Silica sulfuric acid/sodium dichromate dihydrate as an efficient heterogeneous method for the oxidation of alcohols under mild conditions

Article abstract of DOI:10.1080/10426500307835

A combination of silica sulfuric acid and sodium dichromate dihydrate in the presence of wet SiO₂ were used as an effective oxidizing agent for the oxidation of alcohols to their corresponding aldehyde or ketone derivatives in dichloromethane o

Full text of DOI:10.1080/10426500307835

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Phosphorus, Sulfur, and Silicon and the Related
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Silica Sulfuric Acid/Sodium Dichromate Dihydrate as an
Efficient Heterogeneous Method for the Oxidation of
Alcohols Under Mild Conditions
a
b
c
a
BiBi Fatemeh Mirjalili , Mohamad Ali Zolfigol , Abdolhamid Bamoniri & Amin Zarei
a
Yazd University , Yazd, Iran
b
Bu-Ali Sina University , Hamadan, Iran
c
Kashan University , Kashan, Iran
Published online: 27 Oct 2010.
To cite this article: BiBi Fatemeh Mirjalili , Mohamad Ali Zolfigol , Abdolhamid Bamoniri & Amin Zarei (2003) Silica Sulfuric
Acid/Sodium Dichromate Dihydrate as an Efficient Heterogeneous Method for the Oxidation of Alcohols Under Mild Conditions,
Phosphorus, Sulfur, and Silicon and the Related Elements, 178:8, 1845-1849, DOI: 10.1080/10426500307835
To link to this article: http://dx.doi.org/10.1080/10426500307835
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Phosphorus, Sulfur, and Silicon, 178:1845–1849, 2003
Copyright ꢀC Taylor & Francis Inc.
ISSN: 1042-6507 print
DOI: 10.1080/10426500390221528
SILICA SULFURIC ACID/SODIUM DICHROMATE
DIHYDRATE AS AN EFFICIENT HETEROGENEOUS
METHOD FOR THE OXIDATION OF ALCOHOLS
UNDER MILD CONDITIONS
a
b
BiBi Fatemeh Mirjalili, Mohamad Ali Zolfigol,
c
a
Abdolhamid Bamoniri, and Amin Zarei
Yazd University, Yazd, Iran; Bu-Ali Sina University, Hamadan,
a
b
c
Iran; and Kashan University, Kashan, Iran
Received March 25, 2003)
(
A combination of silica sulfuric acid and sodium dichromate dihydrate
in the presence of wet SiO were used as an effective oxidizing agent
2
for the oxidation of alcohols to their corresponding aldehyde or ketone
derivatives in dichloromethane or toluene with excellent yields.
Keywords: Alcohols; aldehydes; oxidation; silica sulfuric acid; sodium
dichromate dihydrate
For oxidation of organic functionalities, one turns often to high-valent
metal oxides or their mineral salts.1 Classic reagents of this type
are manganese dioxide (MnO2), potassium permangenate (KMnO4),
chromium trioxide (CrO3), potassium chromate (K2CrO4), and potas-
2
sium dichromate (K2Cr2O7). These are all frequently used reagents
whether in the laboratory or in industry, and yet they are beset with
multiple liability. For satisfactory and reproducible results, these oxi-
dants demand vigorous control of the experimental conditions. Other
drawbacks against such oxidants and their use in multistage organic
synthesis, in spite of their power, are their lack of selectivity, strong
protic and aqueous conditions, low yields of the products, and tedious
3
work-up. For instance, over-oxidation of aldehydes to carboxylic acids
is often an unavoidable side reaction.
Furthermore, the elevated reflux temperatures required by some oxi-
dation procedures will favor inopportune secondary reactions. Likewise,
Financial support for this work by the research affairs, Yazd University, Yazd, Iran
and Bu-Ali Sina University, Hamadan, Iran are gratefully acknowledged.
Address correspondence to M. A. Zolfigol, Department of Chemistry, College of Science,
Bu-Ali Sina University, PO Box 4135, Hamadan 65174, Iran. E-mail: Zolfi@ basu.ac.ir
1
845

