Comparison on thermal decomposition of propionate, benzoate and their chloroderivative salts of Zn(II)

Article abstract of DOI:10.1023/B:JTAN.0000027173.40363.58

The thermal decompositions of propionates, benzoates Zn(II), their chloroderivate and complexes with thiourea have been studied by the means of TG, DTG, DTA, IR and XRD-powder diffraction methods. The investigated decompositions are compared and the resul

Full text of DOI:10.1023/B:JTAN.0000027173.40363.58

Journal of Thermal Analysis and Calorimetry, Vol. 75 (2004) 773–780
COMPARISON ON THERMAL DECOMPOSITION OF
PROPIONATE, BENZOATE AND THEIR
CHLORODERIVATIVE SALTS OF Zn(II)
1
2*
1
J. Skoršepa , E. Godo¹íková and J. ‡ernák
1
Department of Inorganic Chemistry, Faculty of Sciences, P. J. Šafárik University, Moyzesova 11,
0
41 54 Košice, Slovakia
2
Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 043 53 Košice, Slovakia
(
Received February 28, 2003; in revised form November 14, 2003)
Abstract
The thermal decompositions of propionates, benzoates Zn(II), their chloroderivate and complexes
with thiourea have been studied by the means of TG, DTG, DTA, IR and XRD-powder diffraction
methods. The investigated decompositions are compared and the results are presented in this report.
The results showed different features of thermal decomposition of Zn(II) halogenpropionate and
halogenbenzoate. In the case of Zn(II) halogenpropionate the presence of halogen effects different fea-
tures of thermal decomposition and changes character of the final products. In the case of halogen-
benzoate Zn(II) the halogen does not influence neither the character of decomposition nor the charac-
ter of final products.
Keywords: benzoate, thermal decomposition, zinc complexes, zinc propionate
Introduction
Zinc carboxylates [Zn(RCOO) ] with or without additional ligands introduces inter-
2
esting group of compounds with the potential biological activity [1, 2]. Details of
preparation, identification and thermal properties of some carboxylates and halogen-
carboxylates Zn(II) with organic ligands have been already described in the literature
[
3–8]. The group of propionates, benzoates Zn(II) and their chloroderivates with
thiourea is studied in this paper. The influence of presence of the halogen and
thiourea and the carboxylate type on character of thermal decomposition and the
character of final products is compared. The compounds of the following formulae
were investigated:
[
Zn(prop)
2
]
[Zn(benz)
]
2
[
Zn(prop) tu ]
[Zn(benz) tu ]
2
2
2
2
*
Author for correspondence: E-mail: godocik@saske.sk
1
388–6150/2004/ $ 20.00
Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht
©
2004 Akadémiai Kiadó, Budapest

