Preparation and NMR spectra of substituted 2-(4-nitrophenyl)imidazolinones

Article abstract of DOI:10.1135/cccc19960910

A series of 11 substituted 2-(4-nitrophenyl)imidazolinones have been prepared by base catalyzed cyclizations of substituted 2-(4-nitrobenzoylamino)alkanamides. At higher methoxide concentrations the cyclization can be accompanied by reduction of nitro group to azoxy group. All the substances prepared have been identified by ¹H and ¹³C NMR spectra.

Full text of DOI:10.1135/cccc19960910

910
Sedlak, Halama, Kavalek, Machacek, Mitas, Sterba:
PREPARATION AND NMR SPECTRA OF SUBSTITUTED
2-(4-NITROPHENYL)IMIDAZOLINONES
1
2
3
4
Milos SEDLAK , Ales HALAMA , Jaromir KAVALEK , Vladimir MACHACEK ,
5
Petr MITAS and Vojeslav STERBA
Department of Organic Chemistry, University of Pardubice, 532 10 Pardubice, Czech Republic;
e-mail: 1 sedlak@hlb.upce.cz, 2 halama@hlb.upce.cz, 3 kavalek@hlb.upce.cz,
4 machacev@hlb.upce.cz, 5 mitas@hlb.upce.cz
Received December 5, 1995
Accepted March 3, 1996
A series of 11 substituted 2-(4-nitrophenyl)imidazolinones have been prepared by base catalyzed cy-
clizations of substituted 2-(4-nitrobenzoylamino)alkanamides. At higher methoxide concentrations the
cyclization can be accompanied by reduction of nitro group to azoxy group. All the substances pre-
1
pared have been identified by H and 13C NMR spectra.
Key words: 2-Benzoylaminocarboxylic acid amides; 2-Phenyl-5-imidazolinones.
Substituted 2-benzoylaminoalkanamides whose synthesis and NMR spectra were de-
scribed in a previous paper1 can be biologically active2 and can also serve as starting
materials for syntheses of substituted imidazolinones, some of which are commercial
herbicides2.
The aim of the present paper was to prepare substituted imidazolinones 2 by cycliza-
tion reactions of 2-(4-nitrobenzoylamino)alkanamides 1 in the presence of sodium
methoxide. The starting aminoamides were prepared from the respective nitriles by a
known way1. The cyclization of substituted 2-benzoylaminocarboxamides 1 to the sub-
stituted 2-phenyl-4-imidazolinones 2 was carried out in methanolic solutions of sodium
methoxide. The cyclization of the benzoylaminoamides 1a–1c, 1e, 1h–1j without any
substituent at nitrogen proceeds during a 30 min boiling in 1 M methoxide on water
bath. Introduction of a methyl group to the primary nitrogen of the terminal amidic
group retards the cyclization to such an extent that the cyclization product of 2-methyl-
2-(4-nitrobenzoylamino)propane-N-methylamide cannot be isolated in contrast to the
cyclization product of 2-methyl-2-(4-nitrobenzoylamino)propanamide (1c) which could
be isolated in the yield of 82% (Table I). This situation contrasts with the base cata-
lyzed
cyclization
of substituted amides
of hydantoic
acid type
R1NHCONR2CH2CONH2, where – on the contrary – the presence of methyl group at
the nitrogen atom attacking the carbonyl group (R1 = H, CH3) accelerates the cycliza-
tion by about one order of magnitude4. The reason of this different effects of methyl
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

