Bromotoluene Sandmeyer reaction

Method 1. Prepare a solution of cuprous bromide by refluxing 31-5 g. of crystallised copper sulphate, 10 g. of clean copper 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 hoims until the solution acquires a yellowish colour if the blue coloim is not discharged, add a few grams of sodium bisulphite to complete the reduction. 

In a 1 litre flask mix 53 -5 g. of p-toluidine and 400 ml. of water, and then add cautiously 98 g. (53 6 ml.) of concentrated sulphuric acid warm until the p-toluidine dissolves. Cool the flask in a bath of ice and salt to 0-5° add about 100 g. of crushed ice to the contents of the flask in order to accelerate the cooing. Add slowly and with frequent shaking a solution of 35 g. of sodium nitrite in 60 ml. of water until a slight excess of sodium nitrite is present (.see Section IV,60) keep the temperature of the mixture below 10°. 

Equip the 2 5 litre flask holding the cuprous solution for steam distillation (Fig. II, 40, 1) with the addition of a third tube (7-8 mm. in diameter) leading almost to the bottom of the flask attach a short-stemmed. 

Method 2. Prepare 40 g. of cuprous bromide according to Section 11,50,2 (about 75 g. of crystallised copper sulphate are required) and dissolve it in 40 ml. of constant boiling point hydrobromic acid (48% HBr) contained in a 2 5 litre roimd-bottomed flask. 

Prepare a solution of p-tolyldiazonium chloride from 53 5 g. of p-tolui-dine using the proportions and experimental conditions given under hloroioluene (Section IV,61). Add the diazonium chloride solution to the boiling cuprous bromide solution, and proceed as in Method 1. The 3neld of pure, colourless p-bromotoluene, b.p. 182-184° (mainly 183°), is 40 g, m.p. 26°. 

Method 1. Prepare a solution of cuprous bromide by refluxing 

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For the preparation of chlorides or bromides, the diazonium salt is decomposed with a solution of cuprous chloride or bromide in the corresponding halogen acid (Sandmeyer reaction). It is possible to prepare the aryl bromide from the diazonium chloride or sulfate. A variation Involves the use of copper powder and a mineral acid for the decomposition step (Gattermann reaction). Both procedures are illustrated by the syntheses of the isomeric bromotoluenes and chlorotoluenes. The usual conditions of the Sandmeyer reaction fail in the preparation of the chloro- and bromo-phenanthrenes. However, these compounds can be successfully obtained by the interaction of the diazonium compound with mercuric and potassium halides (Schwechten procedure). Another procedure for formation of aryl bromides involves treatment of the amine hydrobromide with nitrogen trioxide in the presence of excess 40% hydro-bromic acid. The Intermediate diazonium perbromide is then decomposed by heat. ... 

The yields in the Gattermann reaction, however (e.g. o-bromotoluene, Expt 6.74), are usually not as high as those obtained by the Sandmeyer method. Copper powder is also employed in the preparation of sulphinic acids (e.g. benzenesul-phinic acid, Expt 6.75) which are obtained when a solution of a diazonium sulphate is saturated with sulphur dioxide and decomposed by the addition of copper powder. 

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