Desulfonation reaction

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In organic chemistry, the desulfonation reaction is the hydrolysis of aryl and naphthyl sulfonic acids: [1]

Contents

RC6H4SO3H + H2O → RC6H5 + H2SO4

It is the reverse of sulfonation. [2] The temperature of desulfonation correlates with the ease of the sulfonation.

Desulfonation reaction equation.svg

Applications in synthesis

This reactivity is exploited in the regiospecific preparation of di- and tri-substituted aromatic compounds. The approach exploits the meta-directing effect of the sulfonic acid group. 2-Chlorotoluene for example can be prepared by chlorination of p-toluenesulfonic acid, followed by hydrolysis. The method is also useful for the preparation of 2,6-dinitroaniline [3] and 2-bromophenol via phenol-2,4-disulfonic acid. [4]

In contrast to the acid-catalyzed desulfonation is the alkaline fusion of aryl sulfonates, which is used to prepare phenols:

ArSO3Na + 2 NaOH → ArONa + Na2SO3 + H2O (Ar = aryl)
ArONa + H+ → ArOH + Na+

The first stage in alkaline fusion entails the dissolution of the aryl sulfonic acid or arylsulfonate salt in molten alkali metal base, such as a mixture of sodium hydroxide-potassium hydroxide at high temperatures, say 250 °C. [5]

References

  1. ↑ Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, p. 749, ISBN   978-0-471-72091-1
  2. ↑ Otto Lindner, Lars Rodefeld "Benzenesulfonic Acids and Their Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry 2005, Wiley-VCH, Weinheim. doi : 10.1002/14356007.a03_507
  3. ↑ Harry P. Schultz (1951). "2,6-Dintroaniline". Org. Synth. 31: 45. doi:10.15227/orgsyn.031.0045.
  4. ↑ Ralph C. Huston; Murel M. Ballard (1934). "o-Bromophenol". Org. Synth. 14: 14. doi:10.15227/orgsyn.014.0014.
  5. ↑ Arthur W. Weston, C. M. Suter (1941). "3,5-Dihydroxybenzoic Acid". Organic Syntheses. 21: 27. doi:10.15227/orgsyn.021.0027.
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