2-(4-Nitrophenyl)imidazolinones
911
group has not been elucidated yet. On the other hand, the replacement of hydrogen by
methyl group at the secondary nitrogen atom of benzoylamino group in compounds 1
brings about an acceleration of the cyclization. In contrast to the above-mentioned com-
pounds, the substances 1d, 1f, 1g, 1h cyclize in 1 M methoxide even at room tempera-
ture.
The prepared substituted 2-(4-nitrophenyl)imidazolinones were identified by both
1
their H and 13C NMR spectra. The chemical shifts of both protons and carbon atoms
of compounds 2 are presented in Tables II and III. The character of both 1H and 13C NMR
spectra of the compounds with NH group is substantially affected by their acid-base
behaviour. The relatively highly acidic hydrogen of NH group (pKA of compound 2a is
12.80 ± 0.05 in methanol) is slightly dissociated in dimethyl sulfoxide, and also tau-
tomeric equilibria can become significant which, however, have not been described yet.
1
In the H NMR spectra there is a very broadened half of AA′XX′ splitting at higher
field, which is adjacent to the heterocyclic part of the molecule. As a rule, the signal of
NH group is missing. In the 13C NMR spectra there are very broadened (or are missing)
the signals of carbon atoms involved in the potentially tautomeric system (C-2 and C-4)
and adjacent carbon atoms (C-6 and C-5). Similar deformations can be seen also in the
1H and 13C NMR spectra of azoxy compounds 3a and 3b.
An addition of trifluoroacetic acid (TFA) suppresses the above-described deforma-
tions, at the same time, however, we can observe changes in chemical shifts of the
previously broadened signals due to partial protonation in the amidine system of the
heterocyclic part of the molecule (pKA’s of the conjugated acids of compounds 2a and
2b in methanol are 3.70 ± 0.07 and 5.81 ± 0.016, respectively). In dimethyl sulfoxide
the respective pKA values are higher by 1 to 2 units, and pKA of trifluoroacetic acid is
3.45 in the same solvent5. Obviously, the protonation takes place at the nitrogen and
not at the oxygen, since ∆pKA between the unsubstituted derivative 2b and the 4-nitro
derivative 2a is 2.1, which corresponds to a ρ constant about 2.6.
In the imidazolinones 2d, 2f, 2g, 2k with N-methyl group, all the signals in both 1H and
13C NMR spectra are sharp when measured in hexadeuteriodimethyl sulfoxide solutions
as well as in (CD3)2SO–TFA mixtures.
In the compounds containing isopropyl group, the paired methyl groups are aniso-
chronous due to molecular symmetry. In isobutyl derivative 2g are anisochronous both
the methyl groups and the protons of methylene group (as it is the case in the ethyl
derivative 2e).
The conclusions about acid-base behaviour of compounds 2 deduced from their
NMR spectra can be confronted with their electron spectra in DMSO. Figure 1 presents
the spectra of compound 2a in dimethyl sulfoxide with addition of 1% acetic acid, 1%
trifluoroacetic acid, or 1% sulfuric acid. The addition of acetic acid to the solution of
compound 2a in DMSO causes practically no change in the spectrum, which means that
the concentration of anion of compound 2a must be very low. The exchange of proton
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

912
Sedlak, Halama, Kavalek, Machacek, Mitas, Sterba:
TABLE I
Characteristic data of compounds 2
Calculated/Found
M.p., °C
Yield, %
Formula
M.w.
Compound
% C
% H
% N
% Cl
2a
2ba
2c
200–202 C13H15N3O3
69 261.3
176–181b C13H17ClN2O
58 252.7
59.76
60.10
5.79
5.84
16.08
15.96
61.77
62.11
6.78
6.43
11.09
10.95
14.03
13.80
213–215 C11H11N3O3
82 233.2
56.65
56.66
4.76
4.80
18.01
17.82
2d
2ea
2f
153–155 C12H13N3O3
81 247.2
197–203b C12H14ClN3O3
86 283.7
58.29
58.53
5.30
5.31
17.00
16.90
50.80
50.65
4.97
5.11
14.81
14.86
12.50
12.44
203–206 C14H17N3O3
64 275.3
168–179b C15H20ClN3O3
49 325.8
275–277 C14H15N3O3
55 273.3
61.08
61.03
6.23
6.19
15.26
15.35
2ga
2h
2i
55.30
55.26
6.19
6.18
12.90
13.10
10.88
10.89
61.53
61.14
5.53
5.52
15.38
15.17
203–205 C16H13N3O3
74 295.3
65.08
65.03
4.44
4.46
14.23
14.29
2j
235–238 C16H12N4O5
77 340.3
56.45
56.80
3.56
3.80
16.47
15.99
2k
261–262 C17H14N4O5
83 354.3
57.62
57.60
3.98
3.88
15.81
15.42
a Hydrochloride. b M.p. with decomposition.
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

