Chemistry of Materials
Article
saturated brine, and dried over Na2SO4. After the volatiles were
removed, 1.27 g (98%) of a white powder was collected. The
compound was subsequently recrystallized from acetonitrile to yield
0.921 g (71%) of 2 as a white powder. Because thiocarbamates begin
to isomerize around 60 °C, it is important not to heat this compound
during synthesis or recrystallization. 1H NMR (400 MHz, 273 K,
CD2Cl2): δ = 2.36 + 2.39 + 2.40 (s, 6H), 7.00−7.07 (m, 2H), 7.18−
7.34 (m, 5H), 7.54 (d, 1H), 8.47 + 8.83 (s, 1H). 13C{1H} (100 MHz,
273 K, CD2Cl2): δ = 20.7, 20.8, 122.05, 122.08, 122.60, 123.67, 129.46,
129.74, 129.80, 129.83, 134.34, 134.90, 136.02, 136.13, 136.55, 150.67,
151.40, 188.00, 188.12. Anal. Calcd for C15H15ONS: C, 70.01; H, 5.87;
N, 5.44. Found: C, 69.71; H, 5.79; N, 5.52. MS (ASAP) m/z calcd for
[C15H15ONS + H+]: 258.10. Found: 258.10.
O-Phenyl-N-methyl(phenyl) Thiocarbamate (3). N-Methylaniline
(1.86 g, 1.88 mL, 17.37 mmol) was added dropwise to a solution of O-
phenyl chlorothionoformate (8.69 mmol, 1.5 g) in dichloromethane
(10 mL). The mixture was stirred at room temperature for 10 min,
washed 3× with water and dried over MgSO4. The volatiles were
removed under vacuum, and the isolated powder was recrystallized
from ethanol to yield 1.554 g (74%) of 3 as a white powder. 1H NMR
(400 MHz, 273 K, CD2Cl2): δ = 3.69 + 3.81 (s, 3H), 6.95−7.93 (m,
10H). 13C{1H} (100 MHz, 273 K, CD2Cl2): δ = 41, 44.8, 122.72,
123.08, 125.84, 125.99, 126.11, 127.09, 127.8, 127.84, 129.28, 129.3,
129.51, 129.61, 143.58, 146.27, 154, 154.13, 187.78, 189.07. Anal.
Calcd for C14H13ONS: C, 69.11; H, 5.38; N, 5.76. Found: C, 68.96; H,
5.14; N, 5.72. MS (ASAP) m/z calcd for [C14H13ONS + H+]: 244.08.
Found: 244.08.
4H), 2.37 (s, 3H), 2.56 (t, 2H), 5.38 (m, 2H), 6.98 (d, 2H), 7.19 (d,
2H). 13C{1H} (100 MHz, CDCl3): δ = 14.22, 20.88, 22.77, 25.02,
27.23, 27.3, 29.16, 29.24, 29.41, 29.62, 29.76, 29.85, 32, 34.4, 121.1,
129.74, 129.88, 130.04, 135.2, 148.65, 172.37. Anal. Calcd for
C25H40O2: C, 80.59; H, 10.82. Found: C, 80.31; H, 10.54. MS
(ASAP) m/z calcd for [C25H40O2 + H+]: 373.31. Found: 373.31.
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Phenyl Oleate. Brown oil. Yield 1.153 g (67%). H NMR (400
MHz, CD2Cl2): δ = 0.89 (t, 3H), 1.20−1.49 (m, 20H), 1.74 (quin,
2H), 1.97−2.10 (m, 4H), 2.54 (t, 2H), 5.36 (m, 2H), 7.03−7.09 (m,
2H), 7.19−7.26 (m, 1H), 7.35−7.41 (m, 2H). 13C{1H} (101 MHz,
CD2Cl2): δ = 14.32, 23.13, 25.32, 27.57, 27.61, 29.49, 29.54, 29.60,
29.76, 29.95, 30.14, 30.22, 32.35, 34.69, 122.10, 126.06, 129.74,
130.13, 130.36, 151.35, 172.67. Anal. Calcd for C24H38O2: C, 80.39; H,
10.68. Found: C, 79.82; H, 11.27. MS (ASAP) m/z calcd for
[C24H38O2 + H+]: 359.30. Found: 359.29.
