Catalytic Dechlorination

Dealkylation, of azolium quaternary salts and betaines, 60, 244 Deazaflavines, bent, 55, 192 5-Deazalumazines, see Pyrido[2,3-(/]pyrimidine-2,4-diones Deaza-purines, -flavines, etc., see the systematically-named ring systems 4-Deazatoxoflavins, syntheses, 55, 182 Dechlorination, catalytic, of chloro-[ 1,2.4]triazolo[ 1,5-a]pyrimidines, 57, 125... 

PCBs can be completely dechlorinated catalytically. Catalysts reported are nickel boride, NaBH4 (Dennis et al. 1979) noble metals (Berg et al. 1972) and LiAlH4 (De Kok et al. 1981). Murena and Schioppa... 

Cyclization of (141) with potassium t-butoxide yielded (142a), which could be dechlorinated catalytically to the parent compound. It has been shown that the true structure of a compound claimed to be (142c) is the... 

The catalytic effect of protons, of bifunctional catalysts, and of base is demonstrated in the amination of chloro derivatives of pyridazine, pyrimidine, and s-triazine (Tables V and VI). Anilino-s-triazines containing NH groups act as catalysts in their own formation. The catalytic action of protons on anhino-dechlorination of 2-chloro-4,6-diamino-s-triazine and of 2-amino-4-chloropyrimidine was reported in the classic paper by Banks. ... 

The production of tetracycline by catalytic dechlorination is described in U.S. Patent 2,699,054 as follows Pure chlortetracycline (4.8 grams) was suspended in 100 ml of methanol and sufficient anhydrous dioxane was added to completely dissolve the product. To the solution was added 0.5 gram of 5% palladium-on-charcoal catalyst. The mixture was placed in a conventional hydrogenation apparatus and subjected to a pressure of 50 psi of hydrogen while being agitated. 

Whether activated or not, halogeno substituents may be removed in favor of hydrogen by chemical reduction or by catalytic hydrogenation (usually in the presence of a base and often accompanied by nuclear reduction). Such dechlorination may also be achieved by loss of hydrogen halide from a nucleus-reduced quinoxaline. The following examples illustrate these procedures. 

Ifi-Ditritiodihenzo- -dioxin, prepared by reductive dechlorination of 1,6-dichlorodihenzo-p-dioxin with tritium gas, is chlorinated in chloroform solution, containing catalytic amounts of iodine and ferric chloride, to produce 1,6-ditritio-2,3,7,8-tefrachlorodibenzo-p-dioxin. 

The catalytic activity of the Ru/Sn02 nanocomposite was eight times higher than that of the most effective Ru metal catalyst reported previously [56]. An o-CAN selectivity over 99.9% at a substrate conversion of 100% was obtained over the Ru/Sn02 catalyst. This selectivity was comparable to the result reported for a boride-modified PVP-Ru colloidal catalyst [56,57], and was better than that of the PVP-Ru catalyst with the same Ru nanoparticles. The Sn02 nanoparticles remarkably promoted both the catalytic activity and selectivity of the Ru nanoclusters. An extremely low dechlorination rate of o-CAN in the absence of o-CNB was observed over this catalyst, which was 20-fold lower than that over the PVP-Ru colloidal catalyst, and was 73-fold lower when compared with a Ru/Si02 nanocomposite catalyst. 

In order to select a suitable catalyst, a variety of Pd/C catalysts were screened. Table 2 shows that the dechlorinated by-product was minimized to the level less than 1% as the catalyst metal loading increased from 3% to 10%. The catalytic activity for the debenzylation reaction was examined and compared based on the rate of hydrogen uptake (Figures 1 and 2). 

The use of electrochemical methods for the destruction of aromatic organo-chlorine wastes has been reviewed [157]. Rusling, Zhang and associates [166, 167] have examined a stable, conductive, bicontinuous surfactant/soil/water microemulsion as a medium for the catalytic reduction of different pollutants. In soils contaminated with Arochlor 1260, 94% dechlorination was achieved by [Zn(pc)] (H2pc=phthalocyanine) as a mediator with a current efficiency of 50% during a 12-h electrolysis. Conductive microemulsions have also been employed for the destruction of aliphatic halides and DDT in the presence of [Co(bpy)3]2+ (bpy=2,2 -bipyridine) [168] or metal phthalocyanine tetrasulfonates [169]. 

