Gas-chromatographic study of hydrazine reaction with metal β-diketonates

Article abstract of DOI:10.1023/A:1020426105849

When treated with hydrazine, metal β-diketonates undergo decomposition to form the corresponding pyrazoles, irrespective of the kinetic stability of the chelates. With substituted metal chelates, the main reaction products are pyrazoles bearing in positio

Full text of DOI:10.1023/A:1020426105849

Russian Journal of General Chemistry, Vol. 72, No. 6, 2002, pp. 899 900. Translated from Zhurnal Obshchei Khimii, Vol. 72, No. 6, 2002,
pp. 962 963.
Original Russian Text Copyright
2002 by Svistunova, Shapkin, Nikolaeva.
Gas-Chromatographic Study of Hydrazine Reaction
with Metal -Diketonates
I. V. Svistunova, N. P. Shapkin, and O. V. Nikolaeva
Far-East State University, Vladivostok, Russia
Received September 22, 2000
Abstract When treated with hydrazine, metal -diketonates undergo decomposition to form the correspond-
ing pyrazoles, irrespective of the kinetic stability of the chelates. With substituted metal chelates, the main
reaction products are pyrazoles bearing in position 4 the -substituent of the compex. Other products are
formed when the substituent has centers sensitive to nucleophilic substitution and/or elimination. The reaction
can be used for structural assessment of the starting -diketonate.
Pyrazoles are most commonly prepared by reaction
of -diketones with hydrazine [1]. In the last few
years a great many metal chelates have been prepared,
whose ligands have never been isolated and some-
times are impossible to isolate [2]. This prompted us
to study the possibility of preparing pyrazoles directly
from metal chelates and, in particular, from -substi-
tuted metal complexes. The reactions were accom-
plished by heating the complexes with excess hyd-
razine in alcohol. The reaction completion was esta-
blished by TLC by the disappearance of the spot of
the starting chelate (with chromium and cobalt com-
plexes) or by the discoloration of the reaction mixture.
The reaction products were analyzed by GC MS.
tuted chromium(III) acetylacetonates VII XIII. Irres-
pective of the nature of substituent X, the major re-
action product was 3,5-dimethylpyrazole bearing
substituent X in position 4.
O
O
N H
N
2
4
Cr/
X
X
3
HN
VII XIII
XIV XX
X = Cl (VII, XIV), Br (VIII, XV), NO (IX, XVI), SPh
2
(
X, XVII), SCH CH Cl (XI, XVIII), SP(O)(OEt) (XII,
2 2 2
XIX), phthalimido (XIII, XX).
The reactions with unsubstituted complexes were
studied using as examples chromium(III), cobalt(III),
Subsitutient at the central carbon atom of the
chelate ring exerts appreciable rate effect on the de-
aluminum(III), iron(III), and copper(II) acetylaceto- composition of the complexes. The reactions with
nates. The reactions all gave 3,5-dimethylpyrazole as
a single reaction product.
chloro-, bromo-, nitro-, thiophenyl, and thiochloro-
ethyl-substituted chelates are as fast as with the un-
substituted complex and are complete within a few
minutes. Complex XII decomposes within 10 h, while
compound XIII does not decompose completely even
after 30-h refluxing.
O
M/n
N
N H
2
4
O
HN
I V
VI
The chromatograms of the decomposition products
of halo-substituted chromium(III) acetylacetonates
contain a large peak of 4-chloro(bromo)-2,5-dimethyl-
pyrazole and a minor peak of 2,5-dimethylpyrazole,
implying elimination of the substituent under the
action of hydrazine. The peak of pyrazole VI com-
prises no more than 20%, by the total ion current, of
the peak of pyrazole XIV or XV.
M = Cr (I), Co (II), Fe (III), Al (IV), n = 3; M = Cu (V),
n = 2.
The reactions are complete within a few minutes
and are equally fast both with the kinetically labile
copper complex and the stable chromium complex.
Chromium(III) formylacetonate reacts in a similar
way to give 3-methylpyrazole.
The chromatogram of the decomposition products
of the phtalimido-substituted complex contains, along
with the peak of pyrazole XX, a large peak assigned,
The reactions between substituted metal complexes
and hydrazine were studied using as examples substi-
1
070-3632/02/7206-0899$27.00 2002 MAIK Nauka/Interperiodica

