Zn(BH4)2/ultrasonic irradiation: An efficient system for reduction of carbonyl compounds to their corresponding alcohols

Article abstract of DOI:10.13005/ojc/300240

Zn(BH4)2 under ultrasonic irradiation is an efficient reducing system in CH3CN. This system reduces a variety of carbonyl compounds to their corresponding alcohols at room temperature in high to excellent yields of the products. Also, a,b-unsaturated aldehydes and ketones was regioselectively reduced to the corresponding allylic alcohols.

Full text of DOI:10.13005/ojc/300240

ISSN: 0970-020 X
CODEN: OJCHEG
2014, Vol. 30, No. (2):
Pg. 695-697
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Free Access, Peer Reviewed Research Journal
www.orientjchem.org
Zn(BH4)2/Ultrasonic Irradiation: An Efficient System
for Reduction of Carbonyl Compounds to their
Corresponding Alcohols
SIAMAK FANARI and DAVOOD SETAMDIDEH*
Department of Chemistry, College of Sciences, Mahabad Branch,
Islamic Azad University, Mahabad, Iran.
*Corresponding author E-mail: d.setamdideh@iau-mahabad.ac.ir
http://dx.doi.org/10.13005/ojc/300240
(Received: April 16, 2014; Accepted: May 15, 2014)
ABSTRACT
Zn(BH4)2 under ultrasonic irradiation is an efficient reducing system in CH3CN.This system
reduces a variety of carbonyl compounds to their corresponding alcohols at room temperature in
high to excellent yields of the products. Also, a,b-unsaturated aldehydes and ketones was
regioselectively reduced to the corresponding allylic alcohols.
Key words: Zn(BH4)2, Ultrasonic Irradiation, Carbonyl Compounds, Alcohols.
INTRODUCTION
methods on organic chemistry 9-10. In this context
we wish to introduce Zn(BH4)2 under ultrasonic
irradiation as a new combination reducing system
for convenient reduction of a variety of carbonyl
compounds such as aldehydes, ketones and á,â-
unsaturated carbonyl compounds to their
corresponding alcohols at room temperature.
Zn(BH4)2 is a non-conventional hydride
transferring agent which has been reported as an
efficient chemo-, regio- and stereoselective
reducing agent in several complex substrates. It is
moderately stable in ethereal solution which can
be used in a range of aprotic solvents such as, THF,
Et2O and DME. Several Combination reducing
RESULTS AND DISCUSSIONS
1
systems of Zn(BH4)2 such as Zn(BH4)2/TMEDA ,
Zn(BH4)2/Me3SiCl 2, Zn(BH4)2/TFA/DME 3, Zn(BH4)2/
We have chosen the reduction of
benzaldehyde as a model in order to determine
the appropriate reaction conditions and evaluate
the efficiency of ultrasonic irradiation.The reduction
of benzaldehyde took place with one molar
equivalent of Zn(BH4)2 in THF within 30 minutes at
4
5
6
H2O , Zn(BH4)2/Al2O3 , Zn(BH4)2/C , Zn(BH4)2/
ZrCl4 and Zn(BH4)2/2NaCl 8 have been used for
7
the different reduction purposes. Also, it is well
known that sonication as unconventional energy is
a well tool to facilities for varieties of synthetic

