Sulphurous Acid, Reaction

The latter is hydrolysed to formaldehyde and ammonium sulphate according to reaction (27). Simultaneously reaction (28) takes place, involving those molecules of cyclonite unaffected by sulphuric acid. Reaction (28) results in the formation of nitrous oxide and formaldehyde. 

The sulphuric acid reaction involves a quantity of acid which is stoichio-metrically equivalent to the reaction ... 

The amount to be applied to the layer in stability testing is governed in particular by the sensitivity of the method of detection and the related question, beyond what degree of decomposition the activity of the preparation becomes really impaired or the decomposition products show an undesireable side effect. An example may be seen in Fig. 168. The resolved steroid mixture can be detected with either dinitrophenyl-hydrazine (Rgt. No. 82) or sulphuric acid (Rgt. No. 241B), followed by inspection in UV light. In this particular case, the sulphuric acid reaction is too sensitive, since it detects impurities and degradation products which are without therapeutic interest [64]. 

Fig. 169. Influence of variation in quality of auxiliary material on the storage properties of oestrenol tablets, a—e tablet extracts with an auxiliary material from various sources R pure substance Layer silica gel H solvent heptane-acetone (80 + 40) CS detection sulphuric acid reagent (No. 241B), inspecting in UV-light quantitative evaluation through sulphuric acid reaction also possible after localisation with iodine vapour (cf p. 147)...

On acetylation it gives acetanilide. Nitrated with some decomposition to a mixture of 2-and 4-nitroanilines. It is basic and gives water-soluble salts with mineral acids. Heating aniline sulphate at 190 C gives sulphanilic add. When heated with alkyl chlorides or aliphatic alcohols mono- and di-alkyl derivatives are obtained, e.g. dimethylaniline. Treatment with trichloroethylene gives phenylglycine. With glycerol and sulphuric acid (Skraup s reaction) quinoline is obtained, while quinaldine can be prepared by the reaction between aniline, paraldehyde and hydrochloric acid. 

It is used in the preparation of benzanthrone by heating with glycerol and sulphuric acid (Skraup s reaction). 

The most widely used reactions are those of electrophilic substitution, and under controlled conditions a maximum of three substituting groups, e.g. -NO2 (in the 1,3,5 positions) can be introduced by a nitric acid/sul-phuric acid mixture. Hot cone, sulphuric acid gives sulphonalion whilst halogens and a Lewis acid catalyst allow, e.g., chlorination or brom-ination. Other methods are required for introducing fluorine and iodine atoms. Benzene undergoes the Friedel-Crafts reaction. ... 

CH OfiSj, H2C(S03H)2- a colourless, crystalline solid which readily absorbs water vapour decomposes on distillation. The potassium salt is prepared by heating methylene chloride with an aqueous solution of potassium sulphite under pressure at 150-I60" C. The free acid is obtained by decomposing the sparingly soluble barium salt with sulphuric acid. The aryl esters are very stable, but the alkyl esters decompose on heating to give ethers. Resembles malonic acid in some of its reactions. 

Nitro-compounds are prepared by the direct action of nitric acid. The reaction is greatly facilitated if a mixture of nitric and sulphuric acid is used. 

Occurs in the high-boiling fraction of coal tar. Most conveniently prepared by Skraup s reaction by healing a mixture of aniline, glycerol, sulphuric acid and nitrobenzene. Used in the manufacture of dyestuffs, and pharmaceutical products. 

The sulphonic acids are usually prepared by the action of sulphuric acid upon a compound. The concentration of the acid and the temperature of reaction are varied according to the reactivity of the compound. Often oleum is used or even chiorosulphonic acid. Alternatively sulphur trioxide complexed to pyridine or dioxan can be used with reactive substrates. Aminosulphonic acids such as sulphanilic and naphthionic acids are most conveniently prepared by heating the sulphate of the amine at ISO C. 

Tin slowly dissolves in dilute hydrochloric, nitric and sulphuric acids, and is in fact the only Group IV element to do so. The reactions with more concentrated acid are rapid. With hydrochloric acid. 

