99861-57-1Relevant academic research and scientific papers
Methylation of polymethylbenzenesulfonic acids by hexamethylbenzene and pentamethylbenzenesulfonic acid in concentrated sulfuric acid
Cerfontain, Hans,Koeberg-Telder, Ankie
, p. 162 - 167 (2007/10/02)
The methylation of a series of polymethylbenzenes (PoMB's) or their sulfonic acids by added hexamethylbenzene (HMB) and pentamethylbenzene-1-sulfonic acid (PeMB-1-S) as reagents in 95.5 and 98.4 percent H2SO4 as solvent has been studied under homogeneous conditions.HMB effects methylation of 2,4,6-trimethylbenzene-1-sulfonic acid (2,4,6-TrMB-1-S),2,3,4,6-tetramethylbenzene-1-sulfonic acid (2,3,4,6-TeMB-1-S) and 2,3,5,6-TeMB-1-S, but not of the sulfonic acids of 1,3-dimethylbenzene (1,3-DMB), 1,2,3-TrMB, 1,2,4-TrMB, and 1,2,3,4-TeMB.PeMB-1-S is less reactive as methylating reagent than HMB.The observed substrate reactivity towards methylation by HMB was observed to decrease in the order 2,3,4,6-TeMB-1-S ca. 2,3,5,6-TeMB-1-S > 2,4,6-TrMB-1-S >> 2,3,4,5-TeMB-1-S, and towards methylation by PeMB-1-S to decrease in the order PeMB-1-S >> 2,4,6-TrMB-1-S.On the basis of a comparison of these orders of substrate reactivities with those predicted for the series of PoMB-1-sulfonates and the corresponding PoMB's, it is concluded that the substrate species undergoing methylation are the PoMB's and corresponding sulfonates.
Aromatic isomerization and related reactions. Part 61. Reactions of the tetra- and pentamethylbenzenesulfonic acids and hexamethylbenzene in concentrated sulfuric acid; the mechanism of the Jacobsen reaction
Koeberg-Telder, Ankie,Cerfontain, Hans
, p. 85 - 103 (2007/10/02)
The chemical behaviour of the sulfonic acids of pentamethylbenzene (PMB) and the three tetramethylbenzenes (TeMB's( in concentrated aqueous sulphuric acid has been studied quantitatively using 1H AND 13C NMR and UV spectroscopy.PMB-sulfonic acid yields (protonated) hexamethylbenzene (HMB) and the 2,3,4,5- and 2,3,4,6-TeMB-1-sulfonic acids in an initial ratio of 9/1/8 up to a substrate conversion of 36percent; the ratio of HMB to the TeMB-1-sulfonic acids remains 1/1 and the only subsequent reaction is the relatively slow conversion of the 2,3,4,6- into the 2,3,4,5-TeMB-1-sulfonic acid which is the only stable TeMB-1-sulfonic acid isomer in concentrated sulfuric acid. 2,3,5,6-TeMB-1-sulfonic acid yields, as initial products, 2,3,5- and 2,4,5-trimethylbenzene(TrMB)-1-sulfonic acid together with PMB-1-sulfonic acid in a ratio of ca. 1/3/4.The subsequent products are the 2,3,4,6- and 2,3,4,5-TeMB-1-sulfonic acids, of which the former slowly isomerizes to the latter, together with some HMB. 2,3,4,6-TeMB-1-sulfonic acid yields the stable 2,3,4,5-isomer.It is proposed that the conversion proceeds via inter-molecular trans-methylations involving 1,3,5-TrMB and PMB as intermediates, the concentrations of which, however, are below the limits of NMR detection.Based on (i) the desulfonation-sulfonation equilibrium data of the TrMB-, TeMB- and PMB-sulfonic acids, (ii) the strong rate decrease for the conversion of both 2,3,4,6- and 2,3,5,6-TeMB-1-sulfonic acid in 98.4percent H2SO4 in the presence of added cyclohexane and (iii) the very strong electron-withdrawing and meta-directing effect of the SO3-/SO3H substituent, it is proposed that all the conversions proceed inter-molecularly, that the trans-methylating reagent is the polymethylbenzene (and not the corresponding sulfonate) and that the substrate undergoing methylation is most likely to be once again the polymethylbenzene rather than its sulfonate ion.
Solvent Effects on Solvolytic Reactivity. A Diagnostic Test for Neighboring-Group Assistance by ? Conjugation in Solvolysis Reactions
Roberts, Donald D.
, p. 2521 - 2526 (2007/10/02)
The solvolysis rates of 13 arenesulfonates have been determined in mixtures of ethanol and water (the E-series solvents) and acetic acid and formic acid (the A-series solvents).The substrates studied include the following: neophyl (1), 2-adamantyl (2), neopentyl (3), and cyclooctyl (4) tosylates; cyclopropylcarbinyl pemsylate (5a) and tosylate (5b); exo-2-norbornyl tosylate (6); cyclobutylcarbinyl (7), cyclobutyl (8), and pinacolyl (9) brosylates; cyclopentyl (10), cyclohexyl (11), and 2-propyl (12) tosylates; and cyclopentylcarbinyl brosylate (13).Correlations of the rate data by eq 1 t(Y) = a + b log kt(neophyl-OTs)> showed that the various substrates responded differently to the examined solvent effects on the solvolytic reactivity.For compounds 2-4, linear correlations were obtained.For compounds 5-9, E-line, A-line dispersions were noted which diverged with increasing ionizing power; for compounds 10-12, parallel E-line, A-line dispersions were obtained; and for compound 13, an E-line, A-line dispersion was observed which converged with increasing ionizing power.Stastistical analyses of the rate data correlations confirmed the significance of the E or A classification of data.The results are interpreted in terms of differences in the involvement of solvent in the transition state for those solvolyses assisted by bridging from those assisted by C-C ? bond hyperconjugation.
