Enolization of acetic acid

Hydroxyl Loss from the Ionized Enol of Acetic Acid... 

This indicates enolization of acetyl bromide is more favorable than enolization of acetic acid. Why The difference in S.E. for acetyl bromide is only 3 kcal, whereas for acetic acid it is 18 - 6 = 12 kcal. Overall, then, the enolization of acetic bromide is favored by 12 - 3 =... 

SO that was the required nucleophile (the enolate of acetic acid synthon is derived from diethyl malonate). The benzylic carbon must have been the electrophile this can be achieved as an alkyl halide (benzyl bromide). An FGl of the alkyl halide concludes the retrosynthesis by working back to the given starting material (toluene). 

Thus, the malonic ester synthesis provides us with a synthetic equivalent of an ester enolate of acetic acid or acetic acid dianion. 

Malonic acid decarboxylates by way of a similar transition state to give an enol of acetic acid that tautomerizes to acetic acid. 

The transition state involves the carbonyl oxygen of one carboxyl group—the one that stays behind—acting as a proton acceptor toward the hydroxyl group of the carboxyl that IS lost Carbon-carbon bond cleavage leads to the enol form of acetic acid along with a molecule of carbon dioxide... 

The initial addition products to alkynes are not always stable. Addition of acetic acid, for example, results in the formation of enol acetates, which are converted to the corresponding ketone under the reaction conditions.151... 

Another example of the formation of an octalin is the conversion of the cyclohexenone 127 into the enol acetate 128 by the action of acetic anhydride and perchloric acid in the presence of acetic acid (equation 65)75. The acid-induced ring-closure of the cyclopentane derivative 129 gives a 85% yield of a mixture of the octahydroazulenes 130 and 131... 

Kinetic studies of the ring opening of (71JA2733) and the cyclization to (74CR(C)(279)697) 2,4,6-triphenylpyrylium salts have been carried out. A bifunctional catalytic action of acetic acid on both the enolization and ring closure of the hemiacetal has been postulated in the latter study. 

An unsuccessful attempt has been made to determine the separate electronic and steric effects of alkyl groups on the acidities of hydrocarbons, acetophenone derivatives, and acetone derivatives CH3COCHR1R2 (at either site) by multivariational analyses of experimental and theoretical acidities for each set.15 A thermodynamic cycle has been used to estimate the aqueous phase p/C, = 22.7 1.0 for the methyl group of acetic acid and p/C, = 3.3 1.0 for the corresponding enol.16 Equilibrium acidities have been determined for several nitroaryl substituted nitroalkanes and cyanomethanes, 2,4,6-TNT, and 9-cyanofluorene17 in acetonitrile the influence of common cation BH+ on the electronic spectra of the anions obtained in the presence of strong guanidine bases (B) has been attributed to formation of two types of ion pair.18... 

The enolization constants of carboxylic acids to form enediols are generally still lower than those of ketones. The pAE of acetic acid is about 20.35 Due to the relatively high acidity of 1,1-enediols, the enol content of carboxylate anions is somewhat higher. When the carboxylate is attached to cyclopenta-dienyl, a strong mesomeric electron acceptor, the conjugate acid of the enol, fulvene-l,l-diol, becomes a strong acid, pAa = 1.3, and the pAE of the enol anion is reduced to 5.0 (Almstead JIK and Wirz J, Unpublished data).36,37... 

In the second step the TMS enol ether collapses in a 3 1 1 mixture of acetic acid,water and THF to the corresponding ketone. Also the TBS protecting group is removed leading in 72 % yield (from 11) to the primary alcohol.15... 

Stacey and Turton61 objected to Isbell s mechanism on two counts first, that he did not specify that a proton acceptor must be used to promote the reaction and second, that the orthoacetate intermediate would not be applicable in the conversion which they demonstrated (by absorption spectra data) to take place on treatment with dilute, aqueous sodium hydroxide. (The presence of the proton acceptor seems implicit in Isbell s general description of the process of enolization.) The mechanism of Stacey and Turton is shown in Formulas XXIV to XXVIII it calls for the donation of electrons by pyridine to the incipient, ionic proton at C2 and elimination of acetic acid between C2 and C3 with the formation of the partially acetylated enediol-pyridinium complex. The pyridinium ion is removed by acetic acid. Electronic readjustment results in the elimination of acetic acid from positions 4 and 5. The final step, conversion of XXVII to XXVIII, was not explained. Stacey and Turton considered that with sodium hydroxide the reaction proceeds after deacetylation by a similar mechanism except that hydroxyl groups take the place of acetyl groups. Neither mechanism requires a free hydroxyl group at Cl, a condition considered by Maurer to be essential to kojic acid formation. 

The industrial synthesis of vinyl acetate [14] via palladium-catalyzed oxidative coupling of acetic acid and ethene using direct 02 reoxidation has already been mentioned (Scheme 3, d). Some NaOAc is required in the reaction medium, and catalysis by Pd clusters, as alternative to Pd(II) salts, was proposed to proceed with altered reaction characteristics [14]. Similarly, the alkenyl ester 37 (Table 5) containing an isolated vinyl group yields the expected enol acetate 38 [55] whereas allylphenol 39 cyclizes to benzofuran 40 with double bond isomerization [56]. 

Any carboxylic acid with a carbonyl group in the jS position is prone to decarboxylate. At the temperature of the hydrolysis, the alkylmalonic acid loses CO2 to give a substituted derivative of acetic acid. Decarboxylation takes place through a cyclic transition state, initially giving an enol that quickly tautomerizes to the product, a substituted acetic acid. 

The alkylmalonic ester has a second acidic proton that can be removed by a base. Removing this proton and alkylating the enolate with another alkyl halide gives a dialkylated malonic ester. Hydrolysis and decarboxylation lead to a disubstituted derivative of acetic acid. 

Edwards, C.G., Reynolds, A.G., Rodriguez, A.V., Semon, M.J., Mills, J.M. (1999) Implication of acetic acid in the induction of slow/stuck grape juice fermentation and inhibition of yeast by Lactobacillus sp. Am. J. Enol. Vitic., 50, 204-210. 

Enamines may be reduced by sodium borohydride to give saturated amines, but only if a protonating species is available to convert the enamine initially into the iminium cation (lo). Steroidal g-amino-g,5-dienes are unreactive to sodium boro-hydride alone, but addition of acetic acid leads to rapid reduction via the iminium ion (10) to give gj -amino-A -steroids [224], The possibility that diborane was the reactive species in the NaBHd/HOAc system was excluded by the virtual non-reactivity of the enamine to externally generated diborane. Reduction of the iminium ion derivative (3) of a 6-formyl enol ether has been exploited in a variant of the Vilsmeier synthesis of 6-methyl steroids [22 ], the reduction product was the 6-aminomethyl enol ether (ii) which suffered hydrogenolysis with Raney nickel to give the 6-methylated enol ether (12). 

In the photoaddition of water (equation 30) or acetic acid (equation 31) to alkynes it seems likely that ionic addition occurs by protonation of the alkyne excited state, particularly in view of the observation that the hydration reaction is speeded up by acid and retarded by base. The sensitized addition of acetic acid to medium-ring cycloalkynes to give enol acetates (equation 32) is strongly reminiscent of the analogous addition to cycloalkenes, which has been shown to go by way of protonation of the highly strained /ra/is-cycloalkene. 

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