spectrum of NH4+‚EPX- and the UV-visible spectrum of EPX-
are shown in Figures 1 and 2, respectively.
Table 2. Schedule of Events for the Optimized
Chromatographic Methoda
P otassium Ethyl (Mono)thiocarbonate (KETC). KETC was
prepared by the reaction of carbonyl sulfide gas with a potassium
ethoxide solution.17,19 Carbonyl sulfide gas was generated by
reacting ammonium thiocyanate with sulfuric acid. Ammonium
thiocyanate, 12 g in 20 cm3 of water, was added to 150 cm3 of 40%
(v/ v) sulfuric acid solution. Liberation of the COS gas was
facilitated by heating the solution to between 40 and 50 °C and
using high-purity nitrogen as a carrier gas. HCN impurities were
removed by passing the COS gas through two solutions of 1 mol
dm-3 potassium hydroxide. The COS gas was then passed into a
potassium ethoxide solution prepared by dissolving 7.8 g of
pulverized potassium hydroxide in 160 cm3 of ethanol. At the
completion of the reaction, the white KETC product was chilled
at 5 °C and filtered. The crude KETC product was recrystallized
twice from warm ethanol. Product purity was determined by
chemical microanalysis (Calcd for C3H5O2SK: C, 24.98; H, 3.49;
O, 22.18; S, 22.23; K, 27.10. Found: C, 24.68; H, 3.38; S, 22.25; K,
time
E1
E2
E3
E4
(min)
(%)
(%)
(%)
(%)
function
0.0
0.1
1.0
3.9
4.0
6.5
12.9
13.0
0
0
2
2
0
0
0
0
50
50
50
50
50
50
50
50
20
20
20
20
20
50
50
20
30
30
28
28
30
0
column equilibration
injection
addition of NaOH
start acetonitrile gradient
stop NaOH addition
complete acetonitrile gradient
end isocratic run
0
30
stop chromatogram
a
E1, 100 mmol dm-3 NaOH; E2, 10 mmol dm-3 TBA+‚OH-, 10
mmol dm-3 phosphoric acid, in 20% (v/ v) acetonitrile-water solution
(pH 8.0); E3, 50% (v/ v) acetonitrile-water solution; E4, Milli-Q water.
purity of the TBA+‚EXT- product was determined by chemical
microanalysis (Calcd for C19H41O4NS4: C, 47.96; H, 8.69; O, 13.45;
N, 2.94; S, 26.96. Found: C, 48.36; H, 8.89; N, 3.07; S, 26.49.).
Traces of CHCl3 (∼3%) were detected in the TBA+‚EXT- product
(via analysis of Cl), and the experimental microanalysis results
listed for the TBA+‚EXT- product have been corrected for the
carbon and hydrogen contributions from CHCl3. Attempts to
remove all traces of CHCl3 from the product resulted in decom-
1
28.6.). H and 13C NMR analysis: δH (D2O, 250 MHz) 1.25 (3H),
4.1 (2H); δC (D2O, 62.9 MHz) 16.4 (CH3), 65.4 (CH2), 188.1
(C(dO)S-). APCI-MS examination of the KETC product yielded
negative ion parent peak at m/ e 105.2, compared to the expected
value of m/ e.105. The FT-IR spectrum of KETC is shown in Figure
1, and the UV-visible spectra of the ETC- anion is shown in
Figure 2.
position of the EXT-, as revealed by HPLC analysis. H and 13C
1
NMR analysis yielded the following results: δH (CDCl3, 250 MHz)
1.41 (3H), 4.64 (2H); δC (CDCl3, 62.9 MHz) 13.3 (CH3), 71.0 (CH2),
211.0 (C(dS)S). Analysis of the product by APCI-MS yielded a
negative ion parent peak at m/ e 233.0, which is equal to that
expected for the dominant ion. The FT-IR spectrum of TBA+‚EXT-
is shown in Figure 1, and the UV-visible spectrum of the EXT-
anion is shown in Figure 2.
