Dichloroacetic acid relative acidity

Because the dissociation of a carboxylic acid is an equilibrium process, any factor that stabilizes the carboxylate anion relative to undissociated carboxylic acid will drive the equilibrium toward increased dissociation and result in increased acidity. An electron-withdrawing chlorine atom, for instance, makes chloroacetic acid (Ka = 1.4 x 10-3) approximately 80 times as strong as acetic acid introduction of two chlorines makes dichloroacetic acid 3000 times as strong as acetic acid, and introduction of three chlorines makes trichloroacetic acid more than 12,000 times as strong. 

Fig. 9. Time dependence of the relative viscosity of 1 g/dl of poly(isopropyl isocyanide in dichloroacetic acid at 30° C A original sample, B repeat determination after recycling the...

Hirvonen et al. (1995) evaluated the feasibility of the UV/H202 process for the removal of trichloroethylene (TCE) and erythromycin (perchloroethylene [PCE]) in contaminated groundwater. The formation of chloroacetic acids (CAs) was used as an indication of partial degradation. The dominant byproduct, dichloroacetic acid (DCA), accounted for the major part of the total yield of CAs. The observed concentrations of trichloroacetic acid (TCA) and DCA were relatively low compared with the total amount of TCE and PCE degraded. The effect of initial concentrations of the parent compounds, hydrogen peroxide, and bicarbonate on the yield of by-product was inves-... 

The haloacetic acids (HAA) are comprised of mono-, di- and trichloroacetic acid, mono-, di-, and tribromoacetic acid, and bromo-chloroacetic acid, bromo-dichloroacetic acid, and dibromo-chloroacetic acid. Toxicological studies showed that these compounds have carcinogenic properties and may have adverse reproductive consequences. HAA have no strong chromophore for sensitive UV detection electrochemical detection has been described. Analysis by GC-MS requires derivatization. Due to their relatively low molecular mass, the LC-MS analysis can be hindered by low-mass background interferences. 

Metabolism is saturable and relatively slow with only a small percentage of the administered dose excreted as metabolites, the major one being trichloroacetic acid. Following exposure to PERC, trichloroacetic acid, and trichloroethanol have been found in the urine of humans and animals. Additionally, oxalic acid, dichloroacetic acid, and ethylene glycol have been reported in the urine of exposed animals. Other reported biotransformation products include inorganic chlorine and ra s-l,2-dichloro-ethylene in expired air. 

Figure 10. Degradation of dichloroacetic acid (expressed as the relative change of TOC) with platinized Ti02 in comparison to pure Ti02 as a function of illumination at pH 3. Data from [350], D. Hufschmidt et al., J. Photochem. Photobiol. A Chem. 148, 223 (2002).

The relative strengths of weakly basic solvents are evaluated from the extent of protonation of hexamethylbenzene by trifluoro-methanesulfonic acid (TFMSA) in those solvents or from the effect of added base on the same protonation in solution in trifluoroacetic acid (TFA), the weakest base investigated. The basicity TFA < di-fluoroacetic acid < dichloroacetic acid (DCA) < chloroacetic acid < acetic acid parallels the nucleophilicity. 2-Nitropropane appears to be a significantly stronger base than DC A by the first approach, although in the second type of measurement, the two have essentially equal basicity. The discrepancy is due to an interaction, possible for hydroxylic solvents such as DC A, with the anion of TFMSA. This anion stabilization is a determining factor of carbocationic reactivity in chemical reactions, including solvolysis. A distinction is made between carbocation stability, determined by structure, and persistence (existence at equilibrium, e.g., in superacids), determined by environment, that is, by anion stabilization. 

Bromophenyl)-9-fluorenyl group (BrPhF), a novel group for safety-catch amine protection. BrPhF is relatively acid-stable and can be successfully activated by Pd-catalyzed cross-coupling reaction of the aryl bromide with morpholine, followed by cleavage under mild conditions using dichloroacetic acid and triethylsUane [S. Surprenant, W. D. LubeU, J. Org. Chem. 2006, 71, 84Sj. 

P-IOMBT in dichloroacetic acid was investigated in an alternating electric field. Experimental data show that the molecules of this polymer, just as those of other mesomorphic polymers, are characterized by a relatively high Kerr constant and the corresponding high dipole moment and orientational polar order. 

It is always important to keep in mind the relative aspect of substituent effects. Thus, the effect of the chlorine atoms in the case of dichloroacetic acid is primarily to lower the energy of the dissociated anion. The acid is more highly dissociated than in the unsubstituted case because of this preferential stabilization of the anion. It is the energy difference bet C een the dissociated and undissociated species, not their absolute energies, that determines the extent of ionization. 

Investigation of kinetic particularities of epoxide interaction with caiboxyhc acids [62-64, 78] showed that proton transfer with formation of protonated epoxide takes place only in case of reaction with strong acids such as trifluoroacetic acid. Interaction with relatively weak dichloroacetic acid leads to formation of complex without proton transfer and involvement of the second molecule of acid is required for epoxide ring operung which corresponds to experimentally determined second order of reaction [63]. 

The hydroxyl groups in polyesters are determined hy acetylation with an excess of dichloroacetic anhydride in dichloroacetic acid, and measurement of the amount of acetylation by chlorine determination. Owing to the low concentration of hydroxyl groups (especially in high relative molecular weight materials), determination of the excess is inaccurate, so determination of the amount of reagent incorporate is much more attractive. 

The hydroxyl groups in these products are determined by acetylation with an excess of dichloroacetic anhydride in dichloroacetic acid at 60 C and measurement of the amoimt of acetylation by a chlorine determination either by potentiometric titration with silver ions after combustion or by X-ray fluorescence spectroscopy of a compressed disc of the polymer. The suitability of this method for a number of samples is demonstrated in Table 1.12. The standard deviation of the method for high relative molecular weight polymers is 0.7 mmol kg whereas for the low relative molecular weight materials, it is about 10 mmol kg ... 

Geminal substituted dibromoalkenes can be prepared by the alkylation of dibromomethyllithium with a-chloroalkyl methyl ethers. Deprotonation of the alkylation products results in the elimination of methanol and the formation of the corresponding 1,1-dibromoalkenes. Despite the lower acidity of 1 -bromo-1 -chloroalkyllithiums relative to the dibromo analogs they exhibit similar nucleophilic proper-ties. Alkyl dichloroacetates can also be deprotonated with lithium diethylamide and alkylated with a range of alkyl halides. ... 

---