2-(4-Nitrophenyl)imidazolinones
TABLE II
913
1H NMR spectra of compounds 2 in hexadeuteriodimethyl sulfoxidea and in mixture hexadeuteriodi-
methyl sulfoxide–trifluoroacetic acidb
R2 = H R2 = CH3 R3 = CH3
CH
(m)
CH(CH3)
Compound Arom.a
Further signals
(brs)
(s)
(s)
(d)
c
2ab
8.40
8.26
–
–
–
–
1.30
1.44
1.59
1.98 1.02; 0.81
J = 6.79
c
2ad
8.50
8.34
–
2.09 1.06; 0.89
J = 6.80
c
2bb,e
8.48 (o)
7.93 (p)
7.77 (m)
–
2.22 1.10; 0.97
J = 6.17
2cb
2cd
2db
2dd
2eb,e
2fb
8.42
8.25
11.74
–
1.34
1.50
1.37
1.59
1.57
1.41
1.69
1.59
–
–
–
–
–
–
–
–
–
–
1.34 (CH3)
c
8.54
8.33
–
–
1.50 (CH3)
1.37 (CH3)
1.59 (CH3)
8.42
8.07
–
–
3.17
3.34
–
8.55
8.20
8.68
8.50
9.2
–
1.97 m (CH2);
0.92 t (CH3); J = 7.37
8.44
8.07
3.13
3.41
3.38
2.12 1.07; 0.87
J = 6.80
2fd
8.57
8.26
–
2.41 1.15; 0.95
J = 6.85
2gb,e
2hb
2ib
8.54
8.26
–
1.64 0.92; 0.87 2.10 and 1.84 (CH2)f
J = 6.60
8.41
8.27
1.78–1.60 m (8 H);
1.53–1.45 m (2 H)
c
–
–
–
–
–
–
–
–
c
8.45
8.36
–
1.73
7.57 (o); 7.41 (m);
7.34 (p)
c
2jb
8.45
8.36
–
–
1.76
1.93
–
–
–
–
8.27 and 7.87 2 × 2 H
(arom.)a
2kb
8.49
8.26
–
3.16
8.31 and 7.72 2 × 2 H
(arom.)a
a AA′XX′ system except for compound 2b. b In hexadeuteriodimethyl sulfoxide. c The signal was not
f
found. d In hexadeuteriodimethyl sulfoxide–trifluoroacetic acid. e Hydrochloride. JAB = 14.87; JAC
=
4.86; JBC = 7.73.
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

914
Sedlak, Halama, Kavalek, Machacek, Mitas, Sterba:
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

2-(4-Nitrophenyl)imidazolinones
915
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

