6-Methyl-2-(3-methyl-5-oxo-2,5-dihydropyrazolyl)-pyrimidin-4(1H)-one as CH acid in Michael reaction

Article abstract of DOI:10.1134/S1070363209070214

Addition of 6-methyl-2-(3-methyl-5-oxo-2,5-dihydropyrazol-1-yl)pyrimidin- 4(1H)-one, a compound with two CH-acidic centers, to 5-benzylidenepyrimidine-2, 4,6(1H,3H,5H)-trione proceeds with the participation of the atom C⁵ of pyrimidine ring. Un

Full text of DOI:10.1134/S1070363209070214

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 7, pp. 1525–1531. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © A.V. Erkin, V.I. Krutikov, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 7, pp. 1168–1174.
6-Methyl-2-(3-methyl-5-oxo-2,5-dihydropyrazolyl)-
pyrimidin-4(1H)-one as CH Acid in Michael Reaction
A. V. Erkin and V. I. Krutikov
St. Petersburg State Institute of Technology, Moskovskii pr. 26, St. Petersburg, 190013 Russia
e-mail: kruerk@yandex.ru
Received March 30, 2009
Abstract—Addition of 6-methyl-2-(3-methyl-5-oxo-2,5-dihydropyrazol-1-yl)pyrimidin-4(1H)-one, a compound
with two CH-acidic centers, to 5-benzylidenepyrimidine-2,4,6(1H,3H,5H)-trione proceeds with the
participation of the atom C5 of pyrimidine ring. Under the realized reaction conditions the latter possesses a
greater nucleophilicity as a result of the priority ionization. The obtained Michael adduct is unstable in the
neutral aqueous medium and is decomposed into initial oxopyrazolylpyrimidinone, pyrimidine-2,4,6-
(1H,3H,5H)-trione, and benzaldehyde.
DOI: 10.1134/S1070363209070214
The study of the chemical transformations of 6-
methyl-2-(3-methyl-5-oxo-2,5-dihydropyrazol-1-yl)-
pyrimidin-4(1H)-one (I) was practically limited to the
investigation of its coupling with aryldiazonium
chlorides [1, 2] and condensations with aromatic [3, 4]
and heteroaromatic [5, 6] aldehydes. Meanwhile
compound I is of undoubtable interest as a CH-acidic
component of Michael reaction. In view of the
presence in the structure of oxopyrazolylpyrimidine I
of two centers possessing potential CH-acidity, the
prediction of the direction of its reaction with the
vinylogs of carbonyl compounds becomes possible
only taking into account the data on the structure of the
ionized form of the reacting component.
The purpose of this work consisted in revealing the
priority direction of ionization of oxopyrazol-
ylpyrimidine I and in the study of the addition of its
ionized form to 5-benzylidenepyrimidine-2,4,6-
(1H,3H,5H)-trione (II).
For the synthesis of compound I by a method
unlike the two-stage one [7,8] we accomplished the
condensation of 2-hydrazino-6-methylpyrimidin-4(3H)-
one (III) with ethyl acetoacetate in water and showed
that the reaction could be carried out without the
intermediate isolation of ethyl acetoacetate (6-methyl-
4-oxo-3,4-dihydropyrimidin-2-yl)hydrazone.
O
O
AcCH2COOEt
HN
N
H
N
H2N
Me
N
H
N
Me
N
N
H
Me
O
III
I
Analysis of IR spectra of crystalline samples of
oxopyrazolylpyrimidine I and the related compounds
allowed [9] to postulate the structure of I as 4-hydroxy-
6-methyl-2-(3-methyl-5-oxo-2,5-dihydropyrazol-1-yl)-
pyrimidine. We believe that the problem of the
structure of compound I is more complex, and a
possibility of the formation of intramolecular bonds of
NH···N and NH···O types involving the appropriate
fragments of pyrimidine and pyrazole rings should be
considered. Formation of such bonds is promoted, on
the first hand, by their coplanar arrangement, and, on
the second hand, by the proximity of the indicated
1525

1526
ERKIN, KRUTIKOV
ε, l mol–1 cm–1
20000
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
2
3
1
4
Fig. 1. Optimized geometry of the molecule of 6-methyl-
2-(3-methyl-5-oxo-2,5-dihydropyrazol-1-yl)-pyrimidin-
4(1H)-one (I) (the hydrogen atoms in 1 and 2 positions of
pyrimidine and pyrazole rings are shown).