1
846
B. F. Mirjalili et al.
the presence of strong acids or bases, which are required adjuncts as
catalysts for some reactions, often leads to detrimental side reactions.
As an example, the oxidation of primary alcohols to aldehydes by a
chromium (VI) salt in sulfuric acid often is accompanied by forma-
tion of an hemiacetal between the resulting aldehyde and the alcohol
substrate, followed by the ready oxidation of this intermediate to an
4
ester.
Along this line, we have introduced potentially useful oxidants
for selective oxidation and oxidative deprotection of different func-
5
tional groups. Therefore, we decided to investigate a new reagent or
reagent systems to overcome the above limitations. In addition, for
our propose a clean and easy work-up also were important. On the
other hand, any reduction in the amount of sulfuric acid needed or
any simplification in handling procedures is required for risk reduc-
6
tion, economic advantage and environment protection. In addition,
there is current research and general interest in heterogeneous sys-
tems because of the importance such systems have in industry and
7
in developing technologies. In continuation of our studies on the ap-
8
plication of solid acids we found that silica gel reacts with chloro-
sulfonic acid to give silica sulfuric acid (I). It is interesting to note
that the reaction is easy and clean without any work-up procedure be-
cause HCl gas is evolved from the reaction vessel immediately. There-
fore, we also find that silica sulfuric acid (I) is an excellent condi-
date for acid sulfuric replacement in organic reactions without any
limitations such as sulfonation of activated aromatic rings and de-
9
–12
struction of acid sensitive functional groups.
Furthermore, the het-
erogeneous reagent systems have many advantages such as simple
experimental procedures, mild reaction conditions, and minimization
8
–12
of chemical wastes as compared to their liquid phase counterparts.
The above facts encouraged us to seek a completely heterogeneous sys-
tem for the oxidation of various alcohols, and we have investigated a
number of different reaction conditions based upon the in situ gen-
eration of H2CrO4 at the surface of SiO2 in low concentration by in-
organic acidic resin, i.e., silica sulfuric acid and sodium dichromate
dihydate. In this article we report a simple and convenient method
for the effective conversion of alcohols (1) to their corresponding alde-
hyde or ketone derivatives (2) under mild and heterogeneous conditions
(
Scheme 1).

Silica Sulfuric Acid/Sodium Dichromate Dihydrate
1847
Different types of alcohols (1) were subjected to oxidation reaction
in the presence of silica sulfuric acid (I), Na2Cr2O7·2H2O (II), and wet
SiO2 in dichloromethane or toluene. The oxidation reactions were per-
formed under mild and completely heterogeneous conditions with excel-
lent yields (Table I). It was also observed that the oxidation of primary
alcohols (1) gives only aldehyde.
SCHEME 1
The present oxidation reaction can be readily carried out only by
placing silica sulfuric acid (I), Na2Cr2O7·2H2O (II), and wet SiO2 in
dichloromethane or toluene in a reaction vessel and efficiently stirring
the resulting heterogeneous mixture at room temperature or under re-
flux conditions. The highly pure aldehyde or ketone derivative (2) can
be obtained by simple filtration and evaporation of the solvent. The
results and reaction conditions are tabulated in the Table I.
In order to show the chemoselectivity of the method we have car-
ried out the successful oxidation of benzyl alcohol in the presence of
cyclohexanol (Scheme 2 and Table I, entry 13).
SCHEME 2
In conclusion, the low cost and the availability of the reagents, easy
and clean work-up, and high yields make this method attractive for the
large-scale operations. This procedure is very simple and contamination
by over oxidation side products is avoided. Moreover, the new element
here is that the reaction is heterogeneous. This could be worthwhile
for overcoming of the limitations of chromium based oxidant. We be-
lieve that the present methodology is an important addition to existing
methodologies.

1
848

Silica Sulfuric Acid/Sodium Dichromate Dihydrate
1849
EXPERIMENTAL SECTION
General
Chemicals such as alcohols, sodium dichromate dihydrate, toluene,
dichloromethane, and silica gel were purchased from Fluka, Merck and
Aldrich chemicals companies. Silica sulfuric acid was synthesized ac-
9
,10
cording to the our previously reported procedure.
The oxidation prod-
1
ucts were characterized by comparison of their spectral (IR, H-NMR),
TLC, and physical data with the authentic samples.
Oxidation of Hydroquinone to p-Benzoquinone.
A Typical Procedure
A mixture of hydroquinone (0.1 g, 1 mmol), sodium dichromate dihy-
drate (0.1 g, 0.33 mm), silica sulfuric acid (0.05 g), and wet SiO2 (60%
w/w, 0.05 g) in 3 mL of dichloromethane was stirred at room tempera-
ture for 25 min. The heterogeneous mixture was filtered and the solvent
was removed under reduced pressure. The solid was crystallized by n-
hexane. The p-benzoquinone was obtained in quantitative yield.
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