Cuprous

Metallic Derivatives, (a) Cuprous Acetylide. CujCg. Prepare an ammoniacal solution of cuprous chloride by first adding dilute ammonia to 2-3 ml. of dilute copper sulphate solution until the initial precipitate just redissolves and a clear deep-blue solution is obtained now add an aqueous solution of hydroxylamine hydrochloride drop by drop with shaking until the solution becomes first green and then completely colourless, the cupric salt being thus reduced to the cuprous derivative. 

Now add this solution to ajar of acetylene as before and shake vigorously. A chocolate-red precipitate of cuprous acetylide is at once formed. 

The cuprous and silver acetylides are both explosive when dry. Therefore when these tests are completed, wash out the gas-jars thoroughly with water. 

Meanwhile, during the cooling of the cuprous chloride solution, prepare a solution of benzenediazonium chloride by dissolving 20 ml. (20-5 g.) of aniline in a mixture of 50 ml. of concentrated hydrochloric acid and 50 ml. of water, and after cooling to 5°, adding slowly a solution of 17 g. of sodium nitrite in 40 ml. of water. Observe carefully the general conditions for diazotisation given in the preparation of iodobenzene (p. 184). 

Potassium cupro-cyanide is the most convenient form in which cuprous cyanide can be used in Sandmeyer s Reaction. It is prepared by adding an excess of potassium cyanide to copper sulphate solution, whereby the cupric cyanide which is formed immediately breaks down to give cuprous cyanide and cyanogen, and the cuprous cyanide then dissolves in the excess of potassium... 

Add 2 -3 drops of phenylhydrazine to about 2 ml. of Fehling s solution in a test-tube and shake the mixture vigorously nitrogen is evolved and reddish-brown cuprous oxide is precipitated. The reaction proceeds rapidly on gentle warming, more slowly in the cold. 

Many diazonium compounds when treated with an ammoniacal cuprous Formerly known as Diphenic acid. 

B) Preparation of the Cuprous Solution, Add 85 ml. of concentrated ammonia solution (d, o-o88) to a solution of 50 g. of crystalline copper sulphate in 200 ml. of water, and cool to 10 . Dissolve 14 5 g. of hydroxylamine hydrochloride (or 17-4 g. of the sulphate) in 50 ml. of water, cool to 10 , and add a solution of 9 g. of sodium hydroxide in 30 ml. of water. Without delay add this hydroxylamine solution with stirring to the copper solution, which will be immediately reduced, but will retain a blue colour. 

Place the cuprous solution in a 1200 ml. beaker, and cool it in ice-water with (mechanical) stirring run in the diazotised... 

The success of the Bart reaction when applied to nuclear- substituted anilines is often much affected by the pH of the reaction-mixture. Furthermore, the yields obtained from some m-substituted anilines, which under the normal conditions are usually low, arc considerably increased by the modifications introduced by Scheller, and by Doak, in which the diazotisation is carried out in ethanolic solution followed by reaction with arsenic trichloride in the presence of a cuprous chloride or bromide catalyst. 

The colour of the precipitate depends upon the size of the cuprous oxide particles, and this in turn upon the rate of reduction, concentration of the solution, etc. 

Reduction of Fehling s solution. Add 5 ml. of the glucose solution to 5 ml. of Fehling s solution and boil. Reduction takes place and a precipitate of cuprous oxide is formed the latter is at first yellow but may become red on standing. 

Reduction of Fehling s solution. Boil i ml. of chloroform gently with 3 ml. of Fehling s solution with constant shaking for 3-4 minutes. Reduction occurs and reddish cuprous oxide slowly separates. 

Disappearance of the deep blue colour and precipitation of cuprous oxide indicates reducing agents such as ... 

Several variations of the chemical method are in use. In the one described below, a freshly prepared Fehling s solution is standardised by titrating it directly against a standard solution of pure anhydrous glucose when the end-point is reached, I. e., when the cupric salt in the Fehling s solution is completely reduced to cuprous oxide, the supernatant solution becomes completely decolorised. Some difficulty is often experienced at first in determining the end-point of the reaction, but with practice accurate results can be obtained. The titrations should be performed in daylight whenever possible, unless a Special indicator is used (see under Methylene-blue, p. 463). 

Cuprous chloride. Hydrated copper sulphate (125 g.) and sodium chloride (32-5 g.) are dissolved in water (400 ml.) boiling may be necessary. An allialine solution of sodium sulphite (from 26 5 g. of sodium bisulphite and 17 -5 g. of sodium hydroxide in 200 ml. of water) or the solution of the sodium bisulphite alone is added to the resulting hot solution during about 5 minutes with constant shaking. The solution will be decolourised or nearly so. It is then cooled to room temperature (or in an ice bath), and the supernatant liquid is decanted... 

Cuprous bromide. The solid salt may be prepared by dissolving 150 g. of copper sulphate crystals and 87 5 g. of sodium bromide dihydrate in 500 ml. of warm water, and then adding 38 g. of powdered sodium sulphite over a period of 5-10 minutes to the stirred solution. If the blue colour is not completely discharged, a little more sodium sulphite should be added. The mixture is then cooled, the precipitate is collected in a Buchner funnel, washed twice with water containing a little dissolved sulphurous acid, pressed with a glass stopper to remove most of the liquid, and then dried in an evaporating dish or in an air oven at 100 120°. The yield is about 80 g. 

