Reaction of nitroanilines with aldehydes. Refinement of the Doebner–Miller reaction mechanism

Article abstract of DOI:10.1134/S1070428016120150

Due to intramolecular hydrogen bonding between the amino and nitro groups, o-nitroaniline is incapable of forming Schiff bases in the reactions with acetaldehyde and crotonaldehyde but is converted to quinoline derivative under Doebner–Miller reaction conditions via addition to the C=C double bond of the α,β-unsaturated aldehyde. Under analogous conditions, p-nitroaniline possessing a free amino group gives rise to the product of Doebner–Miller quinoline synthesis through intermediate formation of Schiff base dimer. The reaction of p-nitroaniline with benzaldehyde also yields the corresponding Schiff base, whereas o-nitroaniline is converted to N-benzyl derivative.

Full text of DOI:10.1134/S1070428016120150

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2016, Vol. 52, No. 12, pp. 1797–1803. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © V.Ya. Denisov, T.N. Grishchenkova, T.B. Tkachenko, S.V. Luzgarev, 2016, published in Zhurnal Organicheskoi Khimii, 2016,
Vol. 52, No. 12, pp. 1806–1812.
Reaction of Nitroanilines with Aldehydes.
Refinement of the Doebner–Miller Reaction Mechanism
V. Ya. Denisov,* T. N. Grishchenkova, T. B. Tkachenko, and S. V. Luzgarev
Kemerovo State University, ul. Krasnaya 6, Kemerovo, 650043 Russia
*e-mail: vik.denisov2017@yandex.ru
Received March 24, 2016
Abstract—Due to intramolecular hydrogen bonding between the amino and nitro groups, o-nitroaniline is
incapable of forming Schiff bases in the reactions with acetaldehyde and crotonaldehyde but is converted to
quinoline derivative under Doebner–Miller reaction conditions via addition to the C=C double bond of the
α,β-unsaturated aldehyde. Under analogous conditions, p-nitroaniline possessing a free amino group gives rise
to the product of Doebner–Miller quinoline synthesis through intermediate formation of Schiff base dimer. The
reaction of p-nitroaniline with benzaldehyde also yields the corresponding Schiff base, whereas o-nitroaniline
is converted to N-benzyl derivative.
DOI: 10.1134/S1070428016120150
Carbonyl compounds (aldehydes, ketones) and
aromatic amines are widely used in organic synthesis
due to their high chemical reactivity. Reactions of
aromatic amines with aldehydes, on the one hand, are
used to obtain practically important compounds (bio-
logically active substances, dyes, luminophores, ana-
lytical reagents, plasticizers, etc.), and on the other,
make it possible to elucidate structure–reactivity
relationships.
Reactions of aromatic amines with carbonyl com-
pounds underlie major methods of quinoline synthesis,
such as Skraup, Doebner–Miller, Combes, Conrad–
Limpach, Friedländer syntheses, etc. [1–6]. The diver-
sity of synthetic methods is determined by diversity of
the amine component (any primary aromatic amine
with a free ortho position with respect to the amino
group), as well as of the carbonyl compounds (alde-
hydes, ketones, β-keto esters), reaction conditions,
catalyst nature, and added oxidants. Mechanisms of
formation of the six-membered nitrogen heterocycle
in each particular method may differ essentially, and
elucidation of factors affecting the reaction mechanism
is a topical problem.
The Doebner–Miller quinoline synthesis implies
heating an aromatic amine with acetaldehyde or its
precursor (ethylene glycol, paraldehyde) in the pres-
ence of sulfuric acid, hydrochloric acid, zinc chloride,
or a mixture of HCl with zinc chloride. Crotonalde-
hyde or some saturated aldehyde capable of under-
going crotonization may be used instead of acetal-
dehyde [1, 5]. There is no common opinion on the
Doebner–Miller reaction mechanism. Formerly, it was
presumed that the mechanism of this reaction is
analogous to the Skraup reaction mechanism according
to which the key stages are the formation of α,β-un-
saturated carbonyl compound, addition of aromatic
amine to the C=C double bond therein to give β-(aryl-
amino)butyraldehyde, cyclization of the latter with
closure of pyridine ring, dehydration, and dehydro-
genation [7].
