Thermal and structural investigation of the reaction between 1,2-propanediol and Ni(NO3)2·6H2O

Article abstract of DOI:10.1023/A:1010100823234

The authors present the results of an investigation concerning the reaction between 1,2-propanediol and Ni(NO₃)₂·6H₂O, leading to a complex containing as ligand the lactate anion (L), suggesting that the oxidation of 1,2-propanediol occurs at the primary hydroxyl group. The obtained solid homopolynuclear combination, [Ni₂(OH)₂L₂(H₂O)₂·0.5H₂O]_n, has been investigated by thermal analysis, electron and IR spectroscopy, and magnetic methods. Nickel oxide obtained by thermolysis of this complex compound was characterized by IR, X-ray spectroscopy and elemental analysis. All the investigations lead to the conclusion that the complex compound is characterized by pseudooctahedral configuration of the nickel(II) ion. Thermal analysis of the homopolynuclear complex compound enabled to prove the thermal decomposition mechanism.

Full text of DOI:10.1023/A:1010100823234

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Journal of Thermal Analysis and Calorimetry, Vol. 63 (2001) 181–189
THERMAL AND STRUCTURAL INVESTIGATION
OF THE REACTION BETWEEN 1,2-PROPANEDIOL
AND Ni(NO3)2·6H2O
M. Niculescu1, N. Vaszilcsin1, M. Bîrzescu1, P. Budrugeac2 and E. Segal3
1University ‘Politehnica’ of Timiºoara, Faculty for Industrial Chemistry and Environmental
Engineering, Piata Victoriei 2, 1900 Timiºoara, Romania
2ICPE – Research and Development Institute for Electrical Engineering, 74204 Splaiul Unirii 313,
Sector 3, Bucharest, Romania
3University of Bucharest, Faculty of Chemistry, Department of Physical Chemistry,
70606 Bd. Elisabeta 4–12, Sector 6, Bucharest, Romania
(Received April 14, 2000; in revised form November 8, 2000)
Abstract
The authors present the results of an investigation concerning the reaction between 1,2-propanediol
and Ni(NO3)2·6H2O, leading to a complex containing as ligand the lactate anion (L), suggesting that
the oxidation of 1,2-propanediol occurs at the primary hydroxyl group. The obtained solid homo-
polynuclear combination, [Ni2(OH)2L2(H2O)2·0.5H2O]n, has been investigated by thermal analysis,
electron and IR spectroscopy, and magnetic methods. Nickel oxide obtained by thermolysis of this
complex compound was characterized by IR, X-ray spectroscopy and elemental analysis. All the in-
vestigations lead to the conclusion that the complex compound is characterized by pseudooctahedral
configuration of the nickel(II) ion. Thermal analysis of the homopolynuclear complex compound
enabled to prove the thermal decomposition mechanism.
Keywords: homopolynuclear combination, hydroxylactate, nitrate, propanediol, thermal analysis
Introduction
The necessity of obtaining oxide systems with irreducible structure and properties,
required by the modern technology in various fields (heterogeneous catalysis, elec-
trocatalysis, electronics, ceramic pigments, physical supports – carriers, brackets –
for the stockage and processing of information, drug industry), has determined the
advent of new unconventional methods for their synthesis. In this respect the thermal
conversion of homo- and heteropolynuclear complexes with anions of carboxylic ac-
ids as ligands is to be mentioned [1–14]. Such ligands include the anions glyoxylate,
malonate, succinate and lactate [15–20]. These compounds decompose at relatively
low temperatures, forming simple or mixed oxides and volatile products (CO, CO2,
H2O).
1418–2874/2001/ $ 5.00
Akadémiai Kiadó, Budapest
© 2001 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

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182
NICULESCU et al.: HOMOPOLYNUCLEAR COMBINATION
Thermal conversion in air of M(II) (M=Ni, Co) homopolynuclear glyoxylates
[15, 16] as well as Ni(II), Cu(II) heteropolynuclear glyoxylates [17] led to non-stoi-
chiometric oxides of the corresponding metal.
The determination of the formation conditions of non-stoichiometric oxides of
Ni and Co led to an original method for obtaining anodes with films electrocataly-
tically active for the oxygen evolution reaction in water and chloralkali electrolysis
[18, 19].
Ni and Co complex compounds have been synthesized as result of the reaction
between 1,3-propanediol and nitrates of these cations [20].
This paper presents the results obtained in the investigation of 1,2-propanediol
oxidation with Ni(NO3)2·6H2O. The obtained complex compound was investigated
from the composition and physical-chemical properties standpoints. It will be shown
that it can be a precursor for NiO obtaining at relatively low temperature.
Experimental
For the synthesis of the complex compound, Ni(NO3)2·6H2O, ‘Reactivul’ – Bucha-
rest, with minimal purity of 98% and 1,2-propanediol, ‘BDH Chemical Ltd. Poole’ –
England with purity of 97% were used. The impurities from the reagents do not influ-
ence the synthesis and purity of the obtained compound as they are removed in the
subsequent purification step. The thermoanalytical curves (TG, DTG, DTA) corre-
sponding to the synthesis and the decomposition of the coordination compound were
recorded on a Q-1500D MOM-Budapest type derivatograph, in static air atmosphere
and in the temperature range of 20–500°C, at a heating rate of 5 K min–1. The coordi-
nation compound was also characterized by the following methods: chemical analy-
sis, IR spectroscopy, electron spectroscopy (diffuse reflectance technique) and mag-
netic methods. The IR spectrum was recorded on a Specord IR 75 Carl Zeiss Jena
spectrometer using the technique of KBr pellets, in the range of 400–4000 cm–1. The
electron spectrum was recorded by diffuse reflectance technique using MgO as a ref-
erence material.
The magnetic measurements were performed according to Faraday’s method, at
room temperature, using Hg[Co(NCS)4] as a standard. The characterization of nickel
oxide obtained by thermal decomposition of the investigated coordination compound
was performed by IR and X-ray spectroscopy. X-ray diffractograms were recorded
on DRON 3 diffractometer.
Results and discussion
Synthesis of the coordination compound
The elaborated method of the synthesis of the coordination compound is based on the
oxidation reaction of 1,2-propanediol in alcohol–water system by nickel nitrate and
the simultaneous isolation of the complex compound in the reaction system. A solu-
tion of water+alcohol+Ni(NO3)2·6H2O in the molar ratio 1,2-propanediol: Ni(NO3)2·
J. Therm. Anal. Cal., 63, 2001

