Thermal behaviour of succinic acid, sodium succinate and its compounds with some bivalent transitions metal ions in dynamic N2 and CO2 atmospheres

ARTICLE

Thermal behaviour of succinic acid, sodium succinate and its compounds with some bivalent transitions metal ions in dynamic N₂ and CO₂ atmospheres

CF. J. Caires; L. S. Lima; C. T. Carvalho; M. Ionashiro^*

Instituto de Química, UNESP, CP 355, CEP 14801-970, Araraquara, SP, Brazil

ABSTRACT

Thermal stability and thermal decomposition of succinic acid, sodium succinate and its compounds with Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) were investigated employing simultaneous thermogravimetry and differential thermal analysis (TG-DTA) in nitrogen and carbon dioxide atmospheres and TG-FTIR in nitrogen atmosphere. On heating, in both atmospheres the succinic acid melt and evaporate, while for the sodium succinate the thermal decomposition occurs with the formation of sodium carbonate. For the transition metal succinates the final residue up to 1180 ºC in N₂ atmosphere was a mixture of metal and metal oxide in no simple stoichiometric relation, except for Zn compound, where the residue was a small quantity of carbonaceous residue. For the CO₂ atmosphere the final residue up to 980 ºC was: MnO, Fe₃O₄, CoO, ZnO and mixtures of Ni, NiO and Cu, Cu₂O.

Keywords: bivalent transitions metals, succinate, thermal behavior.

RESUMO

A estabilidade e a decomposição térmica do ácido succínico, succinatos de sódio, Mn(II), Fe(II), Co(II), Ni(II), Cu(II) e Zn(II) foram investigados empregando termogravimetria e análise térmica diferencial simultânea (TG-DTA) em atmosferas de nitrogênio e dióxido de carbono e TG-FTIR em atmosfera de nitrogênio. Sobre aquecimento em ambas as atmosferas o ácido succínico funde e evapora, enquanto para o succinato de sódio a decomposição térmica ocorre com a formação de carbonato de sódio. Para os succinatos de metais de transição o resíduo final até 1180 ºC em atmosfera de N₂ foi uma mistura de metal e óxido de metal sem relação estequiométrica, exceto para o composto de zinco, onde o resíduo foi uma pequena quantidade de resíduo de carbono. Para a atmosfera de CO₂ o resíduo final até 980 ºC foi: MnO, Fe₃O₄, CoO, ZnO e misturas de Ni, NiO e Cu, Cu₂O.

Introduction

Preparation and investigation on the thermal behaviour and thermal decomposition of several metal-ion succinates have been reported. These papers are concerned with the thermal decomposition of bivalent succinates in the solid-state [1], the thermal, spectral and magnetic studies of succinic acid and compounds of some transition metal ions [2], thermal dehydration of manganese (II) dicarboxylate hydrates [3], synthesis, properties and thermal decomposition of Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) succinates [4], a study of the thermal decomposition of Cu(II) and Zn(II) malonate, maleate and succinate complex [5] and a comparative study on the thermal decomposition of some transition metal carboxylates [6]. As continuation of our previous study on thermal behavior of succinic acid, sodium succinate and its compounds with some bivalent transition metal ions in air atmosphere [7], this paper deals with the thermal behavior and thermal decomposition of these compounds in dynamic N₂ and CO₂ atmospheres.

Experimental

The succinic acid C₄H₆O₄, and its sodium salt Na₂C₄H₄O₄ ·6H₂O, both with 99% purity were obtained from Sigma.

Solid state Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) compounds were prepared by mixing the aqueous suspension of the corresponding metal carbonates in excess with 50.0 mL of succinic acid 0.10 mol L^-1 solution, and heated slowly up to near ebullition, until total neutralization of the acid. The carbonate in excess was removed by filtration and the aqueous solution of the respective metal succinates were evaporated to near dryness in a water bath, dried in air and kept in a desiccator over anhydrous calcium chloride. To avoid the oxidation of Fe(II), all the solutions, as well as the evaporation of the solution in water bath were purged with nitrogen gas.

In the solid-state compounds, metal ions, hydration water and succinate contents were determined from TG curves. The metal ions were also determined by complexometry with standard EDTA solution, after igniting the compounds to the respective oxides and their dissolution in hydrochloric acid solution [8].

Carbon and hydrogen contents were determined by microanalytical procedures, with an EA 1110 CHNS-O Elemental Analyser from CE Instruments.

Simultaneous TG-DTA curves were obtained with the thermal analysis system, model SDT 2960 from TA Instruments. The purge gases were nitrogen and carbon dioxide flow of 100 mL min^-1. A heating rate of 20 ºC min^-1 was adopted, with sample weighing about 7 mg and alumina crucible was used for recording the TG-DTA curves.

