2
SU ET AL.
ꢂ
(compound 5, 59.8% yield) were obtained; m.p. > 300 C, IR (KBr pel-
traditional fluorescent molecular structures such as coumarin, rhoda-
mine and fluorescein. Moreover, the synthesis of such probes is com-
plex and it is more difficult to further derivatize from those structures.
As an important class of heterocyclic compound, there have been
many studies on 1,3,4-oxadiazole in virtue of its excellent biological
ꢁ
1
1
let, cm ): 3440, 2988, 2920, 1649, 1089, and 594. H-NMR
13
(600 MHz, DMSO-d
6
, ppm): 7.65 (s, 4H), 7.07 (s, 2H). C-NMR
(125 MHz, DMSO-d
6
, ppm): 112.62, 140.42, 149.92, 163.52. MS
+
ꢂ
(ESI): m/z = 235 [M + H] . m.p. > 300 C.
[
15]
and optical properties,
been rarely studied.
but its strong fluorescence properties have
By directly dissolving compound 5 in ethanol, the stock solutions
2
of compound
5
ꢁ2
(1 ꢀ 10ꢁ M) were prepared. Different stock
0
2+
2+
2+
3+
2+
+
3+
Here,
a
hetero-tricyclic compound 5,5 -(furan-2,5-diyl)bis
solutions (1 ꢀ 10 M) of Cu , Zn , Mg , Y , Ca , Rb , Ce
,
2
+
2+
3+
2+
(
1,3,4-oxadiazole-2-amine) (5) was synthesized using a one-step-
Ni , Pb , La , and Mn
were prepared by reverse osmosis
(RO) water, in addition, Pd (1 ꢀ 10ꢁ2 M) was placed in dimethyl
formamide (DMF). Then to obtain the corresponding concentration
value, all the stock solutions were diluted with RO water.
2+
process from the condensation of 2,5-furandicarboxyl hydrazide with
bromide cyanogen followed by alkalization. Research shows that com-
pound 5 has very strong fluorescence intensity and that it could react
2
+
with Pd ions in water solvent rapidly, therefore it was designed as a
selective chemical probe with speed, sensitivity, and convenient
properties.
3
3
|
RESULTS AND DISCUSSION
| Synthesis and characterization
.1
2
|
EXPERIMENTAL
Routinely, it is easy to form an oxadiazole ring using the condensation
of cyanogen bromide with amine group compounds promoted using
sulfuric acid, hydrochloric acid, phosphoric acid, sodium bicarbonate,
or sodium hydroxide at different temperatures under alkalescent
All reagents and raw materials were acquired by commercial
procuration.
Compound 5 was synthesized following the procedures described
in Scheme 1. A solution of 0.920 g (5 mmol) dimethyl furan-2,-
0
conditions. The tricyclic compound, 5,5 -(furan-2,5-diyl)bis(1,3,4-
5
-dicarboxylate (1) in 30 ml ethanol was added into a flask (50 ml)
oxadiazole-2-amine) (5), has a pair of oxadiazole rings, consequently
it was synthesized using one-step-process by condensation of
2,5-furandicarboxyl hydrazide with cyanogen bromide in sodium
bicarbonate solution. Caution: cyanogen bromide is toxic, highly irri-
tating, and can cause death; laboratories and personnel must be prop-
erly trained. Note: the target compound was formed under acid or
base conditions, but the reaction mechanism is not clear.
containing a thermometer and magnetic stirrer. The mixture was
ꢂ
heated at 70 C. Then the mixture was added dropwise to 2 ml iso-
thermal hydrazine monohydrate, the reaction mixture was kept at
ꢂ
7
0 C for 30 min. A large amount of flocculent solids separated out,
and the solution was cooled to room temperature. The precipitate
was collected using filtration and gave 0.87 g of compound 1 as a
white flocculent crystal (compound 2, furan-2,5 -dicarboxylic acid
Compound 5 was characterized (Figure S1–S4). Detailed data
analysis is provided as follows.
ꢁ
1
dihydrazide). Yield: 94.6%; FT-IR spectrum (KBr pellet, cm ): 3262,
ꢂ
2
981, 1669, 1638, 1602, 1554, 1489 and 1298. m.p.178–179 C.
Compound 3 (0.552 g, 3 mmol) and potassium bicarbonate (5.544 g,
ꢂ
6
.6 mmol) were suspended in methanol (30 ml) at 0 C. Bromine cya-
3.1.1
|
Spectra date
nide (0.63 g, 6 mmol) was directly added into the mixture above. Then
ꢂ
stirred overnight at 0 C, heated up to room temperature and stirred
To evaluate the effects of different ions on the optical response of
compound 5, UV–Vis spectra of compound 5 with or without differ-
ent metal ions in water were recorded (Figure 1). According to the
UV–Vis absorbance data (Figure 1), the λmax of compound 5 was
for another 24 h. TLC under 365 nm ultraviolet irradiation indicated
that the target compound was mainly produced, the precipitate was
collected and recrystallized from methanol, 0.42 g brown crystals
0
SCHEME 1 Synthesis of 5,5 -(furan-2,5-diyl)bis(1,3,4-oxadiazole-2-amine) (5)