Synthesis of chemodosimeter 3: Aq NH4OH (32% v/v; 5 mL) was
added to a solution of compound 2 (750 mg, 2.14 mmol) in EtOH
(30 mL), and the solution was stirred at RT for 1 h. The solvent was
evaporated in vacuo to give a blue solid (700 mg, 2 mmol, 93%
yield). This blue solid (700 mg, 2 mmol) was dissolved in anhyd
CH3CN (20 mL), and after tert-butyldimethylsilyl chloride (424 mg,
2.2 mmol) and N-methylimidazole (493 mg, 6.6 mmol) were added,
the mixture was stirred at RT for 1 h. The solvent was evaporated
in vacuo, and the crude was dissolved in Et2O (20 mL), washed
with a concd Na2S2O3 (1ꢅ30 mL), dried with Na2SO4, filtered and
purified by column chromatography (alumina; hexane/acetone
9:1 v/v). The chemodosimeter 3 was obtained as a yellowish brown
highly selective and is one of the very few systems for fluoride
that displays sensing features in pure water. Moreover, the op-
tical changes are instantaneous, and, as far as we know, our
system is the fastest reagent for fluoride signalling in an aque-
ous environment using silyl ether-based probes.
Experimental Section
General: UV/Vis spectra were recorded with a JASCO V-650 spec-
trophotometer (Easton, MD, USA). Fluorescence measurements
were carried out in a JASCO FP-8500 spectrophotometer. 1H and
13C NMR spectra were acquired with a 400 MHz Bruker Avance III,
whereas mass spectra were carried out with a TripleTOF T5600
spectrometer (AB Sciex, Framingham, MA, USA).
1
solid (490.6 mg, 1.12 mmol, 56% yield): H NMR (CDCl3, 400 MHz):
d=0.25 (s, 6H), 1.02 (s, 9H), 6.89 (d, J=6.6 Hz, 2H), 7.04 (d, J=
15.0 Hz, 1H), 7.38 (d, J=15.0 Hz, 1H), 7.48 (m, 8H), 7.75 (s, 2H),
8.19 ppm (d, J=6.5 Hz, 4H); 13C NMR (100 MHz, CDCl3): d=À4.2,
18.4, 25.8, 116.1, 122.9, 128.9, 133.0, 135.0, 135.4, 135.6, 136.3,
141.1, 151.8, 161.2, 176.0, 177.4 ppm; HRMS (EI): m/z [M]+ calcd for
C31H34ONSi: 464.2331; found: 464.2403.
Triethyl orthoformate (98%), CH3I (99%), tert-butyldimethylsilyl
chloride (98%), 4-hydroxybenzaldehyde (98%), acetophenone
(99%), anhyd CH3CN (99.8%), magnesium, tetraphenylphosphoni-
um tetrafluoroborate and hexadecyltrimethylammonium bromide
(CTABr) were purchased from Sigma–Aldrich. Analytical grade sol-
vents, aq NH4OH (32% w/v), perchloric acid (60% v/v) and anhyd
MgSO4 were purchased from Scharlau (Barcelona, Spain).
Acknowledgements
Synthesis of 2,6-diphenylpyrylium perchlorate: Acetophenone
(4 mL, 34.3 mmol) and triethyl orthoformate (10 mL, 60.1 mmol)
were placed in a round-bottomed flask (250 mL) under Ar atmos-
phere at 08C. After 15 min of stirring, perchloric acid (60% v/v;
7.4 mL, 86.5 mmol) was added dropwise over 30 min. The reaction
was allowed to react at RT for 1 h. By addition of Et2O (15 mL), the
final 2,6-diphenylpyrylium perchlorate derivative was precipitated
as a yellow solid (10.1 g, 30.4 mmol, 88.6% yield). NMR data of the
synthesized product agreed with those described in the litera-
ture.[20]
Financial support from the Spanish Government (project
MAT2012–38429-C04–01) and the Generalitat Valencia (project
PROMETEO/2009/016) is gratefully acknowledged. S.E. is grateful
to the Generalitat Valenciana for his Santiago Grisolia fellowship.