The measurements of the gaseous products were carried out using a Thermogravimetric Analyzer Mettler TG-DTA coupled to a FTIR spectrophotometer Nicolet is10, with gas cell and DTGS KBr detector. The furnace and the heated gas cell (250 ºC) were coupled through a heated (T = 200 ºC) 120 cm stainless steel line transfer with diameter of 2 mm, both purged with dry nitrogen (50 mL min^-1). The FTIR spectra were recorded with 32 scans per spectrum at a resolution of 4 cm^-1.

Results and Discussion

Succinic acid

The TG-DTA curves and infrared spectrum of the released product during the heating of succinic acid in N₂ and CO₂ atmospheres are shown in Fig.1. The TG-DTA curves, Fig 1a and 1b show mass loss in single step between 165 and 260 ºC (N₂, CO₂) corresponding to the endothermic peaks at 194 and 247 ºC (N₂) or 194 and 250 ºC (CO₂), attributed to the fusion and evaporation of succinic acid, respectively. The product evaporated was monitored and identified mostly on base of their FTIR reference available on Nicolet libraries, as shown in Fig 1c.

Sodium Succinate hexahydrated

For the sodium succinate hexahydrated, the TG-DTA curves in N₂ and CO₂ atmospheres are shown in Fig. 2a and 2b, respectively. These curves show mass losses in two steps and thermal events corresponding to these losses or due to physical phenomenon. The first mass loss between 30 - 130 ºC (N₂) and 30 - 150 ºC (CO₂), corresponding to an endothermic peak at 85 ºC (N₂, CO₂) is due to dehydration with loss of 6H₂O (Calcd. 40.02 %, TG = 39.86 % (N₂), 40.20 %(CO₂)). The endothermic peak at 410 ºC (N₂, CO₂), without mass loss in TG curve is due to fusion of the compound. In both atmospheres the anhydrous compound is stable up to 425 ºC and above this temperature the mass loss occurs between 425 - 525 ºC (N₂) or 425 - 540 ºC (CO₂) with loss of 18.52 % (N₂) and 18.42 % (CO₂), corresponding to the exothermic peak at 490 ºC attributed to the decarboxylation with formation of sodium carbonate accompanied by carbonaceous residue.

Transition metal succinates

TG-DTA Curves

The analytical and thermoanalytical (TG) data for the synthesized compounds are shown in table 1. These results permitted to establish the stoichiometry of these compounds, which are in agreement with the general formula, MC₄H₄O₄.nH₂ O, where M represents Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II), C₄H₄O₄ is succinate and n = 0 (Cu, Zn), 1 (Fe), 2 (Mn), 3 (Co) or 3.5 (Ni).

The simultaneous TG-DTA curves of these compounds obtained in N₂ and CO₂ atmospheres are shown in Fig. 3. These curves show mass losses or gain in two up to six steps, corresponding to endothermic peaks due to dehydration or pyrolysis of the anhydrous compounds and exothermic peaks attributed to physical phenomenon.

The thermal stability of the anhydrous compounds, in both atmospheres, as shown by the TG-DTA curves depends on the nature of the metal ion and they follow the order:

Zn > Co > Ni > Mn > Cu > Fe

For each compound a great similarity is observed concerning the TG-DTA profiles around 400 ºC, in both atmospheres and above this temperature the thermal decomposition depend on the nature of the purge gas used and so the features of each of these compounds are discussed individually.

Manganese compound. The simultaneous TG-DTA curves in N₂ and CO₂ atmospheres are shown in Fig. 3a and 3a*, respectively. The first mass loss between 70 and 230 ºC, corresponding to an endothermic peak at 110 ºC in both atmospheres is due to the dehydration with loss of 2 H₂O (Calcd. 17.41 %, TG = 17.70 % (N₂), 17.35 % (CO₂)). The exothermic peak at 315 ºC observed in both atmospheres is attributed to the crystallization process, as shown in Fig. 4.

The thermal decomposition of the anhydrous compound in N₂ atmospheres occurs in three steps between 320 - 410 ºC, 410 - 510 ºC and 510 - 1150 ºC, with losses of 13.08 % , 19.45 % and 17.50 %, respectively, corresponding to the endothermic peaks at 400 ºC, 455 ºC and 1100 ºC attributed to the thermal decomposition, with formation of a mixture of Mn and MnO in no simple stoichiometric relation.

For the CO₂ atmospheres, the thermal decomposition also occurs in three steps between 320 - 410 ºC, 410 - 505 ºC and 505 - 830 ºC, with losses of 12.34 %, 20.68 % and 15.67 %, corresponding to the endothermic peaks at 400 ºC, 480 ºC and 790 ºC with formation of MnO as final residue (Calcd. = 65.74 %, TG = 66.04 %).

