TABLE 1. Yields and Chemical Data for Sulfonic Acids 2a-2f
Melting points of the
S-benzylthiouronium
salts, °C
Sulfonic Yields,
acids
Chemical shift
Melting
points, °C
%
(300 MHz, C D O, δ, ppm)
3
6
2
a
70 7.74 (s, 1H); 6.95 (s, 1H), 3.91 (s, 3H); 3.26 (m, 1H), 2.61 (s, 3H), 1.19 (d, 6H)
74 7.90 (s, 1H), 6.73 (s, 1H), 3.86 (s, 3H), 3.62 (m, 1H), 2.23 (s, 3H), 0.92 (d, 6H)*
40 7.63 (s, 1H), 6.86 (s, 1H), 3.86 (s, 3H), 2.58 (s, 3H), 2.13 (s, 3H)
103
72
226-228
170-172
174
2
b
2
c
90
2
d
77 7.43 (s, 1H), 7.00 (s, 1H), 3.89 (s, 3H), 3.83 (s, 3H), 2.95 (m, 2H),
100
184-186
1.70 (m, 2H), 0.98 (t, 3H)
2
2
e
f
67 7.33 (s, 1H), 6.74 (s, 1H), 5.96 (s, 2H), 2.92 (m, 2H), 1.63 (m, 2H), 0.93 (t, 3H)
52 7.25 (s, 1H), 6.87 (s, 1H), 6.09 (s, 2H), 3.89 (s, 3H)
-
175
174
104
_
*
_____
Chemical shifts in CDCl3.
The regiospecificity of the bis(trimethylsilyl) sulfate reagent is noteworthy. The drastic conditions used with other
sulfonating reagents can give the so-called abnormally oriented isomers as major products from some ortho-para directing as
well as meta-directing groups [7].
The regiochemistry of the sulfonation of alkoxyphenyl ethers with SO is linked to experimental conditions that lead
3
to a mixture of the ortho-para isomers [8]. In addition, depending on chemical factors (temperature, solvent, etc.) side-reactions
can also occur, such as formation of diaryl sulfones or arylpyrosulfonic acids [9]. Our results show that these problems are
overcome when using bis(trimethylsilyl) sulfate and are in good agreement with results previously obtained by Bourgeois and
Duffaut [3].
In an appropriate round-bottom flask fitted with a Dean and Stark apparatus, a mixture of the phenolic derivative
(
0.02 mol) and bis(trimethylsilyl) sulfate (0.02 mol) in methylcyclohexane (30 mL) were refluxed for 10 h until the expected
volume of water calculated from the global sulfonation equation (described in [4]) was obtained. Sulfonates were hydrolyzed
by the literature method [4]. S-Benzylthiouronium salts and sulfonamides were obtained by literature methods, respectively [4]
and [5].
1
Yields, chemical shifts of H NMR spectra, melting points of the synthesized sulfonic acids, and the corresponding
S-benzylthiouronium salts are given in Table 1.
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1.
2.
3.
4.
5.
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P. Bourgeois and N. Duffaut, Bull. Soc. Chim. Fr., No. 3–4, Pt. 2, 195 (1980).
A. I. Vogel, Vogel’s Textbook of Practical Organic Chemistry, Longman Scientific & Technical, John Wiley &
Sons, New-York, 1978.
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.
A. Aramini, M. C. Cestas, S. Coniglio, C. Byani, S. Colagiora, V. D’Elia, and M. Allegretti, J. Org. Chem., 68,
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911 (2003).
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8
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E. E. Gilbert, Sulfonation and Related Reactions, Intersciences, New–York, 1965.
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