Concentrated Aqueous Sulphuric Acid Research Articles

Selective oxidations by nitrosating agents in liquid and solid acid catalysts

The oxidative properties of N2O3 and NO+ ion towards methyl or methylene groups of enolizable ketones are tested at 25°C in homogeneous and heterogeneous acid systems. The results in concentrated aqueous sulphuric acid show that reasonable good yields (∼95%) of benzoylformic acid from acetophenone are obtained at selected acidity ranges. A kinetic study for the conversion reagents–products and a thermodynamic treatment of the rates was also attempted by using the acidity dependence of rates, the equilibria of the reacting species and the departure from the ideality of the catalytic acid system. On the replacement of aqueous acid solutions with solid acids, benzoyl cyanide is instead obtained, with high yields and selectivity over catalysts with suitable acidic properties. Additional studies of different ketones and of certain alcohols are also reported.

Selective oxidations by nitrosating agents in liquid and solid acid catalysts

The oxidative properties of N 2 O 3 and NO + ion towards methyl or methylene groups of enolizable ketones are tested at 25 °C in homogeneous and heterogeneous acid systems. The results in concentrated aqueous sulphuric acid show that reasonable good yields (∼95%) of benzoylformic acid from acetophenone are obtained at selected acidity ranges. A kinetic study for the conversion reagents–products and a thermodynamic treatment of the rates was also attempted by using the acidity dependence of rates, the equilibria of the reacting species and the departure from the ideality of the catalytic acid system. On the replacement of aqueous acid solutions with solid acids, benzoyl cyanide is instead obtained, with high yields and selectivity over catalysts with suitable acidic properties. Additional studies of different ketones and of certain alcohols are also reported.

Heteroaromatic azo-activated substitutions. Part 4. Kinetics and mechanism of the hydrolysis of 3-(4-methoxyphenylazo)-5-methylisoxazole in aqueous sulphuric acid media

The kinetics of the hydrolysis of the title compound, (3), have been investigated in moderately concentrated aqueous sulphuric acid media at 30 °C. Activation parameters have also been determined. Rate correlation by the Cox–Yates excess acidity method shows that hydrolysis occurs from the monoprotonated substrate by the A-SE2 mechanism of the SNAr type. Nucleophilic attack by water at the aryl carbon and a subsequent proton-transfer equilibrium are fast processes which precede the electrophilically catalysed separation of the leaving group, in which the functional catalysts are all general acids in solution. An abnormal value of 1.4 is obtained for the slope parameter m‡(Kresge's αA); this is discussed in terms of differential solvation of the initial and transition states. The Bunnett–Olsen slope parameter (φ‡–φe) of –2.0 indicates that the transition state of the reaction is substantially less solvated than its initial state. The values of ΔH‡ and ΔS‡ vary to compensate each other and the decreasing ΔS‡ values accord with the ordered transition state proposed.

Molybdenum(VI) and phenol reactions in concentrated aqueous sulphuric acid

Depending on molybdenum, phenol, and acid concentrations, and time and the method of solution preparation, molybdenum and phenol can react in several ways. In 96% sulphuric acid Mo(VI) can be reduced to Mo(V) by adding solid phenol to the solution. In other cases molybdenum and phenol form stable or unstable complexes which can be in equilibrium with each other. For excess phenol the recorded spectra show two bands at around 600 and 423 nm; the first one, decreasing with time, is ascribed to the formation of an unstable complex of phenol and Mo(VI). At approximately equal concentrations of molybdenum and phenol the band at 423 nm does not appear, but two time-dependent absorption maxima are formed at 600 and 470 nm with a well defined isosbestic point at 505 nm. The complex is unstable because of the sulphonation of phenol. In 80% sulphuric acid molybdenum and phenol form a stable 1:1 complex which absorbs at 480 nm; its pKs value is 1.44 ± 0.03 at room temperature.

