Tandem one-pot conversion of aldehydes into ethyl esters

Article abstract of DOI:10.1080/00397911.2010.481749

A facile one-pot synthesis of ethyl esters from aldehydes has been developed. This tandem process involves the formation of a nitrile intermediate obtained from the reaction of an aldehyde with hydroxylamine hydrochloride in dimethylsulfoxide (DMSO) at 100°C and the subsequent reaction of the nitrile with ethanol and sulfuric acid at 130°C. The resulting ethyl ester products were produced in good yields (65-90%) and high purity (>95%).

Full text of DOI:10.1080/00397911.2010.481749

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Tandem One-Pot Conversion of
Aldehydes into Ethyl Esters
a
a
a
Patrick J. Siler , Samuel T. Chill & Robert C. Mebane
a
Department of Chemistry, University of Tennessee at Chattanooga,
Chattanooga, Tennessee, USA
Version of record first published: 21 Mar 2011.
To cite this article: Patrick J. Siler, Samuel T. Chill & Robert C. Mebane (2011): Tandem One-Pot
Conversion of Aldehydes into Ethyl Esters, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 41:8, 1247-1250
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1
Synthetic Communications , 41: 1247–1250, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.481749
TANDEM ONE-POT CONVERSION OF ALDEHYDES
INTO ETHYL ESTERS
Patrick J. Siler, Samuel T. Chill, and Robert C. Mebane
Department of Chemistry, University of Tennessee at Chattanooga,
Chattanooga, Tennessee, USA
GRAPHICAL ABSTRACT
Abstract A facile one-pot synthesis of ethyl esters from aldehydes has been developed. This
tandem process involves the formation of a nitrile intermediate obtained from the reaction
ꢀ
of an aldehyde with hydroxylamine hydrochloride in dimethylsulfoxide (DMSO) at 100 C
ꢀ
and the subsequent reaction of the nitrile with ethanol and sulfuric acid at 130 C. The
resulting ethyl ester products were produced in good yields (65–90%) and high purity
(>95%).
Keywords Aldehyde; ethyl ester; nitrile; nitrile alcoholysis; tandem reaction
Nitriles are versatile synthetic intermediates because they can be transformed into a
variety of other functional groups.
[1,2]
One such transformation is the alcoholysis of
nitriles to form esters. Recently, we described a convenient one-pot synthesis of
[3]
[4]
nitriles from aldehydes using hydroxylamine hydrochloride in dimethylsulfoxide
ꢀ
(DMSO) at 100 C. We extended this synthetic methodology to a tandem, one-pot
conversion of aldehydes into amides employing basic hydrogen peroxide after for-
[5]
mation of the nitrile. We have now further extended this tandem reaction sequence
to the one-pot conversion of aldehydes into esters and describe the results in this
report. We feel this new method is an attractive alternative to recently described
[
6]
procedures for converting aldehydes into esters including the N-iodosuccinimide-
[
mediated conversion of aldehydes to methyl esters, oxidation of aldehydes to esters
7]
[
with oxone, catalytic oxidative esterification of aldehydes with V O -H O ,
8]
[9]
2
5
2
2
[
10]
conversion of aldehydes into esters using acetone cyanohydrin,
titanosilicate-
aldehyde to ester through
oxidation of acetals, and treatment of aromatic aldehydes with manganese dioxide
[
11]
catalyzed oxidation of aromatic aldehydes to esters,
[12]
[13]
and sodium cyanide.
Received October 21, 2009.
Address correspondence to Robert C. Mebane, Department of Chemistry, #2252, University of
Tennessee at Chattanooga, 615 McCallie Ave., Chattanooga, TN 37403-2598, USA. E-mail:
robert-mebane@utc.edu
1
247

1248
P. J. SILER, S. T. CHILL AND R. C. MEBANE
Table 1. One-pot conversion of aldehydes to ethyl esters
b
Yield (%)
Entry
1
Aldehyde
Ethyl ester
c
85
c
2
3
4
75
c
90
d
70
d
5
6
7
8
9
74
d
71
c
68
d
79
c
78
c
65
10
a
b
c
Aldehyde (2.0 mmol), NH
Isolated yields.
2
OH ꢁ HCl (3.8 mmol), DMSO (4 mL), ethanol (10 mL), and H
2 4
SO (5 mL).
Total time for complete reaction ¼ 3 h.
d
Total time for complete reaction ¼ 3.5 h.

CONVERSION OF ALDEHYDES INTO ESTERS
1249
Figure 1. Sequence of possible steps in the conversion of aldehydes into ethyl esters.
The experimental procedure for the one-pot conversion of aldehydes to ethyl
esters is simple and straightforward and affords ethyl esters in good isolated yields
(Table 1). As an illustrative example, 4-methylbenzaldehyde (2.0 mmol) was added
to a solution of hydroxylamine hydrochloride (3.8 mmol) in DMSO (4 mL), and
the resulting reaction solution was stirred and heated for 60 min in a sand bath
ꢀ
maintained at 100 C. Complete conversion of octanal, nonanal, dodecanal,
4-methoxybenzaldehyde, 4-nitrobenzaldehyde, and 3-phenyl-2-propenal to their
respective nitriles only took 30 min as determined by GC=MS. All other aldehydes
took 60 min to reach completion. Ethanol (10 mL) and sulfuric acid (5 mL) were
added, and the reaction mixture was stirred while heated in a sand bath held at
ꢀ
1
30 C for 2.5 h. After cooling to room temperature, water (15 mL) was added, and
the solution was extracted with diethyl ether (4 ꢂ 20 mL). The combined ether layers
were washed once with water (20 mL) and dried (K CO ), and the solvent was
2
3
removed by rotary evaporation and high vacuum to give ethyl 4-methylbenzoate as
1
13
a light oil (2.43 g, 74% isolated yield). The H and C NMR spectra and the mass
spectrum of the isolated ethyl 4-methylbenzoate were identical to authentic
1
13
spectra. The H and C NMR spectra of this ester indicated that its purity was
greater than 95%.
As seen in Table 1, this tandem reaction is general for the preparation of both
aliphatic and aromatic ethyl esters. All the ethyl esters prepared in this study were
1
confirmed by comparison of H and C NMR spectra and mass spectra with
13
1
13
authentic samples. Furthermore, the H and C NMR spectra of the ethyl esters
indicated that the product purities were greater than 95%.
Although no mechanistic studies were performed, it seems reasonable that this
tandem conversion of an aldehyde to an ester first involves the formation of an
aldoxime, which we have previously shown dehydrates under the reaction conditions
[4]
to give a nitrile. Upon the addition of ethanol and acid, alcoholysis of the nitrile
leads to an imidate salt, which is further hydrolyzed under the reaction conditions
[3]
to give an ester.
In conclusion, we have demonstrated that aldehydes can be readily converted
into ethyl esters by heating the aldehyde in DMSO containing hydroxylamine hydro-
chloride followed by selective solvolysis of the subsequent nitrile with ethanol under
acidic conditions. This one-pot, tandem process does not involve expensive materials
and should offer an attractive alternative for converting aldehydes into esters.

1250
P. J. SILER, S. T. CHILL AND R. C. MEBANE
ACKNOWLEDGMENTS
The authors gratefully acknowledge financial support from the Research
Corporation, the University of Chattanooga Foundation, and the Grote Chemistry
Fund.
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