200 220 240 260 280 300 320 340 360 380
λ, nm
atoms (Fig. 1). Considering the IR spectrum of
oxopyrazolylpyrimidine I , one can see that the band at
3110 cm–1 corresponding to the stretching vibrations of
groups NH is shifted significantly to low frequencies
in comparison with the analogous band in the spectrum
of model substance, 2-(3,5-dimethylpyrazol-1-yl)-6-
methylpyrimidine-4(3H)-one (IV) (νNH 3350 cm–1).
We obtained pyrazolylpyrimidinone IV by the reaction
of hydrazinopyrimidine III with 2,4-pentanedione at
elevated temperature without a solvent.
Fig. 2. UV spectra of (1) 6-methyl-2-(3-methyl-5-oxo-2,5-
dihydropyrazol-1-yl)-pyrimidin-4(1H)-one (I), (2) 2-(3,5-
dimethylpirazol-1-yl)-6-methylpyrimidin-4(3H)-one (IV)
in the presence of equimolar quantity of sodium ethoxide,
(3) 6-methyl-2-(3-methyl-5-oxo-2,5-dihydropyrazol-1-yl)-
pyrimidine-4(1H)-one (I) in the presence of equimolar
quantity of sodium ethoxide, and (4) 2-(3,5-dimethyl-
pyrazol-1-yl)-6-methylpyrimidin-4(3H)-one (IV).
equilibrium mixture of tautomers Ia and Ib identified
by the absorption bands in the spectrum of compound I
with maxima at 230, 245 and 277 nm. The presence of
the first band is caused by π → π* transitions in the
hydroxypyrazole ring, which is of aromatic nature, and
of two other bands, by n → π* transitions in pyrazolone
and pyrimidine rings, respectively.
O
HN
Ac2CH2
N
III
Me
N
N
Me
Me
IV
Me
Me
N
N
H
O
O
H
N
N
The absorption bands of the carbonyl groups of
pyrimidine ring near 1676 cm–1 and pyrazole ring at
approximately 1639 cm–1 also were subjected to a low-
frequency shift relative to the bands of the same origin
in the spectra of compound IV (νC=O 1698 cm–1) and 1-
(pyrimidine-2-yl)-5-pyrazolone that have a fixed 5-oxo-
2,5-dihydro configuration [10].
H
H
N
N
N
N
O
Me
O
Me
Ia
Ib
The consideration of intensities of the bands at 230
(ε = 11460) and 245 (ε = 10850) nm indicates that the
ratio of tautomers Ia and Ib in the mixture is nearly
equimolar. The total number of tautomers in the
solutions of oxopyrazolylpyrimidine I is confirmed by
the positive result of the test for the two-component
character of the system [11], based on the constancy
(within the error) of the ratio of optical densities of two
arbitrarily selected solutions at any wavelength (Table 1).
The strong interatomic interactions in the molecule
of oxopyrazolylpyrimidine I may be concluded from
the similarity of its UV of spectrum with the spectrum
of the ionized form of pyrazolylpyrimidine IV (λmax
230, 245 sh, and 274 nm) (Fig. 2) that indicates the
parallel processes of the transfer of the NH group
protons of the of pyrimidine ring to the carbonyl group
of pyrazole ring and of the pyrazole ring NH proton to
the pseudo-deprotonated pyrimidine cycle. A similar
migration of protons leads to the formation of
The addition of sodium ethoxide as a base to the
equilibrium mixture of tautomers Ia and Ib produces
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 7 2009

6-METHYL-2-(3-METHYL-5-OXO-2,5-DIHYDROPYRAZOLYL)-...
