Ammonium sulphates

According to Erdey et al. [915], ammonium sulphate releases ammonia in an endothermic reaction commencing above 523 K, viz. 

This temperature is higher than those given in other reports, 383 K [944] and 413—513 K [945] indicating the possible influence of retained water on the onset of reaction. Although ammonium sulphate does not melt, the product NH4HS04 does and decomposes to NH3 and H2S04 at higher temperatures (623—723 K). 

A review of earlier results is included in a paper by Kiyoura and Urano [946] on the decompositions of (NH4)2S04 (413—513 K) and NH4HS04 (433-473 K). The intermediate formation at 433 K of the double salt (NH4)3H(S04)2 was detected by X-ray diffraction and this salt decomposed to NH4HS04 at 453 K. Decomposition of the ammonium hydrogen sulphate at 473 K proceeded through the formation of molten sulphamic acid 

NH SC - NH2S03H + H20 which then reacted to form the pyrosulphate 

Most mixed and complex ammonium metal sulphates (and selenates) [948,949] lose NH3, H20 and S03 (or Se03) to form the simple metal sulphate (or selenate) some of the ammonia may be oxidized [949]. The basic aluminium ammonium sulphate [950], (NH4)20 3 A1203 4 S03 xH20 (x = 6—8), loses water at 473 K. Deammination and complete dehydration commences at 673 K, and S03 evolution starts at about 873 K to yield residual A1203 which contains traces of S03. a—Time data for most of the stages obeyed the contracting volume equation [eqn. (7), n = 3] [951]. 

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Mohr s salt, (NH4)2S04 FeS04,6H20. Iron ammonium sulphate. 

The extent of dissociation at a given temperature can be determined by measuring the density of the vapour. Since anhydrous sulphuric acid is less volatile than hydrogen chloride, ammonium sulphate does not readily sublime on heating some ammonia is evolved to leave the hydrogensulphate ... 

Uses of ammonia and ammonium compounds. Most of the ammonia produced is used in the manufaeture of nitrogenous fertilisers such as ammonium sulphate. Other uses include nitric acid and synthetic fibre and plastic manufacture. 

Ammonia may be estimated by dissolving the gas in a known volume of standard acid and then back-titrating the excess acid. In a method widely used for the determination of basic nitrogen in organic substances (the Kjeldahl method), the nitrogenous material is converted into ammonium sulphate by heating with concentrated sulphuric acid. The ammonia is then driven off by the action of alkali and absorbed in standard acid. 

Ammonium cyanate, because of its instability in solution, is usually prepared (NHJaSO, + 2KCNO 2NH4CNO + KjSO by mixing aqueous solutions of ammonium sulphate and potassium cyanate. Complete evaporation then gives a mixture of potassium sulphate and urea, from which the urea may be extracted w ith hot absolute ethanol, in which potassium sulphate is insoluble. 

Enzymes are proteins of high molecular weight, several of which have been isolated in a pure State consequently their precise nature is in some instances still obscure. They form solutions in water and in dilute salt solutions, and are precipitated when such solutions are saturated with ammonium sulphate. 

It should be noted that the aqueous extract of the turnips shows weak peroxidase activity before precipitation with ammonium sulphate. 

In the isolation of organic compounds from aqueous solutions, use is frequently made of the fact that the solubility of many organic substances in water is considerably decreased by the presence of dissolved inorganic salts (sodium chloride, calcium chloride, ammonium sulphate, etc.). This is the so-called salting-out effect. A further advantage is that the solubility of partially miscible organic solvents, such as ether, is considerably less in the salt solution, thus reducing the loss of solvent in extractions. 

Wohler s classical synthesis of urea from ammonium cyanate may be carried out by evaporating solutions of sodium cyanate and ammonium sulphate ... 

