Cuprous bromide solution

Prepare a solution of p-tolyldiazonium chloride from 53 -5 g. of p-tolui-dine using the proportions and experimental conditions given under p-Chlorotoluene (Section IV,61). Add the diazonium chloride solution to the boiling cuprous bromide solution, and proceed as in Method 1. The yield of pure, colourless p-bromotoluene, b.p, 182-184° (mainly 183°), is 40 g. m.p. 26°,... 

When the hydrobromic acid-cuprous bromide solution is ready for use, the diazonium solution is prepared. A solution of 107 g. (1 mole) of />-toluidine and 196 g. (1.9 moles) of concentrated sulfuric acid (sp. gr. 1.84) in 1 1. of water is cooled below 200 and diazotized with a solution of 70 g. (1 mole) of sodium nitrite in 125 cc. of water. This requires about twenty to thirty minutes when the temperature is maintained between 150 and 200 by means of an ice bath. 

A 5-I. round-bottom flask containing the hydrobromic acid-cuprous bromide solution, is arranged for steam distillation. After the copper solution is heated to boiling, the diazonium solution is gradually added from a separatory funnel and a vigorous current of steam is passed through the reaction mixture at the same time. This procedure requires about two hours. 

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. 

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... 

Method 1. Prepare a solution of cuprous bromide by refluxing 31-5 g. of erystallised eopper sulphate, 10 g. of elean eopper turnings, 77 g. of crystallised sodium bromide, 15 g. (8-2 ml.) of concentrated sulphuric acid and 500 ml. of water contained in a 2 5 litre round-bottomed flask over a flame for 3-4 hours until the solution acquires a yellowish colour if the blue colour is not discharged, add a few grams of sodium bisulphite to complete the reduction. 

Reaction.—a too c.c. flask to a short upright condenser (see Fig. 86) and to the upper end of the condensei attach a vertical delivery tube, dipping into an ammoniacal cuprous chloride solution. Pour 2—3 c.c. of ethylene bromide into the flask with 4 times its volume of strong methyl alcoholic potash, which is prepared by boiling methyl alcohol with excess of caustic potash on the water-bath with upright condenser. On gently heating, a rapid evolution of acetylene occurs and the characteristic brown copper compound (C2H,Cu,HjO) is precipitated from the cuprous chloride solution. 

By a procedure analogous to that described in the preceding experiment, octalone-2 (12 g, 0.08 mole, Chapter 9, Section III) in ether is added to methylmagnesium iodide in the presence of cuprous bromide (0.2 g). After decomposition with ice-acetic acid, extraction with ether, and washing of the ether extract, the ethereal solution is shaken with an equal volume (50-60 ml) of saturated aqueous sodium bisulfite for 3 hours. The mixture is filtered and the filtrate is reserved. The crystals are washed with ether. The filtrate is separated and the aqueous phase is combined with the filtered solid. The combination is acidified (dilute hydrochloric acid) and heated under reflux for 30 minutes. The product thus liberated is extracted into ether, the ether is washed with bicarbonate, then with saturated aqueous sodium chloride solution, and then dried and evaporated. The residual oil is the desired product, bp 250-254°. 

In the meantime, a mixture of 79 g. (0.55 mole) of cuprous bromide (Note 3) and 80 ml. (0.6 mole) of 48% hydrobromic acid (Note 1) is heated to boiling in a 5-1. round-bottomed thrcc-necked flask, equipped with a condenser set for distillation and provided with a 2-1. receiving flask, a steam inlet tube closed by a screw clamp, and a separatory funnel. About one-fourth of the diazonium solution is transferred to the separatory funnel, without filtration, and immediately run into the cuprous bro-mide-hydrobromic acid solution, which is kept boiling over a free flame, at such a rate that boiling is continuous. When the separatory funnel is nearly empty a further portion of the cold... 