Alternative versions of the Doebner–Miller mecha-
nism have also been proposed. In particular, one of
these involves condensation of aniline with acetalde-
hyde to form the corresponding Schiff base (N-ethyli-
deneaniline), its dimerization, and subsequent cycliza-
tion with elimination of aniline molecule [8]. The
mechanism implying crotonization of aliphatic alde-
hyde, followed by nucleophilic addition of aromatic
amine to the C=C double bond is believed to be
erroneous. Taking into account that the Doebner–
Miller reaction requires heating with excess aromatic
Study of the reactions of o- and p-nitroanilines with
acetaldehyde, crotonaldehyde, and benzaldehyde could
shed light on the effect of intramolecular hydrogen
bond in o-nitroaniline on the direction and mechanism
of the Doebner–Miller and other reactions.
1797

DENISOV et al.
1798
Scheme 1.
OH
O
NH2
N
Me
MeCHO
MeCHO
NHPh
N
H
Me
N
H
Me
NPh
PhNH2
–PhNH2
–H2
N
Me
N
Me
N
Me
N
Me
H
H
H
amine, it is reasonable to presume formation of Schiff
base dimer though it decomposes in acidic medium
(Ardashev’s scheme) [8] (Scheme 1).
plex multistep process with regard to the structure of
intermediate products. Exceptionally valuable are ex-
perimental data concerning the isolation, identification,
and properties of the intermediates. Fokin and
Fomicheva [9] tried to study intermediate stages of the
Doebner–Miller quinaldine synthesis from 1-amino-
anthraquinone and acetaldehyde [9]. 2-Methylnaphtho-
[2,3-h]quinoline-7,12-dione is formed through inter-
mediate 3-[(9,10-dioxo-9,10-dihydroanthracen-1-yl)-
amino]butanal which undergoes cyclization in the
presence of an acid (Scheme 3).
Analogous treatment of the Doebner–Miller reac-
tion mechanism was given in [2]: the quinoline core is
formed as a result of autocondensation of two Schiff
base molecules, where one Schiff base molecule acts
electrophile (in the protonated form), and the other, as
neutral electron-donating species. Gilchrist [3] did not
rule out the possibility of conjugate addition of aro-
matic amine to α,β-unsaturated carbonyl compound
and noted that Schiff bases are the key intermediates;
he proposed an alternative mechanism according to
which the quinoline ring system is formed via con-
densation of two Schiff base molecules through inter-
mediate 1,3-diazetinium ion (Scheme 2). One more
Doebner–Miller reaction mechanism implies formation
of Schiff base from aniline and crotonaldehyde, its
condensation with aniline, and cyclization of the
resulting Schiff base dimer [4, 6].
Assuming that the reactivity of 1-aminoanthra-
quinone is largely determined by intramolecular hydro-
gen bond involving the amino group and the neigh-
boring carbonyl group, we examined the behavior in
the Doebner–Miller reaction of o-nitroaniline (with
intramolecular hydrogen bond between the amino and
nitro group) and p-nitroaniline (which lacks intra-
molecular hydrogen bond) with the goal of finding out
whether the above affect is general or not. By heating
o-nitroaniline with paraldehyde in concentrated aque-
ous HCl (95°C, 3 h) we obtained 2-methyl-8-nitro-
The diversity of views on the Doebner–Miller
reaction reflects insufficient knowledge of this com-
Scheme 2.
R
Ph
H
N
H
R
R
N
N
R
Ph
N
+
N
H
R
N
R
R
R
Ph
Ph
N
R
N
HN
N
R
H
PhNH
R
N
R
N
R
H
H
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 52 No. 12 2016

REACTION OF NITROANILINES WITH ALDEHYDES.
1799
Scheme 3.
Me
Me
CHO
O
O
NH2
O
O
HN
O
O
HN
2MeCHO
H+
AcOH, H+
OAc
Me
O
O
N
Scheme 4.
CHO
Me
HO
Me
NH2
NO2
N
N
N
H+
H
O
H
O
CHO
2MeCHO
Me
N
O
O
3
4
Me
H
N
–H2O
–H2
N
Me
O
NO2
N
O
2
1
By reacting paraldehyde with o-nitroaniline for
a short time (1 h) at room temperature in the presence
of aqueous HCl we obtained the primary cyclization
product of aldehyde 3, 2-methyl-8-nitro-1,2,3,4-tetra-
hydroquinolin-4-ol (4) (Scheme 4). Thus, while study-
ing the reaction of o-nitroaniline with acetaldehyde we
have isolated and identified all intermediate products
of the Doebner–Miller reaction.
quinoline (1), whereas its reaction with acetaldehyde
or crotonaldehyde in acetic acid at room temperature
afforded 2-methyl-8-nitro-1,2-dihydroquinoline (2)
whose subsequent oxidation with trifluoroperoxyacetic
acid in methylene chloride gave compound 1
(Scheme 4). In keeping with the classical scheme of
quinaldine synthesis [7], β-(arylamino)butyraldehyde 3
should be formed as precursor to 2. We failed to detect
aldehyde 3 when the reaction was carried out in acidic
medium. However, treatment of o-nitroaniline with
acetaldehyde at 0–5°C in the presence of oxalic acid
led to the formation of aldehyde 3 which was very
readily converted to 2 by the action of aqueous HCl.