1527
Table 1. Optical densities and their functions for the solutions of 6-methyl-2-(3-methyl-5-oxo-2,5-dihydropyrazol-1-yl)-
pyrimidine-4(1H)-one I at the arbitrary wavelengths
Optical densities of solutions Di at the wavelength λ, nm
Solution
230
245
280
300
1
2
0.6840
0.9355
1.2006
1.4815
1.0754
0.6716
0.8996
1.1367
1.4089
1.0292
0.7144
0.9914
1.2757
1.5686
1.1375
0.5143
0.6882
0.8794
1.0862
0.7920
3
4
Dav
Wavelength λ, nm
Functions of optical density
230
–0.3914
–0.1399
0.1252
0.4061
2.80
245
–0.3576
–0.1296
0.1075
0.3797
2.76
280
–0.4231
–0.1461
0.1382
0.4311
2.89
300
D1 – Dav
D2 – Dav
–0.277
–0.1038
0.0874
0.2942
2.68
D3 – Dav
D4 – Dav
D1 – Dav/(D2 – Dav)
D2 – Dav/(D2 – Dav)
D3 – Dav/(D2 – Dav)
D4 – Dav/(D2 – Dav)
1
1
1
1
–0.89
–2.90
–0.83
–2.93
–0.94
–2.95
–0.84
–2.83
substantial changes in the spectrum: the absorption
band at 230 nm disappears completely while the band
with the maximum at 277 nm undergoes bathochromic
shift by 12 nm and achieves the position of the
absorption band of model substance, 3,6-dimethyl-2-
equilibrium to the side of the tautomer (Ia) that is
characterized by the 4-oxo-3,4-dihydro configuration
of pyrimidine ring, and the isosbestic point near 261
nm which occurst in the spectra of the mixtures of
compound I with sodium ethoxyde at different molar
ratios (Fig. 3b) points to the cleavage of the hydrogen
bond NH···O and the subsequent formation of the
pseudoionized form A.
(3,5-dimethylpyrazol-1-yl)pyrimidin-4(3H)-one
(V)
(λmax = 285 nm) (Fig. 3a). This circumstance con-
vincingly indicates the shift of intermolecular
(b)
(a)
ε, l mol–1 cm–1
D
18000
16000
1.40
1.35
1.30
1.25
1.20
1.15
1.10
1.05
1.00
0.95
0.90
1
14000
12000
10000
8000
6000
4000
2000
0
1
1
2
2
3
3
4
3
2
240
245
250
255 260
265
270
200
250
300
350
400
λ, nm
λ, nm
Fig. 3. (a) UV spectra of the mixtures of 6-methyl-2-(3-methyl-5-oxo-2,5-dihydropyrazol-1-yl)-pyrimidin-4(1H)-one (I) and
sodium ethoxide in different molar ratios: (1) 1:0.23, (2) 1:0.58, (3) 1:0.91, and (4) of 3,6-dimethyl-2-(3,5-dimethylpirazol-1-yl)
pyrimidin-4(3H)-one (V). (b) Isobestic point in the UV spectra of mixtures of 6-methyl-2-(3-methyl-5-oxo-2,5-dihydropyrazol-1-
yl)-pyrimidin-4(1H)-one (I) and sodium ethoxide in different molar ratios: (1) 1:0.23, (2) 1:0.58, and (3) 1:0.91.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 7 2009

1528
ERKIN, KRUTIKOV
O
O
H
N
H
N
N
N
_
OEt
_
N
Ia
N
N
H
Me
_EtOH
N
Me
Me
Me
O
O
A
_OEt
The model compound V was synthesized by the
condensation of 2-hydrazino-3,6-dimethylpyrimidin-
4(3H)-one VI with 2,4-pentanedione in 1-butanol
under the conditions of water removal by the
azeotropic distilliation.
The retention of hydrogen bond NH···N is
confirmed additionally by the similarity of the spectra
of compound I in the presence of equimolar quantity
of sodium ethoxide (λmax 245, 289 nm) and of neutral
form of pyrazolylpyrimidine IV (λmax 242, 292 nm)
(Fig. 2).
O
Me
N
H2N
The break of the hydrogen bond NH···O is
illustrated also by the shift of the band of the stretching
vibrations of the pyrazole ring carbonyl group in the
spectrum of the oxopyrazolylpyrimidine I mono-
sodium salt by 10 cm–1 to the region of higher
frequencies in comparison with the analogous band in
the IR spectrum of the demetallated compound I.
N
H
N
Me
VI
O
N
Varying temperature does not affect noticeably the
process of pseudoionization of oxopyrazolylpyri-
midine I. The UV the spectra of the equimolar
mixtures of compound I and sodium ethoxide recorded
at the temperature of the mixture 25.5, 45.5, 55.3, and
65.1°C, are identical, and the difference in the molar
absorption coefficients ε of the mixtures at the
arbitrarily selected wavelength does not exceed 5%
(Table 2). The revealed similarity of the spectra of the
mixtures of compound I with sodium ethoxide
indicates the invariability of the structure of the
psevdoionized form A over a wide range of
temperatures.
