Reactions of Halogens

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... 

This method is also used with alcohols of the stmcture Cl(CH2) OH (114). HaloaLkyl chlorosulfates are likewise obtained from the reaction of halogenated alkanes with sulfur trioxide or from the chlorination of cycHc sulfites (115,116). Chlorosilanes form chlorosulfate esters when treated with sulfur trioxide or chlorosulfuric acid (117). Another approach to halosulfates is based on the addition of chlorosulfuric or fluorosulfuric acid to alkenes in nonpolar solvents (118). 

The acid-catalyzed additions of bromide and chloride ion to thiiranes occurs readily, with halide preferentially but not exclusively attacking the most substituted carbon atom of the thiirane. The reaction of 1-substituted thiiranes with acetyl chloride shows a slight preference for halide attack at the less substituted carbon atom (80MI50601). For further discussion of electrophilic catalysis of halide ion attack see Section 5.06.3.3.2. The reaction of halogens with thiiranes involves electrophilic attack on sulfur (Section 5.06.3.3.6) followed by nucleophilic attack of halide ion on carbon. 

The reaction of Mc3SiNSO with HgE2 produces the covalent mercury(II) derivative Hg(NSO)2. Carefully controlled reactions of halogens with Mc3SiNSO or Hg(NSO)2 generate A-halosulfinylamines XNSO (X = E, Cl, Br) (Eq. 9.10). ... 

R.C. Paule, Kinetics of Peroxide-Catalyzed Addition Reactions of Halogenated Compounds to Olefins , Florida Univ Contract No nr-1017 (00), ONR (1956) 6) L.P. Kuhn C. Well-... 

Nucleophilic Substitution Hydrolytic Reactions of Halogenated Alkanes and Alkanoates... 

The dangerous reactions of halogenation, which affect either the acetylenic hydrogen atom or the triple bond have just been described. There are also reactions which lead to accidents and affect one of the acetylenic sites. 

Packer, J.E., Willson, R.L., Hahnemann, D. and Asmus, K.-D. (1980). Electron transfer reactions of halogenated aliphatic peroxyl radicals measurements of absolute rate constants by pulse radiolysis. J. Chem. Soc. Perkins Transact. II, 296-299. 

Figure 3.39 Reactions of halogen-bridged 1 1 phosphine complexes.

A number of gaseous oxyhalides of nitrogen are known, including the types XNO (nitrosonium or nitrosyl halides) with X = F, Cl, or Br, and XN02 (nitryl halides) with X = F or Cl. Nitrosonium halides are prepared by the reactions of halogens and NO. 

As a result, the products of reactions of halogens in basic solutions depend on pH, temperature, and the concentrations of the reactants. The acids are unstable compounds that decompose in two ways ... 

Reactions of Halogenation and Nitrosation Nitrones with protons in the a-alkyl group can occur in tautomeric nitrone-hydroxylamine equilibrium (Scheme 2.117) similar to keto-enol and imine-enamine tautomerisms. 

The reactions of halogens and hydrogen halides with alkenes are electrophilic addition reactions. This means that the initial attack on the organic molecule is by an electron-deficient species that accepts a lone pair of electrons to form a covalent bond. This species is called an electrophile. In the case of the reaction with hydrogen bromide, the mechanism for the reaction is as shown. 

Nucleophilic substitutions are in many cases facile processes in heterocyclic chemistry. Also, in the area of the present chapter, many such routine transformations have been carried out. Such transformations are summarized in Table 6, where the structures of the starting compounds, products, the reagents, yields, and references are listed. These include reactions of halogen, methoxy, and methylsulfanyl derivatives with amines or alkoxides. One exceptional case (Table 6, entry 9) should be pointed out this exchange reaction, unlike the others in this table, proceeds via an elimination-addition mechanism. A few related transformations that follow more complicated pathways and therefore could not be classified unambiguously into this table, can be found in Table 7 in Section 11.17.5.6.5. 

