Carboxylic acids reaction mechanisms

Nucleophilic substitution at RSO2X is similar to attack at RCOX. Many of the reactions are essentially the same, though sulfonyl halides are less reactive than halides of carboxylic acids. The mechanisms are not identical, because a tetrahedral intermediate in this case (148) would have five groups on the central atom. Though this is possible (since sulfur can accommodate up to 12 electrons in its valence shell) it seems more likely that these mechanisms more closely resemble the Sn2 mechanism, with a trigonal bipyramidal transition state (148). There are two major experimental results leading to this conclusion. 

This process provides an option to avoid the expense and handling of toxic alkyl halides in the course of conducting Rh based carbonylations to carboxylic acids. The mechanism is still not completely clear and future work will be dedicated to clarifying the key chemical pathways that permitted us to omit the alkyl halides which were previously regarded as indispensable to the reaction. 

Reactivity of Functional Groups. The reactivity of the functional groups of liquid prepolymers significantly affects the processing, cure behavior, and the ultimate mechanical properties of the cured binder and propellant. The reactivity of carboxyl groups of CTPB can be determined by the rate of reaction with n-butyl alcohol. The rate of esterification is measured from the rate of water evolution from the alcohol—carboxylic acid reaction, and a plot of water evolved vs. time then permits the calculation of the corresponding rate constants. 

Reductive deamination 10, 37, 39). This is accompanied by the formation of ammonia and a carboxylic acid. The mechanism proposed by Weeks and Garrison 39) for this reaction involves an initial removal of the amino group by H- ... 

Elimination of carbon dioxide and abstraction of a fluoride ion result in the formation of a terminal C = C bond. The new alkene has one carbon atom fewer than the original carboxylic acid. The mechanism of the reaction is ionic. 

Copolymer Formation by Amine + Anhydride or Amine + Carboxylic Acid Reaction Coran and Patel [1983] have shown that the mechanical properties of dynamically vulcanized... 

Toluene is oxidized in liquid phase to benzoic acid, which is subsequently hydrogenated to cyclohexane carboxylic acid. Reaction of this acid with nitrosylsulfuric acid in oleum then results directly in the formation of caprolactam sulfate by a mechanism that entails simultaneous nitrosation, decarboxylation, and rearrangement of the formed oxime. 

This section discussed the acid and base hydrolysis of the derivatives of carboxylic acids. The mechanisms for all of these reactions are essentially identical, with the only real mechanistic difference being the leaving group. There is an order of reactivity for acid derivatives ... 

Reaction with Diazomethane (Section 17.7B) Diazomethane is used to form methyl esters from carboxylic acids. The mechanism involves protonation of the diazomethane carbon atom by the carboxylic acid to make a methyldiazonium cation, followed by attack of the resulting carboxylate on the methyldiazonium cation to give the methyl ester and Nj. 

The reactivity of [Ir(GO)2l3Me] with other species has also been investigated, in particular, reactions leading to methane, a known byproduct of iridium-catalyzed carbonylation. Methane formation occurs on reaction of [Ir(GO)2l3Me] either with carboxylic acids or with H2 at elevated temperature. In both cases, the reaction is inhibited by the presence of GO, suggesting that GO dissociation from the reactant complex is required. For the protonolysis reaction with carboxylic acids, a mechanism was proposed (Scheme 8(a)) in which the acid coordinates to a vacant site created by GO loss, and methane is then liberated via a cyclic transition state. The hydrogenolysis reaction, which leads cleanly to [Ir(GO)2l3H] , could proceed via oxidative addition of H2 or an rf-Hz complex as shown in Scheme 8(b). 

Amide Formation. Since the initial reports, " DCC has become the most common reagent in peptide synthesis " and in other amide bond-forming reactions of primary and secondary amines with carboxylic acids. The mechanism is considered to be well understood. - ... 

This is an example of the Doebner synthesis of quinoline-4-carboxylic acids (cinchoninic acids) the reaction consists in the condensation of an aromatic amine with pyruvic acid and an aldehj de. The mechanism is probably similar to that given for the Doebner-Miller sj nthesis of quinaldiiie (Section V,2), involving the intermediate formation of a dihydroquinoline derivative, which is subsequently dehydrogenated by the Schiff s base derived from the aromatic amine and aldehyde. 

Solvent Effects on the Rate of Substitution by the S 2 Mechanism Polar solvents are required m typical bimolecular substitutions because ionic substances such as the sodium and potassium salts cited earlier m Table 8 1 are not sufficiently soluble m nonpolar solvents to give a high enough concentration of the nucleophile to allow the reaction to occur at a rapid rate Other than the requirement that the solvent be polar enough to dis solve ionic compounds however the effect of solvent polarity on the rate of 8 2 reactions IS small What is most important is whether or not the polar solvent is protic or aprotic Water (HOH) alcohols (ROH) and carboxylic acids (RCO2H) are classified as polar protic solvents they all have OH groups that allow them to form hydrogen bonds... 

The most apparent chemical property of carboxylic acids their acidity has already been examined m earlier sections of this chapter Three reactions of carboxylic acids—con version to acyl chlorides reduction and esterification—have been encountered m pre vious chapters and are reviewed m Table 19 5 Acid catalyzed esterification of carboxylic acids IS one of the fundamental reactions of organic chemistry and this portion of the chapter begins with an examination of the mechanism by which it occurs Later m Sec tions 19 16 and 19 17 two new reactions of carboxylic acids that are of synthetic value will be described... 

All these facts—the observation of second order kinetics nucleophilic attack at the carbonyl group and the involvement of a tetrahedral intermediate—are accommodated by the reaction mechanism shown m Figure 20 5 Like the acid catalyzed mechanism it has two distinct stages namely formation of the tetrahedral intermediate and its subsequent dissociation All the steps are reversible except the last one The equilibrium constant for proton abstraction from the carboxylic acid by hydroxide is so large that step 4 is for all intents and purposes irreversible and this makes the overall reaction irreversible... 

Alkyl radicals produced by oxidative decarboxylation of carboxylic acids are nucleophilic and attack protonated azoles at the most electron-deficient sites. Thus imidazole and 1-alkylimidazoles are alkylated exclusively at the 2-position (80AHC(27)241). Similarly, thiazoles are attacked in acidic media by methyl and propyl radicals to give 2-substituted derivatives in moderate yields, with smaller amounts of 5-substitution. These reactions have been reviewed (74AHC(i6)123) the mechanism involves an intermediate cr-complex. 

A number of studies of the acid-catalyzed mechanism of enolization have been done. The case of cyclohexanone is illustrative. The reaction is catalyzed by various carboxylic acids and substituted ammonium ions. The effectiveness of these proton donors as catalysts correlates with their pK values. When plotted according to the Bronsted catalysis law (Section 4.8), the value of the slope a is 0.74. When deuterium or tritium is introduced in the a position, there is a marked decrease in the rate of acid-catalyzed enolization h/ d 5. This kinetic isotope effect indicates that the C—H bond cleavage is part of the rate-determining step. The generally accepted mechanism for acid-catalyzed enolization pictures the rate-determining step as deprotonation of the protonated ketone ... 

Avery direct synthesis of certain lactones can be achieved by heating an alkene, a carboxylic acid, and the Mn(III) salt of the acid. Suggest a mechanism by which this reaction might proceed. 

Many carboxylic acids are converted into fluorescent derivatives by oxidation and UV irradiation. The reaction mechanism has not been elucidated. 

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