KF-Al2O3 mediated cross-Cannizzaro reaction under microwave irradiation

Article abstract of DOI:10.1081/SCC-120002005

Aromatic aldehydes are selectively converted to the corresponding alcohols in high yields by cross-Cannizzaro reaction using KF-Al₂O₃ under microwave irradiation in solvent-free condition.

Full text of DOI:10.1081/SCC-120002005

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KF-Al O MEDIATED CROSS-CANNIZZARO REACTION
2
3
UNDER MICROWAVE IRRADIATION*
a
a
a
b
B. V. Subba Reddy , R. Srinivas , J. S. Yadav & T. Ramalingam
a
Organic Chemistry Division-I , Indian Institute of Chemical Technology , Hyderabad, 500
07, India
0
b
Organic Chemistry Division-I , Indian Institute of Chemical Technology , Hyderabad, 500
07, India
0
Published online: 16 Aug 2006.
To cite this article: B. V. Subba Reddy , R. Srinivas , J. S. Yadav & T. Ramalingam (2002) KF-Al O MEDIATED CROSS-
2
3
CANNIZZARO REACTION UNDER MICROWAVE IRRADIATION*, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 32:2, 219-223, DOI: 10.1081/SCC-120002005
To link to this article: http://dx.doi.org/10.1081/SCC-120002005
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SYNTHETIC COMMUNICATIONS, 32(2), 219–223 (2002)
KF-Al O MEDIATED
2
3
CROSS-CANNIZZARO REACTION
UNDER MICROWAVE IRRADIATION*
B. V. Subba Reddy, R. Srinivas, J. S. Yadav,
y
and T. Ramalingam
Organic Chemistry Division-I, Indian Institute of
Chemical Technology, Hyderabad-500 007, India
ABSTRACT
Aromatic aldehydes are selectively converted to the corres-
ponding alcohols in high yields by cross-Cannizzaro reaction
using KF-Al O under microwave irradiation in solvent-free
2
3
condition.
1
Surface mediated solid state reactions coupled with mircrowaves have
received much attention due to their operational simplicity, enhanced
reaction rates, greater selectivities, cleaner reaction products and simple
experimental/isolation procedures. Organic transformations which normally
require longer reaction times at reflux temperature can be achieved con-
veniently and rapidly by microwave irradiation. The Cannizzaro reaction
2
is an important inexpensive process for the preparation of alcohol and acid
*
IICT Communication No. 4420.
Corresponding author.
y
2
19
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

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REPRINTS
2
20
SUBBA REDDY ET AL.
from aromatic aldehydes. This reaction is normally carried out in solution
3
–5
phase employing strong bases like NaOH, KOH and Ba(OH) Á8H O etc.
2
2
6
Recently, cross-Cannizzaro reactions have been reported by using
NaOH and Ba(OH) Á8H O as bases formaldehyde as hydride source to
2
2
produce alcohols in good yields from the corresponding aromatic aldehydes.
Such strongly basic conditions promote substantial amounts of byproducts
due to the side reactions associated with strong bases. Existing processes for
this conversion involve harsh conditions and environmentally unfavourable
solvents. Further, there is an advantage in developing an efficient and rapid
method for the preparation of alcohols using inexpensive and recoverable
catalysts under solvent-free conditions.
Scheme.
In continuation of our interest on microwave-assisted solid state reac-
7
tions, herein we report a rapid, efficient and practical method for cross-
Cannizzaro reaction to produce alcohols in higher yields. The reaction
proceeds efficiently in excellent yields under microwave irradiation in the
absence of solvent. Several substituted aromatic aldehydes underwent clean
and remarkably fast cross-Cannizzaro reaction with paraformaldehyde in
presence of KF-Al O under microwave irradiation. The reactions are quick
2
3
and clean, and afford exclusively alcohols in excellent yields without the
formation of undesirable side products. It is remarkable to observe that
the reactions are slow and afford moderate yields of the products when
unsupported KF is employed in place of KF-Al O . Further, several unde-
2
3
sirable side products were formed along with required alcohols when basic
alumina was used for this transformation under similar reaction conditions.
High conversions were obtained with KF supported on basic alumina. To
confirm the rate enhancement, benzaldehyde was reacted with paraformal-
dehyde in the presence of 37% KF on Al O (3 wt equiv. of aldehyde) under
2
3
microwave irradiation for 5 min to afford benzyl alcohol in 92% yield,
whereas the same reaction under thermal conditions in refluxing dioxane
requires a longer reaction time of 7 h and gave 85% yield of benzyl alcohol.
This clearly shows the role of microwave irradiation in enhancing reaction
rates and yields of the products. Aromatic aldehydes bearing electron
withdrawing substituents are rapidly converted to the corresponding
alcohols in high yields when compared to those possessing electron releasing

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CROSS-CANNIZZARO REACTION
221
Table. KF-Al O Mediated Cross-Cannizzaro Reaction Under Thermal and
2
3
Microwave Irradiation

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2
22
SUBBA REDDY ET AL.
substituents in the ring. The reactions are very clean and free from aromatic
by-products which are normally formed in Cannizzaro reactions under
conventional conditions.
In conclusion, the letter describes a rapid and efficient procedure for
the preparation of alcohols by cross-Cannizzaro reaction using an inexpen-
sive and surface bound reagent KF-Al O under microwave irradiation in
2
3
solvent-free conditions.
EXPERIMENTAL
Method A – Microwave Irradiation: Amixture of benzaldehyde
5 mmol) and paraformaldehyde (10 mmol) was admixed with 37% KF on
(
Al O (3 wt. equiv. of aldehyde) in a pyrex test tube and subjected to micro-
2
3
wave irradiation at 650 W for an appropriate time. On completion of the
reaction, as indicated by TLC, the reaction mass was directly charged on a
silica gel column (Aldrich, 100–200 mesh) and eluted with ethyl acetate–
hexane (2 : 8) to afford benzyl alcohol in 91% yield.
Method B – Conventional Heating: Amixture of benzaldehyde
5 mmol), paraformaldehyde (10 mmol) and KF-Al O (3 wt. equiv. of
2 3
(
aldehyde) was refluxed in dioxane for a specified time as required to com-
plete the reaction. After complete conversion as indicated by TLC, the
reaction mass was filtered and concentrated in vacuo. The resulting product
was purified as above to afford benzyl alcohol in 85% yield.
ACKNOWLEDGMENT
BVS and RS thank CSIR, New Delhi (India) for the award of
fellowships.
REFERENCES
1
. a) Abramovitch, R.A. Org. Prep. Proced. Int. 1991, 23, 685. b) Caddick,
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Texier-Boullet, F.; Jacqualt, P.; Mathe, D. Synthesis 1998, 1213. d)
Verma, R.S. Green Chemistry 1999, 43.
2. a) Cannizzaro, S. Ann. 1853, 88, 129. b) Geissman, T.A. Organic
Reactions 1944, II, 94.

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CROSS-CANNIZZARO REACTION
223
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Received in the UK April 10, 2000

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