Journal of the Chinese Chemical Society, 2008, 55, 1313-1316
1313
Synthesis and Fluorescent Properties of
2-Arylamino-5-(3-aryl-1-phenyl-pyrazol-4-yl)-1,3,4-thiadiazoles
Cun-Kui Li (
College of Chemistry and Chemical Engineering, Xinjiang University, Urumqi Xinjiang 830046, P. R. China
) and Ling-Hua Cao* (
)
A series of novel pyrazolyl-substituted 1,3,4-thiadiazole derivatives (6a-6d, 7a-7d, 8a-8d) were pre-
pared by cyclization of the intermediate 3-aryl-l-phenyl-pyrazol-4-ylformaldehyde 4¢-phenylthiosemicar-
bazones with 0.5 M ferric chloride solution. The structures of the new compounds were confirmed by IR,
1H NMR and elemental analysis. Simultaneously, the compounds were detected by fluorescence spectro-
photometer and had preferable fluorescence activity.
Keywords: 4-Formylpyrazole; 1,3,4-Thiadiazole; Fluorescent property.
INTRODUCTION
Several pyrazole derivatives exhibit anti-inflamma-
5d were synthesized in good yields by the reactions of 3-
aryl-1-phenyl-4-formylpyrazole 1a-1c with 4¢-phenylthio-
semicarbazide 2a-2d.
tory, antimicrobial, analgesic and antipyretic activities.1-4
Various substituted thiadiazoles also exhibit biological be-
havior.5-7 A large number of 1,3,4-thiadiazoles have be-
come very useful compounds in many fields of technology.
Some of the technological applications involve photo-
graphic materials,8 lubricating compositions,9 optically ac-
tive liquid crystals, light-emitting materials10 and many
others. In addition, fluorescent detection is of paramount
importance to biological studies.11,12 The sensitivity of flu-
orescence techniques has reached an extremely high level,
similar to radioactive methods, and can even provide infor-
mation on the dynamic structure of dyebound biomole-
cules. Therefore, interest in the synthesis of pyrazole with a
thiadiazolyl group substituted at a suitable position by a
convenient method is significant. In view of this, some novel
1,3,4-thiadiazoles containing pyrazole ring were synthe-
sized by the reaction of 3-aryl-l-phenyl-pyrazol-4-ylform-
aldehyde 4¢-phenylthiosemicarbazones with 0.5 M ferric
chloride solution (Scheme I).
In this study, we found that the temperature of the re-
action has a great impact on the level of yield. The treat-
ment of 3-aryl-l-phenyl-pyrazol-4-ylformaldehyde 4¢-phen-
ylthiosemicarbazones (3b-5b) with ferric chloride in etha-
nol solution, following by heating under 70 °C in an oil bath
for about 2 h, produced the desired products 6b-8b with
favorable yields (Table 1), while other target compounds
were synthesized under 80 °C.
The IR spectrum of compounds 6a-6d, 7a-7d and
8a-8d showed broad bands at 3400-3200 cm-1, assigned to
their NH. The strong bands appearing at around 1620 cm-1
were attributed to absorption of C=C in pyrazole ring. The
appearance of the absorption at 1450-1600 cm-1 was as-
cribed to benzene skeleton vibration. The signals at 697
cm-1 were identified as C–S–C in thiadiazole ring.
The 1H NMR of compounds 6a-6d, 7a-7d, 8a-8d in
CDCl3 showed a few single peaks at d 8.80-10.60 due to the
proton of N-H, multiple peaks at d 6.90-7.90 ascribable to
aromeric protons and peaks at d 8.39-8.55 assignable to
methylidene proton of the pyrazole group owing to the
deshielding effect of the larger conjugated system formed
by cycle-pyrazole and cycle-thiadiazole.
RESULTS AND DISCUSSION
Thiosemicarbazones exhibit various biological activ-
ities and are extensively applied in medicine-particularly in
the treatment of tuberculosis.13 Numerous compounds with
a thiosemicarbazone moiety also exhibit biological activ-
ity.14 Accordingly, 3-aryl-l-phenyl-pyrazol-4-ylformalde-
hyde 4¢-phenylthiosemicarbazones 3a-3d, 4a-4d, and 5a-
Solid-state fluorescence spectrum of compounds 6a-
6d, 7a-7d and 8a-8d were determined with solid powder on
a quartzround plate with excitation and emission slits of
2.5/2.5 nm by spectrophotometry. The optimum excitation
* Corresponding author. E-mail: clhxj@xju.edu.cn
Li, Cun-Kui