Oily aldehyde 3 was isolated and identified as 2,4-di-
nitrophenylhydrazone; it showed a positive color test
for aldehyde group (crimson color) on treatment with
fuchsin sulfurous acid.
Unlike o-nitroaniline, no intramolecular hydrogen
bond is formed in its para-substituted isomer, so that it
is capable of reacting with aldehydes to give the corre-
sponding Schiff bases. As might be expected, p-nitro-
aniline reacted with benzaldehyde in the presence of
sulfuric acid to give N-(4-nitrophenyl)-1-phenyl-
methanimine (5) whose structure was confirmed by
comparison with an authentic sample prepared as
described in [10] (Scheme 5).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 52 No. 12 2016

DENISOV et al.
1800
Scheme 5.
Ph
OH
Ph
Ph
H
N
H
CHO
N
N
N
H
O
H
O
H+
H
O
H
O
PhC=O
+
–H2O
–PhC=O
N
O
N
O
N
O
N
O
6
Scheme 6.
H
N
N
PhH, 20°C
Me
O2N
NO2
7
8
9
H2SO4, 20°C
O2N
NH2
35% HCl, 20°C
+
MeCHO
N
Me
O2N
H
95% H2SO4, 90–95°C
O2N
35% HCl, 95°C
N
Me
No Schiff base is formed from o-nitroaniline;
instead, benzylation of the nitrogen atom occurs with
retention of the intramolecular hydrogen bond, and the
product is N-benzyl-2-nitroaniline (6). The structure of
6 was confirmed by comparing with a sample syn-
thesized by the Wallach reaction [1]. Formic acid is
commonly used as reducing agent in the Wallach reac-
tion. In our case, excess benzaldehyde acted as
reducing agent. Analogous N-benzylation was reported
previously for 1-aminoanthraquinone and diaminoan-
thraquinones with the amino groups located in the
α-position of the anthraquinone core [11].
room temperature we obtained 2-methyl-6-nitro-1,2-
dihydroquinoline (8) which was also synthesized
directly from p-nitroaniline and acetaldehyde or
paraldehyde in concentrated (35%) aqueous HCl
(Scheme 6). Heating of 8 in 95% sulfuric acid (90–
95°C, 2 h) afforded 2-methyl-6-nitroquinoline (9) in
addition to p-nitroaniline and other compounds.
2-Methyl-6-nitroquinoline (9) was smoothly synthe-
sized by heating p-nitroaniline and paraldehyde in con-
centrated aqueous HCl (95°C, 3 h).
In summary, we have isolated intermediate products
7 and 8 of the Doebner–Miller reaction of p-nitro-
aniline. The mechanism of formation of 7 remains
unclear since it is formed very rapidly so that no pre-
ceding intermediates could be detected. Most probably,
compound 7 results from condensation of p-nitro-
aniline with crotonaldehyde, followed by addition of
the second amine molecule to the C=C double bond of
the Schiff base thus formed. An alternative route
involving Schiff base formation from p-nitroaniline
and acetaldehyde, followed by dimerization, seems
less probable.
The results of the reactions of nitroanilines with
benzaldehyde indicated that the para isomer can be
converted to the corresponding Schiff bases; therefore,
under Doebner–Miller conditions it could give rise to
quinoline derivative according to Ardashev’s or
Gilchrist’s scheme. The reaction of p-nitroaniline with
acetaldehyde in benzene at room temperature quanti-
tatively afforded a dimeric Schiff base, N-[4-(4-nitro-
phenylimino)butan-2-yl]-4-nitroaniline (7). By treat-
ment of dimer 7 with concentrated sulfuric acid at
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 52 No. 12 2016

REACTION OF NITROANILINES WITH ALDEHYDES.
