Aromatic sulfonation 28: Degree ofortho‐substitution in the sulfonation of toluene with sulfur trioxide, methanepyrosulfonic acid and fuming sulfuric acid. A mechanistic picture

Abstract

The reaction of neat toluene with a number of different sulfonation reagents at 25" has been studied. With sulfur trioxide vapour as reagent, the reaction leads to monosulfonation only. The o/(o + m + p) ratio varies with the degree of toluene conversion, the limiting values a t zero and high conversion being 0.34 f 0.03 and 0.1 I & 0.01, respectively. The former value is ascribed to the sulfonation of toluene with sulfur trioxide, the latter to sulfonation in the acid phase with toluenepyrosulfonic acid as the sulfonating entity.The heterogeneous reaction of toluene with a deficient amount of a matured mixture of methanesulfonic acid and sulfur trioxidei.e. with a methanepyrosulfonic acid reagentleads tomonosulfonation only. The o/(o + m + p) ratio varies from 0.1 5 & 0.01 at zero toluene and zero time conversion to 0.1 I * 0.01 a t high toluene conversion. The former value is ascribed to sulfonation in the acid phase of dissolved toluene by methanepyrosylfonic acid, the latter to that by both toluene-and methane-pyrosulfonic acids. Heterogeneous sulfonation with a deficient amount of fuming sulfuric acid takes place mainly (-97 %) in the acid phape. Sulfonation in the toluene phase leads to monosulfonic acids only with 41 =! = 2 % of ortho-substitution.Sulfonation in the sulfuric acid phase yields rnonosulfonic acids and, at the higher sulfuric acid concentrztions, also toluene-2,4-disulfonic acid. ThL degree of ortho-substitution for sulfonation in the acid phase a t 25" changes from 48.5 to 40% on varying the acid concentration from 100.0 to 106.4% H2S04.The mechanism of aromatic sulfonation with sulfur trioxide in aprotic solvents has been the subject of recent studies l-11.

Conversion of Wood-Based Hemicellulose Prehydrolysate into Succinic Acid Using a Heterogeneous Acid Catalyst in a Biphasic System

“…This is comparable to the results obtained by Koeberg-Telder and Cerfontain in the sulfonation of toluene at 25 °C . According to Koeberg-Telder and Cerfontain, toluene is converted into mono- or disulfonic acid when reacted with concentrated sulfuric acid for 1–30 s . However, in our case, the hydrolysis was not affected because tosylic acid itself acts as a strong organic acid that is capable of carrying out the acid hydrolysis.…”

“…In situ, sulfuric acid reacted with the toluene used in the biphasic system and was converted into tosylic acid (Scheme ), which was evident from the formation of a thick slurry immediately after the addition of sulfuric acid to the biphasic system. This is comparable to the results obtained by Koeberg-Telder and Cerfontain in the sulfonation of toluene at 25 °C . According to Koeberg-Telder and Cerfontain, toluene is converted into mono- or disulfonic acid when reacted with concentrated sulfuric acid for 1–30 s .…”

“…This is comparable to the results obtained by Koeberg-Telder and Cerfontain in the sulfonation of toluene at 25 °C. 38 According to Koeberg-Telder and Cerfontain, toluene is converted into mono-or disulfonic acid when reacted with concentrated sulfuric acid for 1−30 s. 38 However, in our case, the hydrolysis was not affected because tosylic acid itself acts as a strong organic acid that is capable of carrying out the acid hydrolysis. Moreover, it was observed that, when the reaction medium was heated to the required temperature, tosylic acid reverted to toluene and sulfuric acid in the presence of water, and the biphasic system was re-formed after 40−60 min of reaction.…”