Carboxylic acids tautomerism

Additional effects can be classified as statistical considerations (e.g., the effect of an additional carboxylic acid group on the pKa of a carboxylic acid), tautomeric, solvation, polarizability, and internal hydrogen bonding effects. Clark, J. Perrin, D, D. Q. Rev. Chem. Soc. 1964, 18, 295. 

Tautomerism Hydroxyl Exist largely in the oxo form Carboxylic acid (two equivalent structures)... 

Benzo[6]furan-2-carboxylic acid, 2-amino-tautomerism, 4, 648... 

Indole-2-carboxylic acid, 5-bromo-l-hydroxy-tautomerism, 4, 197-198 Indolecarboxylic acid chloride synthesis, 4, 288... 

Lumazine-6-carboxylic acid, 7-hydroxy-tautomerism, 3, 271 Lumazine-7-carboxylic acid synthesis, 3, 304 Lumazine-6,7-dicarboxylic acid decarboxylation, 3, 304 reactions, 3, 304 synthesis, 3, 320 Lumazine-6,7-dione catabolism, 3, 322... 

Pteridine-7-carboxylic acid, 6-oxo-synthesis, 3, 310 Pteridinecarboxylic acids structure, 3, 276-277 Pteridine-4-carboxylic acids ethyl ester hydrolysis, 3, 276 Pteridine-6-carboxylic acids properties, 3, 277 reactions, 3, 304 Pteridine-7-carboxylic acids properties, 3, 277 reactions, 3, 304 Pteridine-6,7-dicarboxylic acid properties, 3, 277 Pteridine-2,4-dione, 7-hydroxy-tautomerism, 3, 271... 

PyrimidoX4,5-6]quinoline-2-carboxylic acids synthesis, 3, 224-225 Pyrimido[4,5-6]quinoline-2,4-diones synthesis, 3, 224 Pyrimido[5,4-6]quinolinediones synthesis, 3, 219 Pyrimido[4,5-6]quinolines synthesis, 3, 219, 224, 227, 228, 230, 231 Pyrimido[4,5-c]quinolines synthesis, 3, 224, 227 tautomerism, 3, 205 Pyrimido[5,4-6]quinolines synthesis, 3, 227 Pyrimido[5,4-c]quinolines synthesis, 3, 219, 224, 227, 230 Pyrimido[5,4-6]quinoline-1,3,5-trione, 7-chloro-synthesis, 3, 221... 

Even the earliest reports discuss the use of components such as polymer syrups bearing carboxylic acid functionality as a minor component to improve adhesion [21]. Later, methacrylic acid was specifically added to adhesive compositions to increase the rate of cure [22]. Maleic acid (or dibasic acids capable of cyclic tautomerism) have also been reported to increase both cure rate and bond strength [23]. Maleic acid has also been reported to improve adhesion to polymeric substrates such as Nylon and epoxies [24]. Adducts of 2-hydroxyethyl methacrylate and various anhydrides (such as phthalic) have also been reported as acid-bearing monomers [25]. Organic acids have a specific role in the cure of some blocked organoboranes, as will be discussed later. 

Carbonyl compounds are in a rapid equilibrium with called keto-enol tautomerism. Although enol tautomers to only a small extent at equilibrium and can t usually be they nevertheless contain a highly nucleophilic double electrophiles. For example, aldehydes and ketones are at the a position by reaction with Cl2, Br2, or I2 in Alpha bromination of carboxylic acids can be similarly... 

A complicating feature of studies of carboxylic acid and their corresponding esters, having proximate keto or formyl groups, is the occurrence of ring-chain tautomerism, as in Scheme 1 (Valters and Flitsch, 1985). The rates of conversion of the ring and chain acids ([1] and [2] R = H) are rapid. However, both the pseudo and normal esters ([1] and [2], R = alkyl or aryl) can be isolated in favourable circumstances. The latter esters can also be interconverted by base- or acid-catalysis under suitable conditions. 

Amidation of W-BOC-tetrahydro-l,2-oxazine-6-carboxylic acid 47 with free oxanipecotic acid afforded amide 48 <2003TL3447>. The 3-methyl-substituted 1,2-oxazine Woxide 280 can be selectively transformed into 2-silyloxy-1,2-oxazines 281, upon treatment with silylating reagents (ClSiMe3). Now, the synthetic utility of 2-silyloxy-l,2-oxazine 281 is extended and it can be rearranged into 3-silyloxymethyl-l,2-oxazine 282 and can further react with morpholine to produce 3-morpholinomethyl-l,2-oxazine 283 which exists in a tautomeric equilibrium with the corresponding open-chain oxime <2003JOC9477>. 

Base-catalysed hydrolysis. The hydroxide ion attacks the nitrile carhon, followed hy protonation on the unstable nitrogen anion to generate an imidic acid. The imidic acid tautomerizes to the more stable amide via deprotonation on oxygen and protonation on nitrogen. The base-catalysed amide is converted to carboxylic acid in several steps as discussed earlier for the hydrolysis of amides. 

Earlier attempted interpretations of the hydrogen bond with the help of resonance or delocalization forces, e.g. in the case of the dimeric carboxylic acids (Illa-d) or, in particular, of substances containing intramolecular hydrogen bonds such as o-nitrosophenol (IVa-d), were shown to be untenable by unambiguous experimental evidence. Thus, in the dimer carboxylic acids the proton is not in the centre of the 0. O distance and the C=0 and C—OH distances are not identical [7], and derivatives of ortho-hydroxyazobenzene and of ortho-nitrosophenol have been shown to exist as solvent-dependent tautomeric equilibria (II), in spite of the presence of the internal hydrogen bond in both tautomers [3, 4]. 

Oxetanes can be formed by intramolecular reaction between a carbonyl group and an alkene, and this has been used (4.74) in making analogues of thromboxane A, (one of the compounds responsible for the control of blood clotting), albeit usually as the minor product. A special case of intramolecular reaction is seen for a,p-unsaturated carboxylic acids 14.75), where the product is an oxete that is tautomeric with a p-lactone. Oxetes may also be formed by photocycloaddition of ketones or aldehydes with alkynes the oxete normally ring-opens at room temperature to give an a,p-unsaturated carbonyl compound (4.76), but at lower temperatures its spectral... 

Quinoxalinecarboxaldehydes on treatment with 60% ethanolic potassium cyanide yield quinoxaloins, which are thought to exist in the hydrogen-bonded tautomeric form 163. Aerial oxidation of quinoxaloin gives quinoxalil, and oxidation with concentrated nitric acid yields quinoxaline-2-carboxylic acid.170... 

Tautomerism Hydroxy Exist in oxo form 3.2.3.7.1 Carboxylic acid (two... 

When a carboxylic acid contains hydroxyl groups in both the a and (3 positions, dehydration leads to formation of an enol that can tautomerize to 2-oxo-3-deoxy derivatives of the original acid (Eq. 13-32). 

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