Perchlorofulvalene, by catalytic dechlorination of decachlorobi-2,4-cyclopentadienyl, 46, 95 infrared and ultraviolet absorption, 46, 95... 

Chlordane (1 mM) in methyl alcohol (30 mL) underwent dechlorination in the presence nickel boride (generated by the reaction of nickel chloride and sodium borohydride). The catalytic dechlorination of chlordane by this method yielded a pentachloro derivative as the major product having the empirical formula C10H9CI5 (Dennis and Cooper, 1976). 

In activated sludge, 80.6% degraded after a 47-h time period (Pal et al., 1980). Chemical/Physical. Zhang and Rusling (1993) evaluated the bicontinuous microemulsion of surfactant/oil/water as a medium for the dechlorination of polychlorinated biphenyls by electrochemical catalytic reduction. The microemulsion (20 mL) contained didodecyldi-methylammonium bromide, dodecane, and water at 21, 57, and 22 wt %, respectively. The catalyst used was zinc phthalocyanine (2.5 nM). When PCB-1221 (72 mg), the emulsion and catalyst were subjected to a current of mA/cm on 11.2 cm lead electrode for 10 h, a dechlorination yield of 99% was achieved. Reaction products included a monochlorobiphenyl (0.9 mg), biphenyl, and reduced alkylbenzene derivatives. 

Catalytic dehalogenation (mostly by H2/Pd) and desulfurization (by Raney-Ni) are important tools for structural analysis. This way chlorine can be removed from positions 2, 5, and 7 [64CPB204 66JCS(C)2031]. Zinc was used for dechlorination at C-7 (59YZ903). The 5,7-dichloro-TPs (61CPB801) and 6,7-dichloro-TPs (59CPB903) in the presence of H2/Pd first lose the more reactive chlorine from C-7 the remaining 6-chloro compound can be dechlorinated only by Raney-Ni. 

Three syntheses of 1,2-dicyanocyclobutene (2) have been previously described. The first, involving dehydration of cyclobutene-1,2-dicarboxamide does not specify the yield.9 The second procedure involves a concomitant chlorination and catalytic dehydrochlorination of 1,2-dicyanocyclobutane in the gas phase, yielding 1,2-dicyanocyclobutene (2) in a mixture of several other products.10 The third method consists of dechlorination of 1,2-dichloro-1,2-dicyanocyclobutane using metals, such as zinc copper couple,11 Raney nickel,11 and, especially, Raney cobalt.2 In comparison with this last-mentioned synthesis, the overall yield of the present procedure is 5-10% higher. Furthermore, the reaction is performed in less time and utilizes considerably cheaper reagents. 

The unusual formation of N,N-dimethylaminophenyl substituted pyrimido[4,5-c]-pyridazines (74) by the reaction of the oxo compound (73) with phosphorus oxychloride and iV,AT-dimethylaniline has been reported (71CPB1849). The chlorination of other oxo substituted pyrimido[4,5-c]pyridazines with phosphorus oxychloride has been reported to be unsuccessful. Chloro derivatives of this heterocyclic ring undergo nucleophilic displacement with amines and hydrazine to give the corresponding amino and hydrazino substituted products. The catalytic dechlorination of these chloro substituted heterocycles has also been reported (68JHC523). 

Catalytic hydrogenation of the chloro substituted starting material (103) over palladium on carbon gives the dechlorinated and hydrogenated product (109) (68JHC53). 3,4-Dihy-dropyrazino[2,3-d]pyridazines can be dehydrogenated either with 2,3-dichloro-5,6-dicyanoquinone or potassium ferricyanide (75CPB1505). 

The preparation of OPDA from CNA requires two different catalytic steps, i.e. dechlorination and reduction. Both of these reactions requires hydrogen and are catalyzed by Group VIII metals. Supported palladium is considered as one of the most active catalyst both for hydrodehalogenation [2,3] and reduction of the nitro group [2]. 

The catalytic hydro dechlorination of chlorobenzene has also been studied on Pd/Nb205 catalysts. Also in this case, the catalysts prepared under microwave irradiation are more resistant towards deactivation than the corresponding catalysts prepared under thermal conditions75. 

The present procedure is that described by the submitter.2 Perchlorofulvalene has also been obtained in 57% yield by the catalytic dechlorination of decachlorobi-2,4-cyclopentadienyl at... 

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