916
Sedlak, Halama, Kavalek, Machacek, Mitas, Sterba:
between the presumed anion and neutral compound 2a is slow in the NMR time scale
1
and affects substantially the width of lines in both the H and 13C NMR spectra. In the
presence of trifluoroacetic acid in DMSO, about 20% of compound 2a is protonated,
the proton exchange between compound 2a and its conjugated acid is very fast in the
NMR time scale, hence all the signals in the NMR spectra are sharp. The difference in
chemical shifts of both protons and carbon atoms in the neutral compound 2d (in
DMSO) and the partially protonated compound (in 10% TFA in DMSO) can be seen in
the spectra of compound 2d in the two media (Tables II and III).
If after the base-catalyzed cyclization of a substituted 2-(4-nitrobenzoylamino)alkan-
amide 1 the solution is immediately concentrated (without neutralization), the increas-
ing concentration of the base results in reduction of nitro group and formation of azoxy
compounds. The azoxy compounds are practically insoluble in all current solvents,
0.7
1
A
2
3
FIG. 1
0.2
Electronic spectra of compound 2a dissolved
in dimethyl sulfoxide with addition of 1 vol.%
acetic acid (1), trifluoroacetic acid (2), sul-
280
300
320
furic acid (3)
λ, nm
1.5
A
1.8
A
a
b
1.0
1.2
0.5
0.0
0.6
0.0
250
300
350
250
300
350
λ, nm
λ, nm
FIG. 2
Electronic spectra of compound 2a measured in methanolic solutions of: a 0, 1 . 10–4, 1.5 . 10–4, 2 . 10–4,
3 . 10–4, 5 . 10–4, 7 . 10–4, 1 . 10–3 and 1 . 10–1 mol l–1 HCl (the absorbance decrease with increasing
HCl concentration at 262 nm); b 0. 4 . 10–2, 7 . 10–2, 1 . 10–1, 1.5 . 10–1, 2 . 10–1 and 5 . 10–1 mol l–1
sodium acetate (the spectrum of anion of compound 2a was measured in 0.1 M sodium methoxide;
the absorbance decrease with increasing acetate concentration at 280 nm)
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

2-(4-Nitrophenyl)imidazolinones
917
being very little soluble even in dimethyl sulfoxide. They cannot be purified by crystal-
lization, do not melt, but above ca 300 °C gradually carbonize. Both azoxy compounds 3
1
prepared were identified with the help of their H and 13C NMR spectra, compound 3a
1
by its mass spectrum, too. The H NMR spectra exhibit obvious doubling of all signals
due to the asymmetry of azoxy group. Besides that, both CH groups in CH(CH3)2 are
prochiral, hence the spectrum of compound 3a shows four methyl groups from isopro-
pyl groups. The values of proton chemical shifts depend considerably on concentration
of the solutions, temperature, and amount of the trifluoroacetic acid added. The shape
2
R
3
R
2
3
R R
4
N
R
2
1
1
5
4
R
R
CO N C CONH
2
9
6
4
N
R
O
8
7
1
2
1
2
3
4
R
R
R
R
1, 2
a
b
c
d
e
f
NO
H
H
H
H
CH i-C H
3 3
2
7
7
CH i-C H
3
3
3
3
CH
NO
NO
NO
NO
NO
NO
NO
NO
NO
CH
3
2
2
2
2
2
2
2
2
2
CH CH
CH
3
3
H
CH CH CH
3 2 3
CH CH i-C H
3
3
3
7
9
g
h
i
CH CH i-C H
3
3
4
(CH )
H
H
H
2 5
CH C H
6 5
3
j
CH 4-NO -C H
3
2
6
4
4
k
CH CH 4-NO -C H
3
3
2
6
H
N
H
1
1
R
R
2
2
N
R
R
2
2’
5
4
5’
4’
N N
O
9
9’
6
6’
N
N
O
O
8
7
7’
8’
3
1
2
R
R
3
a
b
CH i-C H
3 7
3
CH CH
3
3
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

