Carboxylic acids electron withdrawing

Sulfonic acids are stronger acids than the corresponding carboxylic acids. Electron-withdrawing groups increase the acidity of both types, but electron-releasing groups decrease the acidity. 

In carboxylic acids, electron-withdrawing groups in the a-position facilitate decarboxylation as anion °2.222,223 Many amino acids undergo this type of reaction in the presence of an acylating agent. In the case of an a-NH2 group 224-226 decarboxylation occurs through... 

In the acid form of the carboxylic acid, electron withdrawal by the C=0 enhances acidity. The conjugate base, the carboxylate anion, is stabihzed by resonance so the two O atoms are equivalent and bear the negative charge equally. 

Allylic Oxidation. The Wacker reaction and related palladium-catalyzed oxidations which proceed via nucleophilic attack on coordinated alkene have been widely practiced in industry to produce acetaldehyde, acetone, and vinyl acetate. An alternative pathway is available to alkenes in the coordination sphere of palladium(ll) complexes, which could lead to another important family of oxidation products. Insertion into the allylic C-H bond of 1-alkenes gives TT-allyl complexes which, on attack by external nucleophiles, would produce a family of allylic oxidation products including a,fi-unsaturated alcohols, carbonyl compounds, and carboxylic acids. Electron- withdrawing anionic ligands such as trifluoroacetate enhance the ability of the palladium center to insert into C-H bonds in this manner [26] (Fig. lA). Catalytic conversion of propylene to allyl acetate has been achieved in high selectivity in the presence of catalytic quantities of palladium(ll) trifluoroacetate [27]. 

The electronegative O atoms of the carboxylic acid group withdraw electrons from the whole ring, thereby reducing its overall electron density. Moreover, resonance preferentially removes electrons from the ortho and para positions. To focus on the essentials, only the lone pairs of electrons involved in resonance are shown ... 

Unsymmetrically substituted dipyrromethanes are obtained from n-unsubstitued pyrroles and fl(-(bromomethyl)pyiToIes in hot acetic acid within a few minutes. These reaction conditions are relatively mild and the o-unsubstituted pyrrole may even bear an electron withdrawing carboxylic ester function. It is still sufficiently nucleophilic to substitute bromine or acetoxy groups on an a-pyrrolic methyl group. Hetero atoms in this position are extremely reactive leaving groups since the a-pyrrolylmethenium( = azafulvenium ) cation formed as an intermediate is highly resonance-stabilized. 

A considerable body of data is available on the acidity of substituted benzoic acids Ben zoic acid Itself is a somewhat stronger acid than acetic acid Its carboxyl group is attached to an sp hybridized carbon and ionizes to a greater extent than one that is attached to an sp hybridized carbon Remember carbon becomes more electron withdrawing as its s character increases... 

Table 19 3 lists the ionization constants of some substituted benzoic acids The largest effects are observed when strongly electron withdrawing substituents are ortho to the carboxyl group An o nitro substituent for example increases the acidity of benzoic acid 100 fold Substituent effects are small at positions meta and para to the carboxyl group In those cases the values are clustered m the range 3 5-4 5... 

Carboxylic acids are weak acids and m the absence of electron attracting substituents have s of approximately 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 m the carboxylate anion (resonance effect)... 

Pyrrole Carboxylic Acids and Esters. The acids are considerably less stable than benzoic acid and often decarboxylate readily on heating. However, electron-withdrawing substituents tend to stabilize them toward decarboxylation. The pyrrole esters are important synthetically because they stabilize the ring and may also act as protecting groups. Thus, the esters can be utilized synthetically and then hydrolyzed to the acid, which can be decarboxylated by heating. Often P-esters are hydrolyzed more easily than the a-esters. 

Similarly, carboxylic acid and ester groups tend to direct chlorination to the / and v positions, because attack at the a position is electronically disfavored. The polar effect is attributed to the fact that the chlorine atom is an electrophilic species, and the relatively electron-poor carbon atom adjacent to an electron-withdrawing group is avoided. The effect of an electron-withdrawing substituent is to decrease the electron density at the potential radical site. Because the chlorine atom is highly reactive, the reaction would be expected to have a very early transition state, and this electrostatic effect predominates over the stabilizing substituent effect on the intermediate. The substituent effect dominates the kinetic selectivity of the reaction, and the relative stability of the radical intermediate has relatively little influence. 

Furan-2-carboxylic acid reacts with sulfur tetrafluoride at 0 °C to give 2-furoyl fluoride, but attempts at further fluorination results in resin formation [222] A second carboxylic group and/or electron withdrawing substiments, such as the nitro or tnfluoromethyl group, stabilize the furan ring Thus, turandicar-... 

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