Aromatic sulphonation. Part 91. The sulphonation of anisole, phenol, phenyl methanesulphonate, potassium phenyl sulphate, and a series of methyl-, bromo-, and chloro-substituted anisoles and phenols in concentrated aqueous sulphuric acid

The (homogeneous) sulphonation of a number of aromatic ethers and alcohols, viz. anisole (1), 3- methyl-(2), 4-methyl-(3). 2-bromo-(4), 4-bromo-(5), 2-chloro-(6), and 4-chloro-anisole (7), phenol (8), 2-methyl-(9), 3-methyl-(10), 4-methyl-(11), 4-bromo-(12), 2-chloro-(13), and 4- chloro-phenol (14), phenyl methanesulphonate (15), and potassium phenyl sulphate (16) in concentrated aqueous sulphuric acid at 25.0 °C has been studied, and rates and isomer distributions have been determined. The sulphonation is first-order in the aromatic substrate, and from the rate measurements it is concluded that the species undergoing sulphonation in the phenyl ring is an unprotonated substrate species. In the lower acid concentrations the sulphonating entity is H3SO4+. With increasing sulphuric acid concentration there is a gradual change-over in the sulphonating entity from H3SO4+ to H2S2O7. The acid concentrations of equal rate contribution by the two entities for anisole and phenol are 87 and 90 ± 1%, respectively. Sulphonation on the oxygen atom (i.e., sulphation) does not occur. The o/p-ratios for (1) and (8) do not vary over the studied sulphuric acid range of 75–90% H2SO4. Partial rate factors for the 2- and 4-position of (1) and (8) are reported. The very low partial rate factors for the 4-substitution of (1) and (8) and the observed extreme suppression and compression of the reactivities of the substrates (1)–(14) are ascribed to hydrogen bonding of the substrates with the acidic solvent species present. It is tentatively suggested that the relatively high contents of sulphonation ortho to –OR with anisole (36%) and phenol (48%) are due to specific complexation of the substrates with the sulphonating electrophile.

Aromatic sulphonation. Part 92. Sulphonation of the three methylphenols and the six dimethylphenols in concentrated aqueous sulphuric acid; and the lsomerization of some of the resulting sulphonic acids and of m-xylene-2-and o-xylene-3-sulphonic acid

The isomer distributions for the mono- and di-sulphonation of the three methylphenols in 81.6–90.0% sulphuric acid and of the six dimethylphenols in 84.9% sulphuric acid at 35 °C have been determined by means of 1H n.m.r. spectroscopy. Products that would result from demethylation, disproportionation, or ipso-substitution have not been observed. The monosulphonation isomer distribution of each of the three methylphenols is independent of the sulphuric acid concentration. 2,4-Dimethylphenol in 84.9% H2SO4yields 19% 5- and 79% 6-sulphonic acid, and 2,6-dimethylphenol yields 28% 3- and 72% 4-sulphonic acid. With the phenols (2), (3), (5), and (7), which have positions both ortho and para to the –OH substituent available for sulphodeprotonation, the yield of ortho-substitution is relatively high, viz. 44, 45,36, and 27%, respectively. The mono- and di-sulphonic acids of which the sulpho group is between the –OH and an –Me group are unstable under the reaction conditions employed, with the exception of the 3,5-dimethylphenol-2-sulphonic acid. It is proposed that their isomerization proceeds by protiodesulphonation followed by resulphonation to yield the more stable sulphonic acid isomer(s). From a kinetic analysis of the calculated first-order rate coefficients for protiodesulphonation, it is concluded that the unprotonated substrate species is the entity undergoing the protiodesulphonation.

On the Behaviour of Nitrate Esters in Acid Solution. II. Hydrolysis and oxidation of nitroglycol and nitroglycerin

AbstractThe behaviour of ethylene glycol dinitrate (nitroglycol) and nitroglycerin in moderately concentrated aqueous sulphuric acid, as models of “spent acids”, has been studied. The nitrate esters initial reaction is the simple hydrolysis to yield the alcohols which are eventually oxidized by nitric acid. This reaction, however, is unmeasurably slow in the absence of nitrous acid.

Aromatic sulphonation. Part 64. Sulphonation of biphenylmonosulphonic acids and some other biphenyls, containing a deactivating substituent, in concentrated sulphuric acid

