Protonated sulfuric acid

Cation B is first deprotonated to give the hydroxycamphene derivative C. C reacts with an electrophile of unknown structure that is generated from sulfuric acid under these conditions. In the discussion of the sulfonylation of aromatic compounds (Figure 5.17), we mentioned protonated sulfuric acid H3S04 and its dehydrated derivative HS03 as potential electrophiles, which might assume the same role here. In any case, the reaction results in the formation of carbenium ion E. 

Figure 5.13b. Energy profile for isobutene interaction with protonated sulfuric acid (H3SOJ). (a) tt-...

For reactions in H2O an analogous discussion applies as for reactions with the protonated sulfuric acid form. The reactive intermediate now, however, is H3O+. H3O+ has a much stronger OH bond than H3SO4 +, and hence its reactivity is much less. The species that is formed by reaction with alkene in an aqueous solution can best be compared with protonated alcohols forms typically known as alkyl oxonimn ionsl l Protonated alkene is hydrated in aqueous media. The formation of alkyloxonimn ions instead of the carbenium ions in H2O can be viewed as due to the basicity of water. The major difference between solid acids and acidic solutions arises because the hydrogen atoms in solid acids are part of strong covalent bonds and are not present as protons that are present in in the solution phase. In a solution there is a equilibrium between non-dissociated acid molecules and the... 

Table 14.3 lists the six strong acids. The first five acids in the table are monoprotic adds, acids containing only one ionizable proton. Sulfuric acid is an example of a diprotic acid, an acid that contains two ionizable protons. 

ANSWER The mechanism for the transformation of benzenesulfonic acid into benzene is the reverse of the mechanism for formation of benzenesulfonic acid from benzene (Figs. 14.25 and 14.26). Protonation gives a cyclohexadienyl cation that can either lose a proton to revert to benzenesulfonic acid, or lose the sulfonic acid group to give benzene and protonated sulfuric acid, which will lose its proton to water. 

The hydrolysis of solid PET in the presenee of acids is a heterogeneous reaction catalyzed by protons. Sulfuric acid, nitric acid and hydrochloric acid were employed to obtain TPA, EG and other products. The reaction is affected by the diffusion of reagents and produets, the heat transfer inside the PET related to the low heat conductivity and the crystallinity of the PET, as well. 

Alkenes react with sulfuric acid to form alkyl hydrogen sulfates A proton and a hydrogen sulfate ion add to the double bond in accordance with Markovnikov s rule Alkenes that yield tertiary carboca tions on protonation tend to polymerize in concentrated sulfuric acid (Section 6 21)... 

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... 

When applied to the synthesis of ethers the reaction is effective only with primary alcohols Elimination to form alkenes predominates with secondary and tertiary alcohols Diethyl ether is prepared on an industrial scale by heating ethanol with sulfuric acid at 140°C At higher temperatures elimination predominates and ethylene is the major product A mechanism for the formation of diethyl ether is outlined m Figure 15 3 The individual steps of this mechanism are analogous to those seen earlier Nucleophilic attack on a protonated alcohol was encountered m the reaction of primary alcohols with hydrogen halides (Section 4 12) and the nucleophilic properties of alcohols were dis cussed m the context of solvolysis reactions (Section 8 7) Both the first and the last steps are proton transfer reactions between oxygens... 

Step 1 Proton transfer from the acid catalyst (sulfuric acid) to the oxygen of the alcohol to produce an alkyloxonmm ion... 

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... 

Acid—Base Chemistry. Acetic acid dissociates in water, pK = 4.76 at 25°C. It is a mild acid which can be used for analysis of bases too weak to detect in water (26). It readily neutralizes the ordinary hydroxides of the alkaU metals and the alkaline earths to form the corresponding acetates. When the cmde material pyroligneous acid is neutralized with limestone or magnesia the commercial acetate of lime or acetate of magnesia is obtained (7). Acetic acid accepts protons only from the strongest acids such as nitric acid and sulfuric acid. Other acids exhibit very powerful, superacid properties in acetic acid solutions and are thus useful catalysts for esterifications of olefins and alcohols (27). Nitrations conducted in acetic acid solvent are effected because of the formation of the nitronium ion, NO Hexamethylenetetramine [100-97-0] may be nitrated in acetic acid solvent to yield the explosive cycl o trim ethyl en etrin itram in e [121 -82-4] also known as cyclonit or RDX. 

