60 JOURNAL OF CHEMICAL RESEARCH 2013
1-(4-Tert-butylphenyl)-2-hydroxypropan-1-one (3b): Yellow liquid
(86%); 1H NMR (300 MHz, CDCl3) δ 7.86 (d, J = 9.0 Hz, ArH, 2H),
7.51 (d, J = 8.7 Hz, ArH, 2H), 5.16 (q, J = 6.6 Hz, 1H), 3.81 (s, –OH,
1H), 1.41 (d, J = 6.8Hz, –CH3, 3H), 1.35 (s, -t-Bu, 9H); Anal. Calcd
for C13H18O2: C, 75.69; H, 8.80. Found: C, 75.36; H, 9.01%; GC-MS
(m/z) 206.19. Calcd 206.28.
Experimental
General information
Flash chromatography was performed using Merck-EM type 60 (230–
400 mesh) silica gel (flash). Melting points are obtained using a capil-
lary melting point apparatus and are uncorrected. Elemental analysis
1
was performed using a Flash EA-1112 analyser. H NMR spectra
Synthesis of 1-aryl-propan-1,2-diones (4); general procedure
Compound 3 (0.018 mol) was added to a mixture of CuSO4·5H2O
(10.16 g, 0.038 mol) in pyridine (7 mL) and water (3 mL). The mix-
ture was heated under reflux and monitored using thin-layer chroma-
tography [TLC, ethyl acetate:n-hexane (1:3)] and then extracted with
ethyl acetate (100 mL) and water (150 mL). The organic layer was
dried with sodium sulfate and evaporated in vacuo. The crude product
was purified by column chromatography over silica gel with ethyl
acetate:n-hexane (1:3) as the eluent, to yield compounds 4a and 4b.
1-[4-(Diphenylamino)phenyl]propan-1,2-dione (4a): Orange solid,
(88%), m.p. 126 °C; 1H NMR (300 MHz, CDCl3) δ 7.88 (m, ArH, 3H),
7.42 (m, ArH, 4H), 7.25 (d, J = 8.7 Hz, ArH, 2H), 7.15 (d, J = 8.7 Hz,
ArH, 2H), 6.99 (m, ArH, 3H), 2.15 (s, –CH3, 3H); Anal. Calcd for
C21H17NO2; C, 79.98; H, 5.43; N, 4.44. Found: C, 79.64; H, 5.49;
N:4.28%; GC-MS (m/z) 315.04. Calcd 315.37.
were recorded on a VARIAN UnityInova 300 MHz FT NMR spec-
trometer. UV-Vis and fluorescence spectra were measured using
SCINCO S-4100 and Shimadzu RF-5301PC spectrophotometers.
The fluorescence quantum yield (Φ) was determined by a compara-
tive method using Rhodamine B (Φf = 0.69 in ethanol) as a reference
and using the following net equation.32
2
A
PL
UV
nA
A
ref
ΦA = Φ
ref
2
UV
PL
n
ref
ref
where PL is the integrated area under the corrected emission spectrum
and UV is the absorbance of the solution at the given excitation wave-
length. Subscripts “A” and “ref” refer to the unknown and reference
solutions respectively, and “n” is the refractive index of the corre-
sponding solutions. Cyclic voltammetry (CV) experiments were
performed using a BAS-100 electrochemical analyser with a three-
electrode configuration consisting of a Pt disk working electrode, an
Ag/AgCl reference electrode, and Pt wire counter electrode. All mea-
surements were taken in acetonitrile with 0.1 M tetra-n-butylammo-
nium tetrafluoroborate (TBABF4) as the supporting electrolyte.
HOMO energy levels were calculated from the oxidation potential
using the following equation.33,34
1-(4-tert-Butylphenyl)propan-1,2-dione (4b):Yellow liquid, (75%);
1H NMR (300 MHz, CDCl3) δ 7.92 (d, J = 9.0 Hz, ArH, 2H), 7.51 (d,
J = 8.7 Hz, ArH, 2H), 2.13 (s, –CH3, 3H), 1.34 (s, t-Bu, 9H); Anal.
Calcd for C13H16O2: C, 76.44; H, 7.90. Found: C, 76.64; H, 8.09%;
GC-MS (m/z) 204.04. Calcd 204.26.
