Short Communication
CSIRO PUBLISHING
Aust. J. Chem. 2005, 58, 603–606
Solventless Rapid Synthesis of Oxime, Semicarbazone,
and Phenylhydrazone Derivatives from Carbonyl
Compounds under Microwave Conditions
R. KamakshiA and Boreddy S. R. ReddyA,B
A Industrial Chemistry Laboratory, Central Leather Research Institute, Adyar, Chennai 600020, India.
B Corresponding author. Email: induchem2000@yahoo.com
A rapid and efficient method for the synthesis of oximes, semicarbazones, and phenylhydrazones has been reported
under solventless conditions using microwave irradiation.
Manuscript received: 1 May 2005.
Final version: 21 June 2005.
O
NOH
Oximes are one of the most important intermediates in
organic synthesis. Methods to synthesize oximes have been
reported.[1,2] This paper describes the synthesis of oximes
under solventless conditions in dry media within 1–2 min,
withexcellentyieldsintherange80–97%. Further, aldoximes
are shown by 1H NMR to occur more frequently as cis- than
as trans-isomers (Scheme 1, Table 1).
K2CO3/NH2OH·HCl
MW 1–2min
R
RЈ
R
RЈ
RЈ ϭ H,alkyl
Scheme 1.
Oximes are required as precursors in Beckmann rear-
rangements for the synthesis of oxazoles, oxazines, and for
various heterocycles. Oximes are also the synthons for 1,3-
dipolar addition reactions and form the main intermediates in
the synthesis of azirines and pyridine derivatives.[3] Phenyl
hydrazones, on treatment with Lewis acids, give carbazoles
that have antimicrobial activity. Oximes, phenylhydrazones,
and semicarbazones have been found to be biologically
active,[4] and thus their synthesis assumes importance.
In the conventional method of synthesis of oximes, either
water or ethanol/pyridine are used as solvents along with
bases and hydroxylamine.This process requires careful main-
tenance of pH in the solvent during the reaction. This
issue is eliminated while performing the reaction in dry
media. Also, synthesis of aldoximes is easier compared with
ketoximes. In this procedure, ketoximes are also formed. We
tried the same procedure on the formation of phenyl hydra-
zones and semicarbazones, and they both offered good yields
(Table 2).
techniques are gaining popularity with synthetic organic
chemists as they offer easy work-up.
Microwave-assisted techniques are applied to the rapid
synthesis of intermediates in various organic syntheses.[7,8,9]
Reactions that are sluggish and require very stringent con-
ditions may be carried out easily in a microwave oven. In
this article, we report the synthesis of oximes under dry
reaction media using anhydrous potassium carbonate under
microwave conditions. The reaction proceeded to completion
within 1–2 min. Although the solventless procedure is con-
venient, under thermal conditions the time taken for some
oximes is 5 h.[10] However, this time is minimized by the use
of microwave irradiation. Basic oxides such as metal oxides
and metal carbonates enhance the formation of Z-oximes.[11]
Although the reaction is stereo-selective for the formation
of oximes, it was not found be so with semicarbazones or
phenylhydrazones.Theprocedureinvolvesanextremelysim-
ple work-up procedure that makes the reaction attractive to
use. Interestingly, α,β-unsaturated ketones are also converted
to their respective oximes without any side reaction caused
by the addition of the –NHOH group to the β-unsaturated
carbon.
Solvent-free reaction conditions are convenient,[5,6]
because the reaction media is easy to handle without the need
for extensive purification. Yields are high and the reactions
proceed to completion rapidly. In addition, such conditions
are cost-effective and environmentally benign. Traditional
techniques with solvents yield only 50–60% of oximes with
both the isomers being nearly equally distributed. Moreover,
there is some loss of the product during precipitation and
recrystallization. This loss is avoided in the solventless pro-
cedure, since the products are sufficiently pure. Solventless
In conclusion, the procedure described is a fast, neat, and
inexpensive method for the synthesis of oximes and other
derivatives. The advantages of this procedure are stereo-
selectivity and simplicity.
© CSIRO 2005
10.1071/CH05107
0004-9425/05/080603
Kamakshi
