Acetyl p-Toluenesulfonate

[26908-82-7]  · C9H10O4S  · Acetyl p-Toluenesulfonate  · (MW 214.24)

(selective ether cleavage agent;1 acylating agent2)

Physical Data: mp 54-56 °C; d 1.092 g cm-3.

Solubility: sol acetonitrile, dichloromethane, toluene.

Form Supplied in: colorless crystals; commercially available, or readily prepared from Acetyl Chloride and p-Toluenesulfonic Acid.3

Analysis of Reagent Purity: NMR spectroscopy; traces of free acid and sulfonic anhydride may be present.

Handling, Storage, and Precautions: the solid is readily hydrolyzed, so it must be protected from contact with moisture; thermal decomposition is also possible.

Ether Cleavage.

Reaction conditions are relatively mild (25-130 °C, 2-48 h, usually in acetonitrile) and added Lewis acid catalysts are not necessary for effective reaction. Higher yields are more often obtained than with other reagents, and cleavage of unsymmetrical ethers occurs with high regioselectivity (eqs 1-4).1,4,5

The mechanism of cleavage of ethers is thought to proceed by initial acylation of the ether oxygen, followed by SN1-like cleavage to an acetate and an ion pair, which can collapse to give the tosylate. Thus cleavage of mixed ethers should favor cleavage of the bond to the more substituted carbon. In addition, the longer lifetime of a carbocation thus generated allows alternative pathways to compete with immediate ion pair collapse.

Mixed acetate sulfonate diesters are obtained from cyclic ethers. These have useful synthetic applications since the tosylate group is readily displaced by nucleophiles.

Acetylation Agent.

Acetyl p-toluenesulfonate is also used as a mild acetylation agent2 for furans (eq 5), thiophenes (eq 6), and anisoles (eq 7). High yields (75-96%) are readily attained using a 10-50% excess of reagent under mild reaction conditions (25 °C to reflux, 2-24 h, in acetonitrile or benzene). Once again, no Lewis acids are necessary. Acetyl p-toluenesulfonate is also a highly reactive acetylation agent for anilines, alcohols, and phenols.

Related Reagents.

Acetyl Methanesulfonate; Boron Tribromide; Iodotrimethylsilane.

1. (a) Karger, M. H.; Mazur, Y. JACS 1968, 90, 3878. (b) Karger, M. H.; Mazur, Y. JOC 1971, 36, 532.
2. (a) Karger, M. H.; Mazur, Y. JOC 1971, 36, 540. (b) Pennanen, S. I. H 1976, 4, 1021.
3. (a) Karger, M. H.; Mazur, Y. JOC 1971, 36, 528. (b) Lin, J. S.; Sleezer, P. D. U.S. Patent 4 219 495, 1980.
4. Bosworth, N.; Magnus, P. D. CC 1971, 618.
5. Corse, J.; Kuhnle, J. S 1972, 618.

Peter P. Giannousis

Ciba-Geigy Corporation, Summit, NJ, USA

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