Hans J. A. Lambrechts

Aromatic sulphonation—80: Sulphur trioxide sulphonation of some tri- and tetra-methylnaphthalenes☆

Abstract 1,2,3-Trimethylnaphthalene (1,2,3,-Me 3 N), 1,4,5-Me 3 N, 1,6,7-Me 3 N, 1,2,3,4-Me 4 N and 1,4,6,7-Me 3 N have been sulphonated with SO 3 in nitromethane and the isomer distributions of the mono- and di-sulphonic acid mixtures, obtained by reaction with 1 equivalent of SO 3 at 0° and 3 equivalents of SO 3 at 12° respectively, are reported. The sulphodeprotonation isomer distribution follows the reactivity order predicted by the localization energies, provided that steric factors are taken into account, i.e. that sulphodeprotonations peri to a methyl and sulpho group do not occur. Disulphonation of 1,4,5-Me 3 N and 1,4,5,8-Me 4 N leads predominantly to the 3,6- and 2,7-disulphonic acid respectively, i.e. the “non-crossed” disulphonic acids.

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 94. Sulphonation and sulphation of the three 2- and 4-hydroxy- and 2- and 4-methoxy-benzenesulphonic acids in concentrated sulphuric acid

The sulphonation of 2-methoxy-(1) and 4-methoxy-benzene sulphonate (2) and 1-(3), 3-(4), and 4-hydroxybenzenesulphonate (5) in 86.9–98.5% H2SO4 at 25 °C has been studied. Substrates (1)–(3) and (5) all yield the corresponding 2,4-disulphonic acid as the exclusive product, whereas (4) yields a mixture of 2-hydroxybenzene-1,4- and 4-hydroxybenzene-1,2-disulphonic acid. 3- and 4-Hydroxybenzenesulphonic acids in sulphuric acid (>87% H2SO4) are present in part as their hydrogen sulphates and the sulphuric acid concentration of 50% sulphation is 97.5 and 100.5 ± 0.2% H2SO4. The sulphonation is first order in the aromatic substrate. From the rate dependence on the sulphuric acid concentration it is concluded that the substrate species undergoing ring sulphonation is the –O3SC6H4OR (R = H; Me) species with H2S2O7 as the sulphonating entity. From the observed proportionality between [–O3SC6H4OSO3H]/[–O3SC6H4OH] and aSO3 it is concluded that the aromatic species undergoing sulphation is again –O3SC6H4OH.

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.

Aromatic sulphonation. Part 93. Sulphonation of the three t-butylphenols, four di-t-butylphenols, and 2,4,6-tri-t-butylphenol

The (homogeneous) sulphonation of the three t-butyl-phenols, 2,4-, 2,5-, 2,6-, and 3,5-di-t-butyl-phenol, and 2,4,6-tri-t-butylphenol with a number of sulphonating reagents has been studied, and product compositions have been determined. The formation of the several initial and eventual sulphonation products is explained in terms of sulphodeprotonation, protiode-t-butylation, sulphode-t-butylation, and isomerization, the relative importance of which is discussed for the various substrates. 2-(1) and 4-t-butylphenol (3), 2,4-(4), and 2,6-di-t-butylphenol (6), and 2,4,6-tri-t-butylphenol (8) in 98.5% H2SO4 at 35 °C after 10 days of reaction all yield 50 ± 2% 4-t-butylphenol-2,6-(9) and 50 ± 2% phenol-2,4-disulphonic acid (10). With both (1) and (6) the initial step is a rapid 1,3-shift of the t-butyl group from the 2- to the 4-position. With (1) this is then followed by sulphodeprotonation at the 2- and 6- position and with (6) by protiode-t-butylation at the 6-position followed by sulphodeprotonation at the 2- and 6-position. The formation of (9) from the substrates (3), (4), and (8) and the formation of (10) from (1), (3), (4), (6), and (8) is explained by protiode-t-butylation and subsequent sulphode-protonation.