S-benzylation of arylidene thiobarbituric acids under phase-transfer catalysis

Full text of DOI:10.1134/S1070363209100302

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 10, pp. 2276–2277. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © A.I. Rakhimov, S.A. Avdeev, 2009, published in Zhurnal Obshchei Khimii, 2009, Vol. 79, No. 10, pp. 1753–1754.
LETTERS
TO THE EDITOR
S-Benzylation of Arylidene Thiobarbituric Acids
under Phase-Transfer Catalysis
A. I. Rakhimova and S. A. Avdeevb
a Volgograd State Technical University,
ul. Lenina 28, 400131 Volgograd, Russia
e-mail: organic@vstu.ru
b Institute of Environmental Chemical Problems, Volgograd, Russia
e-mail: rakhimov@sprint-v.com.ru
Received March 12, 2009
DOI: 10.1134/S1070363209100302
It has been established earlier that the use of dibenzo-
18-crown-6 as a phase-transfer catalyst for S-benzylation
of 5-benzylidene-2-thioxodihydropyrimidine-4,6-(1H,5H)-
dione allows to obtain the end product with the yield of
35% using toluene and potassium hydroxide aqueous
solution as organic and water phases respectively.
In this report we show that use of methyltrio-
ctylammonium chloride (aliquat 336) as phase-transfer
catalyst makes it possible to increase yields of the S-
benzylation products of thiobarbituric acid arylidene
derivatives to 60–75%. Acetonitrile was used as the
organic phase.
O
O
H
H
N
N
Aliquat 336, CH3CN
−
S
N
H
O
R
S
N
O
R
O
H
C6H5CH2Cl
N
S
N
O
R
R = H (I), CH3 (II), OCH3 (III), F (IV), NO2 (V).
Reactivity of the S-anion generated from thio-
barbituric acid arylidene derivatives by the action of
polar acetonitrile was established by the quantum-
chemical analysis using АМ1 method [1] to depend on
substituent on para-position of benzene ring. The
sulfur atom electron density (S) and S-anion full
energy (E) dependence on substituent R is as follows:
(1) R = H: S = –0.450, E = –2693.8 kcal mol–1;
(2) R = CH3: S = –0.449, E = –2977.2 kcal mol–1;
(3) R = OCH3: S = –0.451, E = –3070.0 kcal mol–1;
(4) R = F: S = –0.443, E = –2710.5 kcal mol–1;
(5) R = NO2: S = –0.421, E = –2878.4 kcal mol–1.
Hence electron-donating substituent (CH3, OCH3)
incorporated in the para-position of benzene ring
causes the full energy of anion A to increase, the sulfur
atom charge to change slightly and therefore reactivity
to decrease negligibly. The presence in the pаrа-
position of the benzene ring of an electron-
withdrawing substituent leads to a decrease in the
2276

S-BENZYLATION OF ARYLIDENE THIOBARBITURIC ACIDS
2277
sulfur atom charge, in the increase of the anion full
energy and hence in high decrease in S-anion reactivity.
(2H, CH2–C6H5), 5.84 s (1H, C=CH–), 6.64–6.98 m
(9H, HAr), 11.4 s (1H, NH). Found, %: N 8.87.
C19H16N2O3S. Calculated, %: N 7.95.
(5Z)-5-Benzylidene-2-(benzylthio)pyrimidine-4,6-
(1H, 5H)-dione. To a suspension of 0.4 g (1.7 mmol)
of I in 15 ml of acetonitrile was added 0.1 ml of aliquat
336. This mixture was stirred at 50°C for 10 min. Then
0.2 ml (1.9 mmol) of benzyl chloride was added and
the mixture was stirred for 2 h at 50°C. The solid
phase was filtered off, washed with water and alcohol,
and recrystalled from anhydrous ethanol. Yield 0.4 g
(5Z)-2-(Benzylthio)-5-(4-fluorobenzylidene)pyr-
imidine-4,6(1H,5H)-dione was prepared similarly
from 0.5 g (2.0 mmol) of IV, 12 ml of acetonotrile,
0.1 ml of aliquat 336 and 0.25 ml (2.2 mmol) of benzyl
chloride. Yield 0.45 g (65%), mp 189–190°C (decomp.).
1H NMR spectrum, δ, ppm: 4.25 m (2H, CH2–C6H5),
5.90 s (1H, C=CH–), 6.92–7.44 m (9H, HAr), 11.6 s
(1H, NH). Found, %: N 9.11. C18H13FN2O2S. Cal-
culated, %: N 8.23.
1
(75%), mp 182–183°C (decomp.). H NMR spectrum,
δ, ppm: 4.26 m (2H, CH2–C6H5), 5.92 s (1H, C=CH–),
6.92–7.45 m (10H, HAr), 11.6 s (1H, NH). Found, %:
N 9.45. C18H14N2O2S. Calculated, %: N 8.69.
(5Z)-2-(Benzylthio)-5-(4-nitrobenzylidene)pyr-
imidine-4,6(1H,5H)-dione was prepared similarly
from 0.5 g (1.8 mmol) of V, 12 ml of acetonitrile,
0.1 ml of aliquat 336 and 0.2 ml (2.0 mmol) of benzyl
chloride. Yield 0.4 g (60%), mp 200–202°C (decomp.).
1H NMR spectrum, δ, ppm: 4.22 m (2H, CH2–C6H5),
6.01 s (1H, C=CH–), 6.84–7.44 m (7H, HAr), 8.02–
8.12 m (2H, –CHAr–NO2–CHAr–), 11.7 s (1H, NH).
Found, %: N 12.05. C18H13N3O4S. Calculated, %: N 11.44.
(5Z)-2-(Benzylthio)-5-(4-methylbenzylidene)pyr-
imidine-4,6(1H,5H)-dione was prepared similarly
from 0.4 g (1.6 mmol) of II, 15 ml of acetonitrile,
0.1 ml of aliquat 336, and 0.2 ml (1.8 mmol) of benzyl
chloride. Yield 0.4 g (74%), mp 190–192°C (decomp.).
1H NMR spectrum, δ, ppm: 2.8 s (3H, CH3), 4.28 m
(2H, CH2–C6H5), 5.87 s (1H, C=CH–), 6.80–7.45 m
(9H, HAr), 11.5 s (1H, NH). Found, %: N 9.21.
C19H16N2O2S. Calculated, %: N 8.33.
REFERENCES
(5Z)-2-(Benzylthio)-5-(4-methoxybenzylidene)pyr-
imidine-4,6(1H,5H)-dione was prepared similarly
from 0.4 g (1.5 mmol) of III, 20 ml of acetonitrile,
0.1 ml of aliquat 336 and 0.2 ml (1.7 mmol) of benzyl
chloride. Yield 0.35 g (70%), mp 172–174°C (decomp.).
1H NMR spectrum, δ, ppm: 3.8 s (3H, CH3), 4.30 m
1. Schmidt, M.W., Baldridge, K.K., and Boatz, J.A.,
J. Comput. Chem., 1993, vol. 14, p. 1347.
2. Stepin, B.D., Tekhnika laboratornogo eksperimenta v
khimii (Laboratory Experimental Technique in The
Chemistry), Moscow: Khimiya, 1999, p. 600.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 10 2009