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FANARI & SETAMDIDEH, Orient. J. Chem., Vol. 30(2), 695-697 (2014)
Table 1: Reduction of Carbonyl Compounds by Zn(BH4)2 under Ultrasonic Irradiation in CH3CN
Entry
Aldehydes
Products
Time/min.
Yieldc/%
1a
benzaldehyde
benzyl alcohol
5
5
95
91
93
93
95
96
94
94
92
92
91
90
90
91
2a
4-bromobenzaldehyde
4-methylbenzaldehyde
3-methylbenzaldehyde
2-methoxylbenzaldehyde
4-methoxybenzaldehyde
cinnamaldehyde
4-bromobenzyl alcohol
4-methylbenzyl alcohol
3-methylbenzyl alcohol
2-methoxybenzyl alcohol
4-methoxybenzyl alcohol
3-phenyl-2-propen-1-ol
1-phenylethanol
1-(4-methylphenyl)ethanol
1-(4-ethoxyaphenyl)ethanol
4-phenyl-3-buten-2-ol
diphenylmethanol
3a
10
10
10
10
5
75
90
120
70
120
120
60
4a
5a
6a
7a
8b
acetophenone
9b
4-methylacetophenone
4-methoxyacetophenone
benzalacetone
Benzophenone
9H-fluoren-9-one
10b
11b
12b
13b
14b
9H-fluoren-9-ol
4-phenylbutan-2-ol
4-phenylcyclohexanone
c
a The reaction has been carried out by Zn(BH4)2 (1 mmol). b The reaction has been carried out by Zn(BH4)2 (2 mmol).
Yields refer to isolated pure products ( 3%).
-10 °C as shown in scheme 1. Among the tested reaction completes within 5 min at room temperature
aprotic and protic solvents i.e. n-hexane, CHCl3, with 95% yields of product as shown in scheme 1.
CH2Cl2, Et2O, DME, CH3CN, THF, CH3OH, C2H5OH This procedure was also applied for the reduction
and solvent-free conditions the reduction of of various aldehydes to the corresponding primary
benzaldehyde was better in CH3CN. The alcohols (Table 1, entries 1-7). All reductions were
optimization study showed that using 1 molar completed within 5-10 min by 1 molar equivalents
equivalents of Zn(BH4)2 in CH3CN (3 mL) is the best of Zn(BH4)2 under ultrasonic irradiation with
conditions. Our observation reveals that reduction excellent yields of the products (91-96%).
Scheme 1:
Scheme 2:

FANARI & SETAMDIDEH, Orient. J. Chem., Vol. 30(2), 695-697 (2014)
697
Our next attempt was the reduction of
ketones to the corresponding secondary alcohols.
The reduction of ketones was also obtained
successfully by 2 molar equivalents of Zn(BH4)2
under ultrasonic irradiation within 60-120 min at
room temperature in CH3CN with excellent yields of
the products (90-94%) (Table 1, entries 8-14).
equipped with a magnetic stirrer bar, a solution of
benzaldehyde (0.1061 g, l mmol) was prepared in
CH3CN (3 mL). To this solution Zn(BH4)2 (0.095 g,
1mmol) was added.The resulting mixture was stirred
under ultrasonic waves at room temperature for 5
min. The progress of the reduction reaction was
monitored by TLC (eluent:CCl4/Et2O:5/2). After
completion of the reaction, distilled water (5 mL)
was added to the reaction mixture and stirred for 5
min. The mixture was extracted with CH2Cl2 (3×10
mL) and dried over anhydrous Na2SO4. Evaporation
of the solvent afforded pure benzyl alcohol (0.102
g, 95% yield).
Also, we have examined the reduction of
cinnamaldehyde (Table 1, entry 7) and
benzalacetone (Table 1, entry 11) as models for a,b-
unsaturated aldehydes and ketones. The reduction
reactions took place to their corresponding allylic
alcohols in excellent yields in CH3CN at room
temperature as shown in scheme 2.
CONCLUSION
EXPERIMENTAL
In this context, we have shown that
Zn(BH4)2 under ultrasonic irradiation as new
reducing system is convenient for the reduction of
aldehydes and ketones to their corresponding
alcohols. Also, , -unsaturated aldehydes and
ketones are regioselectively reduced to the
corresponding allylic alcohols. The reduction
reactions were carried out with Zn(BH4)2 (1-2mmol)
in CH3CN at room temperature. Short reaction times
and easy work-up procedure makes as an attractive
new protocol for the reduction of carbonyl
compoundsto their corresponding alcohols.
Sonication was performed by using a
Bendeline uw 3100 (Germany) high intensity
ultrasonic (600 W, 20 KHz) via a micro-tip probe (vs
1
70t) and 70% amplitude. IR and H NMR spectra
were recorded on Perkin-Elmer FT-IR RXI and 300
MHz Bruker spectrometers, respectively. The
products were characterized by their 1H NMR or IR
spectra and comparison with authentic samples.
TLC was applied for the purity determination of
substrates, products and reaction monitoring over
silica gel 60 F254 aluminum sheet.
ACKNOWLEDGEMENTS
Typical procedure for the reduction of carbonyl
compounds with Zn(BH4)2 under ultrasonic
irradiation in CH3CN
The authors gratefully appreciated the
financial support of this work by the research council
of Islamic Azad University branch of Mahabad.
In a round-bottomed flask (10 mL)
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