Aluminium hydrolysis

The review of Martynova (18) covers solubilities of a variety of salts and oxides up to 10 kbar and 700 C and also available steam-water distribution coefficients. That of Lietzke (19) reviews measurements of standard electrode potentials and ionic activity coefficients using Harned cells up to 175-200 C. The review of Mesmer, Sweeton, Hitch and Baes (20) covers a range of protolytic dissociation reactions up to 300°C at SVP. Apart from the work on Fe304 solubility by Sweeton and Baes (23), the only references to hydrolysis and complexing reactions by transition metals above 100 C were to aluminium hydrolysis (20) and nickel hydrolysis (24) both to 150 C. Nikolaeva (24) was one of several at the conference who discussed the problems arising when hydrolysis and complexing occur simultaneously. There appear to be no experimental studies of solution phase redox equilibria above 100°C. 

Note, however, if the component OH- had been used to define the aluminium hydrolysis reactions the PBE equation would have been formulated differently. 

Hydration of HPP. All factors mentioned above affect the T i value, showing the change in the state of water to be the result of a change in the composition of the water and the surface properties of the disperse phase. Aluminium hydrolysis products are mostly particles of Al(OH)3 with aluminium hydroxyl complexes adsorbed on them, so the change in T can be associated with an altered nature and number of hydrophilic centres. It has been shown5,6 that in all cases the spin-spin relaxation time of water protons decreases with increasing OH/A1 ratio in the coagulant molecule. This is an evidence of increased hydration of particles surface in this direction. 

Gibbsite (aluminium hydroxide) is purified from bauxite (impure aluminium oxide) via the Bayer process, where the bauxite is reacted with sodium hydroxide to form the aluminium hydrolysis species, Al(OH)4, from which gibbsite can then be recovered. Corundum (aluminium oxide) can then be obtained from the gibbsite via calcination. Pyrolusite (manganese dioxide) is often utilised in the... 

K.J. (1993) Aluminium hydrolysis constants to 250 °C from boehmite solubility measurements. Geochim. Cosmochim. Acta, 57, 747-762. 

As indicated, the solubihty of these aluminium oxide and hydroxide phases is important in the production of aluminium at elevated temperature and high pH, where the formation of the hydrolysis species, Al(OH) ", predominates and the behaviour of NaAKOH) is particularly important. The lesser hydrolysed monomeric species of aluminium, AlOH to Al(OH)3(aq), are also known to form. In more concentrated aluminium solutions, a number of polymeric aluminium hydrolysis species have been identified, including Al2(OH)2, Al3(OH)4 and Alj3(OH)32 (or, more correctly, Alj304(0H)24 ). The reaction describing the formation of these species is given by Eq. (2.5) (M = Al ). 

This is an exothermic process, due largely to the large hydration enthalpy of the proton. However, unlike the metallic elements, non-metallic elements do not usually form hydrated cations when their compounds dissolve in water the process of hydrolysis occurs instead. The reason is probably to be found in the difference in ionisation energies. Compare boron and aluminium in Group III ... 

The data in Tables 4.2 and 4.3 refer to ions in aqueous acid solution for cations, this means effectively [MlHjO), ]" species. However, we have already seen that the hydrated cations of elements such as aluminium or iron undergo hydrolysis when the pH is increased (p. 46). We may then assume (correctly), that the redox potential of the system... 

Therefore, when an anhydrous aluminium salt is dissolved in water initially, the octahedral ion [Al(H20)j,] " is formed by hydration of the A1 ion. However, since some hydrolysis occurs, the solution will contain and be acidic. Addition of any molecule or ion... 

Alternatively pure hydrogen sulphide is obtained by the hydrolysis of aluminium(III) sulphide ... 

They are rapidly hydrolysed by water and the hydrolysis of solid aluminium sulphide can be used to prepare hydrogen sulphide ... 

The yield of iso-propylbenzene is influenced considerably by the quality of the anhydrous aluminium chloride employed. It Is recommended that a good grade of technical material be purchase in small bottles containing not more than 100 g. each undue exposure to the atmosphere, which results in some hydrolysis, is thus avoided. Sealed bottles containing the reagent sometimes have a high internal pressure they should be wrapped in a dry cloth and opened with care. 

Hydroxyalkylthiazoles are also obtained by cyclization or from alkoxyalkyl-thiazoles by hydrolysis (36, 44, 45, 52, 55-57) and by lithium aluminium hydride reduction of the esters of thiazolecarboxylic acids (58-60) or of the thiazoleacetic adds. The Cannizzaro reaction of 4-thiazolealdehyde gives 4-(hydroxymethyl)-thiazole (53). The main reactions of hydroxyalkyl thiazoles are the synthesis of halogenated derivatives by the action of hydrobroraic acid (55, 61-63), thionyl chloride (44, 45, 63-66), phosphoryl chloride (52, 62, 67), phosphorus penta-chloride (58), tribromide (38, 68), esterification (58, 68-71), and elimination that leads to the alkenylthiazoles (49, 72). 

Aluminium fluoride (anhydrous) [7784-18-4] M 84.0, m 250°. Technical material may contain up to 15% alumina, with minor impurities such as aluminium sulfate, cryolite, silica and iron oxide. Reagent grade AIF3 (hydrated) contains only traces of impurities but its water content is very variable (may be up to 40%). It can be dried by calcining at 600-800° in a stream of dry air (some hydrolysis occurs), followed by vacuum distn at low pressure in a graphite system, heated to approximately 925° (condenser at 900°) [Henry and Dreisbach J Am Chem Soc 81 5274 1959]. 

