4
K. Chen et al. / Tetrahedron xxx (xxxx) xxx
airborne isocyanates was executed this probe. With the good per-
formance in sensitivity, selectivity and anti-interference, this
strategy can be a reliable method to monitor isocyanates in air. It
also provides a referable approach for quantitative detection of
volatile organic compounds in air.
1.72 (m, 2H), 2.35 (s, 3H), 4.19 (t, J ¼ 7.2 Hz, 2H), 7.2 (d, J ¼ 9 Hz, 2H),
7.32 (d, J ¼ 7.2 Hz, 1H), 7.66 (d, J ¼ 9 Hz, 2H), 7.77 (t, J ¼ 8.4 Hz, 1H),
7.87 (d, J ¼ 7.2 Hz, 1H), 8.00 (d, J ¼ 7.8 Hz, 1H), 8.54 (d, J ¼ 8.4 Hz,
1H), 8.61 (d, J ¼ 7.8 Hz, 1H), 8.66 (d, J ¼ 7.2 Hz, 1H). MS(ESI): m/
z ¼ 413.1[M]þ.
4. Material and methods
4.5. Synthesis of N-buty- 4-(4-vinylphenol)-1,8-naphthalimide
(compound 3)
4.1. Reagents and chemicals
KOH (10 mg, 0.17 mmol) was dissolved in methyl alcohol
(10 mL). Then Compound 2 (50 mg, 0.12 mmol) was added into the
solution and kept stirring for 1 h. Next methyl alcohol was removed
by rotary evaporation. And residues were extracted by dichloro-
methane and water. The organic phase was collected and purified
by column chromatography on silica gel (dichloromethane). Finally
Compound 3 was obtained as orange powder(36 mg, 72%). 1H
NMR(CDCl3, 600 MHz, ppm): 1.00 (t, J ¼ 6 Hz, 3H), 1.46 (m, 2H), 1.75
(m, 2H), 4.21 (t, J ¼ 6 Hz, 2H), 6.93 (d, J ¼ 6 Hz, 2H), 7.30 (d, J ¼ 12 Hz,
1H), 7.57 (d, J ¼ 12 Hz, 2H), 7.76 (d, J ¼ 7.8 Hz, 1H), 7.80 (t, J ¼ 12 Hz,
1H), 8.00 (d, J ¼ 6 Hz,1H), 8.61 (d, J ¼ 6 Hz,1H), 8.65 (d, J ¼ 6 Hz,1H),
8.67 (d, J ¼ 6 Hz, 1H). MS(ESI): m/z ¼ 369.9[M ꢀ H]-.
4-Bromo-1,8-naphthalic
anhydride,
N-butylamine,
4-
acetoxystyrene, tri (o-tolyl) phosphine, palladium acetate, potas-
sium hydroxide, ethyl isocyanate (EI), 4,4-methylenediisocyanate
(MDI), phenyl isocyanate (PI), 2,4-toluene diisocyanate (TDI), hex-
amethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI)
were purchased from Aladdin Reagents. Methanol, ethanol,
dichloromethane, acetonitrile, triethylamine and petroleum ether
were of analytical grade reagents. In addition, the water used in this
work is double-distilled water.
4.2. Instruments
The fluorescence spectra were measured on a Hitachi F-7000
fluorometer. And the Evolution 220 UVevis spectrophotometer
was used for recording UVevis spectra. The Spectrum 100 spec-
trometer (PerkinElmer, America) was used for recording infrared
spectroscopy. 1H NMR spectra were measured on an AV600 nuclear
magnetic resonance spectromete (Bruker, Switzerland). Mass
spectra were obtained through a Bruker Esquire HCT Plus mass
spectrometer. HPLC data were acquired from an Agilent 600 Infinity
liquid chromatograph (Diode Array Detector).
4.6. Apparatus for absorbing gaseous ethyl isocyanate (EI)
To achieve the quantitative determination of ethyl isocyanate
(EI) in air, a gas-liquid mixing apparatus was designed to absorb
gaseous isocyanates efficiently. As shown in Fig. S1, the apparatus
includes two parts, one part equipped two porous plate absorption
tubes in series (section 1 in Fig. S1), the other part is an air sampler
with an air flow valve which can regulate air flow rate during
0.1e1.0 L/min (section 2 in Fig. S1). When it is working, gas from
sample bag flow pass gas-liquid mixing apparatus with a constant
rate, and gaseous isocyanates can be intensively mixed with probe.
