Sulfuric acid protonation of, 581

Two inflexions are obtained, the first attributed to the sulfonic acids and first proton of sulfuric acid and the second for the second proton of sulfuric acid. 

Principle. By means of potentiometric titration (in nonaqueous media) of a blend of sulfonic and sulfuric acids, it is possible to split the neutralization points corresponding to the first proton of sulfuric acid plus that of sulfonic acid, and to the second proton of sulfuric acid. The first derivate of the titration curve allows identification of the second points the corresponding difference in the volume of titrating agent is used as a starting point in the calculation method (Fig. 4). 

Benzene reacts slowly with hot sulfuric acid to produce benzenesulfonic acid. The attacking electrophile, the cation 4, is generated by the self-protonation of sulfuric acid and reacts with the benzene ring in the normal manner (Scheme 5.1). 

This reaction could also be described as an acid-base reaction, where the acid is the proton of sulfuric acid and the base is the oxygen of the carbonyl group. 

The first proton of sulfuric acid is completely ionized, but the second proton is only partially dissociated, with an acidity constant of 1.2 X 10 -. Calculate the hydrogen ion concentration in a 0.0100 M H2SO4 solution. 

Reaction of HF/SbFs with H2SO4 does not result in complete protonation of sulfuric acid because of the presence of the [H30] ions, (a) Explain the origin of the [H30 ions and (b) explain how [H30] interferes with attempts to use HF/ SbFj to protonate H2SO4. 

This analysis translates into a mechanism where the C=C unit in 2-methyl-2-butene reacts as a base with the acidic proton of sulfuric acid (H2SO4) as the first step, generating the more stable tertiary carbocation 30 rather than the less stable regioisomeric secondary carbocation. Only two nucleophiles are present in the medium water and the hydrogen sulfate anion water is (a) present... 

Procedure Titration of Sulfuric Acid in Sulfonic Acids with Cyclohexylamine (23,24) Prepare cyclohexylamine titrant in MeOH or EtOH and standardize by potentiometric titration against sulfamic acid. Weigh about 200 mg sulfonic acid sample into a 100-mL beaker and dissolve in 50 mL methanol or ethanol. Titrate potentiometrically with 0.1 M cyclohexylamine, monitoring the titration with a glass combination pH electrode. The first potentiometric break (see Fig. 1) corresponds to neutralization of the sulfonic acid and the first proton of sulfuric acid. The second break corresponds to neutralization of the second proton of sulfuric acid. 

In this determination, 5 mL of a 0.1 g/L aqueous solution of the surfactant is passed through a cation exchange column (1x15 cm, containing 15 mL Dowex 50W-X8, acid form) to convert the salts to the corresponding acids. The acids are eluted with two 3-mL portions of water and four 6-mL portions of water, then titrated with tetrabutylammonium hydroxide, 0.1 M in 70 30 benzene/methanol. The first inflection corresponds to the total sulfonate, plus the first proton of sulfuric acid. The second inflection corresponds to neutralization of the second proton from sulfuric acid. A third inflection may be observed due to solvent impurities. If necessary because of poor water solubility of the surfactant, the initial sample dissolution and ion exchange is conducted at 55-C. 

Step 3 A rapid proton transfer from the oxygen of sulfuric acid to the oxygen of benzenesulfonate completes the process... 

One reason for the low reactivity of pyridine is that its nitrogen atom because it IS more electronegative than a CH in benzene causes the rr electrons to be held more tightly and raises the activation energy for attack by an electrophile Another is that the nitrogen of pyridine is protonated in sulfuric acid and the resulting pyndinium ion is even more deactivated than pyndine itself... 

The O acylation of phenols with carboxylic acid anhydrides can be conveniently catalyzed m either of two ways One method involves converting the acid anhydride to a more powerful acylatmg agent by protonation of one of its carbonyl oxygens Addi tion of a few drops of sulfuric acid is usually sufficient... 

The purity of a pharmaceutical preparation of sulfanilamide, C6H4N2O2S, can be determined by oxidizing the sulfur to SO2 and bubbling the SO2 through H2O2 to produce H2SO4. The acid is then titrated with a standard solution of NaOH to the bromothymol blue end point, where both of sulfuric acid s acidic protons have been neutralized. Calculate the purity of the preparation, given that a 0.5136-g sample required 48.13 mL of 0.1251 M NaOH. 

Consider, for example, the determination of sulfurous acid, 1+2503, by titrating with NaOlT to the first equivalence point. Using the conservation of protons, we write... 

Step 2 A proton is lost from the 5/r -hybridized car bon of the intermediate to restore the aromaticity of the ring. The species shown that abstracts the proton is a hydrogen sulfate ion formed by ionization of sulfuric acid. 

