Ammonium hydroxide, existence

Ammonolysis with aqueous ammonia should be interpreted as being brought about by NH3, not by NH4OH. As water is only a very weak acid, the ammonia addition product is very unstable, and ammonium hydroxide exists in aqueous ammonia as a weak base present in small amount. To account for the weakness of ammonium hydroxide, it has been assumed that a hydrogen atom acts as a bond ... 

For this second reaction Kjgs = 181 x 10" and hence pK, for ammonia solution is 4.75. The entity NHj. H2O is often referred to as ammonium hydroxide, NH4OH, a formula which would imply that either nitrogen has a covalency of five, an impossible arrangement, or that NH4OH existed as the ions NH4 and OH". It is possible to crystallise two hydrates from concentrated ammonia solution but neither of these hydrates is ionic. Hence use of the term ammonium hydroxide is to be discouraged in favour of ammonia solution . 

The Hofmann elimination route, of which many versions exist, can be carried out at much lower temperatures in conventional equipment. The PX is generated by a 1,6-Hofmaim elimination of amine from a quaternary ammonium hydroxide in the presence of a base. This route gives yields of 17—19%. Undesired polymeric products can be as high as 80% of the product. In the presence of a polymerization inhibitor, such as phenothiazine, DPXN yields can be increased to 50%. 

The hydrous oxide, Hf02 xH20, is precipitated from acidic solutions by addition of ammonium hydroxide or dilute alkaline solutions. However, the hydrous oxide exhibits a limited solubihty in strongly alkaline solutions (65). The existence and relative stabiUty of soluble alkaline peroxy compounds has been demonstrated (66). 

The nitro alcohols available in commercial quantities are manufactured by the condensation of nitroparaffins with formaldehyde [50-00-0]. These condensations are equiUbrium reactions, and potential exists for the formation of polymeric materials. Therefore, reaction conditions, eg, reaction time, temperature, mole ratio of the reactants, catalyst level, and catalyst removal, must be carefully controlled in order to obtain the desired nitro alcohol in good yield (6). Paraformaldehyde can be used in place of aqueous formaldehyde. A wide variety of basic catalysts, including amines, quaternary ammonium hydroxides, and inorganic hydroxides and carbonates, can be used. After completion of the reaction, the reaction mixture must be made acidic, either by addition of mineral acid or by removal of base by an ion-exchange resin in order to prevent reversal of the reaction during the isolation of the nitro alcohol (see Ion exchange). 

The aqueous solubility of ammonia decreases rapidly as temperature increases. The existence of undissociated ammonium hydroxide [1336-21 -6] NH OH,... 

The pyridinium ion (acid 2) as the analyte can be titrated with quaternary ammonium hydroxide (base 3) as it concerns the determination of H+ of the Brensted acid pyridinium, a potentiometric measurement of the pH titration curve and its inflection point is most obvious. In the aprotic, but protophilic, solvent pyridine no stronger acid can exist (see reactions 4.37 and 4.38) than the pyridinium ion itself hence there is a levelling effect but in theory only on the acid side. 

Sato et al. carried out detailed studies on the possibilities of transformation of tetrazolo[l,5-tf]pyrazines 54 to 2-aminopyrazines 56 < 1994S931 >. These authors found that the generally used methods for this conversion fail because the starting compound exists in the stable bicyclic form 54, whereas partial formation of the azide valence bond isomer 55 would be necessary for the success of the transformation. Application of special reaction conditions succeeded, however hydrogenation over palladium catalyst in the presence of ammonium hydroxide or treatment with stannous chloride in a mixture of methanol and hydrochloric acid solved this problem. Thus, a great number of derivatives of 54 was reduced to the corresponding 2-aminopyrazine 56 in medium to high yields (45-100%). 