Thiolcarbonate Synthesis. Thiolcarbonates were synthesized
following a previously reported procedure.50
O,S-Di(p-tolyl) Thiolcarbonate. A solution of p-tolyl chloroformate
(3.41 g, 20 mmol) in CHCl3 (5 mL) was added dropwise to a solution
of 4-methylbenzene thiol (2.48 g, 20 mmol) and potassium hydroxide
(1.12 g) in CHCl3 (20 mL) and ethanol (15 mL). The solution was
stirred for 2 h, filtered, and the volatiles were removed under vacuum,
yielding a white powder (4.268 g) that was subsequently recrystallized
1
from dichloromethane. Yield 2.6077 g (51%). H NMR (400 MHz,
CD2Cl2): δ = 2.34 (s, 3H), 2.39 (s, 3H), 7.01−7.07 (m, 2H), 7.16−
7.21 (m, 2H), 7.22−7.28 (m, 2H), 7.45−7.50 (m, 2H). 13C{1H} (100
MHz, CD2Cl2): δ = 20.53, 21.02, 120.88, 123.71, 129.93, 130.04,
134.86, 136.15, 140.51, 149.14, 169.14. Anal. Calcd for C15H14O2S: C,
69.74; H, 5.46. Found: C, 69.53; H, 5.18. MS (ASAP) m/z calcd for
[C15H14O2S + H+]: 259.08. Found: 259.08.
Thiourea Synthesis. N-Methyl-N,N′-diphenylthiourea (5b). 5b
was synthesized according to Hendricks et al.3 White crystals. Yield
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9.321 g (92%). H NMR (400 MHz, CDCl3): δ = 3.69 (s, 3H), 6.93
(b, 1H), 7.14−7.23 (m, 1H), 7.28−7.4 (m, 6H), 7.41−7.48 (m, 1H),
7.52−7.58 (m, 2H). 13C{1H} (100 MHz, CDCl3): δ = 43.62, 125.71,
126.04, 127.03, 128.63, 128.86, 130.84, 139.30, 143.02, 181.47. Anal.
Calcd for C14H14N2S: C, 69.39; H, 5.82; N, 11.56. Found: C, 68.63; H,
5.26; N, 11.41. MS (ASAP) m/z calcd for [C14H14N2S + H+]: 243.10.
Found: 243.10.
O,S-Di(phenyl) Thiolcarbonate. White crystals. Yield 1.947 g
(42%). 1H NMR (400 MHz, CD2Cl2): δ = 7.15−7.21 (m, 2H), 7.24−
7.30 (m, 1H), 7.36−7.50 (m, 5H), 7.59−7.65 (m, 2H). 13C{1H} (101
MHz, CD2Cl2): δ = 121.64, 126.68, 127.63, 129.71, 129.93, 130.34,
135.31, 151.72, 169.08. Anal. Calcd for C13H10O2S: C, 67.80; H, 4.38.
Found: C, 67.53; H, 4.20. MS (ASAP) m/z calcd for [C13H10O2S +
H+]: 231.05. Found: 231.05.
Dipyrollidinothione (6b). Pyrrolidine (5.42 g, 6.26 mL, 75 mmol)
was added to a solution of thiocarbonyl diimidazole (2.67 g, 15 mmol)
in acetonitrile (75 mL). The solution was stirred at 70 °C for 16 h.
