Trichloroacetate reduction

Salts of trichloroacetic acid are called trichloroacetates. Reduction of trichloroacetic acid results in dichloroacetic acid, a pharmacologically active compound that shows promise for the treatment of cancer. 

Another example is the successive reduction of trichloroacetate to dichloroac-etate, and of dichloroacetate to monochloroacetate... 

Dichloroacetic acid is produced in the laboratory by the reaction of chloral hydrate [302-17-0] with sodium cyanide (31). It has been manufactured by the chlorination of acetic and chloroacetic acids (32), reduction of trichloroacetic acid (33), hydrolysis of pentachloroethane [76-01-7] (34), and hydrolysis of dichloroacetyl chloride. Due to similar boiling points, the separation of dichloroacetic acid from chloroacetic acid is not practical by conventional distillation. However, this separation has been accompHshed by the addition of a eotropeforming hydrocarbons such as bromoben2ene (35) or by distillation of the methyl or ethyl ester. 

Lynestrenol is the des-3-oxo derivative of norethindrone (28). It has been prepared through a similar synthetic pathway as aHylestrenol (37) (52), ie, addition of potassium acetyUde, rather than aHyl magnesium bromide, affords lynestrenol (73). Lynestrenol is also available from norethindrone (28). Reduction of the 3-keto group is accompHshed by treating norethindrone (28) with sodium borohydride in the presence of trifluoro- or trichloroacetic acid... 

Exposure occurs almost exclusively by vapor inhalation, which is followed by rapid absorption into the bloodstream. At concentrations of 150—186 ppm, 51—70% of the trichloroethylene inhaled is absorbed. MetaboHc breakdown occurs by oxidation to chloral hydrate [302-17-OJ, followed by reduction to trichloroethanol [115-20-8] part of which is further oxidized to trichloroacetic acid [76-03-9] (35—37). Absorbed trichloroethylene that is not metabolized is eventually eliminated through the lungs (38). The OSHA permissible exposure limit (PEL) eight-hour TWA concentration has been set at 50 ppm for eight-hour exposure (33). 

The cationic complex [CpFe(CO)2(THF)]BF4 (23) can also catalyze the proton reduction from trichloroacetic acid by formation of Fe-hydride species and may be considered as a bioinspired model of hydrogenases Fe-H Complexes in Catalysis ) [44]. This catalyst shows a low overvoltage (350 mV) for H2 evolution, but it is inactivated by dimerization to [CpFe(CO)2l2-... 

The anaerobic degradation of halogenated alkanoic acids has, however, been much less exhaustively examined. Geobacter (Trichlorobacter) thiogenes was able to transform trichloroacetate to dichloroacetate by coupling the oxidation of acetate to CO2 with the reduction of sulfur to sulfide that carries out the dechlorination (De Wever et al. 2000). 

De Wever H, JR Cole, MR Fettig, DA Hogan, JM Tiedje (2000) Reductive dehalogenation of trichloroacetic acid by Trichlorobacter thiogenes gen. nov., sp. nov. Appl Environ Microbiol 66 2297-2301. 

Exudate collection in trap solutions usually requires subsequent concentration steps (vacuum evaporation, lyophilization) due to the low concentration of exudate compounds. Depending on the composition of the trap solution, the reduction of sample volume can lead to high salt concentrations, which may interfere with subsequent analysis or may even cause irreversible precipitation of certain exudate compounds (e.g., Ca-citrate, Ca-oxalate, proteins). Therefore, if possible, removal of interfering salts by use of ion exchange resins prior to sample concentration is recommended. Alternatively, solid-phase extraction techniques may be employed for enrichment of exudate compounds from the diluted trap solution (11,22). High-molecular-weight compounds may be concentrated by precipitation with organic solvents [methanol, ethanol, acetone 80% (v/v) for polysaccharides and proteins] or acidification [trichloroacetic acid 10% (w/v), per-... 

Ethyl Benzyl Ether [Brpnsted Acid Promoted Reduction of an Aldehyde to an Unsymmetrical Ether].327 To a cooled mixture of benzaldehyde (4.3 g, 41 mmol) and absolute ethanol (3.7 g, 80 mmol) was added trichloroacetic acid (18.2 g, 111 mmol). Et3SiH (6.96 g, 60 mmol) was then added dropwise with stirring while the mixture was maintained at 50-60°. After 4 hours, the reaction mixture was diluted with water, neutralized with aqueous NaHC03 solution, and extracted with Et20. The dried ether extract was distilled and the 170-190° fraction was collected. Distillation from sodium gave ethyl benzyl ether 4.8 g (90%) bp 187-189°. 

