Aromatic halogenation

The following reactions will assist the student in the identification of halogenated aromatic hydrocarbons. 

Properties. As prepared, the polymer is not soluble in any known solvents below 200°C and has limited solubiUty in selected aromatics, halogenated aromatics, and heterocycHc Hquids above this temperature. The properties of Ryton staple fibers are in the range of most textile fibers and not in the range of the high tenacity or high modulus fibers such as the aramids. The density of the fiber is 1.37 g/cm which is about the same as polyester. However, its melting temperature of 285°C is intermediate between most common melt spun fibers (230—260°C) and Vectran thermotropic fiber (330°C). PPS fibers have a 7 of 83°C and a crystallinity of about 60%. 

Commercial PCBs Toxic and Biochemical Effects. PCBs and related halogenated aromatic hydrocarbons ehcit a diverse spectmm of toxic and biochemical responses in laboratory animals dependent on a number of factors including age, sex, species, and strain of the test animal and the dosing regimen (single or multiple) (27—32). In Bobwhite and Japanese quad, the LC q dose for several different commercial PCB preparations ranged from 600 to 30,000 ppm in the diet the LC q values for mink that were fed Aroclors 1242 and 1254 were 8.6 and 6.7 ppm in the diet, respectively (8,28,33). The... 

Aromatic, olefin, halogen aromatic, multihalogen paraffin without active H, monohalogen paraffin -1- -1- -1- 0 -1- 0 0 -1- 0 -1- 0 0... 

Toxic chemicals can enter the body in various ways, in particular by swallowing, inhalation and skin absorption. Skin absorption may lead to dermatitis and this can be a most annoying complaint. Whereas some chemicals may have an almost universal effect on human beings, others may attack only a few persons. A person who has worked with a given chemical for some years may suddenly become sensitised to it and from then on be unable to withstand the slightest trace of that material in the atmosphere. He may as a result also be sensitised not only to the specific chemical that caused the initial trouble but to a host of related products. Unfortunately a number of chemicals used in the plastics industry have a tendency to be dermatitic, including certain halogenated aromatic materials, formaldehyde and aliphatic amines. 

Specific identity of a toxic chemical to be a trade secret, the notice to your customer(s) must contain a generic chemical name that Is descriptive of the structure of that toxic chemical. For example, decabromodiphenyl oxide could be described as a halogenated aromatic. 

Of course, with so many different final products mixed together, the problem is to identify them. What structure is linked to what bead Several approaches to this problem have been developed, all of which involve the attachment of encoding labels to each polymer bead to keep track of the chemistry each has undergone. Encoding labels used thus far have included proteins, nucleic acids, halogenated aromatic compounds, and even computer chips. 

Stock and Baker2 5 9 measured the relative rates of chlorination of a number of halogenated aromatics in acetic acid containing 20.8 M H20 and 1.2 M HC1 at 25 °C and the values of the second-order rate coefficients (103Ar2) are as follows p-xylene (11,450), benzene (4.98), fluorobenzene (3.68), chlorobenzene (0.489), bromobenzene (0.362), 2-chlorotoluene (3.43), 3-chlorotoluene (191), 4-chloro-toluene (2.47), 4-fluorotoluene (9.70), 4-bromotoluene (2.47). Increasing the concentration of the aromatic, however, caused, in some cases, a decrease in the rate coefficients thus an increase in the concentration of chlorobenzene from 0.1 M to 0.2 M caused a 20 % decrease in rate coefficient, whereas with 4-chloro-and 4-bromo-toluene, no such change was observed. 

Busch and Weber (ref. 1) first reported the Pd catalyzed coupling of halogenated aromatic compounds. Their reaction conditions and some examples of their work are shown in equations (4) to (7). 

Muller MD, H-R Buser (1986) Halogenated aromatic compounds in automotive emissions from leaded gasoline additives. Environ Sci Technol 20 1151-1157. 

Important investigations have been directed to persistent halogenated aromatic compounds and different mechanisms for their metabolism have been found ... 

Gibson DT, JR Koch, CL Schuld, RE Kallio (1968) Oxidative degradation of aromatic hydrocarbons by microorganisms. II. Metabolism of halogenated aromatic hydrocarbons. Biochemistry 7 3795-3802. 

Peijnenburg WJGM, MJ t Hart, HA den Hollander, D van de Meent, HH Verboom, NL Wolfe (1992) QSARs for predicting reductive transformation constants of halogenated aromatic hydrocarbons in anoxic sediment systems. Environ Toxicol Chem 11 301-314. 

Cain RB, EK Tranter, JA Darrah (1968) The utilization of some halogenated aromatic acids by Nocardia. Oxidation and metabolism. Biochem J 106 211-227. 

DeWeerd KA, DL Bedard (1999) Use of balogenated benzoates and other halogenated aromatic compounds to stimnlate the microbial dechlorination of PCBs. Environ Sci Technol 33 2057-2063. 

Reineke W, H-J Knackmuss (1978) Chemical structure and biodegradability of halogenated aromatic compounds. Substituent effects on 1,2-dioxygenation of benzoic acid. Biochim Biophys Acta 542 412-423. 

Geakauskas, V., Direct liquid-phase fluorination of halogenated aromatic compounds, J. Org. Chem. 34, 10 (1969) 2835-2839. 

Smith, A.G., Francis, J.E., Cabral, J.R.P., Carthew, P., M.M., M. and Stewart, F.P. (1989). Iron-enhancement of the hep-tatic porphyria and cancer induced by environmental poly-halogenated aromatic chemicals. In Free Radicals in the Pathogenesis of Liver Injury (eds. G. Poli, K.H. Cheeseman, M.U. Dianzani and T.F. Slater) pp. 203-216. Peigamon Press, Oxford. 

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