Precipitation alkali

If the benzoyl derivative is soluble in alkali, precipitate it together with the benzoic acid derived from the reagent by the addition of hydrochloric acid filter and extract the product with cold ether or light petroleum (b.p. 40-60°) to remove the benzoic acid. 

In order to manufacture such polymers, it is first necessary to produce a very pure form of formaldehyde. This is typieally produced from an alkali-precipitated low molecular weight polyformaldehyde which has been carefuly washed with distilled water and dried for several hours under vacuum at about 80°C. The dried polymer is then pyrolysed by heating at 150-160°C, and the resultant formaldehyde passed through a number of cold traps (typically four) at -15°C. Some prepolymerisation occurs in these traps and removes undesirable... 

ZnO particle morphologies are very complex and diversiform in comparison with Ti02. Thus, monodispersed ZnO particles with well-defined morphological characteristics, such as spherical, ellipsoidal, needle, prismatic, and rod-like shapes, have been obtained. Aggregates composed of these basic shape particles have also been achieved. The methods used for synthesis of these ZnO powders include alkali precipitation [214-216], thermal decomposition [217], hydrothermal synthesis [218], organo-zinc hydrolysis [219], spray pyrolysis [220], and other routes. 

Bismuth dissolves in nitric acid and in aqua regia both solutions are precipitated by pure water in the form of a white powder. When the regulus of cobalt is dissolved in these menstrua, it cannot be precipitated from them except by the alkalies fixed alkali precipitates it in the form of a powder which, after being washed, remains dark and black whereas when one precipitates it with volatile alkali, especially if it has been dissolved by aqua regia, it acquires a very red color, which changes to blue, if one exposes it to the fire up to the point of redness (27). 

The Penniman-Zoph process involves the preparation of seeds or nucleating particles by the alkali precipitation of ferrous sulfate. The reaction is carried out at alow temperature using an excess of ferrous ions. The hydroxide is then oxidized to the seeds of hydrated ferric oxide ... 

Fig. 8. A typical commercial soy protein isolate process. The soy proteins are extracted with alkali, precipitated with acid, washed with water, redispersed and dried. (Reprinted with permission from [14], 1989 Institute of Food Technologists)...

Iridium tetrachloride is readily reduced to the trichloride. Its aqueous solution, on dilution, yields hypoehlorous acid and the trichloride. On boiling, a precipitate of oxychloride is obtained. Addition of excess of alkali precipitates part of the iridium as dioxide, the remainder staying in solution as sesquioxide, being precipitated only upon neutralisation of the alkali. Addition of alcohol to the alkaline solution precipitates metallic iridium, aldehydes and alkali formates being simultaneously produced. Reducing agents, such as stannous chloride, sulphur dioxide, nitric oxide, hydrogen sulphide, ferrous sulphate, etc, convert the tetrachloride into trichloride. 

Alkalies precipitate the black hydrated oxide, Ru2Os. 3H20, insoluble in excess, but which is readily soluble in hydrochloric acid, yielding an orange solution containing the trichloride, RuC13. 

Caustic alkalies precipitate basic salts as yellowish brown deposits, soluble in excess. Water, alone, causes partial precipitation from acidulated solutions if acid is only present in very slight excess. 

Alkalies precipitate hydrated osmium dioxide, Os(OH)4, as a brownish red mass, whilst grey anhydrous osmium dioxide is obtained on fusing potassium hexachlor osmate, K30sC16, with sodium carbonate. 

A number of oxazine dye salts, on dissolving in aqueus alkali, precipitated the free radical thus the dye Meldola s blue, which precipitates even in almost neutral solution, yields a very stable solid free radical which can be kept in air and can be used as standard like 2,2-diphenyl-1 -picrylhydrazyl. 

Ferrous sulphite solution readily oxidises in air, yielding a red solution.6 From its colourless solutions alkalies precipitate ferrous hydroxide. 

Night Blue is obtained from paratolyl-a-haphthylamine (P-C7H7NHC10H7) and tetramethyldiamidobenzophenone. These dyestuffs come into commerce as hydrochlorides. They are beautiful blue dyestuffs, easily soluble, and dye cotton prepared with tannic acid similarly to methylene blue, but unfortunately the shades produced are not very fast to light. In general their reactions resemble those of the rosaniline dyestuffs. Alkalies precipitate a reddish-brown base, and acids turn the blue colour to yellow. 

It must be emphasized that the viscosity of povidone solutions is independent of their pH over a wide range. Only in extreme cases does this rule not apply concentrated hydrochloric acid increases their viscosity strong alkali precipitates povidone. However, it usually redissolves on addition of water. 

Humic acid Soluble in alkali, precipitated by acid Humus acid Humic acid Humic acid Humic acid Humus acid Humic acid... 

FIGURE 10.2 Effects of alkali precipitation with different hardness solutions. Extent of alkali precipitation is represented by the lengths of bars and permeability reduction is represented by % (shown beside bars) in flow experiments. Source Cheng (1986). 

In alkaline solution (partly because of the involvement of H in redox equilibrium 21.10, and partly because of the low solubility of the product) Ti(lll) compounds liberate H2 from H2O and are oxidized to Ti02. In the absence of air, alkali precipitates hydrous Ti203 from solutions of TiCls. Dissolution of this oxide in acids gives salts containing [Ti(H20)g]3+, e.g. [Ti(H20)6]Cl3 and CsTi(S04)2-12H20, the latter being isomorphous with other alums (see Section 12.9). 

Form, prisms from ale, mp 226-228°. Freely sol in ale, moderately in ether. Slightly sol in water, chloroform, benzene sol in dil alkalies. Precipitated by carbonates. 

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