918
Sedlak, Halama, Kavalek, Machacek, Mitas, Sterba:
of multiplet of aromatic protons changes considerably with these parameters, which is
obviously connected with the basicity of azoxy group and the ability of forming
oriented structures even in solutions6 which is usual with compounds having extensive
planar structures. The mass spectrum of compound 3a shows a weak signal of M+ ion
with the m/z value 474.3 (C26H30N6O3). From among the high-molecular fragments, the
highest intensities are observed with the signals m/z 458.3 (M – O), documented in the
fragmentation of parent azoxybenzene too7, and ions 431.2 (M – C3H7) and 415.2 –
base peak (M – O – C3H7). Attempts at symmetrization of compound 3a by reductive
removal of oxygen from azoxy group (with various reagents, such as PCl3, P(OCH3)3,
NaBH4 or P(C6H5)3 with [(C2H5)2NCS2]2MoO2 as catalyst8) failed due probably to the
low solubility.
EXPERIMENTAL
The 1H and 13C NMR spectra (δ, ppm; J, Hz) were measured at 400.13 and 100.62 MHz, respec-
tively, using a Bruker AM 400 spectrometer, or at 360.14 and 90.57 MHz, respectively, using a
Bruker AMX 360 apparatus, usually at 25 °C. For the measurements the substances were dissolved
in hexadeuteriodimethyl sulfoxide or its mixture with 10 vol.% TFA. The chemical shifts are refer-
enced to the middle signal of solvent multiplet (δ(1H) 2.55 and δ(13C) 39.60). The groups CH, CH3,
and Cq, CH2 in the 13C NMR spectra were differentiated by the ATP pulse sequence. The assignment
of signals in the spectra of compounds 2f, 2g, 2h, 2i, 2j, and 2k was accomplished on the basis of
the H,C COSY and H,H COSY spectra. The NOE difference spectra were adopted to assign the sig-
1
nals in the H NMR spectrum of compound 2a. The groups CH and CH3 in compound 2g were dif-
ferentiated by the pulse sequence DEPT-90. The pairs of corresponding signals in the 13C NMR
spectra of azoxy compounds 3a, 3b were not assigned. The mass spectrum was measured with a
spectrometer ZAB-EQ, VG Analytical (Manchester, U.K.) using the EI method with the ionizing
voltage of 70 eV. The ion source temperature 200 °C. The elemental composition of selected frag-
ments was determined at the resolution of 10 000. The electron spectra were measured with a HP
8453 Diode Array Spectrometer at 25 °C.
Measurement of dissociation constants. The dissociation constants were measured spectro-
photometrically at the concentration of 5 . 10–5 mol l–1 compound 2a at 25 °C in a 1 cm cell. The
dissociation constant of the protonated form of compound 2a was measured in methanolic solutions
of 10–4–10–3 mol l–1 hydrochloric acid at λ = 262 nm at the temperature of 25 °C. The ionic strength
was not adjusted (Fig. 2a). The dissociation constant of compound 2a was measured in methanolic
solutions of sodium acetate (0.04–0.5 mol l–1) at λ = 272 nm at the temperature of 25 °C. The ionic
strength was not adjusted (Fig. 2b). The pKA values were calculated from the relation pKA = pH – log P,
where P is the concentration ratio of conjugated base and acid calculated from the absorbances
measured. The dissociation constant of compound 2b was determined by potentiometric titration of
methanolic solution of the substance using an RTS 622 (Radiometer Copenhagen) apparatus with
glass and saturated calomel electrode system at 25 °C. The titration was carried out with 0.1 M solution
of tetrabutylammonium hydroxide in absolute methanol, and it was repeated three times. Benzoic
acid was used as the standard (pKA 9.41, ref.3).
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