1801
EXPERIMENTAL
d. o-Nitroaniline, 1.0 g (0.008 mol), was dissolved
in 50 mL of concentrated aqueous HCl, 1.5 mL
(0.012 mol) of paraldehyde was added over a period of
10 min, and the mixture was stirred for 1 h at 20°C.
According to the TLC data (eluent benzene), the mix-
ture contained approximately equal amounts of un-
reacted o-nitroaniline and an orange material remained
at the start. The mixture was poured onto 100 g of
an ice–water mixture, and the precipitate was filtered
off, washed with water, and dried. It was then dis-
solved in benzene and subjected to silca gel column
chromatography. Elution with benzene afforded
o-nitroaniline, and the orange product was eluted with
chloroform. It was identified as 2-methyl-8-nitro-
1,2,3,4-tetrahydroquinolin-4-ol (4). Yield 0.22 g
(15%). IR spectrum (mineral oil), ν, cm–1: 3620 (OH),
3350 (NH), 1600 (C=C), 1470 and 1350 (NO2).
Compound 4 was unstable and was readily converted
into dihydroquinoline 2.
The IR spectra were recorded in the range from 400
to 4000 cm–1 on a Specord M-80 spectrometer. The
1H NMR spectra were taken on a Bruker AC-200
spectrometer using hexamethyldisiloxane as internal
standard. The isolated compounds were identified by
comparing their IR spectra and melting points (no
melting point depression) with those of authentic
samples. The melting points were measured in capil-
laries using a PTP-1 melting point apparatus. The
elemental analyses were obtained at the Organic
Chemistry Department, Kemerovo State University.
The progress of reactions and the purity of products
were monitored by TLC on Silufol plates. Column
chromatography was performed using Silica gel (70–
230 mesh, Fluka) or aluminum oxide of Brockmann
activity grade III.
Reaction of o-nitroaniline with acetaldehyde.
a. Paraldehyde, 0.2 mL (0.06 mol), was added drop-
wise over a period of 10 min to a solution of 5.0 g
(0.04 mol) of o-nitroaniline in 200 mL of concentrated
aqueous HCl. The mixture was heated to 95°C and
stirred for 3 h at that temperature. It was then cooled,
poured into 200 mL of water, and neutralized with
20% aqueous potassium hydroxide. The yellow precip-
itate was filtered off, washed with water, dried, and
recrystallized from water. Yield of 2-methyl-8-nitro-
quinoline (1) 4.8 g (55%), mp 137–138°C [12].
d. o-Nitroaniline, 0.50 g (0.004 mol), was dissolved
in 20 mL of acetaldehyde cooled to 2°C, 40 mg of
oxalic acid was added, and the mixture was stirred for
2.5 h at 0–5°C and kept for 48 h at that temperature. It
was then poured into 100 mL of water and extracted
with benzene (3×50 mL), the extract was washed with
water, the organic phase was separated and dried over
calcined magnesium sulfate, and the solvent was evap-
orated at room temperature. Yield of 3-(2-nitroanilino)-
butanal (3) 0.42 g (56%), yellow oily material. IR
spectrum (mineral oil), ν, cm–1: 3350 (NH), 1715
(CH=O), 1500 and 1340 (NO2).
b. A flat-bottom flask was charged under stirring
with 22 mL of acetic acid and 0.5 g (0.004 mol) of
o-nitroaniline. Acetaldehyde, 0.8 mL (0.014 mol), was
added to the mixture in one portion, and the mixture
was stirred for 48 h at room temperature (20°C). The
mixture was diluted with water (50 mL) and neutral-
ized with 20% aqueous potassium hydroxide, and the
precipitate was filtered off, washed with water, and
dried. Yield of 2-methyl-8-nitro-1,2-dihydroquinoline
(2) 0.42 g (62%). Orange crystals, mp 169–170°C
3-(2-Nitroanilino)butanal 2,4-dinitrophenylhy-
drazone. 2,4-Dinitrophenylhydrazine, 0.29 g
(0.0014 mol), was dissolved in 40 mL of 5% aqueous
HCl, and a solution of 0.30 g (0.0014 mol) of aldehyde
3 in 100 mL of water was added dropwise. After
a time, the yellow precipitate was filtered off, washed
with water, dried, and recrystallized from benzene–
hexane (1:1). Yield 0.27 g (50%), yellow crystals,
mp 148–149°C. IR spectrum, ν, cm–1 (mineral oil):
3335 (NH), 3285 (NH), 1614 (C=N), 1585 (C=C),
1500 (NO2), 1460 (NO2), 1330 (NO2). Found, %:
C 49.56; H 4.34; N 21.37. C16H16N6O6. Calculated, %:
C 49.48; H 4.12; N 21.65.
