The Polyhalogen Compounds

Introduction. Polyhalogen compounds may be divided for the purpose of study into two groups. The first group includes compounds that have two or more halogen atoms on the same carbon atom, as for example, chloroform, CHCU, benzal chloride, CeHsCHCh, and 1,1-dichloroethane, CH3CHCI2. Such compounds on hydrolysis yield carbonyl and carboxyl compounds  

The other group of polyhalogen compounds includes those which contain more than two halogen atoms in the molecule but not more than one halogen on any carbon atom, as, for example, ethylene chloride, CH2CICH2CI, and 1,2,3-tribromopropane, CH2BrCHBrCH2Br. Such compounds on hydrolysis yield polyhydroxy derivatives  

Further action results in the chlorination of the alpha carbon atom, producing trichloroacetaldehyde, or chloral, CI3C—CHO. This compound, having two partially oxidized carbon atoms, on warming undergoes a rupture of the carbon-to-carbon bond  

2 A stock solution of arsenite may be prepared according to directions given in Appendix. 

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Lithium-t-Butanol-Tetrahydrohirane. The insecticides aldrin and isodrin became attractive starting materials for the synthesis of compounds of interesting ring systems with the discovery by Bruck, Thompson, and Winstein of a simple method for effecting their dechlorination, that is, replacement of all the chlorine atoms by hydrogen. The polyhalogen compound is treated with lithium ribbon (3 g. atoms per... 

The [l,2,l]-eliminations as induced by bases or nucleophiles also succeed in the family of the polyhalogen compounds, generally under the influence of organo-lithiums at low temperatures. This suggests initial mctalation. In this way, with a yield of 68-96% the educts 15 react stereoselectively to the (Z)-isomer 16 11 and the alkene 17 opens up an interesting synthesis of the cyclopentyne (18)12), which can be trapped, e.g., to 19 (36%). In the case of several alkenes 20, the reductive [1,2,1]-halogen elimination can be achieved by electrolysis in DMF. Alkynes 21 form in good yields 13). 

A similar synthetic scheme was adopted by Nadel [13] to prepare isothiazolones 34 and 35 from L-cystine derivatives transformed into the corresponding cystine fozs-N-(methylamides) 33a-c (Et0C02Cl, TEA in CH2CI2 then MeNH2/H20, 69- 73%) (Scheme 10). As reported in Table 1, several parameters were evaluated in order to find the best reaction conditions to produce the different isothiazolone derivatives 34 (43-63%) or 35 (52-66%). As by-products, the polyhalogenated compounds 36 and 36 (not separable) were formed in some instances. Finally, the deprotection of the amino group... 

The photolysis of polyhalogenated compounds forms the basis for another monochrome system. Iodoform can undergo photolysis to produce hydrogen iodide, which subsequendy reacts with a di(2-furfuryl) derivative (3) and aromatic amines to produce a colored dye adduct (4) (29). The photolysis scheme and subsequent reactions can be shown by the following ... 

Condensation of vinyl chloride with formaldehyde and HCl (Prins reaction) yields 3,3-dichloro-l-propanol [83682-72-8] and 2,3-dichloro-l-propanol [616-23-9]. The 1,1-addition of chloroform [67-66-3] as well as the addition of other polyhalogen compounds to vinyl chloride are cataly2ed by transition-metal complexes (58). In the presence of iron pentacarbonyl [13463-40-6] both bromoform [75-25-2] CHBr, and iodoform [75-47-8] CHl, add to vinyl chloride (59,60). Other useful products of vinyl chloride addition reactions include 2,2-di luoro-4-chloro-l,3-dioxolane [162970-83-4] (61), 2-chloro-l-propanol [78-89-7] (62), 2-chloropropionaldehyde [683-50-1] (63), 4-nitrophenyl-p,p-dichloroethyl ketone [31689-13-1] (64), and p,p-dichloroethyl phenyl sulfone [3123-10-2] (65). 

The refractory nature of some pollutants, notably, persistent polyhalogenated compounds, has raised problems of bioremediation of contaminated sites (e.g., sediments and dumping sites). There has been interest in the identification, or the production by genetic manipulation, of strains of microorganisms that can metabolically degrade recalcitrant molecules. For example, there are bacterial strains that can reductively dechlorinate PCBs under anaerobic conditions. 

A few examples of dangerous reactions of monohalogen compounds will now be listed ending with the polyhalogens. The table on p.278 provides a general idea. 

One of the first studies to predict log P by using potential energy fields calculated using the GRID and CoMFA approaches was done by Kim [60]. The author investigated H, CH3 and H2O probes, and calculated the best models using the hydro-phobic probe H2O for relatively small series (20 or less compounds each) of furans, carbamates, pyridines and pyrazines. A similar study was performed by Waller [61] who predicted a small series of 24 polyhalogenated compounds. Recently, Caron and Ermondi [62] used a new version of Cruciani s software, VolSurf [63], to predict the octanol-water and alkane-water partition coefficients for 152 compounds with r = 0.77, q = 0.72, SDEP = 0.60 for octanol-water and r = 0.76, q = 0.71, SDEP = 0.85 for alkane-water. 

The reductive removal of halogen can be accomplished with lithium or sodium. Tetrahydrofuran containing /-butanol is a useful reaction medium. Good results have also been achieved with polyhalogenated compounds by using sodium in ethanol. 

The applicability of these methods is restricted to polyhalogenated compounds, since the inductive effect of the halogen atoms is necessary for facilitating formation of the carbanion. 

Atherton, F.R., Openshaw, H.T., and Todd, A.R., Phosphorylation. II. Reaction of dialkyl phosphites with polyhalogen compounds in the presence of bases — method for the phosphorylation of amines, /. Chem. Soc., 660, 1945. 

Nastainczyk W, Ahr H, Ulrich V, et al. 1982a. The mechanism of the reductive dehalogenation of polyhalogenated compounds by microsomal cytochrome P450. 799-808. 

Table 2 Summarized table with the more important compounds included in the surfactants, polyhalogenated compounds, and other industrial residues. Their generic chemical structure and the use or origin are shown. Some reported data regarding their environmental occurrence and the more probably environmental fate are also given... 

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