Arfwedson fused the chrysoberyl three times with caustic potash in a silver crucible. Since a portion of the melt corresponding to about 18 per cent of the mineral failed to dissolve in hydrochloric acid, he reported this residue as silica. It is now known that beryllium hydroxide, when freshly precipitated, dissolves readily in hydrochloric acid, but becomes after a time almost completely insoluble in it (17). Therefore, it is probable that Arfwedson s silica was really the beryllium hydroxide. He then precipitated the alumina by adding ammonium hydroxide to the acid filtrate. To satisfy himself of the purity of his alumina, he saturated the alkaline solution with hydrochloric acid until the precipitate dissolved, and added a large excess of ammonium carbonate. Had any glucina [beryllia] or yttria existed in the matter, said Arfwedson, it would have been dissolved by this excess of carbonate of ammonia, and would have fallen when the filtered liquid was boiled till the excess of ammonia was driven off but the liquid stood this test without any precipitate appearing. Arfwedson was evidently unable to detect beryllia here because he had already filtered it off and reported it as silica. When American chemist Henry Seybert analyzed the same mineral in 1824 he found it to contain 15 to 16 per cent of beryllia (22). 

Several pyrrolopyrrole derivatives were prepared by the cyclization of amides under the influence of basic reagents such as potassium hydroxide, potassium f-butoxide or even ammonium hydroxide. For example, the pyrrolinone amide (190) cyclized to give the pyrrolopyrrole derivative (21/22) under basic conditions (Scheme 68) (71JOC3929). Compound (21/22) exists mainly in the keto form in the solid state, but largely as the enol in polar solvents. Strictly speaking, neither tautomer is a true pyrrolopyrrole, since one ring is always in the form of pyrrolenine. 

Evidence for the existence of OHe(ROH)j, where ROH is an alkyl alcohol, in solutions of alcohols in benzene and in nitrobenzene, has been obtained by Agarwal and Diamond.94 Their studies, which involved the use of various quaternary ammonium hydroxides, indicated that the hydroxide ion is capable of associating with three alcohol molecules, regardless of whether it is in the free form or associated with a cation. 

G. Bredig,1 and R. Bach concluded that while the first acidic function is nearly the same as that of ammonium hydroxide, the second acidic function of the base is so weak in aq. soln. that the corresponding salts are almost completely hydrolyzed. T. Curtius and H. Schulz said that a dihydrate exists in aq. soln. because the cryoscopic data gave a mol. wt. of 68. These data, however, can be interpreted on the basis either of a monohydrate or of a dihydrate. All this, does not decide whether hydrazine is a monoacidic or a diacidic base. E. C. Gilbert also found that in the electrometric titration of a 0-lM-soln. of hydrazine hydrate... 

When ammonium hydroxide dissociates electrolytically it yields the ion NHV". The group of atoms NH4, which is often spoken of as the ammonium radical, resembles in many respects the atom of sodium or potassium. Like these, it can form a monovalent positive ion, or it can form compounds with acid radicals, for example, NH4CI, (NID2SO4 but unlike sodium and potassium, it cannot exist in the uncombined state. 

There are two possibilities of formation of hydrogen bonds in the solution of ammonia in water N — H. . . O and N. . . H — O. The latter case is realized in agreement with expectation in fact nitrogen is a better acceptor (more strongly basic) than oxygen, the OH group a stronger donor (more acidic) than NH. Therefore, ammonia hydrate occurs in a solution of ammonia but ammonium hydroxide does not exist (Van Velden and Ketelaar) 15. 

This statement does not contradict the fact that ammonium hydroxide does really exist this has been proved beyond doubt by various physicochemical measurements. Cf. Mellor s Modern Inorganic Chemistry, revised and edited by G. D. Parkes. 6th edn., Longman 1967, p. 434 et f. 

The presence of the ions NH4 and OH in the aqueous solution of ammonia is proved by its alkaline reaction and electrical conductivity. The presence of these ions necessitates the existence in the solution of some undissociated ammonium hydroxide, NH4 OH, to establish the equilibrium... 