2-(4-Nitrophenyl)imidazolinones
919
2-(4-Nitrophenyl)-5,5-disubstituted-4-imidazolinones 2. General Procedure
Compound 1 (7 mmol) (ref.1), methanol (20 ml), and 5 M sodium methoxide (1 ml) were placed in a
50 ml flask equipped with a reflux condenser. The mixture was boiled 30 min. After cooling and
neutralization with methanolic hydrochloric acid, the solvent was distilled off from a water bath. The
dry residue was washed with water and recrystallized from chloroform. This procedure was adopted
to prepare compounds 2a–2c, 2e, 2h, 2i, 2j.
Compounds 2d, 2f, 2g, 2k were prepared by cyclization at room temperature – standing overnight.
Compounds 2b, 2e, 2g were isolated as hydrochlorides after adding methanolic hydrogen chloride to
the extract of evaporation residue in chloroform. The elemental analyses, melting points, and yields
of the substances prepared are presented in Table I. The substances prepared were identified with the
1
help of their H and 13C NMR spectra (Tables II and III).
Methyl 2-(4-Nitrobenzoylamino)-2-methylpropanoate
2-Amino-2-methylpropanoic acid (15 g, 145 mmol) was dissolved in methanol (250 ml), and gaseous
hydrogen chloride was introduced into the solution 1 h, whereupon the mixture was heated to boiling
8 h, 2.5 ml thionyl chloride being added after each hour. The solvent was distilled off from water bath
until dry to give 22 g raw methyl 2-amino-2-methylpropanoate hydrochloride.
4-Nitrobenzoyl chloride (3.7 g, 20 mmol) was dissolved in 50 ml dry chloroform, and a mixture
of the above-described methyl 2-amino-2-methylpropanoate hydrochloride (3.1 g, 20 mmol) and trie-
thylamine (4.6 g, 46 mmol) in chloroform (50 ml) was added thereto. The reaction mixture was
heated at 60 °C 1 h and left to stand overnight. Chloroform was distilled off and the residue in the
flask was washed with water and filtered off. Recrystallization from a dichloromethane–hexane mixture
gave 3.4 g (75%) title compound, m.p. 164–166 °C. 1H NMR spectrum ((CD3)2SO): 9.03 brs, 1 H
(NH); 8.36 and 8.14 AA′XX′, 2 × 2 H (arom.); 3.65 s, 3 H (OCH3); 1.53 s, 6 H (C(CH3)2). 13C NMR
spectrum ((CD3)2SO): 174.18 (COOCH3), 164.46 (ArCON), 149.23 (C-4), 139.60 (C-1), 129.10 (C-2),
123.51 (C-3), 55.96 (Cq), 52.04 (OCH3), 24.89 (C(CH3)2).
2-Methyl-2-(4-nitrobenzoylamino)propane-N-methylamide
Methyl 2-methyl-2-(4-nitrobenzoylamino)propanoate (2.5 g, 11 mmol) was dissolved in dry benzene
(75 ml), and the solution was saturated with gaseous methylamine (9.3 g, 300 mmol) at 0 °C 45 min.
The mixture was then heated in a glass ampoule at 100 °C 24 h. The ampoule content was evap-
orated, and the residue was purified by chromatography (alumina column 30 × 5 cm, CHCl3–DMF
1
30 : 1) to give 0.8 g (32%) product, m.p. 198–200 °C. H NMR spectrum ((CD3)2SO): 8.64 brs, 1 H
(NH); 8.36 and 8.16 AA′XX′, 2 × 2 H (arom.); 7.69 brq, 1 H (NHCH3); 2.61 d, 3 H, 3J = 4.50
(NHCH3); 1.49 s, 6 H (C(CH3)2). 13C NMR spectrum ((CD3)2SO): 174.15 (CONHCH3), 164.32
(ArCON), 149.01 (C-4), 140.59 (C-1), 129.29 (C-2), 123.32 (C-3), 56.79 (Cq), 26.27 (NHCH3),
25.32 (C(CH3)2).
Attempt at Cyclization of 2-Methyl-2-(4-nitrobenzoylamino)propane-N-methylamide
A mixture of 2-methyl-2-(4-nitrobenzoylamino)propane-N-methylamide (1.86 g, 7 mmol) and 20 ml
0.2 (or 0.4 or 0.8 or 1.2) M sodium methoxide was refluxed 0.5 (or 1, 2 or 3) h. After cooling, the
mixture was neutralized with methanolic hydrochloric acid and the solvent was distilled off until dry
from water bath. The evaporation residue was washed with water and recrystallized from chloroform.
In all the cases only the starting amide was isolated (m.p. and mixed m.p. 198–200 °C).
Collect. Czech. Chem. Commun. (Vol. 61) (1996)