The metallosiloxanes are liable to hydrolysis but the rate of hydrolysis is very dependent on the metal used in the polymer. Examination of three low molecular weight metallosiloxanes indicates the relative rates of hydrolysis to be 2220 27.2 1 for the tin, aluminium and titanium derivatives respectively. Russian workers state that polyorganometallosiloxanes are being used industrially but little detailed information is available. 

Other syntheses of tropic acid have been accomplished by Spiegel, Miiller, Wislicenus and Bilhiiber, Chambon and Natarajan and Swamina. ( > Of these, the most interesting is the reduction of ethyl formylphenylacetate (VIII) CHO. CHPh. COOC Hj in moist ethereal solution by aluminium amalgam to ethyl tropate, from which the acid (IX) HO. CHj. CHPh. COOH, is obtainable by hydrolysis with baryta. 

Hydrogen can be prepared by the reaction of water or dilute acids on electropositive metals such as the alkali metals, alkaline earth metals, the metals of Groups 3, 4 and the lanthanoids. The reaction can be explosively violent. Convenient laboratory methods employ sodium amalgam or calcium with water, or zinc with hydrochloric acid. The reaction of aluminium or ferrosilicon with aqueous sodium hydroxide has also been used. For small-scale preparations the hydrolysis of metal hydrides is convenient, and this generates twice the amount of hydrogen as contained in the hydride, e.g. ... 

Wood preservatives appear not to affect emission of corrosive vapours from wood, suggesting that the hydrolysis of acetyl polysaccharides is chemical, not biochemical. Some copper-base preservatives can give enough leachable copper ions to cause galvanic corrosion of other metals, notably aluminium and steel. 

Benzophenone has been prepared by the distillation of calcium benzoate,1 by the action of benzoyl chloride on benzene in the presence of aluminium chloride,2 by the action of phosgene on benzene in the presence of aluminium chloride,3 by the action of carbon tetrachloride on benzene in the presence of aluminium chloride followed by hydrolysis.4... 

Urea possesses negligible basic properties (Kb = 1.5 x 10 l4), is soluble in water and its hydrolysis rate can be easily controlled. It hydrolyses rapidly at 90-100 °C, and hydrolysis can be quickly terminated at a desired pH by cooling the reaction mixture to room temperature. The use of a hydrolytic reagent alone does not result in the formation of a compact precipitate the physical character of the precipitate will be very much affected by the presence of certain anions. Thus in the precipitation of aluminium by the urea process, a dense precipitate is obtained in the presence of succinate, sulphate, formate, oxalate, and benzoate ions, but not in the presence of chloride, chlorate, perchlorate, nitrate, sulphate, chromate, and acetate ions. The preferred anion for the precipitation of aluminium is succinate. It would appear that the main function of the suitable anion is the formation of a basic salt which seems responsible for the production of a compact precipitate. The pH of the initial solution must be appropriately adjusted. 

Solutions which prevent the hydrolysis of salts of weak acids and bases. If the precipitate is a salt of weak acid and is slightly soluble it may exhibit a tendency to hydrolyse, and the soluble product of hydrolysis will be a base the wash liquid must therefore be basic. Thus Mg(NH4)P04 may hydrolyse appreciably to give the hydrogenphosphate ion HPO and hydroxide ion, and should accordingly be washed with dilute aqueous ammonia. If salts of weak bases, such as hydrated iron(III), chromium(III), or aluminium ion, are to be separated from a precipitate, e.g. silica, by washing with water, the salts may be hydrolysed and their insoluble basic salts or hydroxides may be produced together with an acid ... 

The addition of an acid to the wash solution will prevent the hydrolysis of iron(III) or similar salts thus dilute hydrochloric acid will serve to remove iron(III) and aluminium salts from precipitates that are insoluble in this acid. 

B. Reactions.—(/) Nucleophilic Attack at Phosphorus. A reinvestigation of the reaction between phosphorus trichloride and t-butylbenzene in the presence of aluminium chloride has shown that the product after hydrolysis is the substituted phosphinic acid (11), and not the expected phosphonic acid (12). Bis(A-alkylamino)phosphines have been reported to attack chlorodiphenyl phosphine with nitrogen, in the presence of a base, to give bis-(A-alkyl-A-diphenylphosphinoamino)phenylphosphines (13). In (13), the terminal phosphorus atoms are more reactive than the central one towards sulphur and towards alkyl halides. 

Aveston, J. (1965). The hydrolysis of the aluminium ion ultracentrifugal and acidity measurements. Journal of the Chemical Society, 4438-43. 

The chemistry of aluminium combines features in common with two other groups of elements, namely (i) divalent magnesium and calcium, and (ii) trivalent chromium and iron (Williams, 1999). It is likely that the toxic effects of aluminium are related to its interference with calcium directed processes, whereas its access to tissues is probably a function of its similarity to ferric iron (Ward and Crichton, 2001). The effective ionic radius of Al3+ in sixfold coordination (54 pm) is most like that of Fe3+ (65 pm), as is its hydrolysis behaviour in aqueous solution ... 

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