Calorimetric and thermal investigation of metal derivatives of 6-aminopicolinic acid

Article abstract of DOI:10.1023/A:1010149324423

The comparison of thermal and calorimetric properties of metal derivatives of 6-aminopicolinic acid (APH) is presented. The salts and complexes of APH with Cr(III), Cd(II), Cu(II), Ni(II), Pb(II), Co(II) and Ag(I) have been studied by TG-DTA and DSC methods up to 1200 °C in a nitrogen atmosphere. Decomposition processes are proposed. The decarboxylation, deamination and carbonation of the organic fragments of molecules take place. The compounds decompose to metal or to metal oxides. The values of the transition enthalpy were determinated.

Full text of DOI:10.1023/A:1010149324423

Journal of Thermal Analysis and Calorimetry, Vol. 60 (2000) 163–166
CALORIMETRIC AND THERMAL INVESTIGATION OF
METAL DERIVATIVES OF 6-AMINOPICOLINIC ACID
B. Kowalczyk
Institute of Chemistry, Pedagogical University, 42-201 Czêstochowa, Poland
Abstract
The comparison of thermal and calorimetric properties of metal derivatives of 6-aminopicolinic acid
(APH) is presented. The salts and complexes of APH with Cr(III), Cd(II), Cu(II), Ni(II), Pb(II),
Co(II) and Ag(I) have been studied by TG-DTA and DSC methods up to 1200°C in a nitrogen atmo-
sphere. Decomposition processes are proposed. The decarboxylation, deamination and carbonation
of the organic fragments of molecules take place. The compounds decompose to metal or to metal
oxides. The values of the transition enthalpy were determinated.
Keywords: comparison, decomposition, DSC, enthalpy
Introduction
There was no clear effect of the type of the metal ion on the thermal behaviour of
6-aminopicolinic acid (APH) metal derivatives. There seemed to be an interest in ex-
amining and comparing the thermal properties of these compounds. According to an
IR study, all metal derivatives (except of copper complex) are APH salts [1]. In the
present work the derivatives of APH with Cr(III), Cd(II), Cu(II), Ni(II), Pb(II), Co(II)
and Ag(I) have been studied by the TG-DTA method, and by the DSC method in ni-
trogen atmosphere, at temperatures up to 1200°C. The thermal decomposition pro-
cess was performed by using the Netzsch STA 409 simultaneous thermal analyzer, at
a heating rate 10 K min–1. The mass changes and transformation energetics of the
samples were measured. Data acquisition and evaluation were carried out by using a
standard software package. The analyses of the decomposition processes and those of
the solid products were carried out by using X-ray diffraction, qualitative analysis
methods, the results obtained by thermal analysis [1] and literature data [2–4]. The re-
sults of thermal analysis of Mn, Pb and Cr picolinates, obtained by Setaram thermal
analyzer, were reported previously [5, 6].
Results and discussion
The thermodynamic parameters of the main thermal degradation process of the stud-
ied compounds are presented in Table 1. The graphs of the TG and DSC measure-
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164
KOWALCZYK: METAL DERIVATIVES OF 6-AMINOPICOLINIC ACID
Fig. 1 TG curves of APH metal derivatives
Fig. 2 DSC curves of Cr, Cd, and Cu derivatives with APH
ments are shown in Fig. 1 and Figs 2–4, respectively. The main decomposition pro-
cess takes places between the temperatures of 280–500°C and its character is always
endothermic. The following mode of thermal decomposition of the studied metal
picolinates may be proposed:
240−350o
–6APH, –CO2 , –2-NH2Py
C
350−550o
C
(C6H6N2O2)3Cr 6APH
(C6H6N2O2)2Cr
forms Cr2O3 (0.5)
determination
The total mass loss observed on TG curve is 96.5%, the calculated value being
96.1%.
350−500o
–2CO2 , –2 2-NH2Py
C
(C6H6N2O2)2Cu
forms CuO, partial decomposition to Cu.
J. Therm. Anal. Cal., 60, 2000

KOWALCZYK: METAL DERIVATIVES OF 6-AMINOPICOLINIC ACID
165
The observed total mass loss is 77.3, the calculated 80.0%.
140−210o
–CO
C
430−520o
–CO2 , –2 2-NH2Py
C
(C6H6N2O2)2Ni
(C5H6N2O)2Ni
forms NiO.
The calculated mass losses in the particular decomposition steps are 8.4 and
62.4%, the recorded values are 7.2 and 60.2%, respectively.
270−360o
–CO2 , –2-NH2Py
C
C6H6N2O2Ag
forms Ag2O (0.5), decomposition Ag2O to Ag
The mass loss, according to TG curve, is 48.4, the calculated one is 51.7%.
Fig. 3 DSC curves of Ni and Pb picolinates
Fig. 4 DSC curves of Co and Ag picolinates
Table 1 Thermodynamic parameters of thermal decomposition from TG and DSC curves
Transition
Tonset/°C
T
max peak endo/°C
Compound
Mass loss/%
enthalpy/kJ mol–1
(AP)3Cr 6APH
(AP)2Cd
241.4
359.4
281.5
418.3
292.5
382.5
276.2
307.3
408.1
344.8
450.9
326.6
429.7
322.6
82.71
39.07
63.33
48.07
32.35
45.45
42.92
85.19
55.81
(AP)2Cu
50.72
(AP)2Ni
46.97
(AP)2Pb
39.12
(AP)2Co H2O
(AP) Ag
29.59
11.49
J. Therm. Anal. Cal., 60, 2000

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KOWALCZYK: METAL DERIVATIVES OF 6-AMINOPICOLINIC ACID
The thermal stability of metal picolinates is similar in general, the thermal deg-
radation of the studied compounds consists of the following processes: decarboxy-
lation, loss of the organic molecules (mostly 2-NH2Py) [1], forming metal oxides,
carbonation of the organic parts of molecules, and partial decomposition of metal ox-
ides to metal. The decomposition of Cd, Co and Pb derivatives with 6-aminopicolinic
acid proceeds more slowly. The differences observed on TG curves of these metal de-
rivatives are probably caused by the difficulties and different intensity in carrying
away the gaseous molecules, and the different density of new phases formed during
the decomposition processes. The Cd, Co, and Pb picolinates decompose to the mix-
ture of metal and metal oxides. The DSC peak of Cu(II) compound is distinctly dif-
ferent from other DSC peaks, it is the highest and sharpest one. Probably, this fact is
due to the complex structure of the Cu derivative, opposite to other metal derivatives
which are picolinates.
References
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2 W. W. Wendlandt and J. P. Smith, The Thermal Properties of Transition Metal Amine Com-
plexes, Elsevier, Amsterdam 1967.
3 D. Czakis-Sulikowska, J. Radwañska-Doczekalska, B. Ku¿nik and A. Malinowska, Transition
Met. Chem., 21 (1996) 19.
4 F. Rodante, G. Marossu and G. Katalani, Thermochim. Acta, 194 (1992) 197.
5 B. Kowalczyk, Calorimetry, Experimental Thermodynamics and Thermal Analysis Conference
CETTA’97, Zakopane p. 179.
6 B. Kowalczyk, W. Baran and K. Chaczatrian, Monatshefte für Chemie, 129 (1998) 473.
J. Therm. Anal. Cal., 60, 2000