Me
N
Ac2CH2
N
N
Me
Me
Me
V
The observed isosbestic point occurs in a narrow
interval of the oxopyrazolylpyrimidine I and sodium
ethoxide molar ratio, and this fact together with the
increase in the optical density of the solutions of their
mixtures at the increase in the molar content of the
base indicates that the pseudoionized form A is
protonated via the migration of the proton of pyrazole
ring followed by formation of tautomer Ib:
The pseudoionization of pyrimidine ring leads to an
increase in its nucleophilicity that determines preferred
addition of of benzylidenebarbituric acid II to the
indicated CH-acidic center of oxopyrazolylpyrimidine
I molecule. Actually, by the reaction of compounds I
and II in boiling ethanol in the presence of an
equimolar quantity of sodium ethoxide we obtained
and isolated a single reaction product, (2,4,6-trioxo-
1,2,3,4,5,6-hexahydropyrimidin-5-yl)[2-(5-hydroxy-3-
methylpyrazol-1-yl)-6-methyl-4-oxo-3,4-dihydropyri-
midin-5-yl]phenylmethane (VII).
O
N_
H
N
A
N
N
Me
Me
O
O
HN
The structure of bispyrimidylphenylmethane VII is
N
1
Ib
_
confirmed by the H NMR spectrum, which contains
N
N
Me
_EtO
Me
the characteristic [12] signal of the proton of exocyclic
methine group at 5.9 ppm. Alongside the presence of
O
HOEt
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 7 2009

6-METHYL-2-(3-METHYL-5-OXO-2,5-DIHYDROPYRAZOLYL)-...
1529
Ph
O
O
O
HN
Ph
HN
NH
I +
N
O
N
H
O
O
N
H
O
Me
N
N
Me
HO
II
VII
the signal of the proton at the C5 atom of the
trioxopyrimidine ring near 3.4 ppm, in the spectrum a
signal is absent in the region of 6 ppm characteristic of
the proton of the pyrimidine ring methine group in
oxopyrazolylpyrimidine (I). At the same time the
position of the signal of the proton at the C4 atom of
the pyrazole ring, which in the spectrum of compound
I occurs at about 5.2 ppm, is changed considerably to
appear at 7.3 ppm. Due to the ovelap of the signals of
the methyl group protons and of solvent in the
spectrum of bispyrimidylphenylmethane VII we
registered the spectrum of this compound dissolved in
deuterated trifluoracetic acid and established the
equivalence of these signals and found their chemical
shift, which equaled 3.30 ppm.
EXPERIMENTAL
1
The H NMR spectra were registered on a Briker
WM-400
400.13 MHz), solvent DMSO-d6 [except 3,6-dimethyl-
2-(3,5-dimetylpirazol-1-yl)pyrimidin-4(3H)-one V]
spectrometer
(operating
frequency
(solvent CDCl3), internal references were the signals of
the residual protons of the solvents. The IR spectra
were registered on
a
Shimadzu FTIR-8400S
spectrophotometer from KBr tablets. The UV spectra
were taken on a SF-26 spectrophotometer in the
temperature-controlled quartz cells with the optical
layer thickness 1 cm, in ethanol at the concentration of
substances ~ 1×10–4 mol l–1. For testing on the n-com-
ponent composition were used solutions of 6-methyl-2-
(3-methyl-5-oxo-2,5-dihydropyrazol-1-yl)-pyrimidin-
4(1H)-one I of the following concentrations: 0.54×10–4
(solution 1), 0.74×10–4 (solution 2), 1.05·10–4 (solution
3) and 1.28×10–4 (solution 4) mol l–1. The individuality
of compounds was monitored by the TLC on the
Silufol UV-254 plates in the following systems: 1-
butanol–acetic acid 1:1 + 5 drops of water (eluent A),
acetone–heptane 2:3 (eluent B), 1-butanol–acetic acid–
water, 1:1:1 (eluent C), 1-butanol–acetic acid, 1:1 + 2
drops of water (eluent D) and acetone–heptane, 2:1
(eluent E). Developing of the spots corresponding to
compounds I–VI was achieved by UV irradiation, the
spots of compound VII were developed by treatment
Compound VII is extremely instable even in
neutral aqueous solutions. Already during suspending
bispyrimidylphenylmetane VII in water it begins to
partially decompose, and at boiling it undergoes
complete irreversible degradation. By extracting the
hydrolyzate with ethyl acetate and by the subsequent
study of the compositions of aqueous and organic
phases by TLC it was shown by comparison with
reference compounds that the products of compound
VII decomposition are pyrimidine-2,4,6-(1H,3H,5H)-
trione [Rf 0.82 (A)], oxopyrazolylpyrimidinone I [Rf
0.47 (A)], and benzaldehyde [Rf 0.43 (B)].
