Carboxy late anions

Bunnett and co-workers have shown that an or Ao-carboxy-late anion decreases the rate of reaction of 4-nitrochlorobenzene with methoxide ion but rather strongly increases the reaction rate with piperidine. This effect arises from an accelerative increase in the... 

The insertion of CO into 7r-allylpalladium complexes has been used to prepare various P/y-unsaturated carboxylic acid derivatives. The process can be initiated from preformed allyl complexes,227-235 catalyti-cally from appropriate ir-allyl precursors228,229 236 237 or from diene-Pd complexes.238 239 Particularly mild conditions, involving low pressures and temperatures, to accomplish this insertion have been discovered.235 The key reagent in allowing these mild conditions to be employed was found to be carboxy-late anions.235 For unsymmetrical allyl complexes, CO insertion occurs preferentially at the less-substituted allyl terminus (equations 71-73). 

A similar concept was used in the development of artificial chymotrypsin mimics [54]. The esterase-site was modeled by using the phosphonate template 75 as a stable transition state analogue (Scheme 13.19). The catalytic triad of the active site of chymotrypsin - that is, serine, histidine and aspartic acid (carboxy-late anion) - was mimicked by imidazole, phenolic hydroxy and carboxyl groups, respectively. The catalytically active MIP catalyst 76 was prepared using free radical polymerization, in the presence of the phosphonate template 75, methacrylic acid, ethylene glycol dimethacrylate and AIBN. The template removal conditions had a decisive influence on the efficiency of the polymer-mediated catalysis, and best results were obtained with aqueous Na2CC>3. 

The lower value for kx is attributed to a lower electron density on the betaine carboxy-late anion due to the inductive effect of the ammonium group. 

In this step, carboxylic acid 54 is coupled with secondary alcohol 23 using l-ethyl-3-(3-dimethylaminopropyl)carbodiiniide hydrochloride (EDC) for the activation of the carboxylic acid moiety and 4-di-methylaminopyridine (DMAP) as base. Thus, EDC is protonated by carboxylic acid 54 and is then attacked by the corresponding carboxy-late anion to give intermediate 55. This intermediate is rather like an anhydride with a C=NR group replacing one of the carbonyl groups, and is readily attacked by the alcohol to give the desired ester 56 and stable urea 57. 

We see that the alcohol and alkoxide ion are each represented satisfactorily by a single structure. However, we can draw two reasonable structures (I and II) for the carboxylic acid and two reasonable structures (III and IV) for the carboxy-late anion. Both acid and anion are resonance hybrids. But is resonance equally... 

Section 19.4 Carboxylic acids are weak acids and, in the absence of electron-attracting substiments, have dissociation constants of approximately 10 (pA a = 5). Carboxylic acids are much stronger acids than alcohols because of the electron-withdrawing power of the carbonyl group (inductive effect) and its ability to delocalize negative charge in the carboxy-late anion (resonance effect). 

Kolbe electrolysis /kol-bee/ The electrolysis of sodium salts of carboxylic acids to prepare alkanes. The alkane is produced at the anode after discharge of the carboxy-late anion and decomposition of the radical ... 

There are two fundamental reasons. First, water can hydrogen bond more effectively with the acidic proton in acetic acid, making it easier to remove. Second, water is much better at solvating anions, making it easier to form the carboxy-late anion product. 

The reason for this enhanced acidity of the carboxyl group in an a-amino acid is the inductive effect of the neighboring aminium cation, which helps to stabilize the carboxy-late anion formed when it loses a proton. Loss of a proton from the carboxyl group in a cationic a-amino acid leaves the molecule electrically neutral (in the form of a dipolar ion). This equilibrium is shown in the red-shaded portion of the equation below. 

The Ni + cation shows little discrimination between ligands in propylene carbon-ate. 2 Kinetic parameters have been communicated for reactions of Ni-+ and Co + with ammonia in aqueous methanol and for Ni + with ethylenediamine or 2,2 -bipyridyl in aqueous dimethylformamide, and with 2,2 -bipyridyl derivatives in aqueous ethanol. The kinetics of reaction of Fe + with benzoylacetanilides have also been studied in aqueous ethanol the kinetic pattern for reaction of Fe + with thiocyanate in aqueous carboxylic acids is complicated by parallel complex formation with solvent-derived carboxylate. Copper(ii)-formazan (2) chelate complex formation has been shown to take place in discrete steps in aqueous ethanol. Carboxy-late anion effects on the copper(ii)-tetraphenylporphine reaction have been studied in dimethylformamide. ... 

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