Ca.ta.lysis by Protons. The discovery of hydrogen peroxide hydroxylation of phenol in the presence of strong acids such as perchloric, trifluoromethane-sulfonic, or sulfuric acids allows suppression of all previous drawbacks of the process (18,19). This mode of hydroxylation gives high yields (85% based on H2O2 at phenol conversion of 5—6%). It can be mn without solvents and does not generate resorcinol. Its main advantage rehes on... 

Peroxomonosulfuric acid [7722-86-3] H2SO, when pure, forms colorless crystals that melt with decomposition at 45°C. One of its protons is strong, as ia sulfuric acid, but its other proton, which is on the peroxide group, is weak (pH = 9.4). Peroxomonosulfuric acid is a strong oxidi2iag agent ... 

Amide-Based Sulfonic Acids. The most important amide-based sulfonic acids are the alkenylarnidoalkanesulfoiiic acids. These materials have been extensively described ia the Hterature. A variety of examples are given ia Table 5. Acrylarnidoalkanesulfoiiic acids are typically prepared usiag technology originally disclosed by Lubrizol Corporation ia 1970 (80). The chemistry iavolves an initial reaction of an olefin, which contains at least one aHyhc proton, with an acyl hydrogen sulfate source, to produce a sulfonated intermediate. This intermediate subsequendy reacts with water, acrylonitrile, and sulfuric acid. 

According to Figure 3, hydroperoxides are reduced to alcohols, and the sulfide group is oxidized to protonic and Lewis acids by a series of stoichiometric reactions. The sulfinic acid (21), sulfonic acid (23), sulfur trioxide, and sulfuric acid are capable of catalyzing the decomposition of hydroperoxides to nonradical species. 

In some processes the reactant bases are too weak to be protonated significantly except in the presence of very strong acids such as fuming sulfuric acid or a mixture of concentrated sulfuric and nitric acids, ie, mixed acid. Nitration of toluene, for example, requires such solutions two Hquid phases are present in the reactor. 

Indole can be nitrated with benzoyl nitrate at low temperatures to give 3-nitroindole. More vigorous conditions can be used for the nitration of 2-methylindole because of its resistance to acid-catalyzed polymerization. In nitric acid alone it is converted into the 3-nitro derivative, but in a mixture of concentrated nitric and sulfuric acids 2-methyl-5-nitroindole (47) is formed. In sulfuric acid, 2-methylindole is completely protonated. Thus it is probable that it is the conjugate acid which is undergoing nitration. 3,3-Dialkyl-3H-indolium salts similarly nitrate at the 5-position. The para directing ability of the immonium group in a benzenoid context is illustrated by the para nitration of the conjugate acid of benzylideneaniline (48). 

The NMR spectra of pyrazolium and indazolium ions have been widely studied (Table 10), including both the conjugate acids and the quaternary salts. The spectra obtained in sulfuric acid prove unquestionably that the protonation of these species takes place at position 2 (Section 4.04.2.1.3(iv)). 

Bromopyrazoles (298) react with fuming nitric acid in 80% sulfuric acid to give 4-nitropyrazoles (ipso nitration Section 4.04.2.3.7). When R was an alkyl group, nitration took place at C-3 giving (299) (a small amount of the dinitro derivative (300) was also obtained) (79AJC1727). Nitrodebromination proceeds from the protonated pyrazolium ion whereas 3-and 5-nitration were expected to involve the free base. 

In the section dealing with electrophilic attack at carbon some results on indazole homocyclic reactivity were presented nitration at position 5 (Section 4.04.2.1.4(ii)), sulfon-ation at position 7 (Section 4.04.2.1.4(iii)) and bromination at positions 5 and 7 (Section 4.04.2.1.4(v)). The orientation depends on the nature (cationic, neutral or anionic) of the indazole. Protonation, for instance, deactivates the heterocycle and directs the attack towards the fused benzene ring. A careful study of the nitration of indazoles at positions 2, 3, 5 or 7 has been published by Habraken (7UOC3084) who described the synthesis of several dinitroindazoles (5,7 5,6 3,5 3,6 3,4 3,7). The kinetics of the nitration of indazole to form the 5-nitro derivative have been determined (72JCS(P2)632). The rate profile at acidities below 90% sulfuric acid shows that the reaction involves the conjugate acid of indazole. 

Nitration in 80% sulfuric acid of 4-bromopyrazoles gives rise to considerable nitro-debromination (formation of 4-nitropyrazoles) (79AJC1727). The reaction takes place on the protonated pyrazolium ion (Section 4.04.2.1.4(ii)). 

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