The submitter used commercial cuprous bromide. The checkers prepared cuprous bromide by dissolving 600 g. (2.4 moles) of commercial copper sulfate crystals and 350 g. (3.4 moles) of sodium bromide in 2 1. of warm water the solution was stirred while 151 g. (1.2 moles) of solid sodium sulfite was added over a period of 10 minutes. Occasionally a little more sodium sulfite was required to discharge the blue color. The mixture was cooled, and the solid collected on an 8-in. Buchner funnel, washed once with water, pressed nearly dry, and then dried in... 

A 2-1. three-necked flask, fitted with stirrer, condenser, dropping funnel, and an arrangement for maintenance of an inert atmosphere, is charged with a mixture of 300 g. (3.26 moles) of nor-bomadiene (Note 1) and 0.650 g. (4.53 mmoles) of cuprous bromide (Note 2) in 500 ml. of benzene (Note 3). Dry nitrogen is introduced continuously, and, after the flask contents are brought to reflux, 245 g. (1.26 mole) of 2-butyl perbenzoate (Note 4), dissolved in 100 ml. of benzene, is added over approximately 1 hour to the stirred mixture. The solution immediately becomes blue or blue-green. The modest heat of reaction requires the application of some heat throughout the reaction period in order to maintain reflux. After the addition is completed, the solution is heated at the reflux temperature for an additional 30 minutes (Cautiont Note 5). 

The cuprous bromide was used as obtained from E. H. Sargent Co. One instance of an ineffective batch of cuprous bromide from another source has been reported to the submitters. Cuprous bromide is only slightly soluble in the benzene solution. Greater amounts of catalyst have no effect on the yield of product. 

When a primary aromatic amine, dissolved or suspended in cold aqueous mineral acid, is treated with sodium nitrite, a dlazonlum salt is formed (Unit 13, Class XII). Mixing the solution of freshly prepared diazonium salt with cuprous chloride or cuprous bromide results in the replacement of the diazonium group by -Cl or -Br. 

The jacketed addition funnel is removed and 1.5 g of cuprous bromide-dimethyl sulfide complex (Note 7) is added through a powder funnel. A 500-mL, pressure-equalizing addition funnel (long-tipped) is attached to the flask and flushed with argon. As the anion solution is cooled in a dry ice-isopropyl alcohol bath, a solution of 530 g (2.08 mol) of sublimed iodine in 500 mL of anhydrous tetrahydrofuran is placed in the addition funnel. This solution is added dropwise to the cooled slurry over approximately 90 min (Note 8). The solution is stirred for about 15 min at low temperature. 

To a distillation flask is added 29.0 gm (0.244 mole) of 3-bromopropyne and 2.5 gm (0.0174 mole) of dry cuprous bromide. The flask is attached to a concentric-tube column (25-30 theoretical plates), and the temperature of the flask is controlled so that the takeoff temperature at the head remains at 72.8°-73.5°C. In 24 hr, 24.4 gm (84 %) of bromopropadiene of 75-85 % purity is obtained. The remaining 3-bromopropyne (propargyl bromide) is removed by washing the product with a 40 % aqueous solution of diethylamine. Three to four moles of diethylamine is used for each mole of propargyl bromide in the product as calculated from VPC or refractive index data. After swirling the mixture (acidified with 15 % hydrochloric acid) for hr, the organic layer is separated, washed with water, dried over potassium carbonate, and distilled quickly under reduced pressure into a Dry Ice-cooled receiver to afford pure bromopropadiene, b.p. 72.8°C (9760 mm), w ° 1.5212, 1.5508. 

This complex is prepared from cuprous bromide and dimethyl sulfide according to the procedure of House. The complex must be pure white. Slightly Impure samples will produce pinkish solutions which are unsatisfactory for this procedure. Normally, the complex is dark red when it is first prepared, but the required state of purity can be achieved by two or three recrystallizations under a nitrogen atmosphere as described by House.2 We have found, however, that if the Initially-formed complex has a distinctly green appearance, it cannot be purified satisfactorily. Others have also been concerned about this matter of purification. 

When the solution of the cuprous bromide complex is cooled, a portion of the reagent may precipitate, but this behavior does not affect the overall results of the experiment. 

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