Dechlorination system productivity

The dechlorination of the C-3 and C-5 position of the pyrazinone system was described to be fast under microwave irradiation [29]. Contrary to the reported de-chlorination [26] via palladium-catalyzed reaction with sodium formate 100 °C for 2-4 h and at the C-5 position in 2-3 days, a dramatic rate enhancement was observed under microwave irradiation (Scheme 12). The mono-reduction at C-3 was performed at 190 °C in DMF in merely 5 min, and the reduction of C-5, starting from the mono-reduction product, was performed in n-butanol in 55 min to afford the fois-reduction product in good overall yield. 

Oda et al. reported that under reflux conditions, the zinc-promoted reaction of 2,3-dichloro-l-propene with aldehydes and ketones in a two-phase system of water and toluene containing a small amount of acetic acid gave 2-chloroallylation products (Eq. 8.31).64 No conversion occurred when tin was used as the promoter. The absence of water completely shuts down the reaction. Interestingly, the action of 2,3-dichloropropene plus zinc powder in aqueous ethanol gives the dechlorination product, allene.65... 

TCDD (perz-dechlorination), from one, which does not produce this tetra-CDD isomer (perz-lateral dechlorination). The relative contribution of each pathway (i.e., the ratio of 2,3,7,8- to other tetra-substituted congeners) observed is dependent on the system tested, whereby the presence of phenolic compounds appears to shift the pathway toward peri-dechlorination and enhances the total yield of lesser chlorinated products [433]. 

Lindane, a widespread insecticide constituted of technical mixtures of hexa-chlorocyclohexane (HCH), was dechlorinated using Pd/C, Pt/C, or Raney-Ni. The product using the multiphasic system was benzene, obtained within 1 hour. The base initially promoted HCl ehmination from HCH to yield trichlorobenzene, which then underwent the usual hydrodechlorination reaction. 

Dieldrin—which belongs to the 12 POPs banned by the Stockholm convention and is in the same class of other pesticides named drins, such as aldrin and endrin—possesses six aliphatic chlorine atoms on a polycyclic skeleton. The multiphasic dechlorination, in the presence of A336, isooctane, aqueous KOH, Pd/C, and hydrogen, proceeded with a different selectivity and degree of dechlorination, depending on the choice of catalyst system, and base concentration. It always required the base and was favored by the presence of A336. It produced a mixture of products derived from the subsequent removal of chlorines, up to a small percentage of monochlorinated derivative. ... 

At least three environmental benefits are derived from PCB dechlorination. First the meta- and /wnz-dechlorination observed in most anaerobic systems removes those chlorines that confer upon PCBs the dioxin-like structure and potential toxicity. Second, the products of anaerobic dechlorination are more soluble and have a decreased tendency to bioaccumulate. Third, the lower-chlorinated products... 

A flask with a septum-capped side tube was attached by rubber vacuum tubing via a U-trap to a vacuum line. The flask was charged with 3,4-dichlorodecafluoro-i m/i-tricyclo[4.2.0.02-5]octane (1.74 g, 4.87 mmol), activated Zn dust (1.05 g, 16.1 mmol), and DMSO (30 mL). The mixture was subjected to 2 freeze-pump-thaw cycles, then the flask was attached to a rocking motor and immersed in an ultrasonic bath. The U-trap was cooled in liquid N2. and the pressure in the system was maintained at ca. 20 Torr while the flask was rocked and subjected to sonication. Dechlorination began immediately and was finished in 20-30 min collection of the product in the U-trap was complete after 2.5 h yield 0.79 g (57%). 

The kinetics show two regimes a low-concentration regime that is zero order in [CPOH], and a second regime at higher concentrations where the rate displays saturation-type kinetics reminiscent of Langmuir-type behavior in solid/gas systems. It suggests that the reaction takes place in the solution bulk at low concentrations of chlorophenol, while at the higher concentrations the reaction occurs predominantly at the gas bubble-liquid interface. Chlorophenols are decomposed and dechlorinated almost quantitatively to form hydroxylated aromatic intermediate products subsequently, species with fewer carbon atoms remained undetectable under these conditions. 

During the reductive dechlorination of chloroethylenes such as PCE and TCE, a suite of reduction products have been identified, including trans- and cis- dichloroethylenes, vinyl chloride, methane, ethane, ethylene, acetylene, and small amounts of C3-C6 hydrocarbons (Burris et al., 1995 Orth and Gillham, 1996). Dichloroethylene isomers and vinyl chloride can be further reduced in the ZVI system, forming ethene and ethane (for dichlorothylene) and ethene (for vinyl chloride) as main products (Roberts et al., 19% Alien-King et al., 1997 Deng et al., 1999). Less chlorinated ethylenes are reduced... 

Nucleophilic Attack at Halogen. The reactions occurring in the triphenylphosphine-carbon tetrachloride system continue to attract attention. The salt (67), which is the first isolable product from the reactions of the above system, undergoes ready dechlorination on treatment with trisdimethylaminophosphine (TDAP) to form the ylide (68) and the dichlorophosphorane (69). This reaction offers a convenient route to the ylide (68), and enables the course of other reactions occurring in the triphenyl-... 

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