Over-bromination

In a development on the reaction of monohaloalkyl aryl ketoximes with tetrasulfur tetranitride, the introduction of two halogens such as chlorine, bromine, or fluorine at the a-position of alkyl aryl ketoximes significantly improved the yields of thiadiazoles <1998J(P1)109>. The preferential displacement of chlorine over bromine or fluorine allowed the preparation of monobromo- and monofluoro-3-aryl-thiadiazoles 195 from a,a-chlorobromoalkyl- and a,a-chlorofluoro-alkyl aryl ketoximes 194 (Equation 41). 

The reaction is difficult to control in batch mode, with ready over-bromination to the di- and tribromo products. 

As yet, little is available in terms of properly documented iodine treatment case histories, but it is difficult to see the advantages of iodine chemistry over bromine chemistry for most general-purpose cooling systems. 

In spite of the difference in bond strengths, hydrogen abstraction is favoured over bromine abstraction by a factor of about 2 1. All the processes discussed above represent chain propagating steps, but often the chains are short and... 

Betts, K. S. Mounting concern over brominated flame retardants. Environmental Science and Technology, 35 274A-275A (2001). 

Coarse or fine crystalline graphite, in a weighing bottle, is allowed to stand over bromine in a desiccator for many hours at room temperature. The maximum weight gain of the graphite is 0.82-0.84 g. per g. of C. 

Environmental concerns over brominated, and other halogenated products will negatively impact on their future growth as end users pursue less controversial substitutes including non-halogenated phosphorus, magnesium hydroxide and silicone compounds. 

Procedure. The sample is drawn over unglazed porcelain (streak plate or the unglazed bottom of an evaporation dish). The scratch is held for 2-3 minutes over bromine water and then spotted with alkali stannite solution. When bismuth is present, the scratch becomes dark and the metal deposited remains in place when washed with water. 

Results of the chemical equilibrium calculations including over-bromination reactions (Reactions (20 to 22)) are summarized in Table 7. Major conclusions were ... 

Traces of bromine, carried over with the gas, are removed by the copper turnings as black copper bromide if the level of the blackened copper in tube F rises appreciably, excessive amounts of bromine are being carried over. 

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. 

Place 50 g. (57 ml.) of dry A.R. benzene and 0 5 ml. of dry p rridine (1) (dried over potassium hydroxide pellets) in a 500 ml. round-bottomed flask. Attach a reflux condenser to the flask and an inverted funnel (just dipping into some water in a beaker) to the top of the condenser (Fig. II, 13, 8, b). Partially immerse the flask in a bath of cold water, supported upon a tripod and gauze. Carefully pour 125 g, (40 ml.) of bromine (for precautions to be taken with bromine, see Section 111,35, Note 1) through a condenser and immediately insert the absorption device into the upper end of the condenser. A vigorous reaction soon occurs and hydrogen bromide is evolved which is absorbed by the water in the beaker when the reaction slackens, warm the bath to 25-30° for... 

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... 

METHYL y-BROMOCROTONATE JV-Bromosuccinimide. Dissolve, with the aid of rapid mechanical stirring, 80 g. of pure succinimide (Section V,14) in a mixture of 150 g. of finely crushed ice and a solution of 32 g. of sodium hydroxide in 200 ml. of water contained in a litre beaker and cooled externally by ice. Immediately the imide has dissolved, continue the vigorous stirring and introduce 42 -5 ml. of bromine in one lot from a separatory funnel supported over the beaker it is essential that the bromine be instantly suspended in the solution. After stirring vigorously for 2 minutes, filter at the pump and... 

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