Table 2. Molar absorption coefficients of the mixtures of 6-methyl-2-(3-methyl-5-oxo-2,5-dihydropyrazol-1-yl)-pyrimidine-
4(1H)-one I with sodium ethoxide at various temperatures and wavelengths
Molar absorption coefficients ε (l mol–1 cm–1) at wavelength λ, nm
Temperature, °С
230
255
270
295
25.5
45.5
55.3
65.1
9468
9921
9835
9752
9430
9589
9549
9433
8865
9281
9281
9244
12245
12342
12342
12194
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 7 2009

1530
ERKIN, KRUTIKOV
with iodine vapor followed by the UV irradiation of
the chromatographic plate. Elemental analysis was
carried out on a Leco CHNS-932 analyzer.
of precipitate, and the filtrate was evaporated in a
vacuum to dryness. The solid residue was
recrystallized from cyclohexane, and 0.3 g (52%) of
compound V was isolated. After drying in a vacuum
Commercial
5-benzylidenepyrimidinee-2,4,6-
1
mp 115°C, Rf 0.58 (E). H NMR spectrum, δ, ppm:
(1H,3H,5H)-trione II was purified by recrystallization
from a mixture of anhydrous acetic acid and DMF (4:
1), repeated washing with benzene, and drying at 80°C
for 8 h.
2.26 s (3H, Me), 2.27 s (3H, Me), 2.34 s (3H, Me),
3.39 s (3H, MeN), 5.99 s (1H, CH), 6.29 s (1H, CH).
Found, %: C 60.53; H 6.47; N 25.67.. C11H14N4O.
Calculated, %: C 60.47; H 6.21; N 25.09.
2-Hydrazino-6-methylpyrimidin-4-(3H)-one III and
2-hydrazino-3,6-dimethylpyrimidin-4-(3H)-one VI were
synthesized according to procedures [8] and [13]
respectively.
(2,4,6-Trioxo-1,2,3,4,5,6-hexahydropyrimidin-5-
yl)[2-(5-hydroxy-3-methylpyrazol-1-yl)-6-methyl-4-
oxo-3,4-dihydropyrimidin-5-yl]phenylmethane (VII).
A mixture of 1.03 g of oxopyrazolylpyrimidine I and
1.08 g of benzylidenebarbituric acid II in 35 ml of
anhydrous ethanol containing 0.37 g of sodium
ethoxide was refluxed for 2 h. On cooling, the
suspension was acidified by adding a calculated
quantity of acetic acid, then stirred for 5 min, the
prcipitate formed was filtered off and recrystallized
twice from the glacial acetic acid. The purified product
was boiled with 20 ml of anhydrous benzene and after
drying in a high vacuum we obtained 0.43 g (20%) of
compound VII, mp > 300°C, Rf 0.76 (C). The 1H NMR
spectrum, δ, ppm: 3.42 s (1H, CH), 5.88 s (1H, CH),
6.90–7.11 m (5H, the pHs), 7.34 m (2H, CH+OH).
Found, %: C 55.16; H 3.70; N 18.23. C20H18N6O5.
Calculated, %: C 56.87; H 4.30; N 19.90.
The geometry optimization of the 6-methyl-2-(3-
methyl-5-oxo-2,5-dihydropyrazol-1-yl)pyrimidin-4(1H)-
one I molecule was carried out by the Fletcher-Reeves
method with the use of the HyperChem™ Release 6.03
for Windows Molecular Modeling System.
6-Methyl-2-(3-methyl-5-oxo-2,5-dihydropyrazol-
1-yl)-pyrimidin-4(1H)-one (I). A mixture of 1.26 g of
hydrazinopyrimidine (III) and 1.17 g of ethyl
acetoacetate in 30 ml of water was refluxed for 1 h.