Y = OEt) have been detected in the reactions of halogen with a cyclic phosphite 40 the reaction with chlorine gave a resonance at dp +35 and bromine gave a resonance at dp +195 p.p.m. The latter is at higher field than the tribromo-compound (21 X = Y = Br dp +189 p.p.m.) and the chlorodibromo-compound (21 X = Br,... 

Rate Constants for Reactions of Halogenated Carbon-Centered Radicals with Silicon Hydrides... 

Several reactions of halogen-substituted carbon-centered radicals with silanes have been studied, but limited kinetic information is available for reactions of halogen-substituted radicals with tin hydrides. A rate constant for reaction of the perfluorooctyl radical with Bu3SnH was determined by competition against addition of this radical to styrenes, reactions that were calibrated directly by LFP methods.93 At ambient temperature, the n-C8F17 radical reacts with tin hydride two orders of magnitude faster than does an alkyl radical, consistent with the electron-deficient nature of the perflu-oroalkyl radical and the electron-rich character of the tin hydride. Similar behavior was noted previously for reactions of silanes with perhaloalkyl radicals. 

The reductive elimination reactions of halogen from 6-11 illustrate several examples of ligand loss from trigonal bipyramidal species B to generate onium species A. Activation parameters in these processes were of 73 to 100 kJ mol and Eyring activation parameters of 70-97 kJ molfor and —4 to... 

Lai M, Schoneich C, Monig J, et al. 1988. Rate constants for the reaction of halogenated organic radicals. Int J Radiat Biol 54 773-785. 

Baulch, D. L., Duxbury, J., Grant, S. J., and Montague, D. C., Evaluated kinetic data for high temperature reactions Homogeneous gas phase reactions of halogen and cyanide containing species, J. Phys. Chem. Ref. Data 4, 10, Supplement No. 1 (1981). 

The reactions of methyl ether 84a with hydroxylamine give under acid or neutral conditions, predominantly, isomeric isoxazolotropones 90 and 91, respectively, in addition to their oximes (Section IV,A,8,b) and other products (Scheme 22 82JHC525). 3-Acetyltropolones and analogs (e.g., 88, 96) behave similarly (82JHC525 87JHC779). The Schmidt reaction of halogen-substituted 3-acetyltropolones 92 affords oxazolotropones 93 (87JHC779). 

The amount and uniformity of the solid state reaction of halogen with TTF was probed by the electron microprobe technique. In this analytical method, low energy electron irradiation of a sample provides X-ray core level emissions, characteristic of the element and its relative concentration. Our initial analyses indicated a dramatic dependence of the halogen concentration with the energy of the electron beam. To probe this phenomenon further,... 

The reaction of halogenated l,x-naphthyridines with potassium amide in liquid ammonia has been extensively investigated (83AHC(33)95). Both 3- and 4-bromonaphthyridines derived from compounds (l)-(4) react to give mixtures of 3- and 4-amino derivatives. It is assumed... 

Hanson, D. R., and A. R. Ravishankara, Reactions of Halogen Species on Ice Surfaces, in The Tropospheric Chemistiy of Ozone in the Polar Regions (H. Niki and K. H. Becker, Eds.), NATO ASI Series, Vol. 17, Springer-Verlag, Berlin/New York, 1993a. 

Let us now look at some examples to illustrate what we have discussed so far to get a feeling of how structural moieties influence the mechanisms, and to see some rates of nucleophilic substitution reactions of halogenated hydrocarbons in the environment. Table 13.6 summarizes the (neutral) hydrolysis half-lives of various mono-halogenated compounds at 25°C. We can see that, as anticipated, for a given type of compound, the carbon-bromine and carbon-iodine bonds hydrolyze fastest, about 1-2 orders of magnitude faster than the carbon-chlorine bond. Furthermore, we note that for the compounds of interest to us, SN1 or SN2 hydrolysis of carbon-fluorine bonds is likely to be too slow to be of great environmental significance. 

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