The volatiles were removed under vacuum, and the resultant tan solid
was redissolved in dichloromethane (50 mL) and washed with 30
mmol of HCl dissolved in 20 mL of water, saturated brine, and dried
over Na2SO4. After the volatiles were removed, the crude product was
recrystallized with hot acetonitrile to yield colorless crystals. Yield:
Synthesis of CdS Nanocrystals. In a nitrogen-filled glovebox, a
three-neck round-bottom flask was loaded with cadmium oleate (0.18
mmol, 0.122 g), octadecene (14.25 mL, 11.2 g, 44.4 mmol), and oleic
acid (0.102 g, 0.114 mL, 0.36 mmol). A 4 mL vial was filled with the
desired sulfur precursor (0.15 mmol) and diphenyl ether (0.75 mL,
0.75 g). A polar solvent such as diphenyl ether or tetraglyme was
required to dissolve the sulfur precursor. The three-neck round-
bottom flask was transferred to a Schlenk line and heated to 240 °C
under Ar. The sulfur precursor solution was then injected into the
cadmium oleate solution and left to react for the appropriate time. The
resulting nanocrystals were isolated from the reaction mixture by
precipitation with acetone and centrifugation. The yellow residue was
redispersed in hexane (10 mL), and acetone (5−10 mL) was added in
0.5 mL portions to precipitate cadmium oleate, without precipitating
the nanocrystals. This solution was centrifuged. The supernatant was
collected and the nanocrystals precipitated with the addition of 25 mL
of acetone. The nanocrystals were washed three additional times with
toluene/methyl acetate.
Nanocrystal Formation Kinetics. Quantitative aliquots of
approximately 0.1 mL were taken from a CdS nanocrystal reaction
and deposited into a previously weighed vial. A mass of toluene equal
to 2.5× the weight of the aliquot was added to the vial to standardize
aliquot concentration. UV−vis absorption spectra were taken of each
aliquot, and the concentration of CdS in the aliquot was calculated
from the size-dependent extinction coefficient at the first excitonic
absorption maximum using literature29 values and eq 1. Using a
second method, the absorbance at 300 nm was monitored as a proxy
for CdS conversion. This second method was used to assess the
validity of our proposed correction to the size-dependent extinction
coefficient for CdS. The kinetics collected from each method was fit to
first-order, the rate constant of which is reported in Figure 4.
Cadmium Sulfide Reaction Yield Determination. A 2×
reaction scaleup was performed in a three-neck round-bottom flask
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2.76 g (49%). H NMR (400 MHz, CDCl3): δ = 1.94−1.84 (m, 8H),
3.65−3.55 (m, 8H). 13C{1H} (100 MHz, CDCl3): δ = 25.84, 53.08,
184.98. Anal. Calcd for C9H16N2S: C, 58.65; H, 8.75; N, 15.20. Found:
C, 58.80; H, 8.56; N, 15.16. MS (ASAP) m/z calcd for [C9H16N2S +
H+]: 185.11. Found: 185.11.
Carbonate Synthesis. Di-p-tolyl Carbonate (7c). Di-p-tolyl
carbonate was synthesized according to a modified literature
procedure.49 Pyridine (0.87g, 0.88 mL, 11 mmol) was added dropwise
to a solution of p-tolyl chloroformate (1.79 g, 10.5 mmol) and p-cresol
(1.08 g, 10 mmol) in dichloromethane (20 mL). The mixture was then
heated to reflux for 10 min. The cooled solution was washed with
water, sodium hydroxide (1 M), saturated brine, and dried over
Na2SO4. The volatiles were removed under vacuum, and the white
powder was recrystallized from ethanol to yield 0.643 g (25%) of
product. 1H NMR (400 MHz, CDCl3): δ = 2.39 (s, 6H), 7.17 (d, 4H),
7.22 (d, 4H). 13C{1H} (100 MHz, CDCl3): δ = 20.88, 120.6, 130, 136,
148.89, 152.46. Anal. Calcd for C15H14O3: C, 74.36; H, 5.82. Found:
C, 74.54; H, 6.01. MS (ASAP) m/z calcd for [C15H14O3 + H+]:
243.10. Found: 243.10.
Aryl Oleate Synthesis. p-Tolyl Oleate. Pyridine (0.475 g, 0.484
mL, 6 mmol) was added dropwise to a solution of oleoyl chloride
(1.50 g, 5 mmol) and p-cresol (0.52 g, 4.8 mmol) in CH2Cl2 (20 mL).
The mixture was heated to reflux for 10 min and subsequently washed
with water, NaOH (1 M), saturated brine, and dried over Na2SO4 to
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yield 1.44 g (81%) of a brown oil. H NMR (400 MHz, CDCl3): δ =
0.92 (t, 3H), 1.17−1.51 (m, 20H), 1.78 (quin, 2H), 1.97−2.14 (m,
G
Chem. Mater. XXXX, XXX, XXX−XXX