1,2-dibromobenzene

—In order to obtain a good yield of bromobenzene, it is advisable to keep the mixture of benzene and bromine cold during the reaction. The product obtained consists of a mixture of benzene, bromobenzene, and dibromobenzene. The effect of the temperature on the reaction is clearly seen by comparing the method used in this preparation with that employed to prepare dibromobenzene. See the experiment below. 

In this operation and in all similar ones the substance should not be pressed down on the plate with the spatula but laid on with gentle pressure, so that the capillary action of the plate exerts its full effect. In the case of very sticky substances the material is transferred after a few hours with the spatula to an unused part of the plate. 

After drying, the p-dibromobenzene is recrystallised from a little alcohol from which it separates in magnificent colourless prisms. Melting point 89°. 

A useful rule for operations of this kind Set aside a small part of the less accessible substance—here the hydrobromic acid—so that if the neutral point is accidentally passed no difficulty is experienced. 

Pure bromobenzene loses no bromine ions when boiled with potassium hydroxide solution. Check this. 

If it is desired to compare bromobenzene with a halide of the aliphatic series, the saturated ethyl bromide must naturally not be chosen 

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The p-dibromobenzene formed as a by-product in the above reaction usually solidifies when the undistilled residue obtained in the first distillation is chilled. It may then he isolated by adding about lo ml. of methylated spirit and some animal charcoal to the flask, boiling for a few minutes, and filtering hot. On cooling the filtrate in ice-water, crystals of p-dibromobenzene, m.p. 89°, separate recrystallise a second time if necessary to obtain colourless crystals. 

Method 1. Arrange the flask containing the reaction mixture for steam distillation as in Fig. II, 40, 1. Proceed with the steam distillation until crystals of p-dibromobenzene appear in the condenser. Change the receiver and continue with the distillation until all the p-dibromobenzeiie has passed over from time to time run out the water from the condenser so that the crystals melt and run down into the receiver. Reject the residue in the flask. Transfer the first distillate to a separatory funnel, wash it with a httle water, and dry the lower layer with a little anhydrous magnesium sulphate or anhydrous calcium chloride filter. Distil slowly from a small distilling flask use a wire gauze or an air bath (Fig. II, 5, 3). Collect the fraction which passes over at 150-170° pour the residue (R), while it is still hot, into a small beaker or porcelain basin for the isolation of p-dibromobenzene. Redistil the fraction of b.p. 150-170° and collect the bromobenzene at 154-157° (3). The yield is 60 g. 

To isolate pure p-dibromobenzene, filter the second portion of the steam distillate through a small Buchner funnel with suction press the crystals as dry as possible. Combine these crystals with the residue (R) and recrystaliise from hot ethyl alcohol (for experimental details, see Section IV,12) with the addition of 1-2 g. of decolourising charcoal use about 4 ml. of alcohol (methylated spirit) for each gram of material. Filter the hot solution through a fluted filter paper, cool in ice, and filter the crystals at the pump. The yield of p-dibromobenzene, m.p. 89°, is about 12 g. 

Isolate the pure p-dibromobenzene from the residue in the basin by the procedure described in Method 1. The yield is about 10 g. 

The following give abnormal results when treated with chlorosulphonio acid alone, preferably at 50° for 30-60 minutes —fluobenzene (4 4 -difluorodiplienyl-sulphone, m.p. 98°) j iodobenzene (4 4 -di-iododiphenylsulplione, m.p. 202°) o-diclilorobenzene (3 4 3. -4 -tetrachlorodiphenylsulphone, m.p. 176°) and o-dibromobenzene (3 4 3 4 -tetrabromodiphenylsulphone, m.p. 176-177°). The resulting sulphones may be crystallised from glacial acetic acid, benzene or alcohol, and are satisfactory for identification of the original aryl halide. In some cases sulphones accompany the sulphonyl chloride they are readily separated from the final sulphonamide by their insolubility in cold 6N sodium hydroxide solution the sulphonamides dissolve readily and are reprecipitated by 6iV hydrochloric acid. 

Bromobenzene and p dibromobenzene (IV,18, iV scale when reaction slackens, heat on a water hath at 65-70° for 30 minutes). 

In the reaction of o-dibromobenzene, disubstitution is faster than monosubstitution, and the disubstituted product is obtained as a major product. Similarly, 1,2,4,5-tetrabromobenzene reacts with styrene to give the tetrasub-stituted product[29]. The bridged, annulated [2,2]paracyclophanedieiie 22 was... 

Bromination can be conveniently effected by transfer of bromine from one nucleus to another. As the Friedel-Crafts isomerization of bromoaromatic compounds generally takes place through an intermolecular mechanism, the migrating bromine atom serves as a source of positive bromine, thus effecting ring brominations (161,162). 2,4,6-Tribromophenol, for example, has been prepared by bromination of phenol with dibromobenzene. 

Terephthalic acid has been obtained from a great many /)-disubstituted derivatives of benzene or cyclohexane by oxidation with permanganate, chromic acid, or nitric acid. The following routes appear to have preparative value from />-toluic acid, />-methylacetophenone,2 or dihydro-/)-tolualdehyde by oxidation with permanganate from f>-cymene by oxidation with sodium dichromate and sulfuric acid from />-dibromobenzene or from /i-chloro- or -bromobenzoic acid by heating at 250° with potassium and cuprous cyanides and from />-dibromo-benzene, butyllithium, and carbon dioxide. ... 

DIAZINON AG 600 WBC , diazinon, 50 DIAZOL , diazinon, 50 Diazomethane, 50 Dibenz(a,h)anthracene, 50 Dibenzofuran, 51 DIBK, 51 Diborane, 51 DIBROM , naled, 51 Dibromobenzene, 51 Dibromochloromethane, 51... 

PcH2 was obtained for the first time in 1907 as a byproduct during the preparation of 2-cyanobenzamide.50 However, this discovery initiated no interest at that time. In 1927, PcCu was prepared in 23% yield by heating 1,2-dibromobenzene with copper(I) cyanide in pyridine.51 The term phthalocyanine was first used by Linstead in 1933.52 From 1929 to 1939, Linstead et al. elucidated the structure of phthalocyanines and developed improved synthetic methods for several metal phthalocyanines.52 - 61... 

Phthalocyanines have been synthesized with nearly all metals of the periodic table.77 Normally they are formed in a single-step reaction from available derivatives of phthalic acid, in particular phthalic acid (see Section 2.1.1.1.), phthalic anhydride (see Section 2.1.1.2.), phthalimide (see Section 2.1.1.3.), 2-cyanobenzamide (see Section 2.1.1.4.), phthalonitrile (see Section 2.1.1.5.), isoindolinediimine (see Section 2.1.1.6.), or 1,2-dibromobenzene (see Section 2.1.1.7.), usually in a high-boiling solvent or by heating the neat components.1 4... 

Diamagnetic susceptibility of a spherically symmetrical system, 68 -dibromobenzene p-C6H479Br), ethylene system, 102 quadrupole spectrum, 195 />-dibromophenyl p- (CflH4)279Br2), quadrupole spectrum, 195 radiation resistance of, 200... 

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