Sulfonation of toluene

Sulfonation of toluene has been carried out using 98% H2SO4, 65% oleum, SO3, or even chlorosulfonic acid. As a result of sulfonation, a mixture of all the three isomers of toluene sulfonic acids are formed. However, the distribution of sulfonic acid isomers would follow the sequence maximum p-toluene sulfonic acid followed by o-toluene sulfonic acid and minimum of m-toluene sulfonic acid. In order to produce more m-toluene 

The properties of toluene sulfonic acids isomers are presented in Table 2.2 [7]. 

Component Usual form and molecular wt. Melting points 

Para-toluene sulfonic acid (pTSA) can be separated from a mixture of toluene sulfonic acids by crystallization and centrifuging. 

Para-toluene sulfonic acid is a versatile catalyst being as effective as sulfuric acid. In fact being solid it is less likely to affect the reactants in a process and is sometimes preferred to sulfuric acid. 

The sulfonation of toluene proceeds via a complex scheme of elemental reactions with numerous side and consecutive reactions. Toluene sulfonic acid and sulfur trioxide can read in a consecutive process to give toluene pyrosulfonic acid, which can undergo further reactions [315,316]. Reaction of this acid with another molecule of toluene yields two molecules toluene sulfonic acid or ditolyl sulfone. In addition, toluene sulfonic anhydride may be formed via readion of toluene pyrosulfonic acid with toluene sulfonic acid. 

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The following section describes as an example the sulfonation of toluene to />-toluenesulfonic acid. Concerning the formation of byproducts, see page 81. Figure 24 gives an overview of the process [162]. The maunufacture of p-toluenesulfonic acid follows continuously by the conversion of alkylbenzene with 96-100% sulfuric acid in the mixing vessel Rl. The formed water is re-... 

Sulfonation of toluene Two-stage sulfonation of toluene with H2S04 167... 

Sulfonation of Benzene and Alkylbenzenes. Since the main utilization of ben-zenesulfonic acid was its transformation to phenol, the importance of the sulfonation of benzene has diminished. The process, however, is still occasionally utilized since it is a simple and economical procedure even on a small scale. Excess sulfuric acid or oleum is used at 110-150°C to produce benzenesulfonic acid.97,102 Sulfonation of toluene under similar conditions yields a mixture of isomeric toluenesul-fonic acids rich in the para isomer. This mixture is transformed directly to cresols by alkali fusion. 

The details of protonation of several alkyl-substituted phenanthrenes by superacids have been reported.73 The observed mono- and di-cations are usually in agreement with those predicted by AMI MO calculations. Molecular modelling studies have suggested a multi-step pathway for the sulfonation of toluene widi sulfur trioxide.74 Intermediate 71-complcx. Wheland intermediate and pyrosulfonate species (34) are suggested, the product (p-toluenesulfonic acid) arising from an exothermic reaction between toluene and the acid (35) fonned by a facile prototropic rearrangement of (34). The sulfur trioxide monosulfonation of isopyrene and some derivatives leads usually to sulfonated... 

In the following, the concept of micro modular process engineering is introduced together with the backbone interface developed in order to realize this modular approach. The integration of sensors and an electronic bus system is also described, and the physical characterization of the backbone is discussed within a case study of the enantioselective synthesis of organoboranes. Within the second case study, the sulfonation of toluene with gaseous sulfur tri oxide, the backbone system together with the micro structured devices used is finally assessed based on its application to chemical synthesis. 

Case Study 2 [C 2] Chemical Characterization of the Backbone Using the Sulfonation of Toluene with Caseous S03... 

The highly exothermic sulfonation of toluene with gaseous sulfur trioxide is one reaction which has been investigated. Figure 4.43 shows the process flowsheet of the microstructured reactor plant used at the ACA. 

Figure 4.43 Process flow sheet for the sulfonation of toluene with gaseous S03 [86].

