2- and bromine

Several methods are available for the synthesis of CFsSBr. Either CF2BrSBr is fluorinated at 100°C with antimony trifluoride (186) or CFsSCl is reacted with bromine cyanide over activated carbon at 70°C (86). Apart from that it is obtained always contaminated with CFsSSCFj in the reaction between Hg(SCF8)2 and bromine (31) these compounds react at 0°C to give a mixture composed of 56% CFsSBr and 45% CFjSSCFs. 

A. (o-Bromo-p-chloroacetophenone oxime. A 500-mL, four-necked, round-bottomed flask equipped with a dropping funnel (closed with a giass stopper), mechanicai stirrer, drying tube (calcium chioride, CaCij), and a thermometer is charged with p-chloroacetophenone (38.6 g, 0.25 moi), glacial acetic add (220 mL) and aqueous hydrobromic acid (HBr) [1 mL, 48 % (w/w). Note 1]. The flask is immersed in a water bath (15°C, Note 2) and bromine (40.0 g, 0.25 mol) is added from the dropping funnei at such a... 

In reactions of halogens with substituted rhenium carbonyl halides, the compounds ReX(CO) (diars)2 [X = Br, I diars = l,2-C6H4(AsMe2)2] and bromine or iodine in chloroform give the complexes [ReX2(CO) (diars)2]X3 ... 

Enol 3 reacts with diatomic bromine as a nucleophile to give 6, which loses a proton to give 4. Experiments demonstrate that the key species in this reaction is the enol, and it is reasonable to assume that the reaction of 2 and bromine to give 4, without the acid catalyst, also proceeds by the enol. Without the acid catalysts, only a tiny amormt of enol 3 is available to react with bromine to give 4, but once the enol reacts the acetone will tautomerize to give more 3, which reacts with bromine. In this way, acetone is converted to 4, but it is a slow process. The acid catalyst accelerates this process. 

Though nitrothiophenes are the main substrates for nucleophilic substitution on thiophene, thiophenes substituted by other electron-withdrawing groups can also be substituted by nucleophiles. As an example, the behaviour of thiophenes with a carbonyl group at C-2 and bromine at C-3 and C-5 as leaving groups was investigated (Scheme 121) [177]. 

Compound I is l-metliylq clooctene. One hydrogen atom is bonded at C-2 and none at C-1. Thus, hydrogen adds at C-2 and bromine at C-1. Compound II is methylenecyclooctene. There are two hydrogen atoms at the methylene carbon and none at C-1. Thus, hydrogen adds at the methylene carbon atom and bromine adds at C-1. The product, 1-bromo-l-methylcyclooctane, is the same for both compounds. 

Many of the reactions of halogens can be considered as either oxidation or displacement reactions the redox potentials (Table 11.2) give a clear indication of their relative oxidising power in aqueous solution. Fluorine, chlorine and bromine have the ability to displace hydrogen from hydrocarbons, but in addition each halogen is able to displace other elements which are less electronegative than itself. Thus fluorine can displace all the other halogens from both ionic and covalent compounds, for example... 

The chief reason why ethylenebromonium ion m spite of its strained three membered ring IS more stable than 2 bromoethyl cation is that both carbons and bromine have octets of electrons whereas one carbon has only six electrons m the carbocation... 

Mixtures of 1 2 and 1 4 addition products are obtained when 1 3 butadiene reacts with chlorine or bromine... 

Specifications and Analytical Methods. The commercial aqueous solution is specified as 34% minimum butynediol, as determined by bromination or refractive index. Propargyl alcohol is limited to 0.2% and formaldehyde to 0.7%. 

Chlorine and bromine add vigorously, giving, with proper control, high yields of 1,2-dihaloethyl ethers (224). In the presence of an alcohol, halogens add as hypohaUtes, which give 2-haloacetals (225,226). With methanol and iodine this is used as a method of quantitative analysis, titrating unconsumed iodine with standard thiosulfate solution (227). 

Membranes and Osmosis. Membranes based on PEI can be used for the dehydration of organic solvents such as 2-propanol, methyl ethyl ketone, and toluene (451), and for concentrating seawater (452—454). On exposure to ultrasound waves, aqueous PEI salt solutions and brominated poly(2,6-dimethylphenylene oxide) form stable emulsions from which it is possible to cast membranes in which submicrometer capsules of the salt solution ate embedded (455). The rate of release of the salt solution can be altered by surface—active substances. In membranes, PEI can act as a proton source in the generation of a photocurrent (456). The formation of a PEI coating on ion-exchange membranes modifies the transport properties and results in permanent selectivity of the membrane (457). The electrochemical testing of salts (458) is another possible appHcation of PEI. 

Chlorine and Bromine Oxidizing Compounds. The organo chlorine compounds shown in Table 6 share chemistry with inorganic compounds, such as chlorine/77< 2-3 (9-j5y and sodium hypochlorite/7 )< /-j5 2-5 7. The fundamental action of chlorine compounds involves hydrolysis to hypochlorous acid (see Cm ORiNE oxygen acids and salts). 

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. 

Eastman Chemical Co. uses only cobalt and bromine, and lower temperature oxidations are held at 175—230°C (83). Solution of 4-formylbenzoic acid is obtained by using hydroclones to replace the mother hquor from the first oxidation with fresh acetic acid. A residence time of up to 2 h is used in order to allow for sufficient digestion to take place and to reduce the 4-formylbenzoic acid content to 40—270 ppm (83). Recovery of dry terephthahc acid is as described above. 

Oxidation of saligenin with chromic acid or silver oxide yields saUcyladehyde as the first product. Further oxidation results in the formation of sahcyhc acid, which is also obtained when saligenin is heated with sodium hydroxide at 200—240°C. Chlorination of an aqueous solution of the alcohol gives 2,4,6-trichlorophenol, and bromination in an alkaline medium yields 2,4,6-tribromophenol and tribromosaligenin. When saligenin is heated with one mole of resorcinol in the presence of anhydrous zinc chloride, 3-hydroxyxanthene forms. 

Bromine is moderately soluble in water, 33.6 g/L at 25°C. It gives a crystalline hydrate having a formula of Br2 <7.9H2 O (6). The solubiUties of bromine in water at several temperatures are given in Table 2. Aqueous bromine solubiUty increases in the presence of bromides or chlorides because of complex ion formation. This increase in the presence of bromides is illustrated in Figure 1. Kquilibrium constants for the formation of the tribromide and pentabromide ions at 25°C have been reported (11). 

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