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SKORžEPA et al.: ZINC COMPLEXES
[
Zn(3-Cl-prop)2]
[Zn(2-Cl-benz)2]
[
Zn(3-Cl-prop) tu ]
[Zn(2-Cl-benz) tu ]
2
2
2
2
–
–
(
tu=CS(NH ) , prop=C H COO , benz=C H COO )
2 2 2 5 6 5
Experimental
Synthesis of [Zn(RCOO) ] and [Zn(RCOO) tu ] type salts
2
2
2
The preparation of the studied compounds may be represented by the following reac-
tions:
ZnSO4(aq)+2NaOH(aq) → Zn(OH)2(s)+Na SO
(1)
(2)
(3)
(4)
(5)
2
4(aq)
Zn(OH)2(s)+2RCOOH(aq) → [Zn(RCOO) ] +2H O
2 (aq)
2
Crystallisation
[
Zn(RCOO)2](aq)   → [Zn(RCOO) ]
2 (s)
[
Zn(RCOO)2](aq)+2tu(aq) → [Zn(RCOO) tu ]
2
2 (aq)
Crystallisation
[
Zn(RCOO) tu ]   → [Zn(RCOO) tu ]
2
2 (aq)
2
2 (s)
The Zn(OH) was prepared from ZnSO ⋅7H O (0.053 mol) with stoichiometric
2
4
2
amount of NaOH (0.105 mol) after filtrating and washing with water Eq. (1). Prepared
Zn(OH) was dissolved in stoichiometric amounts of free carboxylic acids and evapo-
2
rated up to the crystallisation in the water bath and then at the room temperature
Eqs (2), (3). In the case of the [Zn(RCOO) tu ] synthesis, the [Zn(RCOO) ] solution
2
2
2
prepared with the mentioned method above Eq. (2) was treated with stoichiometric
amounts of thiourea and evaporated up to crystallisation at the room temperature
Eqs (4), (5). The reached products of crystallisation were dried over silicagel with the
yield amounts of 20–30%. Zinc was determined complexometrically.
Infrared spectroscopy
The infrared spectra of the investigated compounds were measured in the re-
–
1
gion 4000–400 cm on a Specord M-80 spectrometer by using the KBr technique.
The characteristic wavenumbers for the individual compounds are given in Table 1.
Thermal measurements
The thermal decompositions of the investigated compounds were performed on a
Derivatograph OD-102 under the following experimental conditions: massed
–
1
amount – 100 mg; TG – 100; DTA – 1/10; ceramic crucible; heating rate 9°C min ;
static air atmosphere. The courses of thermal decomposition of the investigated com-
pounds are presented in Figs 1, 2.
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X-ray powder diffraction
The final products of decomposition have been identified by X-ray diffractometry us-
ing CuKα radiation. The results have been compared with JCPDS tables
(
Zn – JCPDS-04-0831), ZnO – JCPDS-80-0075).
Results and discussion
The preparation of the investigated compounds exhibits a number of common fea-
tures with the preparation of similar carboxylates and halogencarboxylates [9]. How-
ever, some differences resulted from halogencarboxylic acids properties such as dis-
solution etc., have to be mentioned in this connection.
The presence of characteristic vibration of the studied compounds was proved
by IR spectroscopy. IR spectra of the investigated compounds are shown in Table 1.
Table 1 contains only bands of characteristic vibration which are in accordance with
the literature.
The thermal decompositions have shown that only compounds [Zn(prop) ] and
2
[
Zn(benz) ] have decompositions in a one step, as it follows from Figs 1 and 2. All
2
the other compounds are characterised by the decomposition in two steps.
On the basis results presented in Table 2 and in accordance with thermal decom-
positions of acetates and halogenacetates described in work [10] it is possible to sug-
gest the following decompositions scheme.
1
50–350°C
>350°C
[
[
Zn(C
2
H
5
COO)
2
] → (C
2
H
5
)
2
CO+CO
2
→ ZnO(s)
110–260°C
300–600°C
Zn(CH ClCH COO) ] → CH ClCHO+CO →
2
2
2
2
>600°C
CH CHO+1/2H O+1/2CO+1/2ZnCl → 1/2Zn
3
2
2
(s)
1
10–300°C
330–600°C
[
[
Zn(C H COO) tu ] → 2tu+1/2(C H ) CO+1/2CO →
2
5
2
2
2
5 2
2
>600°C
1
/2(C H )2CO+1/2CO → ZnO
2
5
2
(s)
110–320°C
320–600°C
Zn(CH ClCH COO) tu ] → 2tu+1/2CH ClCH CHO+CO →
2
2
2
2
2
2
>600°C
1
/2CH ClCHO+CH CHO+CO+1/2ZnCl +1/2CO → 1/2Zn
2
3
2
2
(s)
1
80–250°C
>500°C
[
[
[
[
Zn(C H COO) ] → (C H ) CO+CO → ZnO
6
5
2
6
5 2
2
(s)
1
70–360°C
400–700°C
>700°C
Zn(C H COO) tu ] → 2tu+(C H ) CO → CO → ZnO
6
5
2
2
6
5 2
2
(s)
150–400°C
400–700°C
>700°C
Zn(2Cl–C H COO) ] → (C H Cl) CO → CO → ZnO
6
4
2
6
4
2
2
(s)
170–340°C
340–680°C
Zn(2Cl–C H COO) tu ] → 2tu+(C H Cl) CO → CO
6
4
2
2
6
4
2
2
>
680°C

→ ZnO(s)
For confirmation of the intermediate composition it is suitable to use IR spec-
troscopy, XRD-powder diffraction, mass spectrometry and chromatographic mea-
surements combined with IR spectroscopy and XRD-powder diffraction. In our case
the IR spectroscopy was used. The suggested thermal decompositions of prepared
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SKORžEPA et al.: ZINC COMPLEXES
777
2
Fig. 1 Thermal decomposition of the studied compounds: 1 – [Zn(prop) ],
2
2 2 2 2 2
– [Zn(prop) tu ], 3 – [Zn(3-Cl-prop) ], 4 – [Zn(3-Cl-prop) tu ]
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SKORžEPA et al.: ZINC COMPLEXES
2
Fig. 2 Thermal decomposition of the studied compounds: 1 – [Zn(benz) ],
2
2 2 2 2 2
– [Zn(benz) tu ], 3 – [Zn(2-Cl-benz) ], 4 – [Zn(2-Cl-benz) tu ]
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SKORžEPA et al.: ZINC COMPLEXES
compounds are in accordance with IR spectral data of the presumed intermediates. IR
spectral data of the intermediates are not presented in this paper. The results pre-
sented in Table 2 and Figs 1 and 2 refer to different features of the thermal decompo-
sitions of propionates, benzoates and their chloroderivates.
In the case of propionates without a presence of Cl the final product of decompo-
sition is ZnO. The Cl presence causes the formation of ZnCl during thermal decompo-
2
sition. Consequently, the created ZnCl is evaporated (ZnCl m.p. 262°C, b.p. 732°C)
2
2
thus Zn remains as the final product.
In the case that Cl is not present, the organic components are released in a form
of ketones. Otherwise (in Cl presence) they are released as aldehydes. Similar de-
compositions of Zn(II) acetates have been observed [10–12].
Benzoates and chlorobenzoates of Zn(II) are decomposed in the same way, the
organic compounds are released in the form of ketones, irrespective of the Cl pres-
ence ZnO has been identified using the XRD-powder diffraction as the final product.
The common feature of the decompositions is the fact that thiourea is always re-
leased during the first step of decompositions [13].
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