A novel application of Hβ-zeolite in catalytic dehalogenation of halophenols

Article abstract of DOI:10.1016/S0040-4039(03)01617-4

A new application of Hβ-zeolite for debromination of bromophenols and deiodination of iodophenols is presented in this note. The heterogeneous catalyst can be recovered and recycled effectively for subsequent reactions. The catalyst was found ineffective for similar action on chlorophenols.

Full text of DOI:10.1016/S0040-4039(03)01617-4

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 6391–6392
A novel application of Hb-zeolite in catalytic dehalogenation
of halophenols
Subbarayappa Adimurthy, Gadde Ramachandraiah and Ashutosh V. Bedekar*
Central Salt and Marine Chemicals Research Institute, G.B. Road, Bhavnagar 364 002, India
Received 10 May 2003; revised 13 June 2003; accepted 27 June 2003
Abstract—A new application of Hb-zeolite for debromination of bromophenols and deiodination of iodophenols is presented in
this note. The heterogeneous catalyst can be recovered and recycled effectively for subsequent reactions. The catalyst was found
ineffective for similar action on chlorophenols.
©
2003 Elsevier Ltd. All rights reserved.
Recently there has been significant interest in exploring
the possibility of using aromatic bromine as a protect-
methanol, at reflux temperature (Eq. (1)). The course of
the reaction was followed by checking the formation of
2-naphthol 2 by TLC comparison with an authentic
sample. The reaction needed about 48 h for completion
and the debrominated product was isolated in 87%
yield. The analogous deiodination of 1-iodo-2-naphthol
1,2
ing group in synthetic organic chemistry. This con-
cept is supported by the accessibility of aromatic bromo
compounds as well as the conceptually simple debromi-
nation reaction. Generally this electrophilic debromina-
tion reaction is brought about with aqueous
hydrobromic acid (HBr) in the presence of a suitable
bromine scavenger such as aromatic amines like aniline
3
under identical conditions gave a higher yield of 97%,
in accordance with the expectation that the iodonium
species is a better leaving group than the bromonium
ion species. The dechlorination reaction of 1-chloro-2-
naphthol was not found to be feasible under the reac-
tion conditions as the material remained unchanged
even after prolonged reaction.
1
,3
or sodium sulfite. There are a few elegant applica-
tions of utilizing bromine as a protecting group for the
1
preparation of synthetically useful molecules.
The use of hydrobromic acid is cumbersome due to its
hazardous and corrosive nature. Therefore, this may
cause practical difficulties in extending the scope of
utilizing bromine as a protecting group for large scale
preparations. Also in recent years there has been a
trend to explore various solid acid catalysts for pro-
cesses traditionally involving mineral acids. In this
account, we wish to present our preliminary findings on
using Hb-zeolite as a heterogeneous catalyst acting as a
(1)
source
of
protons
to
initiate
electrophilic
2
,4,6-Tribromophenol 4 and 2,4,6-triiodophenol 6 were
debromination.
subjected to similar reaction conditions to give 2,6-
dibromophenol 5 and 2,6-diiodophenol 7 in moderate
yields (Eq. (2)).
The strategy was tested by carrying out debromination
of 1-bromo-2-naphthol 1 with a catalytic quantity of
Hb-zeolite (50% w/w) and an excess of sodium sulfite (5
mol. equivalents) as a bromine scavenger, in dry
(2)
Keywords: debromination; deiodination; heterogeneous catalysis.
*
Corresponding
author.
Fax:
91-0278-2567562;
e-mail:
avbedekar@yahoo.co.in
0
040-4039/$ - see front matter © 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)01617-4

6
392
S. Adimurthy et al. / Tetrahedron Letters 44 (2003) 6391–6392
6
-Bromo-2-naphthol 9 is an important industrial mate-
methanol (10 mL) while the progress of the reaction
was monitored by TLC. After 48 h the reaction mixture
was cooled and filtered through a suitable device; the
catalyst was washed several times with methanol and
diethyl ether to recover the product completely. The
organic solution was concentrated and the pure product
2 was isolated by column chromatography over silica
gel (10% ethyl acetate in hexane) to give a colorless
rial and is prepared by selective debromination of 1,6-
dibromo-2-naphthol 8. Although we succeeded in a
selective debromination at the 1 position and isolated
4
6
-bromo-2-naphthol 9, we also obtained a considerable
amount of 2,2%-dihydroxy-6,6%-dibromo-1,1%-binaphthol
5
1
0, probably formed by the oxidative coupling of 9, see
Eq. (3).
(3)
Debromination of 4-bromoanisole 11 under identical
conditions was not successful even after prolonged
exposure to the catalyst in refluxing methanol (Eq. (4)).
material (0.14 g; 97%), which showed satisfactory spec-
tral data; mp 122°C (lit. 122–3°C).
6
This is probably indicative of the role of the hydroxy3
Thus we present our preliminary results on using Hb-
zeolite as a new heterogeneous catalyst for the debrom-
ination and deiodination of halophenols.
group in stabilizing the intermediate benzonium ion.
(
4)
Acknowledgements
We wish to thank Dr. Pushpito Ghosh for his encour-
agement, Dr. Pragnya Bhatt for her help in XRD
analysis and CSIR, New Delhi for financial assistance
under the Quick Hire Scheme to A.V.B.
The catalyst recovered after the deiodination reaction
of 3 (Eq. (1)) was carefully washed with dilute mineral
acid, water, methanol, acetone and dried. A powder
X-ray diffraction analysis (XRD) and FT-IR spectra of
this material were found to be comparable with fresh
catalyst indicating retention of the physical properties
of the material. The recovered catalyst was used in
another set of deiodination reactions of 3 giving com-
parable results to the first cycle (ca. 94% yield in the
second cycle). This clearly indicates the ability to
recover and reuse the catalyst for repetitive use in
dehalogenation reactions.
References
1. Effenberger, F. Angew. Chem., Int. Ed. Engl. 2002, 41,
1699.
2. Choi, H. Y.; Chi, D. Y. J. Am. Chem. Soc. 2001, 123,
9202.
3. O’Bara, E. J.; Balsley, R. B.; Starer, I. J. Org. Chem. 1970,
3
5, 16.
4. Sabahi, M. PCT Int. Appl. WO 98 11,041; Chem. Abstr.
998, 128, 230147.
Standard reaction conditions
1
Deiodination of 1-iodo-2-naphthol: A mixture of 3 (0.27
g; 1.0 mmol), Hb-zeolite (0.135 g; 50% w/w) and
sodium sulfite (0.63 g; 5.0 mmol) was refluxed in dry
5. Li, T.-S.; Duam, H.-Y.; Li, B.-Z.; Tewari, B. B.; Li, S.-H.
J. Chem. Soc., Perkin Trans. 1 1999, 291.
6. Aldrich Chemical Company catalogue, 2002–2003.