Iron (III) perchlorate adsorbed on silica gel: A reagent for organic functional group transformations

Article abstract of DOI:10.1080/00397910701410772

Adsorption of Fe(ClO4)3(H2O)6 onto chromatographic-grade silica gel in the presence of organic solvents (S=water, acetonitrile, or lower fatty acids) produces a supported reagent, Fe(ClO4)3(S)6/SiO2. This reagent has been found to be effective for the rapid organic functional group transformations such as dimerization of alkynes, aromatic hydrocarbons, selective oxidation of thiols to disulfides, and transannular reactions in 1,5-cyclooctadienes on grinding using pestle and mortar in the solid state. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910701410772

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Iron (III) Perchlorate Adsorbed on Silica Gel:
A Reagent for Organic Functional Group
Transformations
Anupama Parmar a & Harish Kumar a
a Department of Chemistry, Sant Longowal Institute of Engineering and
Technology, Longowal, India
Published online: 11 Jul 2007.
To cite this article: Anupama Parmar & Harish Kumar (2007): Iron (III) Perchlorate Adsorbed on Silica Gel: A
Reagent for Organic Functional Group Transformations, Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 37:14, 2301-2308
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Synthetic Communicationsw, 37: 2301–2308, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701410772
Iron (III) Perchlorate Adsorbed on Silica
Gel: A Reagent for Organic Functional
Group Transformations
Anupama Parmar and Harish Kumar
Department of Chemistry, Sant Longowal Institute of Engineering and
Technology, Longowal, India
Abstract: Adsorption of Fe(ClO4)3(H2O)6 onto chromatographic-grade silica gel in the
presence of organic solvents (S ¼ water, acetonitrile, or lower fatty acids) produces a
supported reagent, Fe(ClO4)3(S)6/SiO2. This reagent has been found to be effective for
the rapid organic functional group transformations such as dimerization of alkynes,
aromatic hydrocarbons, selective oxidation of thiols to disulfides, and transannular
reactions in 1,5-cyclooctadienes on grinding using pestle and mortar in the solid state.
Keywords: iron (III) perchlorate, organic functional group transformations, silica
gel, solid state
Heterogeneous organic reactions have proven useful to chemists in the labora-
tory as well as in industry. These reactions are effected by the reagents
immobilized on the porous solid supports and have advantages over conven-
tional solution-phase reactions because of the good dispersion of active
reagent sites, associated selectivity, and easier workup. The recyclability of
some of these solid supports renders these processes into truly ecofriendly
green protocols.[1] The transition metals have been used for organic functional
group transformations such as oxidation, reduction, carbonylation, radical
addition, C-C coupling, and cycloaddition reactions.[2]
In recent years, considerable attention has been focused on solid-state
organic chemistry.[3–7] We were interested in studying the applications
Received in India November 30, 2006
Address correspondence to Harish Kumar, Department of Chemistry, Sant
Longowal Institute of Engineering and Technology, Longowal 148 106, India.
E-mail: hk67@rediffmail.com
2301

2302
A. Parmar and H. Kumar
of ferric-supported perchlorate[8,9] in the dry medium, and hence this
“supported reagent” was prepared. This reagent has the advantage[10,11] of
being easily removed from the organic product by filtration. A further
advantage of this supported reagent is improved storage stability in
moisture in comparison to Fe(ClO4)3(H2O)6, which is very sensitive to
moisture. The formation of such complexes [Fe(ClO4)3(S)6; S ¼ solvent]
from Fe(ClO4)3(H2O)6 has already been reported.[12]
We herein report a very simple and efficient method for the rapid organic
functional group transformations such as dimerization of alkynes, aromatic
hydrocarbons, selective oxidation of thiols to disulfides, and transannular
reactions in 1,5-cyclooctadienes using Fe(ClO4)3(S)6/SiO2 reagent.
OXIDATIVE DIMERIZATION OF ACETYLENES TO
CONJUGATED DICARBONYL SYSTEMS
One of the most useful properties of terminal acetylenes is their ability to
couple under very mild conditions to form conjugated polyacetylenes. The
two most widely used reactions[13,14] are Glazer coupling and Chodkie-
wiez–Cadiot coupling. We report herein that acetylenes 1a–e, terminal as
well as substituted, were converted into a,b-unsaturated dicarbonyl systems
2a–e in good to excellent yields when reacted with Fe(ClO4)3(H2O)6/SiO2
in dry media (Scheme 1).
The structure of all the products (2a–e) was confirmed from their
elemental analyses, NMR, IR, and GC-mass spectral studies (Table 1).
OXIDATION OF AROMATIC HYDROCARBONS
Aromatic hydrocarbons (entries 1–7 in Table 2), on reaction with
Fe(ClO4)3(MeCN)6/SiO2 in the presence of a small amount of water upon
grinding in pestle and mortar, were converted into corresponding oxidation
products. The naphthalenes (entries 1–3 in Table 2) and diphenylamine
(entry 6 in Table 2) gave the corresponding dimeric products, whereas 1-nitro-
naphthalene did not react even after 5 h. Phenanthrene and anthracene gave
the corresponding oxidation products (Table 2). The structures of all these
products have been confirmed from their NMR, IR, elemental analyses, and
in some cases mass spectra and also with comparison to authentic samples.
Scheme 1.

