Ammonium hydroxide, double decomposition

Double decomposition by NH4OH. A metallic hydroxide may precipitate, insoluble in excess of ammonium hydroxide or ammonium salts. Examples in analytical chemistry are the precipitation of the hydroxides of iron and aluminum... 

Trisodium dithiophosphate, Na3(PS202).llH20, has been prepared from P2S6 and a rather concentrated solution of sodium hydroxide. The solution was heated to 50° to 55° C. until the trithio-salt was decomposed. The salt was precipitated by alcohol, and when re-crystallised from water appeared as colourless six-sided prisms.5 The ammonium salt, (NH4)3(PS202).2H2O, was prepared similarly from aqueous ammonia and P2S5. From these soluble thiophosphates those of the heavy metals may be obtained by double decomposition.5... 

The preparation of ammonium nitrite has been effected by various methods. Examples are the double decomposition of lead9 or barium8 nitrite and ammonium sulphate the action of nitrogen peroxide on ammonium hydroxide, and purification of the nitrite by fractional crystallization 10 passing a mixture of air and ammonia over heated platinized asbestos 11 and heating a very concentrated solution of ammonium chloride and sodium nitrite in vacuum between 60° and 80° C., the ammonium nitrite subliming into the neck of the flask.12 It... 

Hofmann rule The principal alkene formed in the decomposition of quaternary ammonium hydroxides that contain different primary alkyl groups is always ethylene, if an ethyl group is present. Originally given in this limited form by A.W. Hofmann, the rule has since been extended and modified as follows When two or more alkenes can be produced in a P-elimination reaction, the alkene having the smallest number of alkyl groups attached to the double bond carbon atoms will be the predominant product. This orientation described by the Hofmann rule is observed in elimination reactions of quaternary ammonium salts and tertiary sulfonium salts, and in certain other cases. 

Discussion The preparation of ammonia from ammonium chloride and calcium hydroxide resembles the preparation of carbon dioxide from an acid and a carbonate in that a double decomposition is immediately followed by the spontaneous breaking up of one of the products into water and a gas. In both cases also the secondary reaction is reversible and with ammonia this reversal, together with the great solubility of ammonia gas itself, is so marked as to require the use of solid material instead of solutions, in order to reduce as much as possible the amount of water present. 

Discussion The following study of compounds of the alkaline earths is made from the point of view of solubility and affords, in addition to a knowledge of the appearance of certain specific substances, a number of examples of the relation of ionization to precipitation. The underlying principle is that a reaction of double decomposition in solution tends to run to the formation of the least ionized substance. A small concentration of ions may he due to one of two causes, either to a small degree of dissociation, as in the case of ammonium hydroxide and of acetic acid, or to the insolubility of the compound, as in the case of barium sulphate. 

Thermal decomposition of quaternary ammonium hydroxides is different because elimination occurs preferentially to form the least substituted double bond. Thermal decomposition of scc-butyltrimethylammonium hydroxide, for example, gives 1-butene as the major product. 

The impure hydroxide obtained above is purified by converting to a double salt, ammonium beryllium fluoride, which subsequently, on thermal decomposition, gives beryllium fluoride. The latter is heated with magnesium metal... 

Ammonium salt -E hydroxide base NH4OH -E decomposition Double-replacement -E decomposition Salt -E NH3 -E H2O NH4+ + OH- H2O -E NHj... 

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