Homogeneous catalytic hydrodechlorination of CFC and HCFC compounds

Sisak, Attila; Simon, Ottó Balázs; Nyíri, Károly

doi:10.1016/j.molcata.2003.10.059

Cited by 8 publications

(5 citation statements)

References 33 publications

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“…Lee and colleagues [25,26] achieved efficient and selective hydrodechlorination of CF 3 CCl 3 to CF 3 CHCl 2 , as well as CF 2 ClCFCl 2 to CF 2 ClCHClF and CFCl=CCl 2 , by the use of Group VIII transition metal complexes at 80-150 8C and about 1 MPa H 2 pressure. Recently, Sisak and coworkers [29] have found that [py 3 RhCl 3 ]in the presence of pyridine as a base -and in-situ-generated [(Pi-Pr 3 ) 3 Pd], surpassed Pd/Al 2 O 3 , the most active heterogeneous catalyst tested in the selective conversion of CF 3 CHFCl into CF 3 CH 2 F at 120 8C and 8-10 MPa H 2 pressure. Mingos and Vilar [27,28] synthesized the novel methylidyne cluster compounds [(Pt-Bu 3 ) 4 Pd 4 (l 3 -CY)(l-Cl) 3 ] (4) from [Pd 2 (dba) 3 ] (dba = dibenzylideneacetone) and Pt-Bu 3 in the presence of the halides CYCl 3 (Y = H, F).…”

Section: Molecular Hydrogenmentioning

confidence: 99%

“…A stronger nucleophilic metal as well as a better leaving group X (I > Br > Cl > F) facilitates, whereas steric hindrance in R slows these types of oxidative addition [193,194]. S N 2 [27,29,89,117,180,181] and S N Ar [31, 33, 62-67, 95, 100, 107-109] mechanisms have been suggested frequently for zerovalent d 10 complexes such as [L n M] (M = Ni, Pd, Pt; L = tertiary phosphine; n = 2,3,4). S N 2 [27,29,89,117,180,181] and S N Ar [31, 33, 62-67, 95, 100, 107-109] mechanisms have been suggested frequently for zerovalent d 10 complexes such as [L n M] (M = Ni, Pd, Pt; L = tertiary phosphine; n = 2,3,4).…”

Section: S N 2 and S N Ar Reactionsmentioning

confidence: 99%

“…For example, Pd(0) complexes of basic chelating phosphines react substantially more easily with chlorobenzenes than their nonchelating analogues (see Section 18.2.4) [2,100,196]. S N 2 and S N Ar types of oxidative addition as a step of the catalytic dehalogenation have also been proposed in the literature for low-valent Ti [40,114], Zr(II) [115], Ru(II) [20,74,81,98], Rh(I) [18,29,68,81,91] and Pt(II) [82,83] complexes. S N 2 and S N Ar types of oxidative addition as a step of the catalytic dehalogenation have also been proposed in the literature for low-valent Ti [40,114], Zr(II) [115], Ru(II) [20,74,81,98], Rh(I) [18,29,68,81,91] and Pt(II) [82,83] complexes.…”

Section: S N 2 and S N Ar Reactionsmentioning

confidence: 99%

“…Dihydrogen [13,14,17,20,24,29] and hydrosilane [78,81,82] react mostly by oxidative addition [193,209,210]. Dihydrogen [13,14,17,20,24,29] and hydrosilane [78,81,82] react mostly by oxidative addition [193,209,210].…”

Section: Reaction Steps Involving the Reducing Agentsmentioning

confidence: 99%

“…The heterolytic activation of H 2 has been considered in systems containing basic ligands such as pyridine [18,29,209]. Transmetalation proposed for Bu 3 SnH as a reductant resulted in the transformation of the Pd-Br bond into Pd-H [89].…”

