Aromatic halocarbons

Strobel, K. Grummt, T. (1987) Aliphatic and aromatic halocarbons as potential mutagens in drinking water. Toxicol, environ. Chem., 14, 143-156... 

Direct photoreactions are mediated by halocarbon excited state(s) that react to form products. Dehalogenations can involve either photohydrolysis (i.e., photonucleophilic replacement of halogen by OH) or homolysis of the carbon-halogen bond to form free radicals. Photohydrolysis is the most important dehalogenation pathway for aromatic halocarbons. 

Halocarbons Sorbed on Natural Organic Matter, Photoreactions of aromatic halocarbons that strongly absorb solar radiation can be greatly accelerated in natural water samples or in aqueous solutions of NOM or humic substances (Table II). Although these effects can be due in part to indirect photoreactions or formation of photoreactive complexes, the results in Table II can be most simply explained in terms of increases in direct photoreaction rates of sorbed halocarbon in comparison to halocarbon in aqueous solution. 

These discussions indicate that aquatic photochemical processes play an im portant role as sinks for halogenated pollutants and as a source of certai natural halocarbons, including volatile halocarbons that escape from the se to the atmosphere. Those photoreactions that provide sinks often result i dehalogenation. Direct photoreactions such as photohydrolysis are likely to b the dominant photoreactions of aromatic halocarbons that strongly absorb sc lar radiation. 

CoF is used for the replacement of hydrogen with fluorine in halocarbons (5) for fluorination of xylylalkanes, used in vapor-phase soldering fluxes (6) formation of dibutyl decalins (7) fluorination of alkynes (8) synthesis of unsaturated or partially fluorinated compounds (9—11) and conversion of aromatic compounds to perfluorocycHc compounds (see Fluorine compounds, organic). CoF rarely causes polymerization of hydrocarbons. CoF is also used for the conversion of metal oxides to higher valency metal fluorides, eg, in the assay of uranium ore (12). It is also used in the manufacture of nitrogen fluoride, NF, from ammonia (13). 

Other radical reactions not covered in this chapter are mentioned in the chapters that follow. These include additions to systems other than carbon-carbon double bonds [e.g. additions to aromatic systems (Section 3.4.2.2.1) and strained ring systems (Section 4.4.2)], transfer of heteroatoms [eg. chain transfer to disulfides (Section 6.2.2.2) and halocarbons (Section 6.2.2.4)] or groups of atoms [eg. in RAFT polymerization (Section 9.5.3)], and radical-radical reactions involving heteroatom-centered radicals or metal complexes [e g. in inhibition (Sections 3.5.2 and 5.3), NMP (Section 9.3.6) and ATRP (Section 9.4)]. 

In contrast to the dihalogens, there are only a few spectral studies of complex formation of halocarbon acceptors in solution. Indeed, the appearance of new absorption bands is observed in the tetrabromomethane solutions with diazabicyclooctene [49,50] and with halide anions [5]. The formation of tetrachloromethane complexes with aromatic donors has been suggested without definitive spectral characterization [51,52]. Moreover, recent spectral measurements of the intermolecular interactions of CBr4 or CHBr3 with alkyl-, amino- and methoxy-substituted benzenes and polycyclic aromatic donors reveal the appearance of new absorption bands only in the case of the strongest donors, viz. Act = 380 nm with tetramethyl-p-phenylendiamine (TMPD) and Act = 300 nm with 9,10-dimethoxy-l,4 5,8-... 

Table 2. Bond dissociation energies of alkenes, alkynes, and aromatics Table 3. Bond dissociation energies of C/H/O compounds Table 4. Bond dissociation energies of sulfur-containing compounds Table 5. Bond dissociation energies of nitrogen-containing compounds Table 6. Bond dissociation of halocarbons...

Aromatic compounds undergo carbonisation during sonication [44]. The reaction can occur either at the bubble interface or inside the cavity, according to the hydrophUicity of the substrate. Generally it would appear that apolar, hydrophobic compounds, e. g. benzene and halocarbons are pyrolysed inside the bubble [45,46]. 

Eopez-Avila V, Heath N, Hu A. 1987. Determination of purgeable halocarbons and aromatics by photoionization and Hall electrolytic conductivity detectors connected in series. J Chromatog Sci 25 356-363. 

Bozzelli JW, Kebbekus BB. 1982. A study of some aromatic and halocarbon vapors in the ambient atmosphere ofNew Jersey. J Environ Sci Health A17 693-711. 

The range of organic compounds which have been subject to the Simons process is wide and includes aliphatic and aromatic hydrocarbons, halocarbons, ethers, aliphatic and aromatic amines, heterocyclics, thiols, alkyl sulphonic and carboxylic acids, and their derivatives, among others. 

Three purge and trap methods are used to determine 29 halocarbons (Method 601), seven aromatics (Method 602, including four of the halo-carbons), and acrolein and acrylonitrile (Method 603). The three methods are distinctly different in the sorbent trap materials, GC columns, and... 

Saturated hydrocarbons Olefinic hydrocarbons Aromatic hydrocarbons Halocarbons Mercaptans Sulfides CS2 Ethers Ketones Aldehydes Esters Tertiary amines Nitro compounds (without a-H atoms) Nitriles (without a-atoms)... 

A photoionization detector uses a vacuum ultraviolet source to ionize aromatic and unsaturated compounds, with little response to saturated hydrocarbons or halocarbons. Electrons produced by the ionization are collected and measured. 

In conclusion, despite their protective effect as regards degradation, the use of aromatic diluents has been avoided because of their low flash point. The classical diluents selected for PUREX process operations were hydrocarbons, either pure compounds (i.e., n-dodecane), or mixtures of different products (i.e., hydrogenated polypropylene tetramer, odorless kerosene, etc.) (93). Halocarbon diluents had two major drawbacks linked to their radiolytic behavior sensitization of TBP degradation and the production of extremely corrosive chloride ions (89, 93, 95). 

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