Ammonium borates.—Many borates of ammonium have been described, hut their existence as definite chemical individuals is in most instances doubtful.18 Ammonium tetraborate, (NH4)2B407,4H20, is prepared by cooling a warm solution of boric acid in excess of ammonium hydroxide. It forms tetragonal crystals,19 soluble in 12 times their weight of water at the ordinary temperature. 

Ammonia is extremely soluble in water and gives hydrates. The hydrates NH3-H20, NH3-2H20, and 2NH3-H20 have NH3 and H20 molecules linked by H bonds no NH4 or OH" ions or NH4OH molecules exist in the hydrates. The hydrate NH3-H20 has chains of H20 molecules linked by H bonds these chains are cross linked by NH3 into a three-dimensional lattice by O—H—N and O—H—N bonds. In aqueous solution ammonia is probably hydrated in a similar manner. Although aqueous solutions are commonly referred to as solutions of the weak base NH4OH, called ammonium hydroxide, there is reason to believe that it probably does not exist. Solutions of ammonia are best described as NH3(aq), with the equilibrium written as... 

The bismuth(lll) halides are moisture sensitive and are readily converted into the oxyhalides BiOX (equation 1). Addition of acid to aqueous suspensions of the oxyhalides will regenerate BiX3, which exist as complex halo anions in solution. Addition of ammonium hydroxide to such solutions results in the formation of insoluble Bi(OH)3, which is easily dehydrated to the oxide. 

Ammonium, however, is not an element, like sodium, but a compound and not a compound, strictly speaking, but a group of atoms — one atom of nitrogen and four atoms of hydrogen — so related to each other and to other atoms, that they act as one atom of a metal. Such a group of atoms, which is incapable of independent existence, is called a radical. The chemical relations of radicals are exactly the same as elements. Ammonium has never been isolated, or if it has, it is so unstable that it immediately decomposes into ammonia and hydrogen. It is believed that ammonium hydroxide is a solution of an extremely unstable compound. The other compounds of ammonium mentioned above are well defined. 

The reason that the precipitate of cupric hydroxide dissolves in an excess of ammonium hydroxide can be given in the following way. A precipitate of cupric hydroxide is formed because the concentration of cupric ion and the concentration of hydroxide ion are greater than the alues corresponding to the solubility product of cupric hydroxide. If there were some way for copper to be present in the solution without exceeding the solubility product of cupric hydroxide then precipitation would not occur. In the presence of ammonia, copper exists in the solution not as the cupric ion (that is, the hydrated cupric ion), but principally as the cupric ammonia complex Cu(NHg)4++. This complex is far more stable than the hydrated cupric ion. The reaction of formation of the cupric ammonia complex is... 

Molybdenum Hexafluoride, MoFg, the only fluoride known vith certainty to exist, is best prepared by the action of fluorine on the finely divided metal at 60° to 70° C., the product being collected in a vessel cooled by a mixture of solid carbon dioxide and alcohol. It forms white crystals which melt at 17° C., the boLling-poiiit of the liquid being 35° C. It is decomposed by water, yielding the blue oxide (see p. 131), but does not react with chlorine, sul2ihur dioxide, or dry air it is absorbed by alkali or ammonium hydroxides, and fomis double salts vith alkali fluorides. It also reacts with ammonia, vith 2>roduction of a brown powder. 

Ammonium Dimolybdate, (NH4)2Mo.j07.H20, exists as mono-clinic (prismatic) crystals. A compound (NH4).2Mo20,.3NH2 has been prepared by addition of ammonium hydroxide of medium strength to solid ammonium phosphomolybdate. This substance loses ammonia, yielding the dimolybdate. 

Pectic material exists in all woods and often appears in holocellulose preparations, although the amount is small in completely delignified holocellulose. Anderson prepared holocellulose containing 2% of lignin (by the method of Wise ) from Douglas fir and Western hemlock, and extracted the pectic substances with dilute ammonium hydroxide. The... 

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