The (homogeneous) sulphonation of a number of biphenyl derivatives containing a deactivating substituent, viz. the three biphenylsulphonic acids, the three nitrobiphenyls, and some other mainly 4-substitutions biphenyls, in concentrated aqueous sulphuric acid at 25°C has been studied, and rates and/or isomer distributions have been determined. The sulphonation is first-order with respect to the substrate and takes place in the unsubstituted ring, predominantly (>96%), with the exception of biphenyl-2-sulphonic acid, at the 4′-position. From the rate measurement it was concluded (i) that the substrate species undergoing sulphonation are mainly the biphenylsulphonate anions, and unprotonated 4-nitro- and 4-acetyl-biphenyl and biphenyl-4-carboxylic acid, and (ii) that the sulphonating entity is H2S2O7. Partial rate factors for these sulphonations and the σ+ value for the substituents C6H4X (X = 2-SO3–, 3-SO3–, 4-SO3–, 4-NO2, 4-COMe, and 4-CO2H) are reported. The very low partial rate factors for 2′-substitution are explained in terms of steric hindrance between the incoming sulpho-group and the adjacent hydrogen atom or group X at the 2-position of the C6H4X substituent to the formation of the σ-complex leading to the 2′-sulphonic acid. The f4, values of biphenyl-3- and -4-sulphonate anions are substantially greater than unity, indicating enhanced inter-ring mesomeric stabilization in the σ-complexes leading to 4′-substitution as compared with the substrates. The f4, value is appreciably smaller for 4-nitrobiphenyl than for biphenyl-4-sulphonate which is ascribed to the larger –M effect of NO2 as compared with the SO3– substituent.The very low f3, values of the 3- and 4-substituted biphenyls are explained in terms of the absence of inter-ring mesomeric stabilization in the σ-complexes leading to 3′-substitution.

Aromatic sulphonation. Part 55. Reaction of polyisopropylbenzenes with concentrated aqueous sulphuric acid

The reaction of a number of polyisopropylbenzenes, mainly with 98.4% H2SO4 at 25°, has been studied. m- and p-di-isopropylbenzene undergo sulphonation; no side reactions have been observed. 1,2,3-Tri-isopropylbenzene with ClSO3H in CCl4 at 0° yielded 80% 2,4,6-tri-isopropylbenzenesulphonyl chloride and small amounts of the 2,4,5-isomer. 1,3,5-Tri-isopropylbenzene with 98.4% H2SO4 led to the formation of 2,4,6-tri-isopropylbenzene-sulphonic acid which is rapidly converted into the 2,4,5-isomer and 3,5-di-isopropylbenzenesulphonic acid. The ratio of formation of these compounds is 0.53 ± 0.05; their eventual ratio in the reaction mixture was, however, 1.0 ± 0.1. 1,2,4,5-Tetraisopropylbenzene with 9 : 1 (v/v) 98.4% H2SO4–CF3CO2H at 25° yielded initially the corresponding tetraisopropylbenzenesulphonic acid, but eventually 2,4,5-tri- and 3,5-di-isopropylbenzenesulphonic acid in the ratio 6.0 ± 0.6. Mechanisms for the formation of the various products obtained with 1,3,5-tri- and 1,2,4,5-tetra-isopropylbenzene are proposed.

Aromatic sulphonation. Part 62. Sulphonation of biphenyl in concentrated aqueous sulphuric acid

The homogeneous (mono)sulphonation of biphenyl in a large excess of aqueous sulphuric acid (81.5–96.8 wt. %) at 25 °C has been studied, and rates and isomer distributions have been determined. The sulphonation is first-order with respect to the substrate, and takes place predominantly (>90%) at the para-position. Up to an acid concentration of 86 wt. % H2SO4 the active sulphonating entity is H3SO4+. For this type of sulphonation Phfp= 600 ± 300, from which it was calculated that ρ+(H3SO4+)=–10.0 ± 1.2. The high degree of para-substitution indicates substantial conjugative stabilization of the corresponding σ-complex. The relatively low degree of ortho-substitution may be explained in terms of steric hindrance by the adjacent ortho-hydrogen atom of the phenyl substituent to the formation of the σ-complex leading to the ortho-sulphonic acid. The syntheses of the three biphenylmonosulphonic acids and the six biphenyldisulphonic acids containing one sulpho-group per phenyl ring, required as reference compounds for the multicomponent u.v. analysis, are reported.

Aromatic sulphonation. Part 54. Sulphonation of polyethylbenzenes. On the Jacobsen rearrangement of the tetraethylbenzenesulphonic acids

The reaction of m- and p-di-, 1,3,5-tri-, and 1,2,3,5- and 1,2,4,5-tetra-ethylbenzene with concentrated aqueous sulphuric acid leads to clean sulphodeprotonation. m-Diethylbenzene in 95.2% H2SO4 at 25° gives 9% 2-, 90% 4-, and ⩽3% 5-substitution. The monosulphonic acids obtained from the di- and tri-ethylbenzenes are stable in the sulphonation media. In contrast the sulphonic acids obtained from 1,2,3,5- and 1,2,4,5-tetraethylbenzene are unstable in 98.4% H2SO4 and are eventually converted into 2,3,4,5-tetraethylbenzenesulphonic acid. The least stable acid is the 2,3,5,6-isomer which rearranges in part via the 2.3,4,6-isomer and in part directly to the 2,3,4,5-isomer by 1,2-ethyl shifts of the appropriately ring protonated arenesulphonic acids.

