A solution of TFAA/H2SO4 is an atom-efficient liquid-phase system for rapid sulfonation of aromatic structures; H2SO4 is consumed stoichiometrically and the spent trifluoroacetic anhydride (TFAA) is readily recovered as trifluoroacetic acid (TFA) which can be recycled to TFAA.
(a) LindnerO., in Ullmann's Encyclopedia of Industrial Chemistry, 2000, Wiley-VCH Verlag, Weinhein, Germany; see under Benzenesulfonic Acids, and Derivatives
2.
BoothG., in Ullmann's Encyclopedia of Industrial Chemistry, 2000, Wiley-VCH Verlag, Weinhein, Germany; see under Naphthalenesulfonic Acids; www.interscience.wiley.com/ullmanns
3.
SikdarS.K., and HowellS.G., J. Cleaner Prod., 1998, 6, 253–259.
4.
(a) SmythT.P., and CorbyB.W., J. Org. Chem., 1998, 63, 8946–8951
5.
SmythT.P., and CorbyB.W., Org. Process Res. Dev., 1997, 1, 264–267.
6.
GrayA.D., and SmythT.P., J. Org. Chem., 2001, 66, 7113–7117.
7.
Catalysis by H3PO4 with acyltrifluoroacetates was first reported by Galli: GalliC., Synthesis, 1979, 303. Galli interpreted the role of H3PO4 as catalysing formation of the acyltrifluoroacetate (GalliC., J. Chem. Research (S), 1984, 272–273); in our work3a we unambiguously showed the catalytic role of H3PO4 following complete formation of the acyltrifluoroacetate.
8.
BakkerH.B., and CerfontainH., Eur. J. Org. Chem., 1999, 91–96. Reaction of TFA with SO3 is one industrially used method of preparing TFAA yielding H2SO4 as a co-product; use of P2O5 is a convenient lab-scale process.3b
9.
JefferyE.A., and SatchellD.P.N., J. Chem Soc., 1962, 1887–1894; 1913–1917.
10.
MakowskiH.S., LundbergR.D., and SinghalG.S., U.S. Patent 3,870,841, 1975.
11.
This process is exothermic as is the subsequent aromatic sulfonation. We restricted our work to small-scale reactions, and did not examine the reaction calorimetry of the individual steps.
