Benzoic protonation

C = 0 / CsHb Tetrahedral Proton intermediate C=OH CsHb Methyl benzoate Benzoic Proton acid j... 

Many aromatic compounds are sufficiently basic to be appreciably protonated in concentrated sulphuric acid. If nitration occurs substantially through the free base, then the reactivity of the conjugate acid will be negligible. Therefore, increasii the acidity of the medium will, by depleting the concentration of the free base, reduce the rateof reaction. This probably accounts for the particularly marked fall in rate which occurs in the nitration of anthraquinone, benzoic acid, benzenesulphonic acid, and some nitroanilines (see table 2.4). 

Electron delocalization in carbonyl protonated benzoic acid... 

The reaction of 2-phenyl-l-azirine (201) with benzoic acid gaveN-benzoylphenacylamine (204) (67BCJ2938). The overall mechanism of the reaction involves initial protonation on nitrogen followed by addition of the nucleophile to the azirinium ion and finally ring opening. 

The reduction of a benzenoid ring, except in benzoic acid derivatives, occurs only in the presence of a proton donor having a pKa of 19 or less (pKa of ammonia is about 33). With the exception of the vinyl group, the other functional groups listed above do not require a proton donor of this acidity in order to be reduced, although the course of reduction may then be complex, e.g. as with esters. " Consequently, a variety of functional groups should be capable of selective reduction in the presence of a benzenoid ring if the reaction medium does not contain an acid of pKa <19. A few examples of such selective reductions have been reported in the steroid literature. 

Conjugate acid of benzoic acid Methanol Protonated form of tetrahedral intermediate... 

Obtain energies for each ion and for their correspondin precursors benzoic acid,phenol and cyclohexanol). Us this information to calculate the energy for each of the abov deprotonation reactions. (The energy of proton is given left.) Is the trend consistent with the experimental pKa dat (see table at left) Does deprotonation energy parade charge delocalization in these systems Explain ho electron delocalization affects the reactivity of these acidf... 

A ruthenium porphyrin hydride complex was lirst prepared by protonation of the dianion, [Ru(TTP) in THF using benzoic acid or water as the proton source. The diamagnetic complex, formulated as the anionic Ru(If) hydride Ru(TTP)(H )(THF)l , showed by H NMR spectroscopy that the two faces of the porphyrin were not equivalent, and the hydride resonance appeared dramatically shifted upheld to —57.04 ppm. The hydride ligand in the osmium analogue resonates at —66.06 ppm. Reaction of [Ru(TTP)(H)(THF)j with excess benzoic-acid led to loss of the hydride ligand and formation of Ru(TTP)(THF)2. 

Benzoic acid is a weak carboxylic acid that undergoes proton transfer with water. When a 0.125 M aqueous solution of benzoic acid (Cg H5 CO2 H) reaches equilibrium, [H3 O ] = 0.0028 M. What is. eq... 

The equilibrium concentration of hydronium ions is provided, which suggests that one of the products is H3 O. Benzoic acid is a weak acid. Thus the correct chemical reaction is proton transfer from benzoic acid to water ... 

The equilibrium constant for the proton transfer reaction of benzoic acid, determined in Example, is 6.4 X 10. Calculate the equilibrium concentration of benzoic acid and benzoate anions in a 5.0 X 10 M aqueous solution of the acid. 

The net reaction is given. A proton is transferred from a water molecule to a benzoate anion. A small amount of benzoic acid forms as the reaction reaches equilibrium. Notice that Na ions do not participate in the net reaction. 

Measurements of the pH of solutions of acids show that, except for strong acids, the hydronium ion concentration is smaller than would be expected if proton transfer were quantitative. An acid that reaches equilibrium when only a small fraction of its molecules has transferred protons to water is called a weak acid. One example is benzoic acid, treated in Example. A 0.125 M solution of this acid has [H3 ] = 0.0028 M (pH = 2.55). As... 

Another example of 19F coupling, this time in an aromatic system, (4-fluoro benzoic acid) is shown in Spectrum 6.11. Note how the 19F couplings to the aromatic protons give the AA BB system an... 

A combination of steric and electrostatic factors is presumably decisive with regard to the form of the acid most stable in sulfuric acid solution. The simple protonated form XX of benzoic acid is stabilized by resonance structures sterically prohibited in mesitoic acids. The ortho methyl groups of mesitoic acid would interfere with a coplanar dihydroxymethylene group. On the other hand, the inductive and resonance effects of the methyl groups help stabilize the acylium ion form of mesitoic acid as in the formulae XXI. In the case of 2,4,6-tribromobenzoic acid the steric effect and its abetting electronic effects are not sufficient, and this acid behaves like benzoic acid.17 >177... 

Monoprotonation of the [2.1.1]-cryptand occurs rapidly but protonation of the monoprotonated species by hydronium ion and other acids can be followed kinetically in various solvents (Cox et al., 1982, 1983). In methanol, protonation of ii+ species by substituted acetic and benzoic acids to give i+i+ has been studied using the stopped flow technique with conductance detection. The values of the rate coefficients (kHA) for protonation (81) vary with the acidity of the donor acid from kHA = 563 dm3mol-1s-1 (for 4-hydroxy-benzoic acid) to kHA = 2.3 x 105 dm3mol 1s 1 (for dichloroacetic acid). 

The spectrum was run in 10% methylene chloride in carbon tetrachloride with use of benzoic acid as an internal standard, using the N-CH3 protons of methimazole at 3.566 and the aromatic protons of benzoic acid at 7.5 and 8.136 as criteria for analysis (29). 

---