III Bromide

In the following, it is essential to have the hydrobromic acid hot before commencing the addition of the carbonato bromide. This avoids the formation of any cis product. The use of carbonato chloride in lieu of the bromide leads to a product which consistently contains a 5% chloride impurity.4 This contaminant, trans-[Co(en)2Br Cl] Br, is not removed by recrystallization. 

for trans-[Co(C4H 16N4)Br2]Br C, 11.47 H, 3.85 N, 13.38 Br, 57.24. Found C, 11.50 H, 3.91 N, 13.50 Br, 57.32%. The product is analytically and isomerically pure. A crystalline sample maybe obtained from a hot saturated methanol solution by careful addition of diethyl ether and cooling. 

This method is quicker, but the yield is lower. The sequence and timing of the addition of the reagents are important. 

The cis and trans dibromo complexes resemble the dichloro analogs, the properties of which are recorded in References 1,3, and 9. In solution, cis-[Co(en)2Br2] + is olive green to maroon (the colors appear to be different under 

The cis (ty2 12 minutes, 25°) and trans (fy2 83 minutes) dibromo complexes hydrolyze rapidly in dilute acidic aqueous solution to give a mixture of cis- and t wis-Co(en)2(OH2)Br]2+4,5 These aquation reactions are about 5-10 times faster than those of the corresponding dichloro isomers. 

DIBROMO(TETRABENZO[h,/,/,n][ 1,5,9,13]TETRAAZACYCLOHEXA-DECINE)COBALT(III) BROMIDE 

Inorganic Syntheses, Volume XVIII Edited by Bodie E. Douglas Copyright 1978 by John Wiley Sons, Inc. Macrocyclic Ligands and Their Metal Complexes 

The starting material for the preparation of the bromide salt of di-p.-hydroxo-bis[tetraamminerhodium(III)] diol) is the crude dithionate salt, which is obtained by heating ds-tetraammineaqua(hydroxo)rhodium(III) dithionate at 120°. In order to avoid contamination of the bromide with mono-hydroxo bridged monool) species, it is necessary to keep dissolution times and, where possible, temperature to a minimum. 

Hydrated rhodium(III) chloride (0.038 mole, — lOg) and 1,2-ethanediamine dihydrochloride (10.1 g, 0.076 mole) are dissolved with gentle heating in 60 mL of water in a 2S0-mL round-bottomed flask fitted with a condenser. A copious red-brown precipitate is formed when 38 mL of 2.00 Afi sodium hydroxide solution is added. The mixture is heated to boiling under reflux. After boiling for 1 min, 2.00 M sodium hydroxide (—45 mL) is added in small portions by means of the reflux condenser over a period of 10 min unti the pH of the clear orange-red solution remains at 6.5. The solution is carefully evaporated to dryness on a vacuum rotary evaporator (water-bath temperature —40°). 

2-ethanediamine)(oxalato)fhodium(III) perchlorate is then obtained as follows. 

Crude cis- and trans-dichlorobis(l, 2-ethanediamine)rhodium(III) perchlorate (5.26 g, 0.0134 mole) and disodium oxalate (3.40 g, 0.0254 mole) are boiled together under reflux in 160 mL of water in a 250-mL round-bottomed flask fitted with a condenser until all the solid has dissolved. After a further 2 min or so, the reflux condenser is removed briefly, and a small speck (—1 mg) of sodium tetrahydroborate( 1 -) is introduced into the boiling solution with a glass spatula, whereupon the solution immediately darkens. The addition of sodium tetrahydro-borate(l—) is repeated twice more at 5-min intervals, and the dark, cloudy solution is finally boiled under reflux for an additional 10 min. 

The hot solution is then filtered quickly by suction through a fine-porosity 4-cm sintered glass funnel into a 500-mL suction flask. The flask and funnel are washed twice with 10 mL of boiling water. To the combined filtrate and washings is added a solution of sodium perchlorate monohydrate (10.0 g) in 10 mL of water. The mixture is then kept in a refrigerator for 24 hr. 