5-[4-(Diphenylamino)phenyl]-6-methylpyrazine-2,3-dicarbonitrile
(5a): A solution of 1-[4-(diphenylamino)phenyl]propane-1,2-dione
(5.0 g, 0.016 mol), diaminomaleonitrile (DAMN) (1.73 g, 0.016 mol)
in methanol (200 mL) and a small amount of p-toluenesulfonic acid as
the catalyst was heated under reflux for 2 h. Methanol was poured into
the mixture and stirred for 1 h at room temperature. The precipitate
was filtered off and washed with methanol. The crude product was
purified by column chromatography over silica gel with ethyl acetate:
n-hexane (1:5) as the eluent to yield compound 5a as a yellow solid,
(45%), m.p. 103 °C; 1H NMR (300 MHz, CDCl3) δ 7.60 (d, J = 8.7 Hz,
ArH, 2H), 7.46 (d, J = 8.7 Hz, ArH, 2H), 7.15–7.26 (m, ArH, 10H),
2.86 (s, –CH3, 3H); Anal. Calcd for C25H17N5; C, 77.50; H, 4.42; N,
18.08. Found: C: 77.41; H: 4.38; N: 18.16%; GC-MS (m/z) 386.96
Calcd 387.44.
5-(4-tert-Butylphenyl)-6-methylpyrazine-2,3-dicarbonitrile (5b): A
solution of 1-(4-tert-butylphenyl)propane-1,2-dione (40 g, 0.14 mol),
DAMN (15.2 g, 0.14 mol) in methanol (200 mL) and a small amount
of p-toluenesulfonic acid as the catalyst was heated under reflux for
2 h. Methanol was poured into the mixture and stirred for 1 h at room
temperature. The precipitate was filtered off and washed with metha-
nol. The crude product was purified by column chromatography over
silica gel with ethyl acetate:n-hexane (1:3) as the eluent, to yield com-
pound 5b as a white solid, (50%), m.p. 111 °C; 1H NMR (300 MHz,
CDCl3) δ 7.62 (d, J = 8.7 Hz, ArH, 2H), 7.54 (d, J = 8.7 Hz, ArH, 2H)
2.85 (s, –CH3, 3H), 1.39 (s, t-Bu, 9H); Anal. Calcd for C17H16N4:
C, 73.89; H, 5.84; N, 20.27. Found: C, 73.74; H, 5.99; N, 19.91%;
GC-MS (m/z) 276.15. Calcd 276.34.
(E)-5-[4-(Diphenylamino)phenyl]-6-[4-(diphenylamino)styryl]pyr
azine-2,3-dicarbonitrile (6a): A solution of 5a (3.0 g, 7.74 mmol),
4-(diphenylamino)benzaldehyde (2.12 g, 7.74 mmol) in benzene
(20 mL) and a small amount of piperidine as the catalyst was heated
under reflux for 21 h under an N2 atmosphere. After the reaction was
complete, the mixture was cooled to room temperature. Methanol was
poured into the mixture and stirred for 1 h at room temperature. The
precipitate was filtered off and washed with methanol. The crude
product was purified by column chromatography over silica gel with
ethyl acetate:n-hexane (1:3) as the eluent, to yield compound 6a as a
red solid, (45%); m.p. 150 °C, FT-IR (KBr pellet), νmax/cm−1 2232
(C≡N), 1602 (C=C), 1489, 1296; 1H NMR (300 MHz, CDCl3) δ 7.82
(m, ArH, 4H), 7.78 (d, J = 15.6 Hz, 1H), 7.42 (m, ArH, 8H), 7.32 (m,
ArH, 8H), 7.18 (d, J = 15.6 Hz, 1H), 7.15 (d, J = 8.7 Hz, ArH, 4H),
6.97 (m, ArH, 4H); Anal. Calcd for C36H29N5: C, 82.22; H, 4.70, N,
13.08. Found: C, 81.25; H, 5.61; N. 13.37%; FAB-MS (m/z) 642.12.
Calcd 642.75.