All parts of this system are connected by rubber tubes.
4.3. Synthesis of N-buty-4-bromine-1,8-naphthalimide (compound
1)
To a stirred solution of 4-bromo-1,8-naphthalic anhydride (0.5 g,
1.8 mmol) in ethanol, butylamine (0.36 mL, 3.6 mmol) was added.
Then the mixture was heated to 85 ꢁC and kept it overnight under
nitrogen atmosphere. Then the mixture was cooled to room tem-
perature, and ethanol was removed by rotary evaporation. The
residue was extracted by water and dichloromethane. And the
organic phase was collected and dried under vacuum at 50 ꢁC. The
crude product was further purified by column chromatography on
silica gel (dichloromethane). Finally, Compound 1 was obtained as a
light yellow powder (386 mg, 77%). 1H NMR(CDCl3, 600 MHz, ppm):
0.96 (t, J ¼ 9 Hz, 3H), 1.44 (m, 2H), 1.70 (m, 2H), 4.13 (t, J ¼ 7.2 Hz,
2H), 7.75 (t, J ¼ 7.8 Hz, 1H), 7.94 (d, J ¼ 7.8 Hz, 1H), 8.32 (d, J ¼ 7.8 Hz,
1H), 8.44 (d, J ¼ 9 Hz, 1H), 8.57 (d, J ¼ 7.2 Hz, 1H). MS(ESI): m/
z ¼ 353.5[MþNa]þ.
4.7. Fluorescence method for quantitative detection of gaseous
isocyanates(EI)
To build a standard work curve between fluorescence emission
ratio and amounts of EI, fluorescence spectra of probe solution
(2 mM) containing different weight of EI were measured respec-
tively. Fluorescence emission ratio I527/I570 values were calculated
according to fluorescence spectra. The standard work curve was
obtained by versus I527/I570 values and weights of EI. To execute the
quantitative detection, six samples were made by volatilizing
certain content EI in gas sampling bags. The sample flow through
porous plate absorption tubes with rate at 1 L/min for 30 min.
Finally, the concentration of gaseous EI samples can be calculated
according to the linear equation and the total volume of tested gas.
4.4. Synthesis of N-buty-4-(4-acetoxystyrene)-1,8-naphthalimide
(compound 2)
4.8. Absorption spectrophotometry for quantitative detection of
gaseous ethyl isocyanates(EI)
Compound 1 (0.37 g, 0.9 mmol) was added into the mixed so-
lution of acetonitrile and triethylamine (1: 3 in V/V) and kept
The absorption spectrophotometry method was used as refer-
ence method to detect gaseous EI samples in this work. And DMSO-
HCl (1:1 in V/V) solution was used as absorption solution, in which
isocyanates could be hydrolyzed to ethylamine. Then ethylamine
was treated with 2,4-dinitrofluorobenzene, and 2,4-dinitrophenyl
ethylamine will generate. And the mass of isocyanates can be
calculated based on the amount of this component, which can be
quantified by measuring absorbance at 420 nm. Hence, a standard
work curve can be built by plotting absorbance at 420 nm versus
weight of EI. Then six samples were tested with the similar oper-
ation. These results from the reference method were used as
standard values to evaluate fluorescence probe method.
stirring for 5 min. Then 4-acetoxystyrene (204
mL, 1.26 mmol),
palladium acetate (1.2 mg, 0.0054 mmol) and tri (o-tolyl) phos-
phine (14.4 mg, 0.036 mmol) were added into the solution. Then
the solution was heated to 105 ꢁC and kept for 48 h under nitrogen
atmosphere. Then solution was cooled to room temperature and
extracted by water and dichloromethane. After that the organic
phase was collected and dried. The residue then was purified by
column chromatography on silica gel (dichloromethane: methyl
alcohol ¼ 10: 1) to obtain Compound 2 (102 mg, 26%). 1H
NMR(CDCl3, 600 MHz, ppm): 0.99 (t, J ¼ 7.2 Hz, 3H), 1.48 (m, 2H),
Please cite this article as: K. Chen et al., A novel ratiometric fluorescent probe for quantitative detection of isocyanates in air, Tetrahedron,