Chemoselective solvent-free deoximation by (NH4) 2Cr2O7 in the presence of ZrCl4 on wet SiO2

Full text of DOI:10.1023/B:RUJO.0000010193.00479.52

Russian Journal of Organic Chemistry, Vol. 39, No. 8, 2003, pp. 1191 1192. Translated from Zhurnal Organicheskoi Khimii, Vol. 39, No. 8, 2003,
pp. 1262 1263.
Original Russian Text Copyright
2003 by Shirini, Zolfigol, Pourhabib.
SHORT
COMMUNICATIONS
Chemoselective Solvent-free Deoximation by (NH4)2Cr2O7
in the Presence of ZrCl4 on Wet SiO2
F. Shirini1, M. ali Zolfigol2, and A.Pourhabib2
1Department of Chemistry, College of Science, Guilan University, Rasht, Iran, e-mail: Shirini@cd.gu.ir
2Department of Chemistry, College of Science, Bu-Ali Sina University, Hamadam, 65174 Iran, e-mail:Zolfi@basu.ac.ir
Received January 17, 2003
Protection of carbonyl compounds as oximes is of
great interest to synthetic chemists for the oximes are
readily prepared highly stable compounds [1, 2].
Oximes are also extensively used for characterization
of carbonyl compounds and in preparation of amides
via the Beckmann rearrangement [3]. Since oximes
can be prepared from noncarbonyl compounds, such
as alcohols [4], olefins [5], primary aliphatic amines
[6], and nitriles [7] the recovery of carbonyl com-
pounds from oximes provides an alternative method
for aldehydes and ketones preparation. Some of the
reagents applied for deoximation [1. 8, 9] are toxic,
expensive, or not readily available, they need to be
freshly prepared, or the reaction requires drastic
conditions, long time, and tedious workup.
monium dichromate in the presence of ZrCl2 and wet
SiO2 under solvent-free conditions (see table).
Our experiments show that oximes are converted
into their corresponding carbonyl compounds in good
to high yields at room temperature. Semicarbazones
do not undergo the cleavage of the C=N bonds by
this method (see table, runs nos. 8 14). Therefore
this procedure is suitable for selective deprotection
of oximes leaving the semicarbazones intact. This fact
was proved by a competitive reaction of 4-methyl-
acetophenone oxime and acetophenone semicarb-
azone: Within 2.8 h all 4-methylacetopheneone oxime
In this paper we report on a convenient method for
deoximation of aldehydes and ketones oximes into
their corresponding carbonyl compounds using am-
R1R2
= Alk, Ar (see table)
Oximes deoximation by ammonium dichromate in the presence of ZrCl2 and wet SiO2 at room temperature
Run no.
Substrate
4-Nitrobenzaldoxime
3-Nitrobenzaldoxime
4-Chlorobenzaldoxime
4-Methylbenzaldoxime
Acetophenone oxime
4-Methylacetophenone oxime
Cyclohexanone oxime
Benzaldehyde semicarbazone
3-Nitrobenzaldehyde semicarbazone
4-Methoxybenzaldehyde semicarbazone
Benzophenone semicarbazone
Acetophenone semicarbazone
1-Naphthaldehyde semicarbazone
Cyclohexanone` semicarbazone
Reaction product
Time, h
Yield, %a
1
2
3
4
5
6
7
8
9
10
11
12
13
14
4-Nitrobenzaldehyde
3-Nitrobenzaldehyde
4-Chlorobenzaldehyde
4-Methylbenzaldehyde
Acetophenone
4-Methylacetophenone
Cyclohexanone
Benzaldehyde
3-Nitrobenzaldehyde
4-Methoxybenzaldehyde
Benzophenone
Acetophenone
1-Naphthaldehyde
Cyclohexanone
4
4
1
1
72
75
78
85
70
85
83
0
0
0
0
0
4
2.7
0.5
4
4
4
4
4
4
4
0
0
a
Yield of the isolated reaction product.
1070-4280/03/3908-1191$25.00 2003 MAIK Nauka/Interperiodica

1192
SHIRINI et al.
was converted into 4-methylacetophenone whereas
the acetophenone semicarbazone was recovered
unchanged.
chromatography on silica gel in an yield indicated in
the table. We gratefully acknowledge the Research
Council of Guilan University for partial support of
this study.
It should be noted that these deoximation reactions
did not proceed at the use either of ammonium di-
chromate, ZrCl4, or wet SiO2 alone.
REFERENCES
In conclusion we can state that a mild, efficient,
and chemoselective deoximation method has been
developed. The deoximation occurs at room tempera-
ture under solvent-free conditions.
1. Greene, T.W. and Wuts, P.G., Protective Groups in
Organic Synthesis New York, 1991.
2. Bandgar, B.P., Lalita, B.K., and Thote, J.I., Synth.
Commun., 1997, vol. 27, p. 1149.
3. Bosch, A.L., Cruz, P., Diez-Barra, E., Loupy, I.,
and Langa, F., Synlett., 1995, p. 1259.
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Soc., 1961, vol. 83, p. 4083.
5. Kadzyauskasand, P.P. and Zefirov, N.S., Russ.
Chem. Rev., 1968, vol. 37, p. 543.
6. Kahr, K. and Berther, C., Chem. Ber., 1960, vol. 93,
p. 132.
7. Touster, O., Org. React., 1953, vol. 7, p. 327.
8. Kabalka, G.W., Pace, R.D., and Wadgaonkaf P.P.,
Synth., Commun., 1990, vol. 20, p. 2453.
9. Bandgar, B.P., Shaikh, S.I., and Iyyer, S., Synth.
Commun., 1996, vol. 26, p. 1163.
10. Shirini, F., Zolfigol, M.A., and Pourhabib, A.,
J. Chem. Res., 2001, p. 102.
EXPERIMENTAL
Oximes deoximation (general procedure). To a
mixture of ZrCl4 (0.69 g, 3 mmol) and 0.4 g of wet
SiO2 (SiO2 to H2O 4:1 by weight) and ammonium
dichromate (0.252 g, 1 mmol) was added an appropri-
ate oxime (1 mmol). The resulting mixture was stir-
red at room temperature for a time specified in the
table (TLC or GLC monitoring). After completion of
the reaction CH2Cl2 (5 ml) was added to the mixture,
and 15 min later the solution obtained was filtered
and dried on anhydrous MgSO4. The solution was
filtered off, the solvent was evaporated, and the
carbonyl compound formed was isolated by column
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 8 2003