Desulfonation reaction
In organic chemistry, the desulfonation reaction is the hydrolysis of aryl and naphthyl sulfonic acids:[1]
- RC6H4SO3H + H2O → RC6H5 + H2SO4
It is the reverse of sulfonation.[2] The temperature of desulfonation correlates with the ease of the sulfonation.
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]
Related reaction
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
- ^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
- ^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
- ^Harry P. Schultz (1951). "2,6-Dintroaniline". Org. Synth. 31: 45. doi:10.15227/orgsyn.031.0045.
- ^Ralph C. Huston; Murel M. Ballard (1934). "o-Bromophenol". Org. Synth. 14: 14. doi:10.15227/orgsyn.014.0014.
- ^Arthur W. Weston, C. M. Suter (1941). "3,5-Dihydroxybenzoic Acid". Organic Syntheses. 21: 27. doi:10.15227/orgsyn.021.0027.