C17-0128. Pure sulfuric acid (H2 SO4) is a viscous liquid that causes severe bums when it contacts the skin. Like water, sulfuric acid is amphiprotic, so a proton transfer equilibrium exists in pure sulfuric acid, (a) Write this proton transfer equilibrium reaction, (b) Construct the Lewis stmcture of sulfuric acid and identify the features that allow this compound to function as a base, (c) Perchloric acid (HCIO4) is a stronger acid than sulfuric acid. Write the proton transfer reaction that takes place when perchloric acid dissolves in pure sulfiaric acid. 

Numbers used in this cycle AG° for dissociation of sulfuric acid to sulfur tri-oxide AG° for hydrolysis of bis-p-nitrophenyl sulfate, estimated as described above AG° for hydrolysis of mono-p-nitrophenyl sulfate AG° for esterification to give pNP0S02, estimated as described above AG° for ionization of protonated SO3, estimated as described above AG° for ionization of p-nitrophenol. )... 

Upon addition of a solution of sulfuric acid in D20 the reaction of A-acetoxy-A-alkoxyamides obeys pseudo-unimolecular kinetics consistent with a rapid reversible protonation of the substrate followed by a slow decomposition to acetic acid and products according to Scheme 5. Here k is the unimolecular or pseudo unimolecular rate constant and K the pre-equilibrium constant for protonation of 25c. Since under these conditions water (D20) was in a relatively small excess compared with dilute aqueous solutions, the rate expression could be represented by the following equation ... 

As a result, the acid strength of the proton is approximately equivalent to that of sulfuric acid in nonaqueous media. In view of the excellent miscibility of this anion with organic nonpolar materials, Armand et al. proposed using its lithium salt (later nicknamed lithium imide , or Lilm) in solid polymer electrolytes, based mainly on oligomeric or macro-molecular ethers. In no time, researchers adopted its use in liquid electrolytes as well, and initial results with the carbonaceous anode materials seemed promising. The commercialization of this new salt by 3M Corporation in the early 1990s sparked considerable hope that it might replace the poorly... 

The removal of potassium cations makes the results of the liquid-phase and electrode reactions similar. In the presence of crown ether, the eight-membered complex depicted in Scheme 2.16 is destroyed. The unprotected anion-radicals of azoxybenzene are further reduced by cyclooctatet-raene dianion, losing oxygen and transforming into azodianion. The same particle is formed in the electrode reaction shown in Scheme 2.13. In the chemical reduction, stabilization of azodianion is reached by protonation. Namely, addition of sulfuric acid to the reaction results in the formation of hydrazobenzene, which instantly rearranges into benzidine (4,4 -diamino-l,l"-diphenyl). The latter was isolated from the reaction, which proceeded in the presence of crown ether. 

Nitration of an aromatic ring using nitric acid also requires the presence of sulfuric acid. Nitric acid is protonated by the stronger sulfuric acid, leading to... 

In concluding this section, we should touch upon phase boundary concentration data for poly(p-benzamide) dimethylacetamide + 4% LiCl [89], poly(p-phenylene terephthalamide) (PPTA Kevlar)-sulfuric acid [90], and (hydroxy-propyl)cellulose-dichloroacetic acid solutions [91]. Although not included in Figs. 7 and 8, they show appreciable downward deviations from the prediction by the scaled particle theory for the wormlike hard spherocylinder. Arpin and Strazielle [30] found a negative concentration dependence of the reduced viscosity for PPTA in dilute Solution of sulfuric acid, as often reported on polyelectrolyte systems. Therefore, the deviation of the Ci data for PPTA in sulfuric acid from the scaled particle theory may be attributed to the electrostatic interaction. For the other two systems too, the low C] values may be due to the protonation of the polymer, because the solvents of these systems are very polar. 

Manganese pentacarbonyl is a free radical and spontaneously dimerizes to dimanganese decacarbonyl. Iron pentacarbonyl is a weak Lewis base and can be protonated by sulfuric acid, forming a metal-hydrogen bond. We will make extensive use of the isolobal... 

Anionic substituents that are considered are the salts of carboxylic acids, phosphoric acids, and sulfur acids. The salts of sulfur acids are chosen based on their low pKa values that allow these derivatives to remain un-protonated (anionic) throughout the pH range used in and experienced by pharmaceutical formulations. Figure 7 shows the chemical structures of the three different families of anionic CD derivatives... 

Autoionization of sulfuric acid results in the formation of the hydrogen sulfate (bjsulftte) ion and a solvated proton ... 

---