Iron Compound. The simultaneous TG-DTA curves in N₂ and CO₂ atmospheres are shown in Fig. 3b and 3b*, respectively. The first mass loss between 70 - 215 ºC (N₂) and 70 - 225 ºC (CO₂), corresponding to the endothermic peak at 200 ºC (N₂) and 205 ºC (CO₂) is due to dehydration with loss of 1 H₂O (Calcd. = 9.49 %, TG = 9.24 % (N₂), 9.63 % (CO₂)).

The thermal decomposition of the anhydrous compound in N₂ atmosphere, occurs in four steps between 215 - 300 ºC, 300 - 480 ºC, 565 - 635 ºC and 635 - 900 ºC, corresponding to the endothermic peaks at 295 ºC and 605 ºC, with losses of 9.25 %, 26.78 %, 19.13 % and 6.06 %, respectively. Calculations based on the mass losses observed up to 900 ºC, are in agreement with the formation of Fe (Calcd. = 70.59 %, TG = 70.46 %). The mass gain (5.66 %) observed between 900 and 1180 ºC is attributed to the partial oxidation of Fe with formation a mixture of Fe and FeO. No thermal event is observed corresponding to the second and fourth mass losses, probably because endothermic and exothermic events must to occur simultaneously and the net heat or the small heat involved in these steps is insufficient to produce a thermal event.

For the CO₂ atmosphere, the thermal decomposition occurs in three steps between 225 - 300 ºC, 300 - 480 ºC and 500 - 800 ºC, corresponding to the endothermic peaks at 295 ºC, 355 ºC, 455 ºC and 760 ºC, with losses of 9.97 %, 25.78 % and 34.95 %, respectively. The mass losses up to 800 ºC, suggest the formation of a mixture of FeO and Fe₃O₄. The mass gain (1.12 %) observed between 800 and 980 ºC is attributed to the oxidation of FeO with the formation of Fe₃O₄, as final residue (Calcd. = 59.37 %, TG = 59.61 %).

Cobalt Conpound. The simultaneous TG-DTA curves in N₂ and CO₂ atmospheres are shown in Fig. 3c and 3c*, respectively. The first mass loss between 70 and 200 ºC, corresponding to an endothermic peak at 140 ºC, in both atmospheres is due to dehydration with loss of 3 H₂O (Calcd. 23.60 %, TG = 23.45 % (N₂), 23.29 % (CO₂)). The exothermic peak at 290 ºC (N₂, CO₂) without mass loss in the TG curve is attributed to the irreversible solid phase transition, which was confirmed by X-ray powder, with sample before and after the exothermic peak.

The thermal decomposition of the anhydrous compound in N₂ occurs in two steps between 365 - 520 ºC, corresponding to the endothermic peak at 465 ºC and 520 - 1180 ºC, with losses of 41.40 % and 6.90 %, respectively. No thermal event corresponding to the second mass loss in observed in the DTA curve, probably because the small mass loss occurs so slowly that the heat involved in this step is not sufficient to produce a thermal event. Calculations based on the mass losses up to 510 ºC suggest the formation of Co₃O₄ (Calcd. = 64.69 %, TG = 64.32 %) and up to 1180 ºC a mixture of Co and CoO, in no simple stoichiometric relation.

For the CO₂ atmosphere the thermal decomposition occurs in two steps between 375 - 480 ºC and 480 - 575 ºC, corresponding to the endothermic peaks at 470 ºC and 545 ºC, with losses of 32.91 % and 19.17 %, respectively. The total mass loss up to 575 ºC is in agreement with the formation of Co as final residue (Calcd. = 74.27 %, TG = 74.57 %). The mass gain (5.07 %) observed between 575 - 980 ºC is attributed to the partial oxidation of Co with the formation of a mixture of Co and CoO.

Nickel Compound. The simultaneous TG-DTA curves in N₂ and CO₂ atmospheres are shown in Fig. 3d and 3d*, respectively. The first mass loss between 70 - 250 ºC, corresponding to an endothermic peak at 155 ºC in both atmospheres is attributed to the dehydration with loss of 3.5 H₂O (Calcd. = 26.51 %, TG = 26.77 % (N₂), 26.76 % (CO₂)). The thermal decomposition of the anhydrous compound occurs in two steps between 360 - 430 ºC (N₂, CO₂) and 430 - 1180 ºC (N₂) or 430 - 560 ºC (CO₂), corresponding to endothermic peaks at 405 ºC (N₂) or 415 ºC and 540 ºC (CO₂), with losses of 41.40 % and 6.90 % (N₂) or 40.80 % and 8.66 %, respectively. The total mass losses up to 1180 ºC (N₂) suggest the formation of a mixture of Ni and NiO and up to 560 ºC (CO₂) is in agreement with Ni (Calcd. = 75.32 %, TG = 75.22 %). The mass gain (2.72%) observed between 560 - 980 ºC (CO₂) is attributed to the partial oxidation of Ni to a mixture of Ni and NiO.

