Chloroacetic acid, protonation

The extra electron-withdrawing inductive effect of the electronegative chlorine atom is responsible for the greater acidity of chloroacetic acid by making the hydroxyl proton of chloroacetic acid even more positive than that of acetic acid. 

The second reason is that Satchell [78] has shown that in the protonation of m-xylene by catalysts composed of stannic chloride and acetic acid or the three chloroacetic acids as co-catalysts, the rate of reaction is inversely related to the aqueous acidity of these acids. Satchell rightly points out that, since the polymerisations are complicated reactions the rates of which are also affected by the terminating efficiency of the anion derived from the co-catalyst, no valid conclusions can be drawn from such studies about catalytic efficiency in any fundamental sense. He interprets the order of effectiveness of the cocatalysts in terms of the stability of the complexes which they form with the metal halide. 

Deno el a/.20, on the basis of their equilibrium studies, have concluded that substituents which stabilize carbonium ions also stabilize RC02H2+ relative to RCO,H, and RCO+ relative to RC02H2+. In fact the differences are small for simple aliphatic acids. There is, however, a marked effect in the expected direction for chloroacetic acid, which is half converted to the protonated form only in 100% H>S04, and remains predominantly in this form up to 65% S03 in H2S0420. 

A small part of the primary product rearranges to form diphenylacetic acid. The reaction rate is proportional to the product of concentrations of substrate and H30+, and the solvent isotope effect (kH/kD ) is larger than 1 (Table 19) [220, 221]. General catalysis by chloroacetic acid has been observed [220]. The reaction rate is increased by electron-releasing substituents and decreased by electron-withdrawing substituents at the aromatic ring. The data follow Hammett s rule with a p value of —2.38 [221]. There is no doubt that the reaction takes place with ratedetermining proton transfer in the first step (A-SE2 mechanism). The same conclusion may be drawn on the basis of similar evidence for the acid catalyzed hydrolysis of 2-diazoacenaphthenone [222]. 

Reaction of 3//-imidazo[4,5-y]quinoline-2-thione (404) with chloroacetic acid gives acid 405 which, on treatment with a mixture of acetic anhydride and pyridine, undergoes cyclization to furnish a product confirmed by the appearance of a band at 1735 cm (N—C=0) and molecular ion peak [M] at m/z 241. Thiazolo[2, 3 2,3]imidazo[4,5-y]quinolin-6(7//)-one (406), in preference to the other possible isomer thiazolo[3, 2 l,2]-imidazo[4,5-y]quinolin-8(7//)-one (409), was assigned to the cyclized product on the basis of the comparative studies of proton signals of the cyclized product (406 or 409) with those of 407 or 408 (obtained by the reaction of 404 and 1,2-dibromoethane), as well as with the proton signals of acid 405 [86IJC(B)264] (Scheme 93). 

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. 

Fig. 36. General acid-catalysed aminolysis of isocyanic acid [121] Eigen type curvature consistent with diffusion limiting proton transfer. CA, chloroacetic acid Dabco, l,4-diazabicyclo-(2,2,2)-octane AC, acetic add AN, anilinium ion PM, iV-propargylmorpholinium ion CEM, 2-chloroethylmorpholinium ion, MeM, iV-methylmorpholinium ion EG, ethyl glycinate BOR, boric acid MBA, methyl j8-alaninate ET, ethylammonium ion Q, quinuclidinium ion PIP, piperidinium ion ACET, acetamidinium ion Gu, guanidium ion.

The crystal structure of a-chloroacetic acid has revealed that it exists as a hydrogen-bonded tetramer, which allows for the presence of two non-equivalent chlorine atoms. The equilibrium constants and enthalpy changes for the 1 1 association reaction between chloride ion and a variety of proton donors HR have... 

When you have finished the calculations, display all three maps on the screen at the same time. To compare them, you must adjust them all to the same set of color values. This can be done by observing the maximum and minimum values for each map in the surface display menus. Once you have all six values (save them), determine which two numbers give you the maximum and minimum values. Return to the surface plot menu for each of the molecules and readjust the limits of the color values to the same maximum and minimum values. Now the plots will all be adjusted to identical color scales. What do you observe for the carboxyl protons of acetic acid, chloroacetic acid, and trichloroacetic acid The three minimum values that you saved can be compared to determine the relative electron density at each proton. 

Activation parameters and deuterium isotope effects indicate that there is a difference of mechanism between [Co(acac)3] and the other three complexes. In all cases it is thought that the mechanism involves the generation of a monodentate acac intermediate, but this rate-determining step is thought to be dissociative for cobalt (AH = 36.4 kcal mol" A5 positive) but associative for the other metals (27.4 A// 28.8 kcal mol A5 negative).The exchange of acetylacetone with [Co(acac)3] has also been studied in acetonitrile and in dimethyl sulfoxide and dioxan. In the latter investigation effects of added protons were studied by addition of chloroacetic acid. 

Trialkyl phosphates form volatile 1 1 adducts with acids such as nitric and chloroacetic, from which the esters are recovered by base treatment. I.r. and n.m.r. spectral data suggest that these are hydrogen-bonded complexes. At low temperatures, in FSOaH-SbFj, trialkyl phosphates were shown (by n.m.r.) to give protonated species in which there appears to be considerable pir-d-rr back-donation from oxygen to phosphorus. These species are not stable the tri-n-butyl ester decomposing over the course of two days to MeaC+ and (HOiP. ... 

Similar to the carboxymethylation of tertiary fatty amines to alkyl betaines, the pH value in the carboxymethylation of alkylamidoamines needs to be controlled and kept between 7.5 to 10.5 (9). If the pH of the reaction medium is below approximately 7.5, the carboxymethylation will slow down due to the increasing protonation of the amine, while the undesired hydrolysis of chloroacetate will result in large amounts of glycolic acid. When the pH exceeds approximately 10.5, hydrolysis of the amide group may occur, which leads to undesired high contents of fatty acids and carboxymethylated amine derivatives, and finally to decomposition of the final product. 

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