The MCactivity coefficient function for acid–base equilibria. Part 4. Limitations of empirical relationships involving observed nitration rates and acidity functions

The empirical linear relationships, for moderately concentrated aqueous sulphuric acid solutions, between the observed nitration rates of aromatic compounds and the H0, HR, and (HR+ log aw) functions, are discussed. In particular, their utilization as a criterion of mechanism is investigated. The rate profiles of nitration of halogenobenzenes, for which wide acidity ranges are experimentally available, are used in the analysis. The results obtained show the breakdown of previous relationships because of either their incompatibility with the mechanism of nitration (H0 function) or the approximation intrinsic in HR acidity function. The latter, however, should be consistent with the nitration model, providing slopes of unity are rigorously observed. A new experimental linear relationship, consistent with nitration through NO2+ ions, via a Wheland intermediate, has been found. The extension of the MC activity coefficient treatment to acid–base equilibria involved in the nitration is presented.

Aromatic sulphonation. Part 53. Kinetics and mechanism of sulphonation of ω-phenylalkane-1-sulphonic acids in sulphuric acid. Comparison of the side-chain SO3H and OSO3H substituent effects

The sulphonation of a series of sulphonic acids of the general structure Ph[CH2]nSO3H (n= 1,2,3–6) in concentrated aqueous sulphuric acid at 25 °C has been studied, and partial rate factors are reported. With benzenesulphonic acid the SO3H substituent exhibits a –M effect in addition to the combined inductive and direct field effect. The results of the ω-phenylalkane-1-sulphonic acids are explained in terms of the competing deactivating effect of the SO3H group (a combined relayed inductive and direct field effect) and the activating hyperconjugative electron release of the benzylic CH2 group. The former effect decreases with increasing n, whereas the latter effect only slightly increases upon increasing n from 1 to 2.As judged from a comparison with the fp of the sulphates of the general structure Ph[CH2]nOSO3H (n 2) the electronic effects of the [CH2]nOSO3H and the [CH2]nSO3H groups are about the same.

Aromatic sulphonation. Part 52. Ionization, sulphation, sulphonation, and alkylation of ω-phenylalkan-1-ols in sulphuric acid

The reaction of a series of phenylalkanols of the general structure Ph[CH2]nOH (n= 2,3,4,5,6, and 10) in concentrated aqueous sulphuric acid at 25 °C has been studied. At acid concentrations >50% H2SO4 protonation dod sulphation of the alkanols take place. Half-protonation of 2-phenylethanol occurs at 75 ± 0% H2SO4. The rate constants for the sulphation of the alkanols and for the hydrolysis of the corresponding hydrogen sulphates increase with increasing acid concentration and so does the hydrogen sulphate/alkanol equilibrium ratio.

Aromatic sulphonation. Part L. Sulphonation of the trimethylbenzenes: isomer distributions and hydrogen kinetic isotope effect

Isomer distributions for the sulphonation of 1,2,3- and 1,2,4-trimethylbenzene with concentrated aqueous sulphuric acid at 25.0° have been determined. The results are discussed in terms of sulphonation by H3SO4+ and H2S2O7 as sulphonating entities. The isomer distributions for the H2S2O7 mechanism are 90 ± 1% 4- and 10 ± 1% 5- substitution for the 1,2,3-isomer and 75 ± 2% 5- and 25 ± 2% 6-substitution for the 1,2,4-isomer, those for the H3SO4+ mechanism are 86 ± 1% 4- and 14 ± 1% 5-substitution with the former isomer andd 89 ± 2% 5- and 11 ± 2% 6-substitution by the latter. The deviations of the observed isomer distributions and of the partial rate factors for the H3SO4+ mechanism from those calculated on the basis of the additivity principle are discussed. The sulphonation of 1,3,5-trimethylbenzene with sulphur trioxide proceeds without a primary hydrogen kinetic isotope effect, kH/kD being 1.15 ± 0.13 and 0.98 ± 0.09 for nitromethane at 0° and trichlorofluoromethane at –35° respectively.