920
Sedlak, Halama, Kavalek, Machacek, Mitas, Sterba:
Bis-4,4′-(5-methyl-5-isopropyl-4-imidazolinon-2-yl)azoxybenzene (3a)
2-(4-Nitrobenzoylamino)-2,3-dimethylbutanamide(1a; 2 g, 8 mmol), methanol (20 ml), and 5 M sodium
methoxide (1 ml) were placed in a 50 ml flask equipped with a reflux condenser, and the mixture
was refluxed 8 h, whereupon the solvent was distilled off until dry from a water bath. The residue
was neutralized with methanolic hydrogen chloride, and the substance obtained was collected by suc-
tion, washed with water and with acetone. After drying, the product was reprecipitated from di-
methylformamide with water to give 1 g (29%) yellow microcrystalline compound 3a, m.p. 312 °C
(dec.). 1H NMR spectrum ((CD3)2SO–TFA): 11.70 brs, 1 H (NH); 11.59 brs, 1 H (NH); 8.58 and
8.45 AA′XX′, 2 × 2 H (arom.); 8.48 and 8.31 AA′XX′, 2 × 2 H (arom.); 2.19 sept, 1 H (CH(CH3)2);
2.11 sept, 1 H (CH(CH3)2); 1.56 s, 3 H (CCH3); 1.46 s, 3 H (CCH3); 1.11 d, 3 H, J = 6.99
(CH(CH3)); 1.09 d, 3 H, J = 6.94 (CH(CH3)); 0.97 d, 3 H, J = 6.79 (CH(CH3)); 0.91 d, 3 H, J = 6.76
(CH(CH3)). 13C NMR spectrum ((CD3)2SO–TFA): 182.32 and 180.26 (CO), 166.28 and 164.92 (C-2,2′),
151.23 and 148.90 (C-9,9′), 130.71 and 130.48 (C-7,7′), 127.82 and 122.59 (C-6,6′), 125.60 and
123.57 (C-8,8′), 71.84 and 70.95 (C-5,5′), 32.02 and 34.88 (CH(CH3)2), 19.69 and 19.38 (CCH3),
16.62, 16.50, 16.44, and 16.33 (CH(CH3)2).
Bis-4,4′-(5,5-dimethyl-4-imidazolinon-2-yl)azoxybenzene (3b)
Compound 3b was prepared from compound 1c in the same way as compound 3a, yield 45%, m.p.
1
300 °C (dec.). H NMR spectrum ((CD3)2SO–TFA): 11.65 brs, 1 H (NH); 11.55 brs, 1 H (NH); 8.46
and 8.26 AA′XX′, 2 × 2 H (arom); 8.23 and 8.19 AA′BB′, 2 × 2 H (arom.); 1.37 s, 6 H (C(CH3)2);
1.36 s, 6 H (C(CH3)2). 13C NMR spectrum ((CD3)2SO–TFA): 181.38 and 180.28 (CO), 165.33 and
164.64 (C-2,2′), 151.51 and 148.86 (C-9,9′), 130.71 and 130.65 (C-7,7′), 127.18 and 122.72 (C-6,6′),
125.70 and 123.70 (C-8,8′), 65.04 and 64.31 (C-5,5′), 22.93 and 22.86 (CH3).
The authors are indebted to Dr Miroslav Ludwig from Department of Organic Chemistry, University
of Pardubice, for carrying out the titration determination of pKA. The research was supported by the
Grant Agency of the Czech Republic (Grant No. 203/94/0123).
REFERENCES
1. Sedlak M., Halama A., Kavalek J., Machacek V., Sterba V.: Collect. Czech. Chem. Commun. 60,
150 (1995).
2. Wepplo P.: Pestic. Sci. 39, 293 (1990).
3. Pytela O., Kulhanek J., Ludwig M., Riha V.: Collect. Czech. Chem. Commun. 59, 627 (1994).
4. Machacek V., Svobodova G., Sterba V.: Collect. Czech. Chem. Commun. 52, 140 (1987).
5. Bordwell F. G.: Acc. Chem. Res. 21, 456 (1988).
6. Schumann C. in: Handbook of Liquid Crystals (H. Kelker and R. Hatz, Eds), p. 426. Verlag
Chemie, Weinheim 1980.
7. Efremov Y. A., Fedyaynov N. V.: Zh. Obshch. Khim. 19, 224 (1983).
8. Xiyan Lu, Junhui Sun, Xiaochun Tao: Synthesis 1982, 185.
Collect. Czech. Chem. Commun. (Vol. 61) (1996)