Instrumentation. A Dionex DX300 chromatography system
was used in this study, consisting of a model AGP-I gradient pump
(Dionex) and a multiport valve injector fitted with a 50-µL sample
loop. The column eluant was monitored with a multiwavelength
(rapid-scanning) UV-visible detector (Linear PHD 206) which was
configured to record full spectra over the wavelength range 200-
360 nm in 5-nm steps. In addition, the specific wavelengths of
221, 289, 301, and 348 nm were monitored. The analytical column
used was a Waters (Milford, MA) Nova-Pak C-18 column (150
mm by 3.9 mm i.d.) fitted with a C-18 guard column, held in a
Guard-Pak module. The chromatographic data were collected and
processed with a Dionex AI-450 program.
Tetrabutylammonium Ethyl Xanthyl Thiosulfate (TBA+‚
EXT-). TBA+‚EXT- was prepared using a method adapted from
Jones and Woodcock.6 A 1.2-g sample of KEX and 1.92 g of sodium
thiosulfate pentahydrate were dissolved in 20 cm3 of water. Iodine,
2.08 g dissolved in 25 g of ethanol, was added to the ethyl
xanthate/ thiosulfate mixture until a slight excess of iodine was
observed. As reported by Jones and Woodcock,6 the reaction
products include EXT-, (EX)2, and tetrathionate (S4O62-), as well
as excess iodine. The (EX)2 and iodine were removed by washing
three times with 30 cm3 of chloroform and three times with 30
cm3 of diethyl ether. The EXT- remaining in the aqueous phase
was then precipitated as a partially water insoluble material by
the addition of tetrabutylammonium bromide (TBA+‚Br-). The
quantity of TBA+ required was determined by measurement of
the solution concentration of EXT-, using the extinction coefficient
of the 289-nm absorption band determined in this work (see Figure
2 and Table 3). The TBA+‚EXT- was extracted with two portions
2-
of 60 cm3 of diethyl ether, with the S4O6 remaining in the
The eluant flow rate was fixed at 2.0 cm3 min-1 for all eluant
compositions described in this paper. Whenever the composition
of the eluant was changed, the column was reequilibrated with
the new mobile phase for at least 20 min prior to injecting the
sample. Each species was loaded onto the column using a 25%
acetonitrile-water eluant containing 2.5 mM TBA+ and 2.0 mM
phosphoric acid. All data points were obtained in at least duplicate.
All the experiments were conducted at 21 ( 1 °C.
aqueous phase. The two diethyl ether extracts were combined
and washed with 25 cm3 of 0.1 mol dm-3 potassium iodide in order
to convert any remaining iodine into I3-, which would be
transferred to the aqueous phase. The diethyl ether fraction was
dried with Na2SO4 and evaporated, yielding a crude TBA+‚EXT-
oil-like product. The crude TBA+‚EXT- was dissolved in 5-10
cm3 of ethanol and added dropwise to 50 cm3 of rapidly stirred
water. The redispersed TBA+‚EXT- was extracted into 30 cm3 of
chloroform; the chloroform phase was dried (Na2SO4) and
evaporated to yield a more pure TBA+‚EXT- oily product. Aqueous
solutions of the sparingly soluable TBA+‚EXT- product were
shown by ion interaction chromatography to be free of UV-visible-
absorbing impurities, in particular, iodine, S4O62-, and (EX)2. The
1
The high-field H and 13C NMR spectra were recorded on a
Bruker AC250 NMR spectrometer at 250.13 and 62.90 MHz,
respectively. All chemical shifts are reported in ppm relative to
tetramethylsilane (TMS). FT-IR spectra shown in Figure 1 were
recorded using a Perkin-Elmer 2000 FT-IR spectrometer. UV-
visible spectra shown in Figure 2 were recorded using a Cary
500 UV-visible-NIR spectrophotometer.
(19) Murphy, C. N.; Winter, G. Aust. J. Chem. 1 9 7 3 , 26, 755-760.
Analytical Chemistry, Vol. 72, No. 20, October 15, 2000 4839