according to a known procedure.16 In a typical experiment,
38.6 mmol (7.5 ml) of freshly distilled thionyl chloride was
added to a 100 ml round-bottom flask containing 28 mmol
(6.0 g) of diphenylacetic acid. After refluxing for 2 h the excess
of thionyl chloride was evaporated. The remaining reaction
mixture was dissolved in 25 ml of dry diethyl ether and
28 mmol (3.44 g) of the aniline derivative (p-anisidine) was
added with stirring, and the reaction mixture was allowed to
stand overnight. The resulting solid was filtered and washed
with a 0.5 M hydrochloric acid solution. Recrystallization
from ethyl acetate–petroleum ether gave an analytically pure
sample. Yield of N-(p-anisyl)diphenylacetamide is 6.65 g
(75%), m.p. 185–188 (lit. 188–189 °C13).
Separation and purification of products for spectral analysis
was conducted by column chromatography using on silica gel
(40–63 μm) and ethyl acetate–hexane as eluent. TLC analyses
were performed by using Merck pre-coated silica gel (0.2 mm)
aluminum [backed] sheets.
5.4 Characterization of products
Benzophenone 1, aniline derivatives 4 and diphenylacetic acid 8
were compared with authentic samples. All other products,
except for 3, are known in the literature.
N-(Diphenylmethyl)acetamide (2).17,18 IR (KBr): A strong
absorption of a carbonyl group at 1630 cm−1; a broad peak of a
secondary amide group at 3285 cm−1; 3055, 2930, 1540, 1500,
1
701; H NMR (in CDCl3, 200 MHz) δ: 1.99 (s, 3H, CH3), 6.22
5.3 Cyclic voltammetry
(d, 1H, J = 8.0 Hz), 6.54 (d, 1H, J = 10 Hz), 7.15–7.37
(m, 10H), 13C NMR (in CDCl3, 200 MHz) δ 23.13 (CH3), 57.04
(CH), 127.39, 128.60, 141.41, 169.51; MS: m/z 225 (M+,
100%), 207, 182, 165, 148, 115, 106, 77, 43, 32.
Analytical grade acetonitrile (99.8% containing up to 0.1%
water) and LiClO4 (99%) were used for cyclic voltammetry
(CV) measurements and controlled potential electrolysis without
further purification. CV measurements were performed in a con-
ventional three-electrode cell under air atmosphere, using 1 mM
of substrate. The working electrode was a glassy carbon disk
(ϕ = 3 mm), the reference electrode was Ag/AgCl (in 3 M
NaCl), and the auxiliary electrode was a Pt cylindrical gauze or
spiral wire. Under scan rate range of 20–400 mV s−1, none of
the oxidation peak potentials was reversible.
2,2-Diphenylacetamide (5).19 IR (KBr): Broad absorptions
bands of primary amide group at 3180 and 3378 cm−1; a strong
absorption of a carbonyl group at 1650 cm−1; 2944, 1500, 1400,
1
1253, 635; H NMR (in CDCl3, 200 MHz) δ 4.95 (s, 1H), 5.68
(s, 1H, NH), 6.42 (s, 1H, NH), 7.17–7.48 (m, 10H), 13C NMR
(in CDCl3, 200 MHz) δ 58.62 (CH), 127.33, 128.77, 139.06,
141.41, 175.07; MS: m/z 211 (M+), 193, 167 (100%), 152, 139,
115, 91, 82, 63, 44.
5.4 Electrolysis procedure
N-(Diphenylmethylene)acetamide (6).20,21 IR (KBr): Two
absorptions of carbonyl groups at 1635 (CvN) and 1695 cm−1
For controlled potential electrolysis (CPE) an H-type two-
compartment cell equipped with a medium glass frit as a
membrane was used. The anode compartment contained a
polished silver wire quasi-reference electrode (commonly
used in organic electrochemistry, approx. + 0.15 V vs. SCE),
immersed in the electrolyte solution in a glass cylinder equipped
with a fine glass frit at its end. Both compartments contained
acetonitrile and 0.1 M LiClO4; the analyte contained also the
substrate (1 mmol in 40 mL electrolyte solution). The latter was
stirred during electrolysis (4–8 h), which was terminated after
passing 3–4 F, when the initial current (50–100 mA, depending
on the substrate) reached a value of 5–8 mA and the unreacted
starting material was 10% or less (monitored by GC-MS).