Once recrystallized (from H20/methanol), [Co(en)2(C03)] Cl (50.0g) is dissolved in hot water (250 mL, 85 ) and quickly filtered into a solution of sodium bromide (90 g) in water (100 mL, 20°). The mixture is shaken regularly while rapidly cooled in ice to facilitate the separation of fine, deep-pink crystals of [Co(en)2(C03)J Br. After 1 hour at 5°, the product is filtered, washed with methanol (3 X 50 mL) followed by diethyl ether (3 X 50 mL), and dried in air. Yield 52.5 g (90%). 

The preparation is essentially identical to that described for lnCl3 (Sec. A), except that 2 g of bromine liquid and 10 mg of [Et4N] Br are added to the solution phase instead of a stream of chlorine gas and [Et4N]C104. The collection and subsequent treatment of the product are as for InCl3. Yield 1.1 g (79%). Anal. Calcd. for InBr3 In, 32.4 Br, 67.6. Found In, 32.1 Br, 66.9. 

Indium tribromide is a white hygroscopic crystalline solid, mp 436° the vibrational spectrum suggests that each indium is surrounded octahedrally by six bromine atoms.4,s The solubility in organic solvents is similar to that for indium(IIl) chloride (see above). 

TRIS(DIMETHYL SULFOXIDE)INDIUM(III) BROMIDE [TRIBROMO-TRIS(DIMETHYLSULFOXIDE)INDIUM(III)j 

The compound is a white crystalline solid whose thermal, spectroscopic, and solubility properties are similar to those of the chloride analogue.6 

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Iron(III) chloride forms numerous addition compounds, especially with organic molecules which contain donor atoms, for example ethers, alcohols, aldehydes, ketones and amines. Anhydrous iron(III) chloride is soluble in, for example, ether, and can be extracted into this solvent from water the extraction is more effective in presence of chloride ion. Of other iron(III) halides, iron(III) bromide and iron(III) iodide decompose rather readily into the +2 halide and halogen. 

The classification of hydrocarbons as aliphatic or aromatic took place m the 1860s when It was already apparent that there was something special about benzene toluene and their derivatives Their molecular formulas (benzene is CgHg toluene is C7Hj ) indicate that like alkenes and alkynes they are unsaturated and should undergo addition reac tions Under conditions m which bromine for example reacts rapidly with alkenes and alkynes however benzene proved to be inert Benzene does react with Bi2 m the pres ence of iron(III) bromide as a catalyst but even then addition isn t observed Substitu tion occurs instead ... 

The active catalyst is not iron itself but iron(III) bromide formed by reaction of iron and bromine... 

Iron(III) bromide is a weak Lewis acid It combines with bromine to form a Lewis acid Lewis base complex... 

Complexation of bromine with iron(III) bromide makes bromine more elec trophilic and it attacks benzene to give a cyclohexadienyl intermediate as shown m step 1 of the mechanism (Figure 12 6) In step 2 as m nitration and sulfonation loss of a proton from the cyclohexadienyl cation is rapid and gives the product of electrophilic aromatic substitution... 

Only small quantities of iron(III) bromide are required It is a catalyst for the brommation and as Figure 12 6 indicates is regenerated m the course of the reaction We 11 see later m this chapter that some aromatic substrates are much more reactive than benzene and react rapidly with bromine even m the absence of a catalyst... 

Step 1 The bromine-iron(III) bromide complex is the active electrophile that attacks benzene... 

Iron(III) bromide [10031-26-2], FeBr, is obtained by reaction of iron or inon(II) bromide with bromine at 170—200°C. The material is purified by sublimation ia a bromine atmosphere. The stmcture of inoa(III) bromide is analogous to that of inon(III) chloride. FeBr is less stable thermally than FeCl, as would be expected from the observation that Br is a stronger reductant than CF. Dissociation to inon(II) bromide and bromine is complete at ca 200°C. The hygroscopic, dark red, rhombic crystals of inon(III) bromide are readily soluble ia water, alcohol, ether, and acetic acid and are slightly soluble ia Hquid ammonia. Several hydrated species and a large number of adducts are known. Solutions of inon(III) bromide decompose to inon(II) bromide and bromine on boiling. Iron(III) bromide is used as a catalyst for the bromination of aromatic compounds. 