The precipitate formed on cooling was filtered off and
recrystallized from water, and after drying at 80°C for
7 h was obtained 0.79 g (43%) of compound I, mp
1
203°C (published: mp 204°C [8]), Rf 0.45 (C). H
NMR spectrum, δ, ppm: 2.19 s (3H, Me), 2.23 s (3H,
Me), 5.20 s (1H, CH), 5.96 s (1H, CH), 11.55 br.s (1H,
NH).
ACKNOWLEDGMENTS
The authors express deep gratitude to Novbytkhim
Co. Saint Petersburg, for the support of this
investigation.
2-(3,5-Dimethylpyrazol-1-yl)-6-methylpyrimidin-
4(3H)-one (IV). A mixture of 1 g of hydrazino-
pyrimidine (III) and 0.71 g of 2,4-pentanedione was
maintained at 120–130°C for 1 h. On cooling the
hardened reaction mixture was ground with 5 ml of
benzene, the precipitate was filtered off, washed with
benzene, and dried in air. Dry product was re-
crystallized from water and after drying at 80°C for 7 h
we obtained 0.57 g (39%) of compound (IV), mp 140°C
REFERENCES
1. Baldea, I., Ghirisan, A., and Panea, I, J. Chem. Soc.,
Perkin Trans. 2, 1992, no. 10, p. 1715.
2. Panea, I., Ghirisan, A., Cristea, I., Gropeanu, R., and
Silberg, I.A., Heterocyclic Communications, 2001, vol. 7,
no. 6, p. 563; C.A., 2002, vol. 137, 109250e.
1
(published data: mp 135–137°C [14]), Rf 0.73 (D). H
NMR spectrum, δ, ppm: 2.21 s (3H, Me), 2.25 s (3H,
Me), 2.58 s (3H, Me), 6.11 s (2H, CH), 11.67 br.s (1H,
NH).
3. Cristea, I., Stud. Univ. Babes-Bolyai, Chem., 1988,
vol. 33, no. 2, p. 61.
4. Cristea, I. and Panea, I., Stud. Univ. Babes-Bolyai,
Chem., 1995, vol. 40, nos. 1–2, p. 171.
5. Panea, I. and Cristea, I., Stud. Univ. Babes-Bolyai,
Chem., 1996, vol. 41, no. 1, p. 9.
6. Lovasz, T., Paizs, C., Cristea, I., and Irimie, F.D., Stud.
Univ. Babes-Bolyai, Chem., 1998, vol. 43, nos. 1–2, p. 145.
3,6-Dimethyl-2-(3,5-dimethylpirazol-1-yl)pyrimidin-
4(3H)-one (V). To a suspension of 0.5 g of N-me-
thylhydrazinopyrimidine (VI) in 30 ml of anhydrous 1-
butanol heated to 110°C was added 0.32 g of 2,4-
pentanedione. The mixture was refluxed with the
Dean–Stark trap for 2 h. After slow cooling the
mixture was filtered to remove an insignificant amount
7. Cristea, I. and Farcasan, V., Rev. Chim., 1987, vol. 38,
no. 8, p. 674.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 7 2009

6-METHYL-2-(3-METHYL-5-OXO-2,5-DIHYDROPYRAZOLYL)-...
1531
8. Erkin, A.V., Krutikov, V.I., and Chubraev, M.A., Zh.
Obshch. Khim., 2004, vol. 74, no. 4, p. 466.
(Spectrophotometric Analysis in Organic Chemistry).
Leningrad: Khimiya, 1986.
9. Baldea, I., Ghirisan, A., Silberg, I.A., and Cristea, I.,
Rev. Roum. Chim., 1997, vol. 42, no. 9, p. 767.
10. Sano, M., Itoh, I., Nakai, Y., and Naito, T., Chem.
Pharm. Bull., 1969, vol. 17, no. 7, p. 1485.
12. Moskvin, A.V., Polkovnikova, I.I., and Ivin, B.A., Zh.
Obshch. Khim., 1995, vol. 65, no. 3, p. 507.
13. Erkin, A.V. and Krutikov, V.I., Zh. Obshch. Khim.,
2007, vol. 77, no. 1, p. 133.
11. Bershtein, I.Ya. and Kaminskii, Yu.L., Spektrofo-
14. US Patent 3040047 (1962); C.A., 1963, vol. 58, P534c.
tometricheskii analiz
v
organicheskoi khimii
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 7 2009