Keywords: chemodosimeter
hydrolysis · silyl ether
· colour change · fluoride ·
Synthesis of 4-methyl-2,6-diphenylpyrylium tetrafluoroborate
(1): Magnesium (1 g, 41.1 mmol) was dissolved in anhyd Et2O
(20 mL), and the resulting solution was added dropwise to
a round-bottomed flask containing CH3I (5 mL, 80.3 mmol) dis-
solved in anhyd Et2O (30 mL). The mixture was stirred at RT for 1 h,
and was added dropwise to a round-bottomed flask containing
2,6-diphenylpyrylium perchlorate (2 g, 8.6 mmol) in anhyd Et2O
(50 mL) under Ar atmosphere. The crude reaction was stirred at RT
for 10 h and poured onto H2O (20 mL). After the organic layer was
washed with saturated aq NH4Cl (2ꢅ30 mL) and H2O (2ꢅ20 mL),
dried with anhyd MgSO4 and filtered, the solvent was evaporated
in vacuo. The sticky residue was dissolved in CH3CN (50 mL), and
triphenylcarbenium tetrafluoroborate (3 g, 9.1 mmol) was added.
The solution was stirred for 3 h at RT. After the solvent was evapo-
rated in vacuo, the residue was dissolved in a minimum volume of
acetone, and final product 1 was precipitated with n-hexane to
give a reddish brown solid (1.9 g, 5.7 mmol, 66% yield): 1H NMR
(400 MHz, [D6]DMSO): d=2.84 (s, 3H), 7.78 (t, J=6.5 Hz, 4H), 7.85
(t, J=6.5 Hz, 2H), 8.42 (d, J=6.5 Hz, 4H), 8.83 ppm (s, 2H).
b) R. H. Dreisbuch, Handbook of Poisoning, Lange Medical Publishers,
Los Altos, CA, 1980.
[4] WHO (World Health Organization), Geneva, 2002.
b) K. Kaur, R. Saini, A. Kumar, V. Luxami, N. Kaur, P. Singh, S. Kumar,
N. R. Song, J. H. Moon, M. Kim, E. J. Jun, J. Choi, J. Y. Lee, C. W. Bielawski,
[7] a) V. Amendola, D. Estebꢂn-Gꢀmez, L. Fabbrizzi, M. Licchelli, Acc. Chem.
demir, F. Sozmen, O. Buyukcakir, R. Gulyev, Y. Cakmak, E. U. Akkaya, Org.
[11] A. K. Atta, I. H. Ahn, A. Y. Hong, J. Heo, C. K. Kim, D. G. Cho, Tetrahedron
Synthesis of 4-((E)-2-(2,6-diphenylpyryliumtetrafluroborate-4-yl)-
vinyl)phenol (2): 4-Hydroxybenzaldehyde (184 mg, 1.5 mmol) was
added to a solution of compound 1 (500 mg, 1.5 mmol) in EtOH
(50 mL). The reaction was carried out at reflux for 12 h. The solvent
was evaporated in vacuo, and the final residue dissolved in a mini-
mum volume of acetone. Precipitation with n-hexane gave com-
pound 2 as a reddish solid (463.6 mg, 1.13 mmol, 75% yield):
1H NMR (400 MHz, [D6]DMSO): d=7.00 (d, J=6.6 Hz, 2H), 7.45 (d,
J=15.0 Hz, 1H), 7.79 (m, 8H), 8.38 (d, J=6.5 Hz, 4H), 8.67 (d, J=
15.0 Hz, 1H), 8.74 ppm (s, 1H).
[13] B. Zhu, F. Yuan, R. Li, Q. Wei, Z. Ma, B. Du, X. Zhang, Chem. Commun.
ꢄ 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemistryOpen 2013, 2, 58 – 62 61