Antimony Tribromide and Triiodide. Antimony(III) bromide [7789-61-9] SbBr, is a colorless, crystalline soHd having a pyramidal dimorphic molecular stmcture and an acicular (a-SbBr ) and a bipyramidal (P-SbBr ) habit. 

Arsenic tribromide (arsenic(III) bromide), AsBr, is similar to the trichloride. The dielectric constant at 35°C is 8.33. The compound is usually made by treating arsenic with a solution of bromine in carbon disulfide. 

Bismuth Tribromide. Bismuth(III) bromide is a hygroscopic, golden-yeUow, crystalline soHd made up of pyramidal molecules. X-ray analysis has shown that the three bromines are 0.263 0.002 nm from the bismuth and the Br—Bi—Br angles are 100 4°. More recent nqr experiments indicate that the bromines are not equivalent (20). The soHd has a density of 5.72 g/mL and that of the Hquid is 4.572 g/mL at 271.5°C. 

Feiri-. ferric, ferri-, iron(III). -acetat, n. ferric acetate, iron(IIl) acetate, -ammonsulfat, n. ammonium ferric sulfate, -bromid, n. ferric bromide, iron(III) bromide, -chlorid, n. ferric chloride, iron(lll) chloride, -chlor-wasserstoff, -chlorwasserstoffsMure, /. fer-richloric acid. -cyan, n. ferricyanogen. -cyaneisen, n. ferrous ferricyanide (Turn-bull s blue), -cyanid, n. ferric cyanide, iron(III) cyanide ferricyanide. 

Phosphor-athcr, m. phosphoric ether (ester of phosphoric acid, specif, ethyl phosphate), -basis, phosphorus base, -bestimmung, /. determination of phosphorus, -blei, n. lead phosphide Min.) pyromorphite. -bombe, f. phosphorus bomb. -brandgranate, /. phosphorus incendiary shell, -brei, m. phosphorus paste, -bromid, n. phosphorus bromide, specif, phosphorus pentabromide, phos-phorus(V) bromide, -bromijr, n. phosphorus tribromide, phosphorus(III) bromide, -bronze, /. phosphor bronze, -calcium, n. calcium phosphide, -chlorid, n. phosphorus chloride, specif, phosphorus pcntachloride, phosphorus(V) chloride, -chloriir, n. phosphorous chloride (phosphorus trichloride, phosphorus(III) chloride), -dampf, tn. phosphorus vapor or fume, -eisen, n. ferrophos-phorus iron phosphide, -eisensinter, m. diadochite. 

Self-Test 16.3B (a) Name the compound [CoBr(NH ),JS04. (b) Write the formula of tetraamminediaquachromium(III) bromide. 

Arenes are unsaturated but, unlike the alkenes, they are not very reactive. Whereas alkenes commonly take part in addition reactions, arenes undergo predominantly substitution reactions, with the TT-bonds of the ring left intact. For example, bromine immediately adds to a double bond of an alkene but reacts with benzene only in the presence of a catalyst—typically, iron(III) bromide—and it does not affect the bonding in the ring. Instead, one of the bromine atoms replaces a hydrogen atom to give bromobenzene, C H Br ... 

The bromination of benzene illustrates the difference between addition to alkenes and substitution of arenes. First, to achieve the bromination of benzene it is necessary to use a catalyst, such as iron(III) bromide. The catalyst acts as a Lewis acid, binding to the bromine molecule (a Lewis base) and ensuring that the outer bromine atom has a pronounced partial positive charge ... 

Scheme 9 Iron(III) bromide-mediated cyclization of aryl glycidyl ethers to 3-chromanols...

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