Compounds of halogens

Of the halogens, only fluorine attacks siUca readily, forming SiF and O2. A number of halogen compounds of the nonmetals and metalloids react more or less readily with siUca, forming volatile siUcon halogen compounds (Table 1). The formation of SiCl by direct chlorination of mixtures of siUca and carbon is of some technical importance. 

Table 1. Relative Rates of Base-Promoted Dehydrohalogenations of Halogenated Compounds...

II. Mass Spectra of Halogenated Compounds (Other Than Fluorinated Compounds)... 

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-... 

The catalyst (spheres or rings with a diameter of 3-10 mm) contains 7-20% silver on high-purity a-AI203 having a surface of only <2 m2/g. Cesium or another alkali or earth alkali salt is added in an amount of 100-500 mg/kg catalyst for upgrading the selectivity. However, small amounts of halogen compounds, e.g., dichloroethane, are added to the ethylene/oxygen mixture to inhibit the total oxidation of the ethylene. 

Attention is drawn to the dechlorination by anaerobic bacteria of both chlorinated ethenes and chlorophenolic compounds that serve as electron acceptors with electron donors including formate, pyruvate, and acetate. This is termed dehalorespiration and is important in the degradation of a range of halogenated compounds under anaerobic conditions, and is discussed further in Chapter 3, Part 2 and Chapter 7, Part 3. 

A strain of Rhodococcus opacus isolated by enrichment with chlorobenzene was able to grow at the expense of a wide range of halogenated compounds. These included 1,3- and 1,4-dichlorobenzene, 1,3- and 1,4-dibromobenzene, 2-, 3-, and 4-fluorophenol, 2-, 3-, and 4-chlorophenol, 4-nitrophenol, 3- and 4-fluorobenzoate, and 3-chlorobenzoate (Zaitsev et al. 1995). 

Van der Meer JR, TNP Bosma, WP de Bruin, H Harms, C Holliger, HHM Rijnaarts, ME Tros, G Schraa, AJB Zehnder (1992) Versatility of soil column experiments to study biodegradation of halogenated compounds under environmental conditions. Biodegradation 3 265-284. 

Thome, already quoted (note p.63), tried to estimate the possibilities of theoreticai forecasts of flashpoints by using hydrocarbon mixtures in a study that was carried out in order to modei fuel flashpoints and to study the effect of halogenous compounds on these hydrocarbons. 

Promoters may influence selectivity by poisoning undesired reactions or by increasing the rates of desired intermediate reactions so as to increase the yield of the desired product. If they act in the first sense, they are sometimes referred to as inhibitors. An example of this type of action involves the addition of halogen compounds to the catalyst used for oxidizing ethylene to ethylene oxide (silver supported on alumina). The halogens prevent complete oxidation of the ethylene to carbon dioxide and water, thus permitting the use of this catalyst for industrial purposes. 

BFRs are one of the last classes of halogenated compounds that are still being produced worldwide and used in high quantities in many applications. In order to meet fire safety regulations, flame retardants (FRs) are applied to combustible materials such as polymers, plastics, wood, paper, and textiles. Approximately 25% of all FRs contain bromine as the active ingredient. More than 80 different aliphatic, cyclo-aliphatic, aromatic, and polymeric compounds are used as BFRs. BFRs, such as polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), and tetrabromobisphenol A (TBBPA), have been used in different consumer products in large quantities, and consequently they were detected in the environment, biota, and even in human samples [26, 27]. 

Complex (16), which has a similar structure to Co11 salen, catalyzes the electrocarboxylation of arylmethyl chlorides.274 The enhancement of the catalytic life of (16) as compared to Co-salen may be due to the absence of imino bond in its ligand. The catalytic reduction of halogenated compounds has also been attempted at poly[Mn(salen)]-coated electrodes (M = Ni,253 Co275), which might have potential use for determination of organohalide pollutants.275... 

Schmal D, van Erkel J, van Duin PJ (1986) Electrochemical reduction of halogenated compounds in process wastewaters, Inst Chem Eng Symp Ser 1986,98 (Electrochem Eng) 281 Chem Abstr 105 158252e... 

Pigment Yellow 138,56300, has the chemical structure 138 with X = C1 [4], The synthesis of halogenated compounds (138), for instance P.Y.138, can also be achieved by stepwise heating of tetrachloro phthalic anhydride and 8-amino-chinaldine in molten benzoic acid from 125 to 140 and then to 160°C [5],... 

Transport Rates. The amount of halogenated compounds in the hexane layer increased linearly with time for up to 12 h for all compounds transported. For many compounds the relationship remained linear for at least 24 h and then it started to level off. This increase, expressed as a transport rate in ug/h was a linear function of the amount added to the flask (Table I). 

Two types of electrogenerated carbon bases have commonly been used (1) dianions derived from activated alkenes, and (2) carbanions formed by reductive cleavage of halogen compounds or by direct reduction of weak carbon acids. In both cases, the efficiency of the proton transfer reaction relies on a thermodynamically favored proton transfer or a fast follow-up reaction of the deproto-nated substrate. 

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