A similar oxidation reaction occurs with concentrated sulphuric acid but in this case hydrated tin(IV) ions remain in solution ... 

The gas is passed through caustic soda solution to remove any sulphur dioxide or carbon dioxide produced in side reactions. Carbon monoxide is also obtained when an ethanedioate (oxalate) is heated with concentrated sulphuric acid ... 

If this reaction is carried out at 273 K some unstable lead(IV) chloride is initially formed (p. 200). Other oxidising reactions of lead(lV) oxide include the evolution of oxygen when heated with concentrated sulphuric acid ... 

Hence sulphuric acid is used up and insoluble lead(II) sulphate deposited on both plates. This process maintains a potential difference between the two plates of about 2 V. If now a larger potential difference than this is applied externally to the cell (making the positive plate the anode) then the above overall reaction is reversed, so that lead dioxide is deposited on the anode, lead is deposited on the cathode, and sulphuric acid is re-formed. Hence in the electrolyte, we have ... 

Nitric acid is prepared in the laboratory by distilling equal weights of potassium nitrate and concentrated sulphuric acid using an air condenser, the stem of which dips into a flask cooled by tap water. The reaction is ... 

Industrially. phosphoric(V) acid is manufactured by two processes. In one process phosphorus is burned in air and the phos-phorus(V) oxide produced is dissolved in water. It is also manufactured by the action of dilute sulphuric acid on bone-ash or phosphorite, i.e. calcium tetraoxophosphate(V). Ca3(P04)2 the insoluble calcium sulphate is filtered off and the remaining solution concentrated. In this reaction, the calcium phosphate may be treated to convert it to the more soluble dihydrogenphosphatc. CafHjPOjj. When mixed with the calcium sulphate this is used as a fertiliser under the name "superphosphate . 

The replacement of the —OH group by a chlorine atom (reaction 9.4) is a very general reaction of phosphorus pentachloride. For example, if concentrated sulphuric acid is written as (H0)2S02 then its reaction with phosphorus pentachloride may be written ... 

Arsenic present only in traces (in any form) can be detected by reducing it to arsine and then applying tests for the latter. In Marsh s test, dilute sulphuric acid is added dropwise through a thistle funnel to some arsenic-free zinc in a flask hydrogen is evolved and led out of the flask by a horizontal delivery tube. The arsenic-containing compound is then added to the zinc-acid solution, and the delivery tube heated in the middle. If arsenic is present, it is reduced to arsine by the zinc-acid reaction, for example ... 

Oxygen can be produced by certain reactions in solution, for example the oxidation of hydrogen peroxide by potassium manganate(VII) acidified with sulphuric acid ... 

Ozone is formed in certain chemical reactions, including the action of fluorine on water (p. 323) and the thermal decomposition ofiodic(VII) (periodic) acid. It is also formed when dilute (about 1 M) sulphuric acid is electrolysed at high current density at low temperatures the oxygen evolved at the anode can contain as much as 30% ozone. 

The formation of an insoluble film of barium sulphate soon causes the reaction to cease, but addition of a tittle hydrochloric acid or better phosphoric(V) acid to the sulphuric acid allows the reaction to continue. 

Although sulphur dioxide, as a gas, is a reducing agent in the sense that it unites with oxygen, free or combined (for example in dioxides or peroxides) most of its reducing reactions in aqueous solution are better regarded as reactions of sulphurous acid (in acid solution), or the sulphite ion (in alkaline solution). 

The conversion of sulphur trioxide to sulphuric acid arises as a separate reaction only in the Contact process. 

Concentrated sulphuric acid is an oxidising agent, particularly when hot, but the oxidising power of sulphuric acid decreases rapidly with dilution. The hot concentrated acid will oxidise non-metals, for example carbon, sulphur and phosphorous to give, respectively, carbon dioxide, sulphur dioxide and phosphoric(V) acid. It also oxidises many metals to give their sulphates cast iron, however, is not affected. The mechanisms of these reactions are complex and the acid gives a number of reduction products. 

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