(E)-5-(4-tert-Butylphenyl)-6-[4-(diphenylamino)styryl]pyrazine-
2,3-dicarbonitrile (6b): A solution of compound 5b (5.0 g, 0.018 mol),
4-(diphenylamino)benzaldehyde (4.95 g, 0.018 mol) in benzene
(20 mL) and a small amount of piperidine as the catalyst was heated
under reflux for 21 h under an N2 atmosphere. After the reaction was
complete, the mixture was cooled to room temperature. Methanol was
poured into the mixture and stirred for 1 h at room temperature. The
HOMO (eV) = –4.8 – [Eonset – E1/2(ferrocene)]
where Eonset is the onset oxidation potential (V) and E1/2(ferrocene) is
the half-wave potential (V) of ferrocene in the solution. The electronic
level of the analytes was calculated from the difference between the
onset redox potential and the half-wave potential of ferrocene.
Synthesis of 1-aryl-2-bromopropan-1-ones (2); general procedure
One equivalent of Br2 was added dropwise to a solution of the appro-
priate 4-substituted propanophenone 1 (0.04 mol) in CCl4 (30 mL)
with stirring at 10°C. After subsequent stirring for 2 h at room tem-
perature, the mixture was diluted with ice water and extracted with
CHCl3 (100 mL). The organic layer was washed with water and dried
with anhydrous sodium sulfate. The mixture was concentrated under
reduced pressure to form the compounds 2a and 2b.
2-Bromo-1-[4-(diphenylamino)phenyl]propan-1-one (2a): Yellow
solid (70%), m.p. 64 °C; 1H NMR (300 MHz, CDCl3) δ 7.89 (m, ArH,
4H), 7.44–7.41 (m, ArH, 5H), 7.01 (m, ArH, 5H), 5.23 (q, J = 6.6 Hz,
Br–C–H, 1H), 1.88 (d, J = 6.3 Hz, –CH3, 3H). Anal. Calcd for
C21H18BrNO: C, 66.33; H, 4.77; N, 3.68. Found: C, 66.12; H, 4.82; N,
3.70%; GC-MS (m/z) 379.75. Calcd 380.28.
2-Bromo-1-(4-tert-butylphenyl)propan-1-one (2b): Yellow liquid
(94%); 1H NMR (300 MHz, CDCl3) δ 7.92 (d, J = 8.7 Hz, ArH, 2H),
7.48 (d, J = 8.7 Hz, ArH, 2H), 5.20 (q, J = 6.3 Hz, Br–C–H, 1H), 2.11
(d, J = 6.8 Hz, –CH3, 3H), 1.40 (s, t-Bu, 9H). Anal. Calcd for
C13H17BrO: C, 58.01; H, 6.37. Found: C, 58.19; H, 6.41%; GC-MS
(m/z) 269.04. Calcd 269.18.
Synthesis of 1-aryl-2-hydroxypropan-1-ones (3); general procedure
Brominated precursor 2 (0.047 mol) and potassium acetate (0.166
mol) were heated under reflux in acetone (100 mL). The solution was
filtered and the solvent was removed in vacuo. The intermediate α-
acetoxy ketone was hydrolysed using 10% methanolic NaOH solution
(100 mL) under reflux for 1 h. The mixture was diluted with water
(200 mL) and then extracted with ethyl acetate (100 mL). The organic
layer was washed with water, dried with sodium sulfate and evapo-
rated in vacuo. The crude product was purified by column chromato-
graphy over silica gel with ethyl acetate:n-hexane (1:3) as the eluent,
to yield the compounds 3a and 3b.
1-[4-(Diphenylamino)phenyl]-2-hydroxypropan-1-one (3a):Yellow
1
solid (45.9%), m.p. 79 °C; H NMR (300 MHz, CDCl3) δ 7.88 (m,
ArH, 3H), 7.46 (m, ArH, 4H), 7.42 (d, ArH, 2H, J = 8.7 Hz), 7.16 (d,
ArH, 2H, J = 8.7 Hz), 7.03 (m, ArH, 3H), 5.05 (q, J = 6.6Hz, 1H), 4.14
(s, –OH, 1H), 1.46 (d, J = 6.3 Hz, –CH3, 3H); Anal. Calcd for
C21H19NO2: C, 79.47; H, 6.03; N, 4.41. Found: C, 79.10; H, 6.26; N,
4.53%; GC-MS (m/z) 317.11. Calcd 317.38.