Copper solution, alkaline, reaction with

Chemical Reactivity - Reactivity with Water Dissolves to form an alkaline solution. The reaction is non-violent Reactivity with Common Materials Forms explosion-sensitive materials with some metals such as lead, silver, mercury, and copper Stability During Transport Stable but must not be in contact with acids Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Reactions with aqueous solutions. Uniform dissolution or corrosion of metals in acid, alkaline or neutral solutions (e.g. dissolution of zinc in hydrochloric acid or in caustic soda solution general corrosion of zinc in water or during atmospheric exposure). Reactions with non-aqueous solution (e.g. dissolution of copper in a solution of ammonium acetate and bromine in alcohol). 

Most simple inorganic salt solutions cause virtually no attack on aluminium-base alloys, unless they possess the qualities required for pitting corrosion, which have been considered previously, or hydrolyse in solution to give acid or alkaline reactions, as do, for example, aluminium, ferric and zinc chlorides. With salts of heavy metals —notably copper, silver, and gold —the heavy metal deposits on to the aluminium, where it subsequently causes serious bimetallic corrosion. 

Discussion. Minute amounts of beryllium may be readily determined spectrophotometrically by reaction under alkaline conditions with 4-nitrobenzeneazo-orcinol. The reagent is yellow in a basic medium in the presence of beryllium the colour changes to reddish-brown. The zone of optimum alkalinity is rather critical and narrow buffering with boric acid increases the reproducibility. Aluminium, up to about 240 mg per 25 mL, has little influence provided an excess of 1 mole of sodium hydroxide is added for each mole of aluminium present. Other elements which might interfere are removed by preliminary treatment with sodium hydroxide solution, but the possible co-precipitation of beryllium must be considered. Zinc interferes very slightly but can be removed by precipitation as sulphide. Copper interferes seriously, even in such small amounts as are soluble in sodium hydroxide solution. The interference of small amounts of copper, nickel, iron and calcium can be prevented by complexing with EDTA and triethanolamine. 

Reduction of substituted nitrobenzenes under alkaline conditions, usually with aqueous sodium acetate as electrolyte and a nickel cathode, is the classical method due to Elbs [45] for the formation of azo- and azoxy-compounds. Protons are used in the electrochemical reaction so that the catholyte becomes alkaline and under these conditions, phenylhydroxylamine reacts rapidly with nitrosobenzene to form azoxybenzene. Finely divided copper has long been known to catalyse the reduction of nitrobenzene to aniline in alkaline solution at the expense of azoxybenzene production [46]. Modem work confirms that whereas reduction of nitrobenzene at polycrystalline copper in alkaline solution gives mainly azoxybenzene, if the electrode is pre-oxidised in alkaline solution and then reduced just prior to the addition of nitrobenzene, high yields of aniline are obtained with good current efficiency... 

Tetrammino-palladous Hydroxide, [Pd(NII3)4](OH)2, may be obtained by decomposing the sulphate with barium hydroxide. It separates as a colourless crystalline substance which is soluble in water and has a strong alkaline reaction. The aqueous solution is capable of precipitating copper, iron, cobalt, and nickel from solutions of their salts, and it also decomposes ammonium salts. 

Only moderate yields of biphenyls result from the Gomberg reaction, in which an acidic solution of a diazonium salt is made alkaline with sodium hydroxide solution in a two-phase mixture with an aromatic hydrocarbon such as benzene (Scheme 8.20). A variation of this reaction uses a copper catalyst. The reaction is more successful in the intramolecular version and the Pschorr reaction (discussed in Chapter 12) offers a useful route to phenanthrene. 

A mixture of 50 g. (0.24 mole) of 4-hromoisoquinoline (p. 50), 160 ml. of concentrated ammonium hydroxide solution, and 3 g. of hydrated copper sulfate is heated in a shaking autoclave at 165-170° for 16 hours. The reaction mixture is made alkaline with dilute sodium hydroxide solution and extracted with five lOO-mh"portions of benzene. After being dried over anhydrous potassium carbonate and treated with charcoal, the benzene solution is concentrated to a volume of 70 ml. Cooling precipitates 24 g. (70%) of 4-aminoiso-quinoline, m.p. 107-107.5°. Two recrystallizations from benzene raise the melting point to 108.5°. 

Reduction of Fehling s Solution.—The reaction of sugars with an alkaline tartrate solution of copper sulphate, known as, Fehling s solution, while not giving any information as to the constitution of sugars, is of importance in distinguishing certain sugars and other carbohydrates, and of still more value as the basis of analytical methods for their quantitative determination. 

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