Bromine/ions/salts

The bridging by bromine prevents rotation about the remaining bond and back-side nucleophilic opening of the bromonium ion by bromide ion leads to the observed anti addition. Direct evidence for the existence of bromonium ions has been obtained from NMR measurements.31 A bromonium ion salt (with Br3 as the counterion) has been isolated from the reaction of bromine with the very hindered alkene adamantylide-neadamantane.32... 

Also two salts are known of molecular formula Co(NH3)5Br(S04) one is reddish violet in colour, and a freshly prepared aqueous solution contains sulphate ions the other is red in colour, and a freshly prepared aqueous solution contains bromine ions but no sulphate ions. The former substance is bromo-pentammino-cobaltie sulphate, [Co(NH3)5Br]S04 the latter is sulphato-pentammino-cobaltie bromide, [Co(NH3)5S04]Br.2 It is interesting to note that in the second compound the sulphate radicle occupies one co-ordinate position, but it also requires two principal valencies, and thus the complex ion is monovalent. 

Trimethyl tellurium bromide, (CH3)3TeBr, is obtained from the /3-base and hvdrobromic acid. It forms large, transparent, colourless tablets, slowly decomposing between 250° and 280° C., readily soluble in cold water but almost insoluble in organic solvents. The neutral solution in water contains bromine ions, and gives no precipitate or coloration with colourless hydriodic acid. It unites with ferric chloride. giving a complex which crystallises as salmon-coloured needles and forms a complex salt with stannic bromide. 

Accordingly the reversibility of sulphonation and bromination of aromatic compounds (cf. also the Perrin s order) the quenching 22b) and (22d)-ion salts with methanol or methanol/diethylamine leads to hexamethylbenzene... 

Chemical shifts are therefore usually reported relative to a common reference compound. In NMR studies of chlorine, bromine and iodine compounds chemical shifts are mostly measured relative to the corresponding halide ion in aqueous solution. Since the ion shifts themselves are dependent on the nature of the counter-ion, salt concentration and temperature they are not ideal references. 

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. 

Iron hahdes react with haHde salts to afford anionic haHde complexes. Because kon(III) is a hard acid, the complexes that it forms are most stable with F and decrease ki both coordination number and stabiHty with heavier haHdes. No stable F complexes are known. [FeF (H20)] is the predominant kon fluoride species ki aqueous solution. The [FeF ] ion can be prepared ki fused salts. Whereas six-coordinate [FeCy is known, four-coordinate complexes are favored for chloride. Salts of tetrahedral [FeCfy] can be isolated if large cations such as tetraphenfyarsonium or tetra alkylammonium are used. [FeBrJ is known but is thermally unstable and disproportionates to kon(II) and bromine. Complex anions of kon(II) hahdes are less common. [FeCfy] has been obtained from FeCfy by reaction with alkaH metal chlorides ki the melt or with tetraethyl ammonium chloride ki deoxygenated ethanol. 

The stereochemistry of addition is usually anti for alkyl-substituted alkynes, whereas die addition to aryl-substituted compounds is not stereospecific. This suggests a termo-iecular mechanism in the alkyl case, as opposed to an aryl-stabilized vinyl cation mtermediate in the aryl case. Aryl-substituted alkynes can be shifted toward anti addition by including bromide salts in the reaction medium. Under these conditions, a species preceding the vinyl cation must be intercepted by bromide ion. This species can be presented as a complex of molecular bromine with the alkyne. An overall mechanistic summary is shown in the following scheme. 

The prototype of the antihistamines based on benzhydrol, diphenhydramine (3), is familiar to many today under the trade name Benadryl . Light-induced bromination of diphenylmethane affords benzhydryl bromide (2). This is then allowed to react with dimethylaminoethanol to give the desired ether. Although no mechanistic studies have been reported, it is not unlikely that I he bromine undergoes SNi solvolysis in the reaction medium the carbonitjm ion then simply picks up the alcohol. It might be noted in passing that the theophyline salt of 4 is familiar to many Iravelers as a motion sickness remedy under the trade name Oram amine . 

A synthetically useful reaction has been reported between alkaline bromine water and dimethyl sulphoxide118, the product being the perbromosulphone (equation 36). A kinetic study of the oxidation of dimethyl sulphoxide by bromate ions, catalysed by ruthenium(III) salts, has also been published but no yield data are available119. 

This method is a modification of the method originally published by Kursanov and Vol pin.6 Tropylium salts have also been prepared by bromination-dehydrobromination of tropili-dene,6 and by the hydride-exchange reaction between tropilidene and triphenylmethyl carbonium ion.7... 

Fluorine comes from the minerals fluorspar, CaF, cryolite, Na3AlF6 and the fluorapatites, Ca,F(P04)3. The free element is prepared from HF and KF by electrolysis, but the HF and KF needed for the electrolysis are prepared in the laboratory. Chlorine primarily comes from the mineral rock salt, NaCl. The pure element is obtained by electrolysis of liquid NaCl. Bromine is found in seawater and brine wells as the Br ion it ts also found as a component of saline deposits the pure element is obtained by oxidation of Br (aq) by Cl,(g). Iodine is found in seawater, seaweed, and brine wells as the I" ion the pure element is obtained by oxidation of I (aq) by Cl,(g). 

As was noted by Jones (ref. 12) the success of a metal bromide as a catalyst for alkylaromatic autoxidations depends on the ability of the metal to transfer rapidly and efficiently oxidizing power from various autoxidation intermediates onto bromide ion in a manner which generates Br-. The fact that no free bromine is observable in this system is consistent with rapid reaction of intermediate bromine atoms with the substrate. Inhibition of the reaction by cupric salts can be explained by the rapid removal of Br2 or ArCH2- via one-electron oxidation by Cu (Fig. 10). 

Bromination can exhibit stereo-, regio- and chemo-selectivity when the reaction is carried out in the presence of nucleophiles (solvent or added salt). When the ionic intermediate is a bromonium ion, a stereospecific but non-regioselective reaction is expected. In contrast, for an open bromo-carbocation, the products should be formed regioselectively but not stereo-specifically. These considerations were understood very early since, in fact, Roberts and Kimball (1937) suggested bridged ions as bromination inter-... 

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