Hydrodechlorination, catalytic

The exact nature of the catalytically active Ni species in these reactions is yet to be conclusively established. Hydrodechlorination proves optimal with a NHC Ni ratio of 2 1 suggesting that 14-electron Ni(NHC)2 is involved, whereas the 1 1 NHC Ni ratio necessary for hydrodefluorination implies that it is the 12-electron mono-carbene adduct Ni(NHC) which is catalytically active [10]. Smdies by Matsubara et al. revealed that treatment of NKacac) with either one or two equivalents of IMes HCl 1 or SlMes HCl 2 in the presence of NaOHu formed the mono-NHC complex Ni(NHC)(acac)j which, upon reduction with NaH in the presence or absence of carbene, formed Ni(NHC)2 [11]. Density functional theory (DFT) calculations suggest that the strength of the Ni-NHC bond (ca. 50 kcal/mol) makes... 

HyChlor Formerly called DHC. A catalytic hydrodechlorination process which converts organic chlorides to hydrogen chloride and saturated hydrocarbons. The UOP HyChlor process recovers and recycles both the organic and inorganic reaction products in order to minimize waste disposal requirements and maximize yield. Used for treating wastes from the production of chlorinated petrochemicals such as vinyl chloride. Developed by UOP but not commercialized as of 1992. 

The reduction of chloro compounds (308), mainly by catalytic means, has been used for the synthesis of a variety of 1,2,4-triazines. For instance, the methoxy- and dimethoxy-triazines (309-311) have been made from the trichloro compound (73) by treatment with methoxide, and hydrodechlorination of the methoxy-halo compounds (66CB1113). 

Similarly, a Pd/Al203 catalyst system for the hydrodechlorination of CCl2F2 to CH2F2 was developed. Microwave irradiation produced the catalyst in a much shorter reaction times, and a twofold increase in catalytic activity was observed76. 

The kinetics associated with catalytic reactions are complex however, some general trends can be determined. Reactions are often first order with respect to the reactant, and the rates of hydrodechlorination are faster than hydrogenation. Polyaromatic compounds react faster than monoaromatic compounds, and chlorinated alkenes react faster than their corresponding alkanes. Finally, the reaction rate often increases with increasing degree of chlorination, though this does not hold true for the chlorinated ethylenes. 

Catalytic Hydrodechlorination ofToxic Organics in Wastewater." AlChE Journal, 38(7), 1003-1012. 

The development of CFC alternatives has focused on non-chlorinated compounds, such as hydrofluorocarbons (HFCs), which have similar physical properties, but break down in the lower atmosphere.110 111 Consequently, hydrodechlorination is a simple method for the production of HFCs and also for destruction of CFCs108,109,112-114. Palladium is unique among the catalytic metals for its activity and selectivity in this process,102-108,115,116 but using Pd-Au/SiC>2 (Pd Au = 60 40) increased the selectivity for difluoromethane from difluorodichloromethane (CFC-12) shown by Pd/Si02 at 453 K from 40 to 95%.109,112-114... 

In situ catalytic hydrodechlorination of chlorinated hydrocarbons in wastewater can be used for detoxification of process wastewater or groundwater contaminated with low-molecular weight chlorinated hydrocarbons such as trichloroethylene and trichloroethane. The advantage of this approach is that it consists of a single-step process which can be carried out under ambient conditions. 

A number of low-grade transition metal ores (for example, minerals containing nickel oxides) can be used as catalysts. Smuda has demonstrated that microwave or radiofrequency irradiation of a mixture of such ores with a carbon source initiates reduction of the oxide to metal. With this approach, poisoning the active sites of the catalyst will not be critical for the process since there will be a constant supply and generation of active catalyst with the feed material. In addition to well-known catalytic properties of nickel in organic reactions, it was also shown that Ni on carbon and other supports, catalyzes hydrodechlorination and dehydrochlorination of chlorinated organic waste streams [22-24],... 

Hydrolytic Reactions. Many pesticides possess bonds that are susceptible to hydrolytic attack. These reactions are most easily characterized according to the type of bond hydrolyzed carboxjlic acid ester, carbamate, oiganophosphate, urea, or chlorine (hydrodechlorination). In many instances the specific hydrolytic enzymes have been purified and characterized and the genes encoding for the enzymes isolated and cloned. It is commonly observed that there are multiple forms of the enzymes catalyzing a particular hydrolytic reaction, which suggests that these catalytic functions have evolved independendy in different bacteria (19). 

Vapor phase catalytic hydrodechlorination of 1,1,1-trichloroethane (TCA) has been studied using various supported platinum catalysts in a plug microflow reactor. The reactor was operated at temperatures ranging from 250 to 350°C, a H2 TCA He ratio of 10 1 89, a space velocity of 24 L/g cat-h, and atmospheric pressure. To study the deactivation process, tests were carried out by dividing the catalyst bed into three segments (inlet, middle, outlet) separated by glass wool plugs. 

Palladium complexes containing basic, bulky phosphines (dippp, dippe, dippb, i-Pr3P) have been demonstrated to efficiently catalyze the hydrodechlorination reaction of chloroarenes with methanol or sodium formate (Eq. 14) [102]. Of the ligands examined, dippp exhibited the highest catalytic activity. 

Remarkable hydrodechlorination activity has been reported over silica supported Ni-Au catalysts [588]. In gas-phase catalytic 2,4-dichlorophenol hydrodechlorination, a co-impregnated, thermally treated Au-Ni/SiOg catalyst was significantly more active than the equivalent Ni catalyst. 

The substitution of chlorine with hydrogen by catalytic hydrodechlorination (HDC) is a well known reaction. Earlier work by Bitner et al. [76] and Gervasutti et al. [77] over Pd/C using CFC-114a showed that the reaction proceeded primarily to HFC-134a although a small amount of HCFC-124 was also obtained (eq 22). 

Hydrodechlorination. exo-2-Phenylthio-endo-3-chloronorbornane (1) was successfully hydrodechlorinated to exo-norbornyl phenyl sulfide (2) when heated for 1 hour at 80° with triphenyltin hydride in the presence of a catalytic amount of azobisisobutyronitrile.3... 

WGSR conditions were found useful for hydrodechlorination of 1,2-dichloroethane [369], The primaiy product of the reaction is ethene (Scheme 3.62) which is reduced further to ethane in a separate catalytic cycle. 

CM King, RB King, NK Bhattacharyya, MG Newton. Organonickel chemistry in the catalytic hydrodechlorination of polychlorobiphenyls (PCBs). J. Organomet. Chem.600 2000,600, 63-70. 

E-J Shin, MA Keane. Gas phase catalytic hydrodechlorination of chlorophenols using a supported nickel catalyst. Appl. Catal. B Environmental 18 241-250, 1998. 

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