1
(from benzene). H NMR spectrum, δ, ppm: 1.20 d
(CH3), 6.38–7.02 m (Harom), 8.25 m (NH). Found, %:
C 62.59; H 5.00; N 14.81. C10H10N2O2. Calculated, %:
C 63.15; H 5.26; N 14.72.
Compound 2 was converted to 2-methyl-8-nitro-
quinoline (1) by treatment with trifluoroperoxyacetic
acid in methylene chloride.
Reaction of o-nitroaniline with crotonaldehyde.
o-Nitroaniline, 0.50 g (0.004 mol), was dissolved in
20 mL of acetic acid, 0.8 mL (0.01 mol) of crotonalde-
hyde and 0.02 mL of concentrated aqueous HCl were
added each in one portion, and the mixture was stirred
for 1 h at room temperature (20°C). After 10 min,
c. Compound 2 was synthesized as described in b in
the presence of 0.04 mL of concentrated aqueous HCl.
The reaction was complete in 0.5 h; yield 60.9%.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 52 No. 12 2016

DENISOV et al.
1802
an orange solid began to separate from the solution.
The mixture was poured into 50 mL of water and
neutralized with 20% aqueous potassium hydroxide,
and the precipitate was filtered off, washed with water,
and dried. Yield of 2-methyl-8-nitro-1,2-dihydroquino-
line (2) 0.43 g (64%). After recrystallization from
benzene, orange crystals with mp 168–169°C were
obtained. The product was identical to that isolated in
the reaction of o-nitroaniline with acetaldehyde as
described above in b.
phenylimino)butan-2-yl]aniline (7) 0.51 g (87%),
yellow crystalline powder, mp 115–116°C. IR spec-
trum (mineral oil), ν, cm–1: 3380 (NH), 1615 (C=N),
1520 (C=C), 1500 (NO2), 1350 (NO2). Found, %:
C 58.36; H 4.52; N 16.87. C16H16N4O4. Calculated, %:
C 58.53; H 4.88; N 17.07.
d. p-Nitroaniline, 0.50 g (0.004 mol), was dissolved
at 20°C in 3 mL (0.06 mol) of acetaldehyde. After 1–
2 min, a yellow solid separated and was filtered off,
washed with benzene, dried, and recrystallized from
benzene. Yield of 7 0.52 g (89%); the product was
identical to a sample isolated as described above in c.
Reaction of p-nitroaniline with acetaldehyde.
a. Paraldehyde, 4.5 mL (0.025 mol), was added over
a period of 10 min to a solution of 3.2 g (0.022 mol) of
p-nitroaniline in 200 mL of concentrated aqueous HCl.
The mixture was heated to 95°C, stirred for 3 h at that
temperature, cooled, poured into 200 mL of water, and
neutralized with 20% aqueous potassium hydroxide to
pH 8. The precipitate was filtered off, washed with
a 5% alkali solution, dried, and dissolved in benzene,
and the solution was subjected to alumina column
chromatography. Elution with chloroform gave 0.22 g
(33%) of 2-methyl-6-nitroquinoline (9) (yellow zone),
yellow crystals, mp 163–164°C [13]. IR spectrum
(mineral oil), ν, cm–1: 1600 (C=Carom), 1465 and 1390
Reaction of p-nitroaniline with crotonaldehyde.
p-Nitroaniline, 0.50 g (0.004 mol), was dissolved in
25 mL of acetic acid, and 1 mL (0.014 mol) of
crotonaldehyde was added. After 1 min, a yellow solid
separated and was filtered off, washed with 10% acetic
acid, and dried. The product was purified by reprecip-
itation from chloroform with hexane. Yield of
2-methyl-6-nitro-1,2-dihydroquinoline (8) 0.31 g
(45%), mp 200–202°C. The product was identical to
a sample obtained as described above in b.
Reactions of nitroanilines with benzaldehyde.
a. p-Nitroaniline, 1.38 g (0.011 mol), was dissolved in
5 mL of benzaldehyde, 0.1 mL of 50% sulfuric acid
was added, and the mixture was heated for 20 h on
a water bath (90°C). According to the TLC data,
almost no reaction occurred under these conditions.
