Solvent free ion exchange catalysis in the oxidation of organic compounds with sodium bromate

Article abstract of DOI:10.1081/SCC-120018684

The oxidation of organic compounds under solvent free ion exchange resin (IER) catalysis by sodium bromate has been studied at room temperature. Primary benzylic and secondary alcohols are converted to aldehydes and ketones and alkylarenes are oxidized to the corresponding α-ketones. The experimental procedure is simple and products are easily isolated in high yields at room temperature.

Full text of DOI:10.1081/SCC-120018684

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Solvent Free Ion Exchange Catalysis in the Oxidation of
Organic Compounds with Sodium Bromate
a
b
Ahmad Shaabani & Donald G. Lee
a
Chemistry Department, Shahid Beheshti University, Tehran, Iran
Department of Chemistry, University of Regina, Regina SK, Canada
b
Version of record first published: 15 Aug 2006
To cite this article: Ahmad Shaabani & Donald G. Lee (2003): Solvent Free Ion Exchange Catalysis in the Oxidation of Organic
Compounds with Sodium Bromate, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 33:8, 1255-1260
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Õ
SYNTHETIC COMMUNICATIONS
Vol. 33, No. 8, pp. 1255–1260, 2003
Solvent Free Ion Exchange Catalysis in the
Oxidation of Organic Compounds
with Sodium Bromate
1
,
2
Ahmad Shaabani * and Donald G. Lee
1
Chemistry Department, Shahid Beheshti University,
Tehran, Iran
2
Department of Chemistry,
University of Regina, Regina SK, Canada
ABSTRACT
The oxidation of organic compoundsunder so lvent free ion exchange
resin (IER) catalysis by sodium bromate has been studied at room
temperature. Primary benzylic and secondary alcohols are converted
to aldehydesand ketonesand alkylarenesare oxidized to the
corresponding a-ketones. The experimental procedure is simple and
products are easily isolated in high yields at room temperature.
*
Correspondence: Ahmad Shaabani, Chemistry Department, Shahid Beheshti
University, P.O. Box 19396-4716, Tehran, Iran; Fax: þ98-21-2403041; E-mail:
a-shaabani@cc.sbu.ac.ir.
1
255
DOI: 10.1081/SCC-120018684
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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256
Shaabani and Lee
Key Words: Sodium bromate; Ion exchange catalysis; Alkylarenes;
Alcohols; Solvent free; Oxidation.
Sodium bromate is commercially available as a stable solid, which
potentially isan inter et si ng candidate for the oxidation of organic
compoundsbeca ue s of itscapability in multi-electron tra nf es r.
Thermodynamically sodium bromate is a strong oxidant, but according
to the literature, bromate itself is not able to oxidize organic compounds.
It is usually used in aqueous media in the presence of co-reactants such as:
[
1]
[2]
[3]
[4–6]
[7]
NaHSO3, HBr, Br2, NH Cl,
4
FeCl3, cerium(IV) ammonium
[11]
[8]
[9]
[10]
nitrate (CAN), H SO , KHSO4,
HClO4.
[CH (CH ) ] NHSO ,
and
In most of these oxidation systems the removal of excess
2
4
3
2 3 4
4
[
12]
sodium bromate from reaction mixture and separation of bromate
or bromide from co-reactant salts is difficult (except of HBr and Br2).
In continuation of our studies on the oxidation of organic
[
4–7,11]
compoundswith os dium bromate,
we have used a combination
of solvent free reaction strategy and solid ion exchange resin catalysis
in the oxidation of a wide range of organic compoundsby os dium
bromate which not only overcomes the above mentioned disadvantages,
but also has other advantages: easy and quick separation of the products
from the oxidant and catalyst, better selectivity because of lower activity
þ
of H in the solid state, high yields and faster reactions. Because of
higher concentration of oxidant, lower reaction temperature, less toxic
effluent can be used and other waste problems can be minimized,
the catalyst is regenerable and does not have the problem of the limited
use of bromate due to its insolubility in almost all organic solvents.
As shown in Table 1, a wide variety of secondary alcohols and
primary benzylic alcoholscould be eai sl y oxidized to corre ps onding
carbonyl compoundsin high yieldsat room temperature (Sch. 1).
Also, this reagent selectively oxidizes secondary aliphatic and benzylic
alcoholsto ketonesin the pr ee sn ce of primary aliphatic alcohols
(
Table 1 Entries16, 17, and 18).
Alkylarenesare converted into the corre ps onding a-ketonesunder
these conditions (Table 2). As indicated in Sch. 2, the reaction displays
an interesting selectivity for compounds containing oxygen as part of
a cyclic side chain without C–O bond cleavage. When oxygen is in the
b-position, lactones are obtained in good yields (Entries 7 and 8); when it
isin the a-position the reaction is completely inhibited (Entry 9).
The unique selectivity in the oxidation reaction demonstrated in
Sch. 2 is an attractive synthesis, since the resulting ketones are
useful intermediates for preparing indenes and their homologues via