Copper Compound. The simultaneous TG-DTA curves in N₂ and CO₂ atmospheres are shown in Fig. 3e and 3e*, respectively. These curves show that the anhydrous compound is stable up to 305 ºC, in both atmospheres and above this temperature the thermal decomposition occurs in three steps. These curves also show that the first two steps occur through fast processes and overlapping one between 305 - 375 ºC and 375 - 420 ºC, corresponding to the endothermic peaks at 365 ºC and 400 ºC (N₂, CO₂) with losses of 27.77 % and 31.80 % (N₂) or 30.60 % and 30.79 % (CO₂). Calculations based on the mass losses up to 420 ºC suggest the formation a mixture of Cu and CuO. The last step that occurs through a slow process between 420 - 1000 ºC (N₂) or 420 - 750 ºC (CO₂) with losses of 0.7 % and 3.15 %, respectively, is attributed to the reduction of the mixture (Cu, CuO) to Cu, as final residue (Calcd. = 64.22 %, TG = 64.48 % (N₂), 64.54 % (CO₂). The endothermic peak at 1090 ºC (N₂) is due to the fusion of Cu.

Zinc Compound. The simultaneous TG-DTA curves in N₂ and CO₂ atmospheres are shown in Fig. 3f and 3f*, respectively. These curves show that the anhydrous compound is stable up to 430 ºC and above this temperature the thermal decomposition occurs in two steps between 430 - 535 ºC and 535 - > 1080 ºC (N₂) or 430 - 525 ºC and 525 - 885 (CO₂), corresponding to the endothermic peaks at 505 ºC, 1020 ºC and 1050 ºC (N₂) or 505 ºC and 885 ºC (CO₂), with losses of 40.10 % and 51.95 % (N₂) or 41.88 % and 13.08 % (CO₂).

For the CO₂ atmospheres the mass lost up to 885 ºC is in agreement with the formation of ZnO as final residue (Calcd. = 55.16 %, TG = 54.95 %). For the N₂ atmospheres in the last step occurs the reduction of Zn(II) to Zn followed by ebullition (boiling point = 907 ºC). The final residue (7.95 %) up to 1080 ºC is attributed to the carbonaceous residue, which was confirmed after to analysis the crucible residue.

The mass gain attributed to the oxidation reaction of Fe to FeO in N₂ atmosphere or Co to CoO and Ni to NiO in CO₂ atmosphere occurs, probably because the equipment is not hermetically sealed and/or a trace of oxygen in the N₂ or CO₂ which were used as purge gas.

Evolved gas analysis

The gaseous products evolved during the thermal decomposition in dynamic nitrogen atmosphere of the sodium and transition metal ion compounds studied in this work were monitored by FTIR and identified on basis of their FTIR references available on Nicolet libraries. For the sodium succinate the gaseous products evolved during a thermal decomposition were identified as methane, acetone, CO, and CO_2; for the cobalt and nickel compounds were methane, propanoic acid, CO, and CO₂; for the copper compound were propenoic acid, CO, and CO₂ and for the manganese, iron, and zinc compounds were methane, CO and CO₂. The IR spectra of the gaseous products evolved during the thermal decomposition of sodium, manganese, nickel and copper as representative of other compounds, are shown in Fig. 4.

Conclusion

The present study showed that the succinic acid melt and evaporate, without decomposition.

In the sodium and all the synthesized compounds, the evolved products during the thermal decomposition in nitrogen atmosphere was CO and CO₂, besides methane and acetone for sodium succinate, propanoic acid for cobalt and nickel compounds and propenoic acid for nickel compound.

Acknowledgements

The authors thank FAPESP, CAPES and CNPq foundations (Brazil) for financial support.

• [1] H. Yokobayashi, K. Nagase, K. Muraishi, Bull. Chem. Soc. Jpm. 48 (1975) 2789.
• [2] J. R. Allan, B. R. Carson, Thermochim. Acta 158 (1990) 91.
• [3] Y. Suzuki, Thermochim. Acta 255 (1995) 155.
• [4] W. Brzyska, B. Galkowska, Polish J. Chem. 72 (1998) 498.
• [5] A. K. Nikumbh, S. K. Pardeshi, M. N. Raste, Thermochim. Acta 374 (2001) 115.
• [6] B. S. Randhawa, K. Gandotra, J. Therm. Anal. Cal. 85 (2006) 417.
• [7] F. J. Caires, L. S. Lima, C. T. Carvalho, M. Ionashiro, Thermochim. Acta 500 (2010) 6.
• [8] C. N. de Oliveira, M. Ionashiro, C. A. F. Graner, Ecl. Quim 10 (1985) 7.

Publication Dates

• Publication in this collection
  23 Aug 2011
• Date of issue
  2010