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NICULESCU et al.: HOMOPOLYNUCLEAR COMBINATION
183
6H2O= 3:2 was prepared. This mixture was heated in a thermostat in the following
steps of thermal treatment: 60°C (2 h); 70°C (2 h); 80°C (2 h); 90°C (2 h); 100°C
(2 h); 110°C (2 h); 120°C (10 h). The end of the reaction corresponds to the end of the
gas evolution.
The solid reaction product has been heated in an acetone – water mixture, fil-
tered and washed with acetone. Finally, it was maintained in air until constant mass.
The thermal behaviour of an aqueous solution of Ni(NO3)2·6H2O – 1,2-propan-
ediol has been investigated. The heating of the solution put in a plate shaped platinum
crucible has been performed in static air atmosphere at temperature between 20 and
500°C, using a heating rate of 5 K min–1 and α-Al2O3 as reference material. Figure 1
shows the thermoanalytical curves of the system Ni(NO3)2·6H2O – 1,2-propanediol –
H2O. From the DTA curve one can see that at a temperature of about 130°C a peak is
registered, which is attributed to the oxidation reaction of the diol with the nickel ni-
trate and the complex generation. Complex generation takes place practically in the
temperature range of 100–150°C, when the TG and DTG curves show a mass loss
corresponding to NO2 elimination (NO+½O2→NO2) coupled with the simultaneous
formation of the complex compound.
Fig. 1 Thermoanalytical curves of the Ni(NO3)2 – 1,2-propanediol – H2O system
J. Therm. Anal. Cal., 63, 2001

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184
NICULESCU et al.: HOMOPOLYNUCLEAR COMBINATION
The evolution of the reaction between 1,2-propanediol and Ni(NO3)2·6H2O was
also investigated by IR spectroscopy. As the reaction advances, the bands due to the
nitrate ion decrease in intensity, proving that the nitrate ion is consumed in the reac-
tion [21]. At the same time, the appearance and the increase of band intensity in the
range of 1580–1680 cm–1 (νasCOO–) is observed, which is specific to the ligands of
the complex compounds which contain at least two oxygen atoms as donors such as
the carboxylic anions of the acids.
In order to separate and identify the ligand, the complex has been treated with
RH cationite. After the retention of the metal cations, the resulted lactic acid has been
identified by specific reactions (haloform reaction, reaction with FeCl3 solution). The
elemental analysis results (Table 1) as well as the IR investigation confirm the fol-
lowing empirical chemical formula for the coordination compound: Ni(OH)L(H2O)·
0.25H2O, where L is the lactate anion.
Table 1 Composition and elemental analysis data
Ni(II)/%
C/%
H/%
Compound
(compound formula)
calc.
31.35
exp.
calc.
exp.
calc.
4.54
exp.
4.63
Ni(OH)L(H2O)·0.25H2O
31.10
19.23
19.30
These results as well as those previously reported [15, 16] concerning the oxida-
tion of ethyleneglycol with M(II) nitrate (M=Ni, Co) suggest that the oxidation of the
1,2-propanediol with Ni(NO3)2·6H2O occurs at the primary hydroxyl group, which is
more reactive and can be oxidized to carboxylate ion. The secondary hydroxyl has a
lower reactivity and is not involved in the oxidative process under the reaction condi-
tions. Consequently, we suggest the following mechanism for the reaction between
1,2-propanediol and Ni(NO3)2:
CH3–CH–CH2+H2O→CH3–CH–C=O+4e–+5H+
(a)
|
|
OH OH
|
|
OHO–
NO– +3e–+4H+→NO+2H2O
(b)
(c)
3
3CH3–CH–CH2+4NO– +H+→3CH3–CH–C=O+4NO+5H2O
3
|
OH OH
|
|
|
OH O–
[Ni(H2O)x]2++H2O→[Ni(OH)(H2O)(x–1)]++H3O+
(d)
(1)
C3H5O– +[Ni(OH)(H2O)(x-1)]+→Ni(OH)C3H5O3 yH2O+(x–1–y)H2O
.
3
NO+½O2→NO2
(2)
From this reactions one may notice the necessity of the presence of protons in-
volved in the (c) stage in order to potentiate the oxidation activity of the nitrate ion.
The necessary protons are generated by Ni(II) hydrated cation hydrolysis, as shown
in the (d) process.
J. Therm. Anal. Cal., 63, 2001