Halogenation products

Another factor potentially affecting the market for halogenated fire retardants is the waste disposal of plastics (see Wastes, industrial). As landfiU availabihty declines or becomes less popular, two alternatives are incineration and recycling (qv). The nature of the combustion products from halogenated products requires carefiil constmction and maintenance of incinerators (qv) to avoid damage to the incinerator itself and a pubHc health problem from the exhaust. The ease of recycling used products also has a potential effect on fire retardants. 

Methane is also used for the production of several halogenated products, principally the chloromethanes. Due to environmental pressures, this outlet for methane is decreasing rapidly. 

CS esters react with hydrogen haUdes (28,29,31) to yield deoxy halogenated products. 

Furan reacts vigorously with chlorine and bromine at room temperature to give poly-halogenated products. Low temperature (-40 °C) reaction of furan with chlorine in dichloromethane yields mainly 2-chlorofuran and reaction of furan with dioxane dibromide at 0 °C affords 2-bromofuran in good yield. 2-Iodofuran is obtained by treatment of 2-furoic acid with iodine and potassium iodide in aqueous sodium hydroxide. 

A second a-hydrogen may also be replaced by halogen. In some cases it may be difficult to obtain the mo o-halogenated product. a-Fluorinated or a-iodinated carboxylic acids cannot be prepared by this method. 

Hell-VoLhard-Zelinskii (HVZ) reaction, in which an acid is treated with Bc2 and PBr3. The a-halogenated products can then undergo base-induced E2 elimination to yield a,j6-unsaturated carbonyl compounds. 

Dialdehyde (11) is not such an obvious halogenation product, but bromination of p-xylcne can be controlled lo give a reasonable yield of tetrabromidc (13) which is hydrolysed to (11) in acid. 

The formation of halogenation products from Grignard reagents and sulfonic acid anhydrides is the result of an oxidative reaction pathway . This side-reaction can be reduced by using sulfonic acid esters, however, in these cases alkylations as well as twofold sulfonylations (cf. corresponding results with sulfonyl fluorides ) are competing (equations 64 and 65). 

Table 7.4 Typical mass fractions, w, of the halogenated products found in the combustion of organohalogen compounds [42,64]...

Chlorinated micropoUutants are harmful for man and environment due to their toxicity, persistence, and bioaccumulation. Persistent compounds are very stable and difficult to get metabolized and mineralized by biological and chemical processes in the environment, and as a result, they have become ubiquitous in water, sediments, and the atmosphere bioaccumulation is the result of the lipophilicity of these compounds. Polychlorinated dibenzodioxins and -furans (PCDD/F) are not produced purposely like many of other chlorinated technical products, such as chlorinated biocides DDT, lindane, and toxaphene. The production and use of persistent organic pollutants (POPs), the dirty dozen has now been banned worldwide by the Stockholm protocol. It should be mentioned that about 3000 halogenated products have now been isolated as natural products in plants, microorganisms, and animals," but the total amount of these products is much smaller compared to xenobiotics. 

Bean RM, Thomas BL, Neitzel DA. 1985. Analysis of sediment matter for halogenated products from chlorination of power plant cooling water. In Proceedings of the 5th Water Chlorination Conference. Chelsea, Ml Lewis Publishers, Inc., 1357-1370. 

Although the use of N,N-dimethylformamide permits satisfactory chlorination or bromination of primary positions at room temperature, side reactions can occur between carbon tetrahalides, triphenylphosphine, and JV,N-dimethylformamide that can, in some cases, result in low yields of halogenated products (see also, Section II, 2c p. 230). 

Chlorine and bromine react with thiophene to give successively the halogenation products shown (70-73). The bromination can be interrupted at the intermediate stages monochloro and dichloro derivatives have been obtained preparatively by chlorination with MeCONHCl. Addition products are also formed during chlorination prolonged action (with Cl2-I2) gives the dihydrothiophene derivative (74 Z = S). Iodination (I2-HgO) results in mono- and di-iodothiophenes (70) and (71) (X = I) only. Substituted compounds are halogenated as expected, e.g. (75). 

Chlorination of ethylene with CI2 in C2FI4CI2 solution has been studied with and without FeCl3 catalysis at 293-308 K. Simultaneous addition and substitution was detected97. The yields of the styrene low-temperature halogenation products with DMF.CI2 or DMF.Br2 have been found to exceed the yields using free halogen in DMF solution98. 

Propane and cyclopentane give isopropyl chloride and cyclopentyl chloride, respectively, whereas isobutane is transformed to ferf-butyl chloride under the same reaction conditions (yields are 69%, 74%, and 76%, respectively). Neopentane undergoes isomerization to yield 2-chloro-2-butane (88%). When saturated, hydrocarbons were allowed to react with methylene bromide and SbF5 bromoalkanes were obtained in comparable yields (64-75%). Formation of the halogenated product can be best explained by the mechanistic pathway (I) depicted in Scheme 5.55. Since SbF5 always contains some HF, mechanism (II) may also contribute to product formation (Scheme 5.55). 

However, it has been found that a by-product arising from the interaction of formaldehyde and hydrogen chloride is bis(chloromethyl)ether (BCME), which is a potent carcinogen. For this reason the classical chloromethylation route to side-chain halogenated products should not be regarded as a desirable synthetic procedure, and in general should only be used if the required compound cannot be readily prepared by other methods. When used, effective precautions should be taken during the reaction and in the disposal of the reaction residues.12 13... 

Herrmann H, Majdik Z, Ervens B, Weise D (2003) Halogen Production from Aqueous Tropospheric Particles. Chemosphere 52 485... 

Verhagen FJM, Swarts HJ, Kuyper TW, Wijnberg JBPA, Field JA (1996) The Ubiquity of Natural Adsorbable Organic Halogen Production Among Basidiomycetes. Appl Microbiol Biotechnol 45 710... 

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