900
SVISTUNOVA et al.
by the mass spectrum and the retention time, to
+
+
Cr(acacH) . In the thin-layer chromatogram of the
3
N
H
X
reaction mixture this compound was not found. There-
fore, it was assumed that the latter product is formed
by pyrolysis of undecomposed complex XIII in the
injector of the gas chromatograph.
X
N
+
V, XIV
N
X
Among minor decomposition products of
Cr[acacSP(O)(OEt)2]3 we identified PirzS Spirz
HN
N
(Pirz is 2,5-dimethylpyrazole) and PirzSEt. The total
HN
intensity of these two peaks was 10% of the intensity
of the peak of PirzSP(O)(OEt)2.
XIV, XV, XIX
The most intricate decomposition pattern is charac-
teristic of Cr(acacSCH CH Cl) . The chromatogram
Fragmentation
by substituent
2
2
3
contains two peaks of equal intensity, assigned to
PirzSCH CH Cl and PirzSCH CH OCH CH . In
XVI, XVIII, XX
2
2
2
2
2
3
addition, two less intense peak are present, whose
mass spectra correspond to PirzS SPirz and PirzSH.
The peak of PirzSCH CH Cl comprises 33 35% of
X = SH (XIV, XV, XIX), S (XVI, XVIII, XX).
EXPERIMENTAL
2
2
the total ion current. Probably, such an intricate reac-
tion pattern is explained by occurrence of substitution
and elimination reactions involving the chlorine atom.
Chelate, 20 30 mg, and 200 mg of hydrazine were
heated under reflux in 2 ml of alcohol until the
complex decomposed. The reaction mixture was
diluted with 20 ml of water, and the reaction product
was extracted with 1 ml of chloroform. The organic
extract was analyzed on a gas chromatograph with a
mass-selective detector under the following conditions:
HP-5890 (series II)/5972 GC MS system (Hewlett
Packard), injection volume 1 l, split 1:20, carrier
Attempted reaction of hydrazine with metal
chelates in DMF or DMSO failed. The complexes
undergo decomposition even upon prolonged heating.
Replacement of ethanol by methanol has no effect of
the reaction pattern. These finding suggest that solvent
is directly involved in reaction. Probably, alcohol
reversibly expels ligands from the coordination sphere, gas helium (0.7 ml/min), scan range m/z 50 410,
thus making them available for reaction with hydra- injector temperature 280 C, detector temperature
zine. Such reactions have been described for iron and 280 C, temperature program 50 to 280 C at
chromium complexes [3].
20 deg/min, and ionizing energy 70 eV.
The mass spectra of the pyrazoles obtained all
contain molecular ion peaks (100 80% of the base
peak). The principal fragmentation pathways are
shown below.
REFERENCES
1. Roberts, J.D. and Caserio, M., Basic Principles of
Organic Chemistry, New York: Benjamin, 1975,
2
nd ed. Translated under the title Osnovy organiches-
The reaction we described here can be used for
structural assessment of metal chelates, since the low
volatility of these compounds, lability under chroma-
tographic conditions, and paramagnetic nature makes
them difficult to study by traditional mathods.
koi khimii, Moscow: Mir, 1978, vol. 2.
2. Cativiela, C., Serrano, J.L., and Zurbano, M.M., J. Org.
Chem., 1995, vol. 60, pp. 3068 3074.
3. Kasuga, K., Itou, T., and Yamamoto, Y., Bull. Chem.
Soc. Jpn., 1974, vol. 47, no. 2, pp. 1026 1027.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 72 No. 6 2002