Iron(III) Perchlorate on Silica Gel
2303
Table 1. Structures of products 2a–e formed from acetylenes 1a–e
Sr. Reaction
no. Reactant (Ia–e) time (hr)
Yield
(%)
Product (IIa–e)
;;
1a Ph-C C-H
2
65
72
60
52
44
;;
1b Ph-C C-Ph
2
;;
1c Ph-C C-Me
2.5
2.5
3
;;
1d Ph-C C-Et
;;
1e Ph-C C-Me
OXIDATION OF SULFIDES TO DISULFIDES
Alkyl or aryl thiols on reaction with Fe(ClO4)3(MeCN)6/SiO2 in the presence
of a small amount of water upon grinding in a pestle and mortar were
converted into corresponding disulfides (3a–g) (Scheme 2).
The structures of all these products have been confirmed from their com-
parison to authentic samples (Table 3). It is noteworthy that further oxidation
of disulfides to sulfoxides or sulfones did not take place under the reaction
conditions.
TRANSANNULAR REACTIONS
Cycloocta-1,5-diene on reaction with Fe(ClO4)3(RCOOH)6/SiO2 [R55CH32
,
CH3CH22, CH3CH2CH22, (CH3)2CHCH22] underwent transannular reaction

Table 2. Oxidation of aromatic hydrocarbons using Fe(ClO4)3(MeCN)6/SiO2
Reaction
time (h)
S. no.
1
Reactant
Producta/yield (%)
1.5
2
3
2
2

4
5
5
No reaction
2.5
6
7
3
6
aThe structures of all these products have been confirmed from their NMR, IR, elemental analyses, and in some cases mass spectra and also with
comparison to authentic samples.

2306
A. Parmar and H. Kumar
Scheme 2.
upon grinding in a pestle and mortar to give the corresponding bicy-
clo[3.3.0]octane-2-carboxylic esters (4a–d) (Table 4).
The structures of these esters (4a–d) were confirmed from the results of a
series of reactions [basic hydrolysis followed by oxidation with pyridinium
chlorochromate (PCC) and finally by derivatization with semicarbazide] as
given in Scheme 3. The melting point of the semicarbazone (5) was found
to be 180–1818C (literature[15] m.p. 1818C).
In conclusion, the “supported reagent” described here for various organic
functional group transformations is simple, unaffected by moisture, easy to
use, efficient, and easily separable from the reaction mixture, has greater
storage stability, and avoids many disadvantages of the previous methods.
EXPERIMENTAL
All melting points recorded are uncorrected, open capillary measurements,
using a sulphuric acid bath. IR spectra were recorded using KBr pellets on
a Perkin-Elmer spectrophotometer. NMR spectra were recorded on EM-390,
90-MHz instrument using TMS as internal standard.
Preparation of Fe(ClO4)3(S)6/SiO2 Reagent
An appropriate amount of Fe(ClO4)3(H2O)6 is dissolved in the corresponding
solvent (water, acetonitrile, or carboxylic acid). Enough solvent is added to
ensure the complete dissolution of Fe(ClO4)3(H2O)6. To this, the appropriate
Table 3. Oxidation of alkyl/aryl thiols to
disulfides
Disulfide
R
Yield (%)
3a
3b
3c
3d
3e
3f
C2H5
n-C3H7
82
88
83
90
93
90
88
i-C3H7
n-C4H9
C6H5CH2
o-NH2-C6H4
HOCH2CH2
3g

Iron(III) Perchlorate on Silica Gel
Table 4. Bicyclo [3.3.0] octane-2-carboxylic esters
2307
Ester
R
Yield (%)
4a
4b
4c
4d
CH3
C2H5
85
89
90
92
n-C3H7
(CH3)2CHCH2
amount of chromatographic-grade silica gel is added. The mixture is mixed
properly and allowed to stand for 1 h. The excess solvent is filtered off
under vacuum. The supported reagent at this point is reproducibly a homo-
geneous, free-flowing, shining cream–yellow powder. The supported
reagent is stored in a bottle after drying in air for 1–2 days. The reagent is
unaffected by light or moisture.
Determination of Iron (III) Present in Fe(ClO4)3(S)6/SiO2 Reagent
A weighed sample of Fe(ClO4)3(S)6/SiO2 reagent was analyzed to determine
the amount of iron present by a series of redox reactions.[16]
General Procedure for Organic Functional Group Transformations
Equimolar amounts of “supported reagent” and the reactants were mixed
together and ground in a pestle and mortar for 15 min. Usually an
immediate color change was observed. The reaction mixture was allowed to
stand for 2–3 h. To this crude reaction mixture, methylene chloride
(50 mL) and distilled water (5 mL) were added to quench the reaction
mixture as well as destroy any inorganic complexes that may have formed
during the reaction. The mixture was stirred for 5 min and then suction
filtered. The spent reagent was washed twice with methylene chloride
(10 mL each). The combined organics were washed with saturated NaHCO3
solution followed by 1% hydrochloric acid and water, then dried over
Scheme 3. (i): Fe(CIO4)3 (RCOOH)6/SiO2; (ii): NaOH/MeOH; (iii): PCC; (iv) NH2-
CONHNH2 [R ¼ CH3-, CH3CH2-, CH3CH2CH2-, (CH3)2CHCH2-].

2308
A. Parmar and H. Kumar
sodium sulphate, and the solvent was removed under reduced pressure. This
crude reaction mixture was analyzed and purified in a conventional manner.
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