Precise control of concentration and residence time can increase the selectivity of the sulfonation of toluene, as this allows to optimally set the interplay between the readions 4.4.1-4.4.4 [315,316], The highly exothermic nature of the reaction demands for good temperature control. A single microreador is not suited to condud the various readion steps with all their different needs on temperature and residence time. Thus, a continuously operated plant with many microflow tools was developed. The plant design was based on a fluidic backbone providing unitized ports and plant unit sites to facilitate the connection of microstructured components from different suppliers (see Figure 4.49). 

Direct sulfonation of toluene with concentrated sulfuric acid gives a mixture of ortho and para sulfonic acids from which about 40% of toluene para sulfonic acid can be isolated as the sodium salt. The free acid is important as a convenient solid acid, useful when a strong acid is needed to catalyse a reaction. Being much more easily handled than oily and corrosive sulfuric acid or syrupy phosphoric acid, it is useful for acetal formation (Chapter 14) and eliminations by the El mechanism on alcohols (Chapter 19). It is usually called tosic add, TsOH, or PTSA (para toluene sulfonic acid). 

Sulfonation of toluene with 98-102% H2SO4 to produce toluene sulfonic acids has been discussed in detail in Chapter 2. The process can be extended to xylene for production of xylene sulfonic acid. Thus sulfonation of m-xylene with 95% sulfuric acid or chlorosulfonic acid yields a product consisting predominately of 2,4-dimethylbenze sulfonic acid which on caustic fusion at 320°C produces 2,4-xylene with 79% yield [1]. On heating the sulfonation mixture to approx. 220°C the more stable 3,5-dimethyl sulfonic acid which on fusion with excess alkali gives 3,5-xylenol [1,50]. 

Sulfonation of toluene produces along with sulfonic acids some water which is usually entrained with excess toluene and is removed azeotropically and the reaction mass is thereafter neutralized with soda ash (Na2C03) or sodium sulfite (Na2S03) which is recovered as a hy-product in the cresols plant. 

While mixed cresols (m-p-cresols) are mostly recovered from natural feedstocks as discussed above, para-cresol and coproduct ortho-cresol are produced via sulfonation of toluene. Meta-cresol is commercially produced as a co-product during manufacture of BHT from meto-para-cresols mixture. This is discussed in some details in the next chapter. 

Similarly, sulfonation of toluene with SO3-SO2 mixture at relatively low temperature of 25-50° C leads to a toluene sulfonic acid mixture practically free from metaisomer. 

Mitsui Petrochemical Industries Limited and Sumitomo Chemical Co. Ltd., Japan have been operating two 20,000 tpa plants wherein they produce mixed cresols (60% m-cresol and 40% p-cresol mixture) for the last many years. However, they do not separate the mixture of meta- and para-cymenes but convert the cymenes mixture to meto-para-cresols. M/s. Yanshen Petrochemicals, China near Beijing have been operating a similar 20,000 tpa meto-para-cresols plant based on alkylation of toluene. Both the Japanese and Chinese plants have been producing pure meto-cresol and BHT. Through a recent agreement, Sumitomo Chemicals sell 10,000 tpa cresols mixture to Merisol and the remaining 10,000 tpa m-p-cresols are converted pure meto-cresol and BHT. From environmental point of view, cresol plants based on alkylation of toluene are much cleaner and more eco-friendly than those based on sulfonation of toluene. 

Because of somewhat lower boiling point compared to m-cresol andp-cresol, o-cresol is obtained as a co-product during fractionation of cresols from coal tar acids or during production of para-cresol based on sulfonation of toluene. Most of the p-cresol manufacturers such as PMC, INSPEC (now Laporte), Atul and others are producing o-cresol in the range of 600-1500 tpa depending on p-cresol production. 

McNeil, D. Sulfonation of toluene. In Toluene, Xylenes and their Industrial Derivatives, Hancock, E.G., Ed. Elsevier Scientific Publishing Company Amsterdam, 1982, 228—231 pp. 

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