1
226
Can. J. Chem. Vol. 83, 2005
hence, is relatively disfavoured. However, ionization
Scheme 2) is not similarly disadvantaged. Thus, the pKa
values of ca. 10 found for 4a and 4b may be compared (3, 4,
5, 26) with corresponding values of ca. 13 for picramide
and N-alkylpicramides (13). In a related fashion, the acidity
in water–DMSO (20:80, v/v) of 7-anilino-4-nitrobenzo-
phosphate, were measured using a Jenway 3020 pH meter,
calibrated using aqueous buffers. All other materials and sol-
vents were the purest available commercial specimens.
(
1
2
H NMR spectra were measured using Bruker Ultrashield
400 MHz or Varian Inova 500 MHz spectrometers. Parent
2
molecules were dissolved in [ H ]-DMSO. Measurements in
6
furazan (14, pK 7.68) has been found (27) to be higher than
solutions containing sodium sulfite or sodium deuteroxide
were made in water–DMSO (80:20, v/v) using deuteriated
solvents. Parent concentrations were in the range 0.005–
a
that of 2,4,6-trinitrodiphenylamine (pK 8.20).
a
–
3
0
.01 mol dm with the nucleophile concentration (ca.
R
H
Ph
H
–
3
N
N
0.1 mol dm ) in large excess. UV–vis spectra and kinetic
measurements were made at 25 °C with a PerkinElmer
Lambda 2 spectrophotometer, a Shimadzu UV-2101 PC
spectrophotometer, or an Applied Photophysics SX-17 MV
stopped-flow instrument. Reported rate constants are the
mean of several determinations and are precise to ±5ꢀ.
O N
2
NO2
N
N
O
NO2
NO2
1
3
14
Acknowledgement
The high reactivity of 4c and 4d towards hydrolysis
Scheme 3) may be attributed to the contribution of the reso-
We thank the Royal Society, London, for financial assis-
tance to allow C. Isanbor to visit Durham.
(
nance from 9 to the structure. This gives the carbon–nitrogen
bond iminium ion character, hence explaining (28) the reac-
tivity towards the attack of hydroxide. The values obtained
References
3
–1 –1
for k of ca. 1 dm mol
s may be compared (29) with val-
7
1
2
3
. H. Mayr, B. Kempf, and A.R. Ofial. Acc. Chem. Res. 36, 66
2003).
. B. Kempf, N. Hampel, A.R. Ofial, and H. Mayr. Chem. Eur. J.
, 1 (2003).
. E. Buncel, M.R. Crampton, M.J. Strauss, and F. Terrier. Elec-
tron deficient aromatic- and heteroaromatic-base interactions.
Elsevier, Amsterdam. 1984.
3
–1 –1
ues of 0.0031 and 0.015 dm mol
attack of hydroxide on 1-piperidino- and 1-pyrrollidino-
,4,6-trinitrobenzene, respectively. It is interesting that in al-
s
for the corresponding
(
2
9
kaline solutions, 4a and 4b, where anion formation predomi-
nates, are very slowly hydrolysed. This is likely to involve
hydroxide attack on low concentrations of the parent mole-
cules. As in previous work (10), there is no evidence for an
attack of sulfite at the 7 position of 4-nitro-7 substituted
benzofurazans, presumably owing to unfavourable steric in-
teractions.
4
. F. Terrier. Nucleophilic aromatic displacement. VCH, New
York. 1991.
5. F. Terrier, S. Lakhdar, R. Goument, T. Boubaker, and E.
Buncel. Chem. Commun. 22, 2586 (2004).
6
. F. Terrier, A.-P. Chatrousse, and F. Millot. J. Org. Chem. 45,
666 (1980).
. C.F. Bernasconi. J. Am. Chem. Soc. 72, 4682 (1970).
2
Experimental
7
Compounds 4a–4d were prepared from 7-chloro-4-nitro-
benzofurazan by reaction with 4 equiv. of the appropriate
amine in DMSO. Mixtures were stirred for 5 h at room tem-
perature and quenched in ice-cold dilute hydrochloric acid.
The precipitates were filtered, washed with water and etha-
8. M.R. Crampton, J. Delaney, and L.C. Rabbitt. J. Chem. Soc.
Perkin Trans. 2, 2473 (1999).
9. L.C. Rabbitt. Ph.D. thesis, University of Durham, Durham,
UK. 2000.
10. M.R. Crampton, L.M. Pearce, and L.C. Rabbitt. J. Chem. Soc.
Perkin Trans. 2, 257 (2002).
1. M.R. Crampton, R.E.A. Lunn, and D. Lucas. Org. Biomol.
1
nol, and recrystallized from ethanol. H NMR spectra are re-
1
ported in Table 1, and indicated the absence of impurities.
+
Chem. 1, 3438 (2003).
12. P.B. Ghosh, B. Ternai, and M.W. Whitehouse. J. Med. Chem.
4
(
a: mp 164 °C. MS (ES ) m/z 209 corresponds to C H N O
8
9
4
3
+
+
M + H ). 4b: mp 90 °C. MS (ES ) m/z 237 corresponds to
C H N O (M + H ). 4c: mp 166 °C. MS (ES ) m/z 249
+
+
11, 305 (1968).
1
0
13
4
3
+
13. P.B. Ghosh, B. Ternai, and M.W. Whitehouse. J. Med. Chem.
15, 255 (1972).
corresponds to C H N O (M + H ). 4d: mp 210 °C. MS
1
1
13
4
3
+
+
(
ES ) m/z 235 corresponds to C H N O (M + H ).
10 11 4 3
1
4. M.W. Whitehouse and P.B. Ghosh. Biochem. Pharmacol. 17,
58 (1968).
5. B.S. Baines, G. Allen, and K. Brocklehurst. Biochem. J. 163,
89 (1977).
Sulfite solutions were prepared from AnalaR sodium sul-
1
fite. To check that no depletion of sulfite concentration oc-
curred because of hydrolysis when making kinetic and
equilibrium measurements, measurements were also made in
solutions buffered at pH 8.3 using mixtures of sodium sulfite
and sodium hydrogen sulfite. The values of rate and equilib-
rium constants obtained were identical, within experimental
error, to those obtained in unbuffered solutions with the
same sulfite concentration. Solutions of known hydroxide
concentration were made by dilution of AnalaR sodium hy-
droxide solution. The pH values of buffer solutions, borax or
1
1
1
1
1
6. T. Hiratsuka and T. Kato. J. Biol. Chem. 262, 6318 (1987).
7. A. Chattopadhyay. Chem. Phys. Liquids, 53, 1 (1990).
8. S. Uchiyama, T. Santa, and K. Imai. J. Chem. Soc. Perkin
Trans. 2, 2525 (1999).
9. J.M. Boon, R. Shukla, B.D. Smith, G. Licini, and P. Scrimin.
Chem. Commun. 260 (2002).
1
20 C.F. Bernasconi and R.G. Bergstrom. J. Am. Chem. Soc. 95,
3603 (1973).
©
2005 NRC Canada