Bromine and chlorine compounds

From the point of view of thermal decomposition behaviour, it is convenient to group the organic bromides and chlorides together because of kinetic features which are common to both these sets of compounds. The usual products of pyrolysis of brominated and chlorinated hydrocarbons are hydrogen halide and alkenes, but rearrangement reactions may also occur. Many of these decomposition reac- 

The first significant attempt to study the kinetics of the thermal decomposition of chlorinated and brominated hydrocarbons and related compounds was by Lessig in 1932. These studies were complicated by the catalytic activity of the pyrex or quartz glass walls of the vessels in which the gas phase reactions were carried out. It was later found that the heterogeneous reactions could be suppressed by using seasoned reaction vessels in which a fine coating of carbonised material had formed on the walls from previous decompositions of similar compounds. Substances such as allyl bromide and 3-chloro-2-methyl-propene have been found particularly effective in producing carbonised films. 

Pyrolytic reactions of chlorides and bromides may be grouped into two main classes in terms of kinetic behaviour  

Class 1. Characteristics (i) The decomposition in seasoned vessels exhibits first-order kinetics and there are no apparent induction periods (i7) the rate is unaffected by packing the reaction vessel or by the addition of known radical-chain inhibitors such as propene iii) the Arrhenius pre-exponential factor is of the order of 10 sec L This behaviour is consistent with a unimolecular mechanism for the decomposition. Among reactions in this class are included the dehydrohalogena-tion of monochlorinated saturated hydrocarbons containing /S-hydrogen atoms e.g., chloropropane 2-chloropropane f-butyl chloride) and of most of the secondary and tertiary monobrominated saturated hydrocarbons. 

Class 2. Characteristics (i) the decomposition may deviate from first-order kinetics and/or there are often marked induction periods (i7) the rate is substantially reduced by the addition of propene, cyclohexene, toluene, or other radical-chain inhibitors, and may be affected by packing the reaction vessel Hi) the Arrhenius preexponential factor may differ significantly from 10 sec . This behaviour is consistent with the presence of radical-chains. Reactions in this class 

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The absorption spectra of iodine compounds are generally shifted toward longer wavelengths compared to those of both bromine and chlorine compounds. 

The mass spectra ofbromacil and terbacil and their A-methyl derivatives show only weak molecular ions, but they have the isotope patterns expected from bromine and chlorine compounds, respectively. The major ions arise from [M—55] and [M—56] and also reflect the halogen substituent. Less abundant, but highly characteristic ions, corresponding to [M-99Y and [M-98], are formed by retro Diels-Alder fragmentations. 

Radical-type decompositions of bromine and chlorine compounds... 

Table IV. Retention Times, MID Ions, Parent Ions, and Quantitation Ions of Sulfur, Bromine, and Chlorine Compounds...

It was expected that the rate of polymerization would be small and for this reason some attention was paid to additives which might have the effect of increasing the yield of polymer. Brominated and chlorinated compounds were tried in view of their known influence on the course of other polymerization reactions (17, 20). 

PVC building wire, similar uses as for bromine and chlorine compounds TV cabinetry, power tools, kitchen appliances... 

Ixol Organic bromine and chlorine compounds Kali Chemie AG, Hannover, Germany... 

The flame-retardant properties of bromine and chlorine compounds are well known. Their effectiveness in a given situation appears to depend very much on the right choice of flame-retardant compound. Since these halogens are believed to exert their effect mainly in the form of hydrogen halide molecules, a great deal depends on the ease with which HCl or HBr is produced from the flame-retardant molecule under pyrolysis conditions. 

In comparing the performance of bromine and chlorine compounds, a fundamental feature influencing the comparison is the strength of the respective carbon-halogen bond. In all analogous combinations the chlorine is more firmly bound. 

The most important halogen used is bromine. Some chlorine compounds are also used. The bromine and chlorine compounds used decompose in the temperature range of 150 to 350°C, well above ordinary temperatures, but below 500°C, the lowest decomposition temperature of the carbon-hydrogen bonds. Iodine compounds are not sufficiently stable to be generally useful, and fluorine compounds are too stable. 

S. Echigo, X. Zhang, R.A. Minear, and M.J. Plewa. Differentiation of total brominated and chlorinated compounds in total organic halide measurement a new approach with an ion-chromatographic technique. ACS Sym. Ser., 761 330-342, 2000. 

Easily dehydrohaiogenated or dehydrated compounds, such as hydrated oxides, reduce the formation of flammable products by the endothermic effect that accompanies their transformation. Examples are AI2O3 - 3H2O used for epoxy resins [37] and mainly hydrated aluminum hydroxides [12]. They are cheap in cost but their low efficiency, compared to halides, necessitates that a large quantity (50-80% by weight) be used, and this affects the properties of plastic materials. In spite of this, aluminum hydroxides represent about 50% of all flame retardants used in the United States, the rest being made of Sb203, bromine and chlorine compounds, phosphates, and phosphorus-halide compounds [38]. 

A liquid flame retardant plasticizer containing bromine and chlorine compounds. Improves on low tenqperature brittleness and lower smoke than conventional brominated phthalate diesters used in wire and cable industry applications. 

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