Bromine temperature

Figure 20 Difference between the degree of polymerization of the adsorbing segments in System I (PS) and System II (4-BrS) in PBr 3-CUD and PBr 3 NB as a function of the moie fraction of 4-BrS in the PBr S copolymer. For each system, the data split into two groups depending on the bromination temperature. Bromination of PS below 7= 32.8 °C produces PBr RCPs with a random-blocky distribution of the 4-BrS segments (b-PBr 3)- Bromination of PS above r=32.8°C produces PBr RCPs with a more random distribution of the 4-BrS segments (r-PBr ).

White and red phosphorus combine directly with chlorine, bromine and iodine, the red allotrope reacting in each case at a slightly higher temperature. The reactions are very vigorous and white phosphorus is spontaneously inflammable in chlorine at room temperature. Both chlorine and bromine first form a trihalide ... 

Phosphorus(III) oxide reacts slowly with oxygen at ordinary temperatures to give the pentoxide, P40,g. The reaction is rapid if the oxide is heated in air. It is oxidised vigorously by chlorine and bromine which form the oxidehalides, POX3. 

Dissolve 36 g. of sodium hydroxide in 160 ml. of water contained in a 500 ml. conical flask, and chill the stirred solution to 0-5° in ice-water. Now add io-8 ml. (32-4 g.) of bromine slowly to the stirred solution exercise care in manipulating liquid bromine ) during this addition the temperature rises slightly, and it should again be reduced to 0-5°. Add a solution of 12 g. of acetamide in 20 ml. of water, in small portions, to the stirred hypobromite solution so that the temperature of the mixture does not exceed 20° the sodium acet-bromoamide is thus obtained in the alkaline solution. Now remove the flask from the ice-water, and set it aside at room temperature for 30 minutes. 

Dissolve I g. of finely powdered acetanilide in 5 ml. of cold glacial acetic acid contained in a 25 ml. conical flask. Then in another small flask prepare a solution of 0 42 ml. (1 34 g.) of bromine (care ) in 6 ml. of glacial acetic acid, and add this solution slowly to the acetanilide solution, shaking the latter throughout the addition to ensure thorough mixing. Allow the final mixture to stand at room temperature for 15 minutes. Then... 

Note. (1) Most sulphur compounds are completely oxidised if the tube is heated under the conditions described for the estimation of halogens. Sul-phonic acids and sulphones are more difficult to oxidise completely and the tube should be slowly heated to 300 and maintained at this temperature for at least 6 hours. The oxidation may be facilitated by adding a few crystals of sodium or potassium bromide to the organic material in the small tube, so that bromine shall be present to intensify the oxidation during the heating. 

Method 2 (from potassium bromide and sulphuric acid). Potassium bromide (240 g.) is dissolved in water (400 ml.) in a litre flask, and the latter is cooled in ice or in a bath of cold water. Concentrated sulphuric acid (180 ml.) is then slowly added. Care must be taken that the temperature does not rise above 75° otherwise a little bromine may be formed. The solution is cooled to room temperature and the potassium bisulphate, which has separated, is removed by flltration through a hardened Alter paper in a Buchner funnel or through a sintered glass funnel. The flltrate is distilled from a litre distilling flask, and the fraction b.p. 124 127° is collected this contains traces of sulphate. Pure constant boiling point hydrobromic acid is obtained by redistillation from a little barium bromide. The yield is about 285 g. or 85 per cent, of the theoretical. 

I hour. Finally raise the temperature of the bath to 65-70° for a further 45 minutes or until all the bromine has disappeared (no red vapours visible) and the evolution of hydrogen bromide has almost ceased. Keep the solution of hydrogen bromide in the beaker (2). 

The mono-bromination of phenol at low temperatures in carbon disulphide or carbon tetrachloride solution results in almost exclusive para substitution ... 

Place a solution of 50 g. of p bromoacetophenone (Section IV,138) in 100 ml. of glacial acetic acid in a 500 ml. flask. Add very slowly (about 30 minutes) from a dropping funnel 40 g. (12-5 ml.) of bromine shake the mixture vigorously during the addition and keep the temperature below 20°. p-Bromophenacyl bromide commences to separate as needles after about half of the bromine has been introduced. When the addition is complete, cool the mixture in ice water, filter the crude product at the pump, and wash it with 50 per cent, alcohol imtil colourless (about 100 ml. are required). RecrystaUise from rectified (or methylated) spirit (ca. 400 ml.). The yield of pure p-bromophenac bromide (colourless needles, m.p. 109°) is 50 g. 

Apply the test to compounds which contain chlorine or bromine. If the compound is a solid, dissolve 0 1 g. in the minimum volume of pure, dry acetone. To 1 ml. of the sodium iodide acetone reagent add 2 drops of the compound (if a hquid) or the acetone solution (if a sohd). Shake and allow to stand at room temperature for 3 minutes. Note whether a precipitate is formed and also whether the solution acquires a reddish-brown colour (liberation of iodine). If no change takes place at rocrm temperature, place the test-tube in a beaker of water at 50°. After 5 minutes, cool to room temperature, and observe whether a reaction has occurred. 

To a stirred, cooled (0°C) solution of I52.15g (1.0 mol) of vanillin in 1000ml of methanol was added during 20 min 176.Og (1.1 mol) of bromine at such a rate that the temperature was kept below 20°C. The mixture was stirred at room temperature for lh, cooled to 0°C, and treated during 30 min with 500 ml of cold (5°C) water. Stirring was continued for 15 min and the product was collected by filtration. It was washed with water (4x500 ml), then with 500 ml of... 

To a mixture of 250 ml of ether and 3 moles of freshly distilled acrolein ivere added about 3 moles of bromine at a rate such that the temperature could easily be maintained between -30 and -90°C (bath of dry-ice-acetone or liquid Nj). After persisting of the browncolour, the temperature was allowed to rise to 0°C. Freshly distilled ethyl orthoformate (3.25 moles) and 96% ethanol (30 ml) were added. 

At elevated temperatures (250-400°C) bromine reacts with thiazole in the vapor phase on pumice to afford 2-bromothiazole when equimolecu-lar quantities of reactants are mixed, and a low yield of a dibromothiazole (the 2,5-isomer) when 2 moles of bromine are used (388-390). This preferential orientation to the 2-position has been interpreted as an indication of the free-radical nature of the reaction (343), a conclusion that is in agreement with the free-valence distribution calculated in the early application of the HMO method to thiazole (Scheme 67) (6,117). 

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