Microwave assisted synthesis of novel organomercurials in 'dry media'

Article abstract of DOI:10.1016/S0277-5387(99)00159-X

New organomercurials of benzoquinone, barbituric acid and thiobarbituric acid with substituted aryl mercuric chloride have been synthesised using microwave irradiation under dry conditions in a domestic microwave oven in a few minutes with improved yields as compared to conventional heating. These organomercurials have a 1:1 stoichiometric ratio of aryl mercury and benzoquinone/barbituric acid/thiobarbituric acid moiety. Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(99)00159-X

Polyhedron 18 (1999) 2641–2643
Microwave assisted synthesis of novel organomercurials in ‘dry media’
*
Mazaahir Kidwai , Preeti Misra, Kumar Ranjan Bhushan
Department of Chemistry, University of Delhi, Delhi-110007, India
Received 9 March 1999; accepted 9 June 1999
Abstract
New organomercurials of benzoquinone, barbituric acid and thiobarbituric acid with substituted aryl mercuric chloride have been
synthesised using microwave irradiation under dry conditions in a domestic microwave oven in a few minutes with improved yields as
compared to conventional heating. These organomercurials have a 1:1 stoichiometric ratio of aryl mercury and benzoquinone/barbituric
acid/thiobarbituric acid moiety.
1999 Elsevier Science Ltd. All rights reserved.
Keywords: Organomercurials; Microwave assisted; Dry media; Solid support; Heterocycle
1. Introduction
and in continuation of our earlier work [21–23] on
microwave assisted synthesis, it was thought worthwhile to
synthesise novel organomercurials under solvent free
conditions using microwaves.
Organomercurials exhibit a wide range of biological
activities [1–3]. Heterocyclic compounds containing mer-
cury [4–7] are very potent fungicides, bactericides and
pesticides. Benzoquinone, barbituric acid and thiobar-
bituric acid are also known for their pharmacological
importance [8–11]. A literature survey shows that many
synthetic strategies have been applied for preparation of
organomercurials [12–14]. Moreover, it is only recently
that microwave ovens have been used for organic synthesis
[15–18]. These procedures are strongly limited by the
presence of solvents, which reach their boiling points
within very short times (.1 min) of exposure to micro-
waves [19]. Consequently, high pressures are developed,
thus causing damage to vessels, materials and occasionally
leading to explosions. Using reagents supported on inor-
ganic solid materials in the absence of solvent (solvent free
conditions) clearly has advantages for environmental
reasons, but they offer the further benefit of shorter
reaction times, especially if microwaves are used [20].
Solvent free conditions coupled with MWI leads to
reaction rate enhancement, improved yields and safe
conditions which make this technique cheap and useful for
synthesis.
2. Experimental
Melting points were taken on an electrothermal ap-
paratus and were uncorrected. IR spectra were recorded on
a 1710 Perkin Elmer FTIR spectrophotometer using KBr
1
discs. H NMR spectra were recorded on a FT NMR
Hitachi R-600 spectrometer operating at 90 MHz using
TMS as internal standard (chemical shift in ppm). Elemen-
tal analyses were performed on a Heracus CHN Rapid
Analyser. A Padmini Essentia microwave oven Model
Brownie at 2450 MHz was used. The purity of the
compounds was checked on silica gel coated Al plates
(Merck).
Barbituric acid and benzoquinone were purchased from
Aldrich USA.
Thiobarbituric acid was prepared by a previously pub-
lished literature method [24].
Keeping in view the importance of organomercurials,
advantages of solvent free conditions coupled with MWI
2.1. General procedure for the synthesis of aryl
mercuric chloride (1a–c)
These were synthesised according to a previously pub-
lished literature method [25].
*Corresponding author. Tel.: 191-11-7256-235; fax: 191-11-7257-
336.
0277-5387/99/$ – see front matter
PII: S0277-5387(99)00159-X
1999 Elsevier Science Ltd. All rights reserved.

2642
M. Kidwai et al. / Polyhedron 18 (1999) 2641–2643
2.2. General procedure for the synthesis of 2-[aryl
mercury(II)]-1,4-benzoquinone (2a–c), 5-
3. Results and discussion
[arylmercury(II)]-pyrimidine-2,4,6-trione (3a–c) and 5-
[arylmercury(II)]-1,3-diphenyl pyrimidine-1,3-dihydro-
4,6-dioxo-2-thione (4a–c)
Organomercurials have been synthesised by the reaction
of benzoquinone/barbituric acid/thiobarbituric acid with
(phenyl/4-chlorophenyl/4-methoxyphenyl) mercuric chlo-
ride on basic alumina using microwaves.
Basic alumina [26] (18 g) was added to a solution of
arylmercuric chloride (0.01 mol) and benzoquinone/bar-
bituric acid/thiobarbituric acid (0.01 mol) dissolved in
acetone (5 ml) at room temperature. The reaction mixture
was dried in air (in a beaker) and placed in an alumina
bath [27] inside the microwave oven. Upon completion of
the reaction (1–3 min) as followed by TLC examination,
the mixture was cooled to room temperature and then the
product was extracted into acetone (4310 ml). Removal of
the solvent yielded the product which was purified by
crystallization from a mixture of acetone–petroleum ether
For the synthesis of these compounds, see Schemes 1 and
2.
This is the first report on the synthesis of organo-
mercurials on solid support using MWI in which benzo-
quinone/barbituric acid/thiobarbituric acid rings are in-
corporated. The salient feature of our approach is coupling
microwaves with a solvent-free technique keeping mod-
ernisation, and simplification of classical procedures,
avoiding volatile and toxic organic solvents, which make it
a clean, efficient and cheap technology to obtain new
organomercurials. Elemental analysis of all compounds
shows a 1:1 stoichiometric ratio of the arylmercury and the
benzoquinone/barbituric acid/thiobarbituric acid moieties.
All the organomercurials are white in colour and stable
Scheme 1.
Scheme 2.

