Supporting Information
Solving the 170-Year-Old Mystery About Red-Violet and Blue
Transient Intermediates in the Gmelin Reaction
Yin Gao, Abouzar Toubaei, Xianqi Kong, and Gang Wu*[a]
chem_201503353_sm_miscellaneous_information.pdf
Supporting Information
Solving the 170 Year Old Mystery about Red-Violet and Blue
Transient Intermediates in Gmelin Reaction
Yin Gao, Abouzar Toubaei, Xianqi Kong, and Gang Wu*
Department of Chemistry, Queen’s University, 90 Bader Lane, Kingston,
Ontario, Canada K7L 3N6
E-mail: [email protected]
1. Experimental details
Materials. All chemicals were obtained from Sigma-Aldrich unless stated otherwise:
sodium nitroprusside (SNP, Na2[Fe(CN)5NO]·2H2O), sodium hydroxide (NaOH), 15N-labeled
sodium nitrite (Na15NO2, 98% 15N), 17O-labeled water (H217O, 41.1% 17O, purchased from
CortecNet), ethylenediaminetetraacetic acid (EDTA, C10H16N2O8), sodium carbonate (Na2CO3),
sodium bicarbonate (NaHCO3), sodium chloride (NaCl), potassium cyanide (KCN), and ionexchange resin (Amberlite IR-120, strongly acidic form).
Synthesis of 15N- and 17O-labelled SNPs. 15N-labeled SNP (Na2[FeII(CN)5(15NO)]·2H2O)
was prepared in aqueous solution by mixing commercial SNP (260 mg) with 1.1 molar
equivalents of NaOH and 5 molar equivalents of Na15NO2. The reaction mixture was kept at
room temperature for 10 min, followed by addition of 285 µL of 4 M acetic acid. The reaction
solution was concentrated to a paste on a rotary evaporator. The residual material was redissolved in 2 mL of 4 M acetic acid and the solvent was evaporated on a rotary evaporator. This
process was repeated once. The obtained solid was treated with 1,4-dioxane (4 mL). The solid
materials were collected by filtration, washed with ethanol (2 × 3 mL), and then dried under
vacuum (153 mg, yield 59%). The 15N enrichment level in the final product was about 80%. 15N
NMR (50.6 MHz, D2O): 371 ppm (referencing to liquid NH3); 13C NMR (125.6 MHz, D2O):
134.81 ppm (Ceq) and 132.84 ppm (Cax). 17O-labeled SNP (Na2[FeII(CN)5(N17O)]·2H2O) was
prepared by mixing 265 mg of commercial SNP and 35.6 mg of NaOH in 300 µL of H217O (41.1%
17
O, purchased from CortectNet). A few grains of Amberlite IR-120 (strongly acidic form) were
gradually added to the reaction mixture and the progress of this reaction was monitored via 17O
NMR spectroscopy. The addition of the acidic resin was stopped once the reaction reached
equilibrium, in order to maximize the formation of [FeII(CN)5(N17O)]2-. The mixture was then
1 treated with 1,4-dioxane (4 mL). The precipitates were then collected via filtration and dried
under vacuum. The 17O-enrichment level of the product was determined to be 20% by 17O NMR.
17
O NMR (67.7 MHz, D2O): 419 ppm (referencing to water), 13C NMR (125.6 MHz, D2O):
134.81 ppm (Ceq) and 132.84 ppm (Cax).
Synthesis of Na2S2. Na2S2 was prepared from the reaction between Na2S and sulfur under
the anaerobic condition. To 10 mL oxygen free deionized water (which was degassed under Ar
for 20 min) was transferred 10.84 g sodium sulfide nonahydrate (Na2S⋅9H2O). The solution was
bubbled with N2 for 10 min while heating to 90°C until all Na2S were dissolved. 1.2 molar
equivalent sulfur (1.75 g) was then added into the Na2S solution. After sulfur was fully dissolved,
the reaction mixture was kept at 75 °C under N2 for 1 hr. After cooling to room temperature, the
orange-red solution was frozen with liquid N2 and then lyophilized to obtain the yellow solid of
Na2S2.
2. Characterization of the blue product from reaction between NP and Na2S2
45567*45528*9:;*<*=5567*45528*:&>9>*?'*@>A*
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(#,-.#(!#/01#
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$"!#
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("'#
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("%#
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!"$#
!"!#
$!!#
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%!!#
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+!!#
+&,)-)'./0*1'23*
Figure S1. UV-vis spectra (0.1 mm pathlength) of the reaction solution containing 25 mM NP
and 75 mM Na2S2 in aqueous solution (pH 11). The inset shows the blue color of the initial
reaction solution.