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Oxidation of Organic Compounds with Sodium Bromate
1257
Table 1. Oxidation of primary benzylic and secondary alcohols to corresponding
carbonyl compoundswith NaBrO
conditionsat room temperature.
3
/ion-exchange resin under solvent free
Reaction
time (h)
Yield
(%)
Entry
Reactant
Product
1
2
3
4
5
6
Benzyl alcohol
Benzaldehyde
0.1
1
95
95
4-Fluorobenzyl alcohol
4-Chlorobenzyl alcohol
4-Bromobenzyl alcohol
1-Phenyl ethanol
Benzhydrol
4-Fluorobenzaldehyde
4-Chlorobenzaldehyde
4-Bromobenzaldehyde
Acetophenone
1
100
100
97
1
0.1
0.3
5
Benzophenone
Benzil
100
70
a
7
Benzoin
1-Indanol
8
9
1-Indanone
3-Pentanone
0.2
5
95
95
3-Pentanol
4-Octanol
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
4-Octanone
Cyclopentanone
Cyclohexanone
5
95
95
Cyclopentanol
Cyclohexanol
5
5
90
85
4-Methylcyclohexanol
2-tert-Butylcyclohexanol
Exo-norborneol
1,3-Pentanediol
2-Ethyl-1,3-hexanediol
4-Methylcyclohexanone
2-tert-Butylcyclohexanone
Norcamphor
7
7
80
70
8
5-Hydroxy-2-pentanone
3-Hydroxymethyl-
10
7
70
90
4
-heptanone
1
a
8
1-Phenyl-1,2-ethanediol
a-Hydroxyacetophenone
2
90
ꢀ
The reaction isperformed at 60 C.
O
OH
NaBrO / IER
3
R
R
R
R'
R, R' = Alkyl
R = Ph and R' = H or Alkyl
0.1 - 8 h, r.t.
7
0-100%
Scheme 1. Oxidation of alcohols.
[
13]
reduction and dehydration
compounds.
and dihydroisocoumarines and similar
[14]
In summary both sodium bromate and IER are cheap and
commercially available reagents, which not only IER is regenerable but
also excess bromate and bromide ion results easily separated from
reaction mixture and recycled.

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Shaabani and Lee
Table 2. Oxidation of alkylarenesto corre sp onding carbonyl compoundswith
NaBrO
Entry
3
/ion-exchange resin under solvent free conditions at room temperature.
Reaction
time (h)
Yield
(%)
Reactant
Ethylbenzene
Product
1
2
3
Acetophenone
4-Fluoroacetophenone
Benzophenone
9-Fluorenone
1-Indanone
24
24
10
8
80
70
85
70
94
80
95
95
—
—
4-Ethyl-1-fluorobenzene
Diphenylmethane
Fluorene
a
4
5
6
7
8
9
Indan
Tetralin
5
1-Tetralone
Phthalide
6
Phthalan
Isochroman
2.5
3
2-Chromanone
No reaction
No reaction
2,3-Dihydrobenzofuran
1-Indanone
24
24
1
0
a
ꢀ
The reaction isperformed at 116 C.
O
NaBrO / IER
3
0
.1 - 8 h, r.t.
94%
O
NaBrO / IER
3
O
O
2.5 h, r.t.
95%
O
NaBrO / IER
3
No Reaction
24 h, r.t.
Scheme 2. Oxidation of alkylarenes.
EXPERIMENTAL
All productsare known compound,s which were identified by
comparison of their physical and spectral data with literature values.
Melting pointswere mea us red on an Electrothermal 9100 apparatus
and are uncorrected. Infrared spectra were recorded as neat films or as