M. Kidwai et al. / Polyhedron 18 (1999) 2641–2643
2643
Table 1
Physical and analytical data of compounds 2a–c, 3a–c and 4a–c
Compd
No.
M.Pt.
8C
Conventional heating
Time (h)/Yield (%)
MWI
Time (h)/Yield (%)
Analytical data %
C
H
N
Hg
2a
2b
2c
3a
3b
3c
4a
4b
4c
235
217
240
223
235
230
227
220
213
11/66
10/57
11/70
8/72
10/68
11/67
8/70
2.5/94
2.0/9.1
2.5/95
1.5/96
2.0/90
1.5/92
1.5.94
1.5/96
2.0/93
(54.54) 54.45
(48.24) 48.35
(53.06) 53.16
(42.25) 42.35
(37.67) 37.56
(38.53) 38.52
(58.40) 58.27
(54.26) 54.27
(57.26) 57.30
(3.03) 3.10
(2.34) 2.32
(3.40) 3.35
(2.81) 2.78
(2.19) 2.25
(3.18) 3.20
(3.53) 3.53
(3.08) 3.05
(3.73) 3.75
(28.16) 28.19
(25.11) 25.10
(25.47) 25.40
(17.69) 17.72
(16.44) 16.53
(16.59) 16.63
(30.30) 30.32
(26.80) 26.75
(27.21) 21.40
(9.85) 9.70
(8.79) 8.80
(8.91) 8.90
(6.19) 6.20
(5.75) 5.72
(5.80) 5.75
10/66
9/72
Table 2
Spectral data of compounds 2a–c, 3a–c and 4a–c
Compound
No.
IR (cm21
)
1H NMR (d, DMSO-d6)
M1 Calc.
(found) (m/z %)
2a
2b
2c
1675(C50), 1590(C5C)
1680(C5O), 1600(C5C)
1690(C5O), 1590(C5C)
7.0 (s, 1H, 3-CH, 7.2 (d, 1H, J59.5 Hz, 5-CH),
7.32 (d, 1H, J59.5 Hz, 6-CH), 8.2–8.5 (m, 4H, ArH)
6.9 (s, 1H, 3-CH), 7.1 (d, 1H, J59.5 Hz, 5-CH),
7.25 (d, 1H, J59.5 Hz, 6-CH), 8.2–8.5 (m, 4H, ArH)
3.6 (s, 3H, –OCH3), 6.92 (s, 1H, 3-CH),
264 (264)
298.5 (297)
294 (293)
7.2 (d, 1H, J59.5 Hz, 5-CH), 7.4 (d, 1H, J59.5 Hz, 6-CH),
8.3–8.4 (m, 4H, ArH)
3a
3b
3c
1640(C5O), 3450(2NH)
1640(C5O), 3400(–NH)
1645(C5O), 3420(–NH)
7.1 (s, 1H, 5-CH), 7.3–7.5 (m, 5H, ArH), 8.8 (brs, 2H, 23NH)
7.3 (s, 1H, 5-CH), 7.5–7.7 (m, 4H, ArH), 8.7 (brs, 2H, 23NH)
3.4 (s, 3H, –OCH3), 7.1 (s, 1H, 5-CH), 7.4–7.6 (m, 4H, ArH),
8.9 (brs, 2H, 23NH)
284 (284)
318.5 (317)
314 (313)
4a
4b
4c
1150(C5S), 1645(C5O)
1155(C5S), 1640(C5O)
1150(C5S), 1645(C5O)
6.8 (s, 1H, 5-CH), 7.1–7.6 (m, 15H, ArH)
6.9 (s, 1H, 5-CH), 7.4–8.3 (m, 14H, ArH)
3.45 (s, 3H, –OCH3), 7.0(s, 1H, 5-CH), 7.6–7.9 (m, 14H, ArH)
452 (450)
486.5 (486)
482 (482)
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found as compared with the conventional method [28]
(Table 1). Spectral data of compounds 2a–c, 3a–c and
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