Section: Reaction Steps Involving the Reducing Agentsmentioning

confidence: 99%

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Dehalogenation Reactions

and¹,

Simon²

2006

The Handbook of Homogeneous Hydrogenation

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Reductive dehalogenation -one of the earliest reactions described in the organic chemical literature -has achieved special significance since the 1980s when the harmful properties of numerous halogenated (chiefly chlorinated) hydrocarbons became clear. The identification of methods capable of neutralizing or, at least, diminishing these dangers, remains a major challenge for chemistry. It is reasonable to convert stocks of the prohibited chemicals (e.g., polychlorobiphenyls, PCBs; chlorofluorocarbons, CFCs) to valuable products as far as possible. At the same time, the halogen-containing wastes should be detoxified by degradation. During the past two decades, the mainly heterogeneous (but also homogeneous) catalytic dehalogenation provided a major share towards solving these problems. Within this period, substantial progress was also made in the application of these reactions in organic syntheses.Hydrodehalogenation -that is, hydrogenolysis of the carbon-halogen bondinvolves the displacement of a halogen bound to carbon by a hydrogen atom. This chapter is devoted to dehalogenations mediated by transition-metal complexes (Eq. (1)): ÀC j j ÀX reducing agent L n Mj 3 ÀC j j ÀH Y 1 where X = F, Cl, Br, I, and [L n M] = a transition metal complex. The use of a wide variety of reducing agents (H 2 , hydrides of metals and metalloids, organic reductants, etc.) under the most diverse reaction conditions (e.g., one-or two-phase systems) has been reported. Organic halides have also been reduced by electrochemical and photochemical methods in the presence of compounds of the type [L n M]. Reductive transformations of organic halides not relevant to Eq.(1) (e.g., coupling reactions) and dehalogenation of acyl halides will not be included here. 513The Handbook of Homogeneous Hydrogenation. Edited by J. G. de Vries and C. J. ElsevierThe reactivity of the carbon-halogen bond in Eq. (1) depends on several factors: · the nature of the halogen atom; · the environment of the halogen atom in the molecule; and · the reagents and conditions used in Eq. (1) [1].The order of reactivity of the C-X bond (generally: I > Br > Cl > F) is consistent with its strength. For instance, the experimentally found dissociation energies for phenyl halides (D Ph-X ) are 528, 402, 339, and 272 kJ mol -1 at 298 K for X = F, Cl, Br, and I, respectively [2]. Consequently, catalytic defluorination in the literature is comparatively rare. The different reactivity of the C-X bonds renders possible the selective dehalogenation of compounds containing two dissimilar halides, leaving intact the stronger C-X bond.

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Section: Molecular Hydrogenmentioning

confidence: 99%

Section: S N 2 and S N Ar Reactionsmentioning

confidence: 99%

Section: S N 2 and S N Ar Reactionsmentioning

confidence: 99%

Section: Reaction Steps Involving the Reducing Agentsmentioning

confidence: 99%

Section: Reaction Steps Involving the Reducing Agentsmentioning

confidence: 99%

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Dehalogenation Reactions

and¹,

Simon²

2006

The Handbook of Homogeneous Hydrogenation

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Kinetics Study of the Hydrodechlorination of Chlorobenzene Catalyzed by Immobilized Copper Complexes

et al. 2005

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The hydrodechlorination of chlorobenzene to benzene and biphenyl was studied using poly(4-vinylpyridine)-immobilized Cu catalysts under CO in basic (NaOH, N(C 2 H 5 ) 3 or Na(CH 3 CO 2 )) aqueous 2-ethoxyethanol medium. This Cu system also catalyzed the water gas shift reaction. The catalytic activities for hydrodechlorination of chlorobenzene to benzene were studied as functions of the reaction parameters (nature of the base, reaction time, [Cu], P(CO), T, and S/C). Among the different base studied activity is maximum for NaOH. The rate of benzene formation displays a first-order dependence on [Cu] over the range 1.25-12.50 wt%. This observation was interpreted in terms of the presence of active species having the same nuclearity. The catalytic activity towards benzene formation proved to be first order dependence on P(CO) over the range 5-35 atm. The kinetics behavior with respect to P(CO) leads to the proposal that CO addition to the catalytic species precedes the rate-limiting step. The catalytic activity proved to be non-linear in chlorobenzene/Cu content, over the range 50-400 molar ratio. The results suggest that the rate-limiting step is preceded by reversible oxidative addition of chlorobenzene to Cu immobilized species.

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Homogeneous catalytic hydrogenolysis of chlorodifluoromethane

Simon

Sisak

2008

Applied Catalysis A: General

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Homogeneous catalytic hydrodechlorination of CFC and HCFC compounds

Cited by 8 publications

References 33 publications

Dehalogenation Reactions

Dehalogenation Reactions

Kinetics Study of the Hydrodechlorination of Chlorobenzene Catalyzed by Immobilized Copper Complexes

Homogeneous catalytic hydrogenolysis of chlorodifluoromethane

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