Pletcher and associates [155, 159, 160] have studied the electrochemical reduction of alkyl bromides in the presence of a wide variety of macrocyclic Ni(II) complexes. Depending on the substrate, the mediator, and the reaction conditions, mixtures of the dimer and the disproportionation products of the alkyl radical intermediate were formed (cf. Section 18.4.1). The same group [161] reported that traces of metal ions (e.g., Cu2+) in the catholyte improved the current density and selectivity for several cathodic processes, and thus the conversion of trichloroacetic acid to chloroacetic acid. Electrochemical reductive coupling of organic halides was accompanied several times by hydrodehalogena-tion, especially when Ni complexes were used as mediators. In many of the reactions examined, dehalogenation of the substrate predominated over coupling [162-165]. 

Both tetrachloroethene and pentachloroethane undergo subsequent hepatic metabolism. Pentachloroethane is reductively dechlorinated by microsomes to yield trichloroethene. (Reductive dechlorination was favored when there were three chlorines on one carbon and at least one chlorine on the vicinal carbon [Thompson et al. 1984], a characteristic shared by hexachloroethane and pentachloroethane). Trichloroethene and tetrachloroethene were then oxidized by hepatic enzymes to form trichloroethanol and trichloroacetic acid as terminal reaction products. Apparently additional dechlorination reactions can occur since labeled dichloroethanol, dichloroacetic acid, monochloroacetic acid, and oxalic acid have been... 

In aprotic solvents, the carbanions, generated by reduction of carbon tetrachloride or ethyl trichloroacetate at mercury, can be trapped by reaction with an added carbonyl compound [74], This reaction has been developed as a useful step in synthesis. Cathodic reduction of a system containing a catalytic amount of carbon tetrachloride, excess chloroform and an aldehyde leads to an effective ionic chain reaction sustained by trichlormethyl carbanions as indicated in Scheme 4.4. A carbon-felt cathode is used with diraethylformamide as solvent [75]. Aldehydes react with cuiTent efficiency of 700 %, which indicates a short chain reaction. Ketones... 

Thus a detailed study on the effect of ligands that stabilize copper(I) on the rates and mechanisms of reduction of trichloroacetic acid, CI3CCO2 was carried out (149). 

Bevington has continued his studies of the initiation reaction and of the reactivities of monomers towards reference radicals (69—71). A study of the polymerization of substituted styrenes was recorded (72). In methyl methacrylate polymerization by ammonium trichloroacetate in the presence of copper derivatives, the complexities of the initiation and termination reactions were elegantly unravelled by Bamford and Robinson using two differently labelled trichloroacetates (73). Apparently cyclic processes involving alternate oxidation and reduction of copper may arise. 

Molybdenum(VI)-catalysed perborate oxidation of sulfides is first order with respect to the sulfide and Mo(VI) but zero order in perborate. The uncatalysed reaction is first order in each the reductant and oxidant. Trichloroacetic acid enhances the oxidation rate. Oxidation of para-substituted. S -phenylmcrcaploacclic acids yielded a Hammett p of -0.54 at 293 K, indicating an electron-deficient sulfur atom in the transition state. 

The formation of active carbanion species and their addition to electrophiles have also been observed in the cathodic reduction of carbon tetrachloride and trichloroacetic acid ester 34), though yields are not always satisfactory. 

Cathodic reduction of the trichloroacetates 673 affords 3-chloro-coumarins in moderate yield (Equation 272). When salicylaldehyde derivatives 674 are reduced a mixture of 3-chloro-coumarins and ( )-l-chloro-2-(2-chloroprop-l-enyl)benzenes 675 are formed (Equation 273) <2003T9161, 1999JEC201>. 

As a reductive condition, treatment of a,a,a-trichloroacetate (233) with a Cu1+-tris(pyridylmethyl)amine complex generates macrocyclic polyether (234) through initial SET from Cu1+ to trichloride, generation of a,a-dichloroacetate radical, 18-endo-trig ring closure, and abstraction of a chlorine atom from the a,a,a-trichloroacetate (233) by the formed carbon-centered radical as shown in eq. 3.92 [239]. 

A recent study showed that 152 behaves mechanistically different from other catalysts in addition reactions of more activated halides 140, such as trichloroacetate to styrene [222]. After initial reduction to Ru(II), chlorine abstraction from substrates 140 is in contrast to all other ruthenium complexes not the rate limiting step (cf. Fig. 36). ESR spectroscopic investigations support this fact. The subsequent addition to styrene becomes rate limiting, while the final ligand transfer step is fast and concentration-independent. For less activated substrates 140, however, chlorine abstraction becomes rate-determining again. Moreover, the Ru(III) complex itself can enter an, albeit considerably slower Ru(III)-Ru(IV) Kharasch addition cycle, when the reaction was performed in the absence of magnesium. This cycle operates, however, for only the most easily reducible halides, such as trichloroacetate. 

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