Aromatic sulphonation. Part XLV. Degree of ortho-substitution and partial rate factors in the sulphonation of some phenyl- and diphenylalkanes with sulphuric acid; evidence for conformational control of ortho-substitution

The degree of ortho-substitution for the sulphonation of some alkylbenzenes, diphenylalkanes, and triphenylmethane with concentrated aqueous sulphuric acid has been determined. The partial rate factor ratios for o- and p-substitution by the H2S2O7 sulphonation mechanism of the primary alkylbenzenes exhibit the order –CH3 > –CH2Me > –CH2CH2R > –CH2CHRR –CH2Ph > –CH2But; for the secondary alkylbenzenes the order is -cyclobutyl > -cyclopentyl > -cyclohexyl =–CHMe2–CHMePh > –CHPh2. The variations in fo/fp are ascribed to variations in fo and are explained in terms of retardation of the formation of the 2-alkyl-1-benzenium-1-sulphonic acid σ-complex and/or retardation of the conversion of the corresponding sulphonate σ-complex into the o-alkylbenzenesulphonic acid as result of repulsive steric interaction between the adjacent alkyl and sulpho-groups. The degreee of retardation correlates qualitatively with that expected from conformational analysis of the 2-alkyl-1-benzenium-1-sulphonic acid σ-complexes and the σ-alkylbenzenesulphonic acids.With diphenylmethane the degree of ortho-substitution for the introduction of the first and second sulpho-group is the same. With 1,1-diphenylethane two o,p′-disulphonic acid conformers are formed. The amount of o,p′,p″-trisulphonic acid formed with triphenylmethane is 3 ± 1%.

Aromatic sulphonation. Part XXXVI. The sulphuric acid sulphonation of some o-dialkylbenzenes, benzocycloalkenes, and their 4-sulphonic acids. Formation of polyxylylene from benzocyclobutene

Isomer distributions for the sulphonation of two o-dialkylbenzenes, indane, tetralin, and 6,7,8,9-tetrahydro-5H-benzocycloheptene with concentrated aqueous sulphuric acid have been determined. The 3-:4-sulphonic acid ratio decreases in the order tetralin > indane > o-xylene > 6,7,8,9-tetrahydro-5H-benzocycloheptene > o-diethylbenzene. The partial rate factors for 3-substitution by the H2S2O7 sulphonation mechanism exhibit the order tetralin ≃ indane > o-xylene > o-diethylbenzene ≃ 6,7,8,9-tetrahydro-5H-benzocycloheptene. The results of tetralin and indane are accounted for by means of a theory recently advanced to explain the Mills–Nixon effect for, e.g., protiodetritiation. The reversed order of indane and o-xylene for sulphonation as compared with protiodetritiation is ascribed to hyperconjugative stabilization of the transition state for sulphonation of indane at the 3-position. Both the lower 3 : 4 ratio and the lower f3 of o-diethylbenzene than of o-xylene and of the benzocycloheptene than of tetralin are ascribed to steric hindrance in the case of the former substrates. Sulphonation of the corresponding arene-4-sulphonic acids leads to the sole formation of the arene-3,5-disulphonic acids. In ca. 100% H2SO4 the rate order is rather similar to that of the parent hydrocarbons. The reaction of benzocyclobutene with 81–98% H2SO4 yields polyxylylene.

Aromatic isomerization reactions. Part III. Kinetics of the isomerization of the sulphonic acids of o- and m-xylene in aqueous sulphuric acid

The kinetics of the isomerization of the monosulphonic acids of o-and m-xylene in concentrated aqueous sulphuric acid have been studied. Pseudo-first-order isomerization rate constants are reported.

General acid catalysis in moderately concentrated aqueous sulphuric acid

Download options Please wait... Article information DOI https://doi.org/10.1039/DF9653900075 Article type Paper Download Citation Discuss. Faraday Soc., 1965,39, 75-83 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions General acid catalysis in moderately concentrated aqueous sulphuric acid A. J. Kresge, L. E. Hakka, S. Mylonakis and Y. Sato, Discuss. Faraday Soc., 1965, 39, 75 DOI: 10.1039/DF9653900075 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author A. J. Kresge L. E. Hakka S. Mylonakis Y. Sato