probably connected with a hydrogen-bonding interaction of benzoic acid with sulphuric acid which is believed to be responsible for a peculiarity in the activity coefficient behaviour of unprotonated benzoic acid in these solutions (see Liler, 1971, pp. 62 and 129). The absence of a pronounced medium effect on the spectra in >85% acid is consistent with dominant carbonyl oxygen protonation. In accordance with this, Raman spectra show the disappearance in concentrated sulphuric acid of the carbonyl stretching vibration at 1650 cm (Hosoya and Nagakura, 1961). Molecular orbital calculations on the structure of the carbonyl protonated benzoic acid have also been carried out (Hosoya and Nagakura, 1964). 

Nitric acid reacts energetically at ordinary temperatures, with formation of the nitrate and of the oxides of nitrogen. The behaviour of the metal with hydrochloric acid is similar to that of lead. The action of concentrated sulphuric acid and of nitric acid finds application in the separation of alloys of gold and silver. The corrosive effect of acids is accelerated by the presence of an oxidizer.5... 

Investigations of the solubilities of aromatic compounds in concentrated and aqueous sulphuric acids showed the activity coefficients of nitrocompounds to behave unusually when the nitro-compound was dissolved in acid much more dilute than required to effect protonation. This behaviour is thought to arise from changes in the hydrogenbonding of the nitro group with the solvent. 

Fig. 2.23 Type 1 behaviour increasing corrosion rate with increasing temperature and concentration, e.g. lead in sulphuric acid. Iso-corrosion lines at 01 g m h" ...

Table 5.26 The corrosion behaviour of tantalum-molybdenum alloys in concentrated sulphuric and hydrochloric acids at 55°C solutions saturated with oxygen...

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