Halogenated organics

These compounds are obtained by action of halogenated organic derivatives on lead alloys (magnesium or alkaline metal alloys). 

Nucleophilic substitution is one of a variety of mechanisms by which living systems detoxify halogenated organic compounds introduced into the environment Enzymes that catalyze these reactions are known as haloalkane dehalogenases The hydrolysis of 1 2 dichloroethane to 2 chloroethanol for example is a biological nude ophilic substitution catalyzed by a dehalogenase... 

Constituents. Complex halogenated organic compounds have been widely used in commerce in the last fifty years. A few representative examples are shown in Eigure 9 pentachlorophenol has been widely used as a wood preservative, and also for termite control. 

A significant advance in flame retardancy was the introduction of binary systems based on the use of halogenated organics and metal salts (6,7). In particular, a 1942 patent (7) described a finish for utilizing chlorinated paraffins and antimony(III) oxide [1309-64-4]. This type of finish was invaluable in World War II, and saw considerable use on outdoor cotton fabrics in both uniforms and tents. 

Flame retardants designated for nylon include halogenated organic compounds, phosphorous derivatives, and melamine cyanurate (160—163). Generally, flame retardants are difficult to spin in nylon because of the high loading required for effectiveness and their adverse effects on melt viscosity and fiber physical properties. 

Flame Retardants. Flame retardants are added to nylon to eliminate burning drips and to obtain short self-extinguishing times. Halogenated organics, together with catalysts such as antimony trioxide, are commonly used to give free-radical suppression in the vapor phase, thus inhibiting the combustion process. Some common additives are decabromodiphenyl oxide, brominated polystyrene, and chlorinated... 

Strong oxidizers and strong acids are incompatible with nikanolamines. Reactions, generating temperature and/or pressure increases, may occur with halogenated organic compounds. Alkan olamines are corrosive to copper and brass and may react. Contact with aluminum by alkan olamines, particularly when wet or at elevated temperatures (60°C), should be avoided. 

Propylene oxide is a useful chemical intermediate. Additionally, it has found use for etherification of wood (qv) to provide dimensional stabiUty (255,256), for purification of mixtures of organosiUcon compounds (257), for disinfection of cmde oil and petroleum products (258), for steriliza tion of medical equipment and disinfection of foods (259,260), and for stabilization of halogenated organics (261—263). 

Catalytic oxidation should not be used when process stream contains halogenated organics (reaction products are often as objectionable as original impurity). 

Using supercritical water is not without its drawbacks, two of which are the high pressures and temperatures involved. Another difficulty is the extreme corrosive nature of water at supercritical conditions. If halogenated organics are treated, special alloy reactors are requited. 

G. R. Lester, "Catalytic Destmction of Ha2ardous Halogenated Organic Chemicals," presented at the 82nd Annual AWMAMeeting oA Exhibition, Anaheim, Calif., June 25—30, 1992. 

The toxicity of chlorine residuals to aquatic life has been well documented. Studies indicate that at chlorine concentrations in excess of 0.01 mg/1, serious hazard to marine and estuarine life exists. This has led to the dechlorination of wastewaters before they are discharged into surface water bodies. In addition to being toxic to aquatic life, residuals of chlorine can produce halogenated organic compounds that are potentially toxic to man. Trihalomelhanes (chloroform and bromoform), which are carcinogens, are produced by chlorination. 

Kirk, K L, Biochemistry of the Halogens, Vol II Biochemistry of Halogenated Organic Compounds Plenum New York, 1991 Peters, R A, Wakelm, R W, Buffa, P, Thomas, L C Proc Roy Soc (London), B1953,140, 497... 

Alloys containing more than 40% rhodium, while very difficult to fabricate, are almost immune from attack by aqua regia. The Pt— lORh alloy is particularly resistant to attack by free wet chlorine such as that produced by the combustion of halogenated organic vapours. 

G.G. Choudhry, O. Hutzinger, Mechanistic Aspects of Thermal Formation of Halogenated Organic Compounds Including Polychlorinated Dibenzo-p-dioxins, Gordon Breach Publ. New York (1983). 

According to EPA regulations, land disposal of halogenated organic solvents (such as trichloroethylene) is restricted (EPA 1987e). Before land disposal of trichloroethylene or trichloroethylene-containing materials is attempted, proper authorization must be obtained from federal, state, and local authorities. 

Andelman JB. 1985a. Human exposures to volatile halogenated organic chemicals in indoor and outdoor air. Environ Health Perspect 62 313 -318. 

Pfaffenberger CD, Peoples AJ, Enos HF. 1980. Distribution of volatile halogenated organic compounds between rat blood serum and adipose tissue. Int J Environ Anal Chem 8 55-65. 

Mowrer 1,1 Nordin (1987) Characterization of halogenated organic acids in flue gases from municipal waste incinerators. Chemosphere 16 1181-1192. 

Morgan P, RJ Watkinson (1989b) Microbiological methods for the cleanup of soil and ground water contaminated with halogenated organic compounds. FEMS Microbiol Revs 63 277-300. 

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