The mixture was then refluxed for 30 min. The
formation of a red compound as the major product was
detected by TLC. The mixture was cooled, and the
precipitate was filtered off, washed with hexane, and
dried. The product was dissolved in benzene and
subjected to alumina column chromatography using
benzene as eluent. N-(4-Nitrophenyl)phenylmethan-
imine (5), 1.19 g (53%), was isolated from the first
fraction as orange–red crystals, mp 117–118°C [10].
1
(NO2). H NMR spectrum (CDCl3), δ, ppm: 2.67 s
(CH3), 6.38 d and 7.32 d (3-H, 4-H, J = 9 Hz), 7.80–
8.56 m (Harom).
b. p-Nitroaniline, 0.50 g (0.004 mol), was dissolved
in 22 mL of acetic acid, 0.8 mL (0.016 mol) of acet-
aldehyde and 0.04 mL (0.001 mol) of 30% aqueous
HCl were added each in one portion, and the mixture
was stirred for 5 h at room temperature. The mixture
was poured into 100 mL of water and neutralized with
20% aqueous potassium hydroxide, and the precipitate
was filtered off, washed with 5% acetic acid, dried,
and purified by reprecipitation from chloroform with
hexane. Yield of 2-methyl-6-nitro-1,2-dihydroquino-
line (8) 0.42 g (58%), yellow crystals, mp 201–202°C.
IR spectrum (mineral oil), ν, cm–1: 3400 (NH), 1600
b. A mixture of 1.38 g (0.011 mol) of o-nitroaniline,
2 mL of benzaldehyde, and 10 mL of formic acid was
heated for 7 h on a water bath (90°C). According to the
TLC data, the initial nitroaniline disappeared, and
an orange product was formed. The mixture was
steam-distilled, and an oily material separated from the
distillate and was extracted into benzene. The extract
was applied onto a chromatographic column charged
with silica gel, and the column was eluted with
benzene. From the first orange–red fraction we isolated
N-benzyl-2-nitroaniline (6). Yield 0.95 g (42%),
yellow crystals, mp 72–73°C [13]. IR spectrum (KBr),
ν, cm–1: 3400 (NH), 2800–2900 (CH2).
1
(C=Carom), 1470 (NO2), 1300 (NO2). H NMR spec-
trum (DMSO-d6), δ, ppm: 1.34 d (CH3, J = 6 Hz),
6.65–7.05 m (3-H, 4-H), 7.68 m (NH), 7.88–8.21 m
(5-H, 7-H, 8-H). Found, %: C 62.64; H 5.06; N 14.81.
C10H10O2N. Calculated, %: C 63.15; H 5.26; N 14.73.
c. p-Nitroaniline, 0.50 g (0.004 mol), was dissolved
in 30 mL of benzene, 0.8 mL (0.018 mol) of acetalde-
hyde was added in one portion, and the mixture was
stirred for 10 min at 20°C. The yellow precipitate was
filtered off, washed with benzene, dried, and recrystal-
lized from benzene. Yield of 4-nitro-N-[4-(4-nitro-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 52 No. 12 2016

REACTION OF NITROANILINES WITH ALDEHYDES.
1803
4. Heterocyclic Compounds, Elderfield, R.C., Ed., New
York: Wiley, 1952, vol. 4. Translated under the title
Geterotsiklicheskie soedineniya, Moscow: Inostrannaya
Literatura, 1955, vol. 4, p. 539.
5. Khimicheskaya entsiklopediya (Chemical Encyclo-
pedia), Moscow: Sovetskaya Entsiklopediya, 1990,
vol. 2, p. 8.
6. Kratkaya khimicheskaya entsiklopediya (Brief Chemical
Encyclopedia), Moscow: Sovetskaya Entsiklopediya,
1961, vol. 1, p. 1034.
7. Beyer, C., J. Prakt. Chem., 1886, vol. 33, p. 424.
8. Ardashev, B.I., Usp. Khim., 1954, vol. 23, p. 54.
c. o-Nitroaniline, 1.38 g (0.011 mol), was dissolved
in 10 mL of benzaldehyde, 0.1 mL of 50% sulfuric
acid was added, and the mixture was heated for 12 h
on a water bath (90°C) and then refluxed for 30 min.
The mixture was cooled and diluted with heptane
(30 mL), and the precipitate was filtered off, dissolved
in benzene, and subjected to alumina column chroma-
tography. From the first fraction we isolated 0.82 g
(36%) of compound 6 which was identical to a sample
obtained as described in b.
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