2 3. Quantum mechanical computations
All quantum chemical calculations were performed on Sun SPARC Enterprise M9000
servers at the High Performance Computing Virtual Laboratory (HPCVL) of Queen’s University.
Each of the servers consists of 64 quad-core 2.52 GHz sparc64 VII processors with 8 GB of
RAM per core (2TB of total memory). Geometry optimizations and NMR parameters
calculations were carried out with Gaussian 09.1 The B3LYP hybrid functional was used,
together with the Watchers2 all-electron basis set (14s11p6d3f)→[8s6p4d1f] for the Fe atom and
6-311++G(3df,3pd) basis set for other atoms. Solvation effects in aqueous solution were
evaluated using the integral equation formalism polarizable continuum model (IEFPCM)3-9 as
implemented in Gaussian 09. The following σref values were used in converting the computed
magnetic shielding constants (σ) to chemical shifts (δ): 15N, 264.5 ppm;10 17O, 287.5 ppm.11 For
13
C chemical shifts, we used σref = 156 ppm, which was based on the computed magnetic
shielding for the reference compound [Fe(CN)6]4– and its experimental 13C chemical shift, δ =
177.0 ppm.
Table S1. Computed and experimental NMR chemical shifts for FeII complexes, nitrite and
nitrate.
Compound
[Fe(CN)5N(O)S]4–
Method
G09
Exp
δ(17O)/ppm
1245
1027
[Fe(CN)5N(O)SS]4–
G09
Exp
1078
939
[Fe(CN)5N(O)SH]3–
G09
[Fe(CN)5N(O)SSH]3–
δ(15N)/ppm
881
700
δ(13Cax)/ppm
167.0
NA
δ(13Ceq)/ppm
175.6
174.7
785
630
164.8
NA
172.3
173.5
965
724
148.2
159.3
G09
856
642
148.1
156.4
[Fe(CN)5NO2]4–
G09
Exp
723
690
664
555
184.0
172.9
177.1
175.2
[Fe(CN)5N(O)OH]3–
G09
695(N=O)
466 (N-O-H)
571
150.2
152.1
[Fe(CN)5NO]2–
G09
Exp
392
419
449
371
117.4
132.3
122.3
134.5
NO2–
G09
Exp
724
661
685
609
NO3–
G09
Exp
427
405
422
367
NA: Not available.
3 Table S2. Comparison of experimental and computed (TD-DFT) UV-vis absorption bands for
[SNO]–, [SSNO]–, [Fe(CN)5N(O)S]4– and [Fe(CN)5N(O)S]4–.
Compound
Method
λmax(nm)
[SNO]–
TD-DFT
Exp.12
TD-DFT
Exp.12
TD-DFT
Exp.
TD-DFT
Exp.
296
325
383
448
446
540
480
570
[SSNO]–
[Fe(CN)5N(O)S]4–
[Fe(CN)5N(O)SS]4–
Oscillator
strength (f)
0.06
Transition (%)
HOMO-2 → LUMO (65%)
0.08
HOMO → LUMO (72%)
0.12
HOMO-2 → LUMO (91%)
0.20
HOMO → LUMO (88%)
Figure S2. Molecular orbitals that contribute to the UV-vis absorption bands shown in Table S2
for (a) [SNO]–, (b) [SSNO]–, (c) [Fe(CN)5N(O)S]4– and (d) [Fe(CN)5N(O)SS]4–
4 4. Aqueous-phase pKa calculations
Aqueous-phase pKa values were calculated using the thermodynamic cycle shown in Figure
S3 and the integral equation formalism polarizable continuum model (IEFPCM).3-9 The generally
accepted experimental-theoretical values for Ggas(H+) and ΔGS(H+) are –6.2813 and –265.9
kcal/mol.14
pKa = –log Ka
pKa = ΔGº/ln 10RT, where ΔGº = ΔGaq
According to Figure S2, ΔGaq can be calculated in the following fashion:
ΔGaq = ΔGgas + ΔGS (H+) + ΔGS (A–) – ΔGS (HA)
ΔGgas = Ggas(A–) + Ggas (H+) – Ggas (HA)
In this work, we used the following equation to convert the ΔGgas reference state (24.46 L
at 298.15 K) from 1 atm to 1 M:
ΔGgas(1M) = ΔGgas(1atm) + RT ln(24.46)
Thus, the pKa values can be calculated using the following equation:
pKa = [Ggas(A–) – Ggas (HA) + ΔGS (A–) – ΔGS (HA) – 270.29]/1.3644
"Ggas
A!gas
AHgas
!"Gs(AH)
+ H+gas
"Gs(A!)
