Heat of bromination

If these chemical chains involving Br or Br3 were ruled out, one could consider an energy chain, in which the exothermic heat of reaction plus the energy of excitation is sufficient to produce the dibromide of cinnamic acid with a high energy content. The heat of bromination alone is estimated at 16,000 calories. These hot molecules of product then pass their energy over to more bromine atoms which then react to form additional dibromide, as follows,... 

Hartley et al. 75) measured the heat of bromination of dimethylmercury via the reactions... 

The heat of bromination of Et2Hg measured by Hartley et al. (76), AH (iii) = —91.25 + 0.3 kcal/mole, combined with the value (70), AH ° (C2H5Br, liq) =—22.1 0.5 kcal/mole, leads to AH ° (Et2Hg, liq) = 6.4 1.0 kcal/mole in close agreement with the value derived from combustion studies. The selected value is... 

Mortimer et al. 122) measured the heat of bromination of Pr2Hg, finding AH (iii) = —91.8 0.5 kcal/mole. Bjellerup 14) has measured the heat of formation of propyl bromide by combustion calorimetry, but his value seems inconsistent relative to available values for EtBr and w-BuBr 154) we prefer to accept an estimated value, AHf° (PrBr, g) = —21.1 + 1 kcal/ mole, corresponding to AH(° (PrBr, liq) = —28.85 kcal/mole. Using this,... 

Pedley and Skinner 127) measured the heat of bromination, finding AH = — 51.8 0.13 kcal/mole for the reaction... 

The heat of bromination of triphenyltin bromide was measured by Pedley and Skinner 127),... 

Isocroionic acid, -crotonic acid, cis-croionic acid. Colourless needles m.p. 14 C, b.p. 169 C. Prepared by distilling -hydroxy-glutaric acid under reduced pressure. Converted to a-crotonic acid by heating at 180 C, or by the action of bromine and sunlight on an aqueous solution. 

Stilbene decolorises bromine only on heating. Proceed as above, but keep the stilbene solution hot during the addition of the CCI4 solution of bromine. Stilbene dibromide has m.p. 237 . 

Dibromobutane (from 1 4-butanediol). Use 45 g. of redistilled 1 4-butanediol, 6-84 g. of purified red phosphorus and 80 g. (26 ml.) of bromine. Heat the glycol - phosphorus mixture to 100-150° and add the bromine slowly use the apparatus of Fig. Ill, 37, 1. Continue heating at 100-150° for 1 hour after all the bromine has been introduced. Allow to cool, dilute with water, add 100 ml. of ether, and remove the excess of red phosphorus by filtration. Separate the ethereal solution of the dibromide, wash it successively with 10 per cent, sodium thiosulphate solution and water, then dry over anhydrous potassium carbonate. Remove the ether on a water bath and distil the residue under diminished pressure. Collect the 1 4-dibromobutane at 83-84°/12 mm. the yield 3 73 g. 

Use a 500 ml. three-necked flask equipped as in Section IV,19, but mounted on a water bath. Place 128 g. of naphthalene and 45 ml. of dry carbon tetrachloride in the flask, and 177 g. (55 ml.) of bromine in the separatory funnel. Heat the mixture to gentle boiling and run in the bromine at such a rate that little, if any, of it is carried over with the hydrogen bromide into the trap this requires about 3 hours. Warm gently, with stirring, for a further 2 hours or until the evolution of hydrogen bromide ceases. Replace the reflux condenser by a condenser set for downward distillation, stir, and distil off the carbon tetrachloride as completely as possible. Mix the residue with 8 g. of sodium... 

Method 2 (from hydrazobenzene). Prepare a solution of sodium hypobromite by adding 10 g. (3-2 ml.) of bromine dropwise to a cold solution of 6-0 g. of sodium hydroxide in 75 ml. of water immersed in an ice bath. Dissolve 9-5 g. of hydrazobenzene (Section IV,87) in 60 ml. of ether contained in a separatory funnel, and add the cold sodimn hypobromite solution in small portions. Shake for 10 minutes, preferably mechanically. Separate the ether layer, pour it into a 100 ml. distilling flask, and distil off the ether by warming gently on a water bath. Dissolve the warm liquid residue in about 30 ml. of alcohol, transfer to a small beaker, heat to boiling on a water bath, add water dropwise to the hot solution until the azobenzene just commences to separate, render the solution clear again with a few drops of alcohol, and cool in ice water. Filter the orange crystals at the pump, and wash with a little 50 per cent, alcohol. Dry in the air. The yield is 8 g. 

Nitrosomethylurea. Acetamide method. To a solution of 59 g. of acetamide in 88 g. (28 ml.) of bromine (1) in a 4-litre beaker add dropwise, with hand stining, a solution of 40 g. of sodium hydroxide in 160 ml. of water. Heat the resulting yellow reaction mixture on a steam bath until eflfervescence sets in (2), after which continue the heating for 2-3 minutes. CrystaUisation of the product from the yellow or red coloured solution usually commences immediately. Cool in an ice bath for 1-2 hours, collect the product by suction filtration, wash with a little ice-cold water, and dry in the air. The yield of colourless acetylmethylurea, m.p. 178-180°, is 50 g. 

It may be neoeasary to heat gently on a steam bath to dissolve the acetamide, and care should be taken that only the minimum amount of bromine is lost during the heating. 

Dibromo-o-cresolsulphonephthalein (bromocresol purple). Dissolve 6 g. of o-cresolsulphonephthalein in 50 ml. of glacial acetic acid, heat to boiling under reflux, add slowly a solution of 2 ml. of bromine in... 

The heats of formation of Tt-complexes are small thus, — A//2soc for complexes of benzene and mesitylene with iodine in carbon tetrachloride are 5-5 and i2-o kj mol , respectively. Although substituent effects which increase the rates of electrophilic substitutions also increase the stabilities of the 7r-complexes, these effects are very much weaker in the latter circumstances than in the former the heats of formation just quoted should be compared with the relative rates of chlorination and bromination of benzene and mesitylene (i 3 o6 x 10 and i a-Sq x 10 , respectively, in acetic acid at 25 °C). 

To a mixture of 0.40 mol of neohexene ( commercially available) and 200 ml of dry diethyl ether 0.35 mol of bromine was added with cooling between -40 and -50°C. The diethyl ether and excess of neohexene were then completely removed by evaporation in a water-pump vacuum.In the second flask was placed a solution of 90 g of commercial KO-tert.-C9H9 (see Chapter IV, Exp. 4, note 2) in 250 ml of DMSO. The dibromo compound was added in five portions during 15 min from the dropping funnel after the addition of each portion the flask was swirled gently in order to effect homogenization. Much heat was evolved and part of the tert.-butylacetylene passed over. After the addition the flask was heated for 30 min in a bath at B0-100°C. 

Acrylonitrile will polymerize violendy in the absence of oxygen if initiated by heat, light, pressure, peroxide, or strong acids and bases. It is unstable in the presence of bromine, ammonia, amines, and copper or copper alloys. Neat acrylonitrile is generally stabilized against polymerization with trace levels of hydroquinone monomethyl ether and water. 

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