CPE was conducted by controlling the potential at the Ep
value for each substrate (Table 1) (vs. Ag wire, which corre-
sponds to +0.2 V vs. Ag/AgCl). A platinum foil (5 cm2)
working electrode and a stainless steel counter electrode were
used. Pulsing (to 0 V for 1 s, every 20 s) was required during
electrolysis to avoid passivation of the working electrode
surface, probably due to the formation of the insulating polymer.
The reaction mixture was evaporated to reach ∼2 ml volume
which was neutralized by saturated aqueous NaHCO3 in order to
transfer any residue of a carboxylic acid to the aqueous phase.
The reaction mixture was extracted into 3 × 30 ml of diethyl
ether. After phase separation, the organic layer was dried over
MgSO4 and filtered. The aqueous phase was acidified by HCl
and extracted into diethyl ether, dried and filtered. The combined
organic phase was subjected to GC-MS to determine the relative
yields of products.
1
(CvO), 2961, 2916, 2861, 1494, 1392, 1139, 1011; H NMR
(in (CD3)2CO, 200 MHz) δ 1.87 (s, 3H), 7.08–7.24 (m, 6H),
7.27–7.53 (m, 4H); 13C NMR (in (CD3)2CO, 200 MHz) δ 23.56
(CH3), 125.81, 126.72, 129.12, 142.85, 168.50 (CvN), 176.40
(CO); MS: m/z 223 (M+), 208, 194, 180 (100%), 165, 152, 104,
77, 43, 32. HRMS (ESI): calculated for C15H13NO + H:
224.1070; found: 224.1071; calculated for C15H13NO + Na:
246.0889; found 246.0891.
2,2-Diphenylacetonitrile (7).22,23 IR (KBr): A sharp absorp-
tion of a cyano group at 2245 cm−1; 3077, 3027, 2946, 2244,
1697, 1587, 1548, 1447, 1339, 1179, 1031, 972, 778, 621, 616;
1H NMR (in CDCl3, 200 MHz) δ 5.15 (s, 1H), 7.34–7.39
(m, 10H), 13C NMR (in CDCl3, 200 MHz) δ 42.51 (CH),
119.68 (CN), 127.67, 128.21, 129.14, 130.01, 132.36; MS:
m/z 193 (M+, 100%), 178, 165, 152, 139, 128, 116, 89, 77,
51, 32.
A 1 : 1 complex 10 between aziridinone 3 and 2,4-dinitroani-
line. IR (KBr): Two medium–weak absorptions (due to hydro-
gen bonding) of carbonyl groups at 1665 cm−1 and 1725 cm−1
;
3450 (broad, NH2), 2968, 2928, 2856, 1609, 1348, 1276, 1096,
1032, 816; UV-Vis (EtOH): λmax = 203, 261 and 307 nm with
1
ε = 14 080, 4540 and 4540, respectively; H NMR (in CDCl3,
500 MHz) δ 2.15 (s, 3H), 7.04 (NH), 7.31–7.50 (m, 10H + NH),
8.47 (dd, 1H, J1 = 11 Hz, J2 = 3 Hz), 9.08 (s (br), 1H), 9.10
(d, 1H, J = 11 Hz); 13C NMR (in CDCl3, 400 MHz) δ 29.59
(CH3), 71.29 (Ph2C), 121.94, 122.11, 128.10, 128.58, 128.72,
130.01, 135.26, 139.14, 139.41, 141.83, 169.65, 170.51; MS
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem., 2012, 10, 3906–3912 | 3911