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Oxidation of Organic Compounds with Sodium Bromate
1259
KBr pelletson a Perkin Elmer FT-IR 1600 ps ectrophotometer. NMR
spectra were recorded on a Bruker AC-200 spectrometer at 200 MHz with
CDCl as os lvent and (CH 3)4Si asinternal ts andard. Yieldsrefer to
3
isolated products or 2,4-dinitrophenylhydrazone derivatives (2,4-DNP)
of carbonyl compounds. The ion exchange resin, Rexyn 101 H, was
obtained from the Fisher Scientific Company.
A Typical Procedure for Oxidation of Alcohols
1
-Phenyl ethanol (0.122 g, 1 mmol) wasadded dropwi se to the oxidant
Finely ground ion exchange resin (0.1 g) and sodium bromate (1.0 g,
.6 mmol) were mixed together in a mortar] in a 25 mL round-bottomed
[
6
flask equipped with a magnetic stirrer. The progress of reaction was
followed by TLC (eluant: CH Cl /EtOAc: 1/1). When the reaction
2
2
completed (6 min), methylene chloride (15 mL) wasadded and the
product mixture was filtered through a sinter glass funnel and the residue
washed with methylene chloride (10 mL). The filtrate was treated with
saturated aqueous sodium thiosulfate (2.5 mL) in order to reduce any
residual oxidant. The organic layer was separated and the aqueous
layer extracted with methylene chloride (10 mL). The combined organic
layerswere dried over anhydrousmagne isu m us lfate. Evaporation of
the solvent gave the pure acetophenone (0.117 g, 0.97 mmol, 97%).
ꢀ
[15]
ꢀ
Themeltingpointofthe2,4-DNPderivativewas245–246 C(Lit. 250 C).
A Typical Procedure for Oxidation of Alkylarenes
Indan (0.118 g, 1 mmol) wasadded dropwi se to the oxidant [Finely
ground ion exchange resin (0.3 g) and sodium bromate (1.0 g, 6.6 mmol)
were mixed together in a mortar] in a 25 mL round-bottomed flask
equipped with a magnetic stirrer. The progress of reaction was followed
by TLC (eluant: n-hexane/EtOAc: 2/1). When the reaction completed
(
6 h), methylene chloride (15 mL) wasadded and the product mixture
was filtered through a sinter glass funnel and the residue washed with
methylene chloride (10 mL). The filtrate wastreated with as turated
aqueous sodium thiosulfate (2.5 mL) in order to reduce any residual
oxidant. The organic layer was se parated and the aqueouslayer extracted
with methylene chloride (10 mL). The combined organic layerswere dried
over anhydrous magnesium sulfate. Evaporation of the solvent gave the
pure 1-indanone (0.124 g, 0.94 mmol, 94%). Thisproduct wasidentified
by comparison with authentic 1-indanone using TLC, melting point

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260
Shaabani and Lee
42 C) and H NMR (200 MHz, CDCl ): ꢀ 2.63
t, J 6.10 Hz, 2H), 3.09 (t, J 6.08 Hz, 2H), 7.08–7.80 (m, 4H).
ꢀ
[16]
ꢀ
1
(41–42 C; Lit.
(
3
ACKNOWLEDGMENT
The authors are pleased to acknowledge finanical support the
Natural Sciencesand Enginearing Re es arch Council of Canada and
Shahid Beheshti University of Iran.
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Received in the NetherlandsApril 14, 2002