"Gs(H+)
"Gaq
AHaq
A!aq
+ H+aq
Figure S3. Thermodynamic cycle used in pKa calculations.
Because it is still a challenge to calculate absolute pKa values to a high degree of accuracy,
it is a common practice that a “calibration” process is performed for a class of closely related
5 compounds. To this end, we first computed pKa values for a set of compounds containing -OH
and -SH functional groups with known experimental pKa values (the “calibration compounds”
shown in Table S3), in order to establish a correlation between pKa (calc.) and pKa(exp). Then
we can apply this correlation to predict the pKa values for the compounds in question (the
“unknown compounds in Table S3). The pKa calibration plot is shown in Figure S4.
Table S3. Computed aqueous pKa values for “calibration compounds” and “unknown compounds”.
pKa (calc.)
pKa (exp)
Calibration compounds
Nitrous acid
Formic acid
Acrylic acid
Phenol
H2 O
H2 S
HSCN
CH3OH
CH3SH
HNCO
3.5
7.6
9.7
17.4
31.0
11.7
-5.9
30.9
17.3
9.1
3.3
3.8
4.3
10
15.7
7
-1.28
15.5
10.4
3.73
Unknown compounds
cis-HSNO
trans-HSNO
HSSNO
trans-nitrous acid
3.5
4.1
0.2
4.2
2.6a
2.9a
1.0a
2.9a
a
Predicted values using pKa(exp) = pKa(calc) × 0.4776 + 0.9; see Figure S4.
6 20
y = 0.4776x + 0.9293
R² = 0.97218
pKa(exp)
10
0
-20
-10
0
-10
10
20
30
40
pKa(cal)
Figure S4. Correlation between pKa(exp) and pKa(cal) for the “calibration compounds” shown in
Table S3.
7 5. FTIR characterization
2051.8
1254.3
a
!4
14N
805.6
" 15N
2055.8
!"#$%&#'()%
!"#$%&#'()%
1358.3
! 4!"#$"%&' !"#$"%('
2200
1800 1600 1400
1200 1000 800 600 400
b22002000
2000 1800 1600 1400 1200 1000 800 600 400
!"#$%&#'()%
N!"#$"%&'
" 151200
N!"#$"%(' 1000 800
2200 2000 1800 1600 141400
2045.6
1295.1
600
400
1254.3
"#'%
c 2000 1800 1600! 1400
2200
1200 1000 800
4
600
400
"#$&%
14N " 15N
2200 2000 1800 1600 1400
1200 1000 800 600 400
"#$% 2200 2000 1800 1600 1400 1200 1000
800 600 400
"#'%
2200
2000
1800
1600
1400
1200
1000
800
600
!"#$%&#'()%
1935.5
2200 2000 1800 1600 1400 1200 1000 800 600
"#"&%
2141.5
660.8
d
!4
400
400
"#$&%
"%
"#$%
14N
!"#"&%
" 15N
"#"&%
2200 2000 1800 1600 1400 1200 1000
800
600
400
2200
20001800
18001600
1600
1400
1200
1000800800
2200
2000
1400
1200
1000
600600
400400
()*+),$%
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"%
(cm 1000
)1000 800
2200
2000
1600
2200
2000 1800
1800 wavenumber
1600 1400
1400 1200
1200
800 600
600 400
400
!"#$%
!"#"&%
!"#$%
4–
4–
4–
Figure
ATR-FTIR
of 800
a) [Fe(CN)
5N(O)S] , b) [Fe(CN)5N(O)SS] , c) [Fe(CN)5NO2] and d)
2200 2000S5.
1800
1600 1400 spectra
1200 1000
600 400
()*+),$%
()*+),-%
2–
[Fe(CN)5NO] (NP) in aqueous solution. The 14N-15N difference spectra (red traces) are also displayed.
Note that, because the 15N labeling level in the complexes is only 60%, the 14N-15N difference peak is not
perfectly anti-symmetric. The spectral noise in the region below 600 cm–1 is the artifact from ATR
measurement.
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