A solution of cuprous bromide may be prepared either by dissolving the solid in hot constant boiling point hydrobromic acid or by refluxing a mixture of 63 g. of crystallised copper sulphate, 20 g. of copper turnings, 154 g. of sodium bromide dihydrate, 30 g. (16-3 ml.) of concentrated sulphuric acid and 1 litre of water for 3-4 hours. If the colour of the solution has not become yellowish after this period of heating, a few grams of sodium sulphite should be added to complete the reduction. 

Cuprous cyanide. Method 1 (Barber, 1943). This is based essentially upon the reaction ... 

Cuprous cyanide solution. The most satisfactory method is to dissolve the cuprous cyanide (1 mol) in a solution of technical sodium cyanide (2 5-2-6 mols in 600 ml. of water). If it is desired to avoid the preparation of solid cuprous cyanide, the following procedure may be adopted. Cuprous chloride, prepared from 125 g. of copper sulphate crystals as described under 1 above, is suspended in 200 ml. of water contained in a 1-litre round-bottomed flask, which is fitted with a mechanical stirrer. A solution of 65 g. of technical sodium cyanide (96-98 per cent.) in 100 ml. of water is added and the mixture is stirred. The cuprous chloride passes into solution with considerable evolution of heat. As the cuprous cyanide is usually emplo3 ed in some modification of the diazo reaction, it is usual to cool the resulting solution in ice. 

The only reaction which calls for comment here is the formation of red cuprous acetylide with an ammoniacal solution of cuprous chloride ... 

Dissolve 3 g. of copper sulphate pentahydrate and 1 g. of sodium chloride in 12 ml. of hot water, and add a solution of 1 g. of sodium bisulphite in 10 ml. of 5 per cent, sodium hydroxide solution. Shake, cool under the tap, and wash the precipitated wlute cuprous chloride with water by decantation. Dissolve the cuprous chloride in a few ml. of concentrated ammonia solution and dilute with water to 10 ml. 

Allyl Chloride. Comparatively poor yields are obtained by the zinc chloride - hydrochloric acid method, but the following procedure, which employs cuprous chloride as a catalyst, gives a yield of over 90 per cent. Place 100 ml. of allyl alcohol (Section 111,140), 150 ml. of concentrated hydrochloric acid and 2 g. of freshly prepared cuprous chloride (Section II,50,i one tenth scale) in a 750 ml. round-bottomed flask equipped with a reflux condenser. Cool the flask in ice and add 50 ml. of concen trated sulphuric acid dropwise through the condenser with frequent shaking of the flask. A little hydrogen chloride may be evolved towards the end of the reaction. Allow the turbid liquid to stand for 30 minutes in order to complete the separation of the allyl chloride. Remove the upper layer, wash it with twice its volume of water, and dry over anhydrous calcium chloride. Distil the allyl chloride passes over at 46-47°. 

It has been stated that many halogen-free compounds, e.g., certain derivatives of pyridine and quinoline, purines, acid amides and cyano compounds, when ignited on copper oxide impart a green colour to the dame, presumably owing to the formation of volatile cuprous cyanide. The test is therefore not always trustworthy. The test is not given by duorides. 

Allyl cyanide. Into a 1 5 litre three-necked flask (1), provided with a mercury-sealed stirrer and two long double surface condensers, place 293 g. (210 ml.) of freshly-distilled allyl bromide, b.p. 70-71° (Section III, 35) and 226 g. of dry cuprous cyanide (Section 11,50,3, Method 1), Remove the mercury-sealed stirrer and replace it by a tightly fitting... 

Dissolve 0-5 g. of the substance in 10 ml. of 50 per cent, alcohol, add 0-5 g. of solid ammonium chloride and about 0 -5 g. of zinc powder. Heat the mixture to boiling, and allow the ensuing chemical reaction to proceed for 5 minutes. Filter from the excess of zinc powder, and teat the filtrate with Tollen s reagent Section 111,70, (i). An immediate black or grey precipitate or a silver mirror indicates the presence of a hydroxyl-amine formed by reduction of the nitro compound. Alternatively, the filtrate may be warmed with Fehling s solution, when cuprous oxide will be precipitated if a hydroxylamine is present. Make certain that the original compound does not aflfect the reagent used. 

The procedure is not usually applicable to aminosulphonic acids owing to the interaction between the amino group and the phosphorus pentachloride. If, however, the chlorosulphonic acid is prepared by diazotisation and treatment with a solution of cuprous chloride in hydrochloric acid, the crystalline chlorosulphonamide and chlorosulphonanilide may be obtained in the usual way. With some compounds, the amino group may be protected by acetylation. Sulphonic acids derived from a phenol or naphthol cannot be converted into the sulphonyl chlorides by the phosphorus pentachloride method. 

The following mechanism of the Sandmeyer reaction has been proposed as a result of a kinetic study, and incidentally accounts for the formation of the azu compounds as by-products. The catalyst is the CuCl ion produced in the dissolution of cuprous chloride in the chloride solution ... 

In the preparation of bromo compounds by the Sandmeyer reaction, the amine is generally diazotised in sulphuric acid solution (or in hydrobromic acid solution), and the resulting aryldiazonium sulphate (or bromide) is treated with a solution of cuprous bromide in excess of hydrobromic acid the addition... 

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