P-Dibromobenzene

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. 

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

From adsorption isotherms and competitive adsorption experiments (ref. 19) the strength of adsorption of the reaction components on zeolite CaY appeared to be HBr > o-dibromo > bromo- > p-dibromobenzene > Br2. 

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

Synonyms AI3-09077 BRN 1904543 4-Bromophenyl bromide p-Bromophenyl bromide 4-Dibromobenzene p-Dibromobenzene EINECS 203-390-2 NSC 33942 UN 2711. 

Dibromobenzene, see 1,4-Dibromobenzene p-Dibromobenzene, see 1,4-Dibromobenzene Dibromochloropropane, see l,2-Dibromo-3-chloropropane... 

Chromatography on silica and alumina is unique among the liquid chromatographic methods in providing maximum selectivity for tfie separation of isomers. It is no problem to separated m- and p-dibromobenzene (a s 1.8 in pentane) (2) or the three nitroanilines (79) on silica or alumina stationary phases with dichloromethane as eluent. 

Dinitro-3,6-dibromobenzene, monoclinic prisms (from CS2 or glac acet ac), mp 159-60° readily sol in hot abs ale insol in w prepd by nitrating p-dibromobenzene with mixed acid, but a p-dibromo-dinitrobenzene isomer... 

D initro-2,3-dibromobenzene, ndls (from CS2, glac acet ac or ale), mp 119-20° obtd with, otber isomers by nitrating p-dibromobenzene with mixed acid (Ref 2)... 

D initro-2,5 -dibromobenzene, pale-yel prisms (from ale or benz + ale), mp 126 27 ° sol in benz. chlf 8c CS2 si sol in eth 8c cold ale insol in w petr eth obtd with other isomers by nitrating p-dibromobenzene (Ref 6)... 

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