In aqueous solution at 100° the change is reversible and equilibrium is reached when 95 per cent, of the ammonium cyanate has changed into urea. Urea is less soluble in water than is ammonium sulphate, hence if the solution is evaporated, urea commences to separate, the equilibrium is disturbed, more ammonium cyanate is converted into urea to maintain the equilibrium and evfflitually the change into urea becomes almost complete. The urea is isolated from the residue by extraction with boiling methyl or ethyl alcohol. The mechanism of the reaction which is generally accepted involves the dissociation of the ammonium cyanate into ammonia and cyanic acid, and the addition of ammonia to the latter ... 

Pimelic acid. Heat a mixture of 18 g. of pentamethylene dicyanide and 250 g. of 50 per cent, sulphuric acid by weight in a 750 ml. round-bottomed flask under reflux for 9 hours. INIost of the pimehc acid separates from the cold reaction mixture. Filter oflF the crystaUine acid upon a sintered glass funnel. Saturate the filtrate with ammonium sulphate and extract it with three 50 ml. portions of ether. Dissolve the residue on the filter (which is shghtly discoloured, but is fairly pure pimehc acid) in the combined ethereal extracts, dry with anhydrous sodium or magnesium sulphate, and remove the ether by distiUation. Recrystallise the residual sohd acid from benzene containing 5 per cent, of ether. The yield of pure pimehc acid, m.p, 105-106°, is 22 g. 

Di lve 20 g. of the cyano ester in 100 ml. of rectified spirit and add a solution of 19 2 g. of pure potassium cyanide in 40 ml. of water. Allow to stand for 48 hours, then distil oflF the alcohol on a water bath. Add a large excess of concentrated hydrochloric acid and heat under reflux for 3 hours. Dilute with water, saturate the solution with ammonium sulphate, and extract with four 75 ml. portions of ether. Dry the combined ethereal extracts with anhydrous sodium or magnesium sulphate, and distil off the ether. RecrystaUise the residual acid from excess concentrated hydrochloric acid, and dry in the air. The yield of pure ew-dimethyl-succinic acid, m.p. 141-142°, is 12 g. 

Dissolve 100 g. of iron alum (ferric ammonium sulphate) in 300 ml. of water at 65°, Pour the solution, with stirring, into a solution of 25 g. of hydroquinone in 100 ml, of water contained in a 600 ml. beaker. The quinhydrone is precipitated in fine needles. Cool the mixture in ice, filter with suction, and wash three or four times with cold water. Dry in the air between filter paper. The yield of quinhydrone, m.p, 172°, is 15 g. It contains a trace of iron, but this has no influence upon the e.m.f, of the quinhydrone electrode provided that the washing of the crude material has been thorough. The quinhydrone should be stored in a tightly-Btoppered bottle. 

The conversion of cyclohexanone to cyclohexanone oxime is brought about by the use of hydroxylamine sulphate. The sulphuric acid is neutralised with ammonia to ammonium sulphate and this is separated from the oxime. In the presence of oleum the oxime undergoes the process known as the Beckmann rearrangement to yield the crude caprolactam. After further neutralisation with ammonia the caprolactam and further ammonium sulphate are separated by solvent extraction (Figure 18.7). 

In one process the resulting solution is continuously withdrawn and cooled rapidly to below 75°C to prevent hydrolysis and then further cooled before being neutralised with ammonia. After phase separation, the oil phase is then treated with trichlorethylene to extract the caprolactam, which is then steam distilled. Pure caprolactam has a boiling point of 120°C at 10 mmHg pressure. In the above process 5.1 tons of ammonium sulphate are produced as a by-product per ton of caprolactam. 

Of the other routes the photonitrosation process involving nitrosyl chloride is in use in Japan. This avoids, at the expense of complicated purification processes, the high yields of ammonium sulphate unavoidably produced in the route involving the Beckmann rearrangement. 

Nienow and Conti (1978) developed a model of partiele abrasion at high solids eoneentration based on Rittinger s law of eomminution. When tested experimentally using eopper sulphate and niekel ammonium sulphate erystals in two non-solvent liquids, measured abrasion rates were eonsistent with a seeond-order dependenee of eoneentration as predieted (Figure 5.12). 

Ammonium sulphate is traditionally produced by reaction of by-product ammonia from coke ovens with sulphuric acid ... 

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