M.H. Patel et al. / Tetrahedron 64 (2008) 2057e2062
2061
with tetramethylsilane as internal standard. Mass measure-
ments were done on Thermo Finnigan TQS Quantum Dis-
covery Mass Spectrometer using electrospray ionization.
Thermal studies were carried out on Mettler Toledo DSC
822e. Powder XRD analysis was performed on Panalytical
X’Pert PRO X-ray Diffractometer. Purity of the synthesized
compounds was ascertained on PerkineElmer 200 Series Liq-
uid Chromatograph with Thermo Electron Betasil C-18 re-
versed phase column (3 mm particle size, 100 mm long and
3.0 mm internal diameter) maintained at 45 ꢃC, mobile phase
composition was methanole0.01% acetic acid (90:10 v/v).
by recrystallization from chloroform. The yield obtained was
74%. The method described is devised by partial modification
of two procedures7,19 reported by Miyano et al. Though one of
these methods describes a two step procedure with 83% yield
in cyclization step, it employs hazardous SCl2 in the first step
and the overall yield is w62%. Thus, the present method is com-
paratively more efficient with reduced steps.
5.3.2. General method for synthesis of phenyl hydroxyl-
amine (partial reduction)
The nitro derivative (7.5 g, ca. 60 mmol) of choice was dis-
solved in chloroform (100 ml), added to a solution of NH4Cl
(7.5 gm in 100 ml water) and stirred for 10 min with the aid of
magnetic stirrer. Zn powder (10 gm) was then added in small
portions (0.3e0.5 g) every 4e5 min until the reduction was
complete. After additional stirring of 15 min the contents were
allowed to cool to ambient temperature. The organic layer was
collected, dried with MgSO4, and concentrated in vacuo until
pale yellow crystals of hydroxylamine were observed. The
concentrate along with crystals was cooled to ꢀ10 ꢃC and fil-
tered rapidly over a glass frit under vacuum. The yield was
60e75%. As aromatic hydroxylamines are very unstable in
air, they were redissolved in dry chloroform and kept at low tem-
perature (0e4 ꢃC) until coupled with acyl chloride.
5.2. Protocol for extraction of vanadium
For complexation studies, stock solution of ligands
(1.0ꢄ10ꢀ2 M) were prepared by separately dissolving 0.01 mol
of each in 1 l of ethyl acetate. The vanadium stock solution
(1.0ꢄ10ꢀ2 M) was prepared by dissolving 0.01 mol of ammo-
nium metavanadate in 5 ml concd HCl and diluting to 1 l with
6 M HCl. Thestock solutions werediluted appropriately to obtain
working solutions of (1.0ꢄ10ꢀ4 M) and (2.0ꢄ10ꢀ4 M) for
ligands and vanadium, respectively. Forextractionstudies, appro-
priate volumes of ligand and metal solutions were mixed, shaken
for 5 min and separated through a separatory funnel, dried with
MgSO4, and diluted uniformly. Solutions thus prepared were
examined for UVevisible absorptions at suitable wavelengths.
The quantitative studies were carried out by ICP-OES measure-
ments at the 309.31 nm emission line for vanadium.
5.3.3. Synthesis of 1,3-alt thiacalix[4]arene
tetraacetate (syn 2)
Compound 1 (18 g, 25 mmol) was suspended in dry acetone
(500 ml) containing a sixfold excess of anhydrous cesium carbo-
nate (38 g, 150 mmol) and an eightfold excess of ethyl bromo-
acetate (33.4 g, 22.3 ml, 200 mmol). The mixture was heated
under reflux for 6 h. After cooling, the solid residue was filtered
and washed with dichloromethane (50 ml) three times. The com-
bined filtrates were evaporated and maintained at 1 mm Hg vac-
uum and 80 ꢃC for 3 h to ensure complete removal of unchanged
ethyl bromoacetate. From the mixture of conformational iso-
mers, the 1,3-alternate isomer 2 was separated by fractional crys-
tallization from ethanolic solution (reported procedure5 employs
column chromatography for separation of conformational iso-
mers). It was recrystallized from chloroformeethyl acetate mix-
ture (4:1 v/v). Yield obtained was 72%.
5.3. Synthesis
Compounds 1, 2, 3, and 4 were synthesized according to pro-
cedures reported in literature with appropriate modifications to
simplify the procedures and/or improve yields, employing com-
monly available/low cost chemicals. Also, the use of hazardous
chemical like SCl2 was deliberately avoided. Simple precipita-
tion and/or fractional crystallization techniques were preferred
over column chromatography for the purpose of purification/
isolation/isomeric separation.
5.3.1. Modified method for synthesis
of thiacalixarene (syn 1)
A mixture of p-tert-butyl phenol (64.5 g, 0.43 mol), elemen-
tal sulfur S8 (14 g, 0.44 mol), and NaOH (8.9 g, 0.22 mol) in
super-dry diphenyl ether (100 ml) was stirred for 15 min, heated
gradually to 160 ꢃC over a period of 1 h and kept at this temper-
ature for further 3 h. Then, the temperature of the reaction mix-
ture was brought down to 80 ꢃC and additional sulfur (14 g,
0.44 mol) was added carefully. The temperature was raised to
230 ꢃC over a period of 3 h and maintained for further 3 h.
The reaction was continuously monitored by TLC [hexanee
chloroform 1:1 (v/v)]. The resulting dark brown reaction mix-
ture was cooled to ambient temperature and diluted with cold
acetonitrile (250 ml). The precipitates thus produced were of
thiacalix[4]arene 1 and were collected by filtration over a sin-
tered glass funnel (preferably G2), and washed with 1 M HCl
to remove any traces of alkali. Further purification was achieved
5.3.4. Synthesis of 1,3-alt thiacalix[4]arene
tetra-acid (syn 3)
To a solution of 2 (18 g, 17 mmol in 1000 ml ethanol) was
added KOH (9 g in 500 ml 50% ethanol) and the mixture was re-
fluxed onawater bath with rapid stirringfor2 h. The mixturewas
cooled to ambient temperature and acidified to pH¼1 using 1 M
HCl to precipitate compound 3 in quantitative yield (98%). The
precipitates were filtered, washed with water, and dried invacuo.
5.3.5. Synthesis of 1,3-alt thiacalix[4]arene tetraacyl
chloride (syn 4)
Compound 3 (1 g, 1 mmol) was suspended in a 20-fold ex-
cess of oxalyl chloride (1.3 ml, ca. 20 mmol) and refluxed un-
til the reaction mixture became homogeneous (ca. 30 min).
The contents were cooled and dry chloroform was added. To
Patel, Mitesh H.
