Research of thermal decomposition of hydrated methanesulfonates

Article abstract of DOI:10.1023/B:JTAN.0000041661.57570.83

Hydrated methanesulfonates Ln(CH₃SO₃) ₃·nH₂O (Ln=La, Ce, Pr, Nd and Yb) and Zn(CH ₃SO₃)₂·nH₂O were synthesized, The effect of atmosphere on thermal decomposition produ

Full text of DOI:10.1023/B:JTAN.0000041661.57570.83

Journal of Thermal Analysis and Calorimetry, Vol. 77 (2004) 825–831
RESEARCH OF THERMAL DECOMPOSITION OF
HYDRATED METHANESULFONATES
J. Tian, H. Jiang*, H. Gong and Z. Sun
College of Petrochemical Engineering, Liaoning University of Petroleum & Chemical
Technology, Fushun 113001, P. R. China
(Received July 25, 2003; in revised form March 22, 2004))
Abstract
Hydrated methanesulfonates Ln(CH3SO3)3⋅nH2O (Ln=La, Ce, Pr, Nd and Yb) and Zn(CH3SO3)2·nH2O
were synthesized. The effect of atmosphere on thermal decomposition products of these methane-
sulfonates was investigated. Thermal decomposition products in air atmosphere of these compounds
were characterized by infrared spectrometry, the content of metallic ion in thermal decomposition
products were determined by complexometric titration. The results show that the thermal decomposition
atmosphere has evident effect on decomposition products of hydrated La(III), Pr(III) and Nd(III)
methanesulfonates, and no effect on that of hydrated Ce(III), Yb(III) and Zn(II) methanesulfonates.
Keywords: infrared spectra, methanesulfonate, rare earths, thermal decomposition
Introduction
The trifluoromethanesulfonate is a kind of Lewis acid catalyst with good waterfast
ability, to which are paid attention in recent years. It is stable and active under common
conditions (acidic conditions and room temperature) in organic synthesis. The main
advantages of this kind of catalyst in organic synthesis are to improve reactivity and
selectivity, simplify separation and recycle the catalysts. It is used for acrylation [1],
alkylation [2], nitration [3] and oxidation [4], and good effects have been obtained.
However, because of expensive price of triflate acid, its application is limited. In our
lab, methanesulfonic acid is used to replace triflate acid to synthesize some
methanesulfonates which are used for esterification and alkylation. Here six kinds of
hydrated methanesulfonates were synthesized. They can be represented by general
formula: Ln(CH3SO3)3⋅nH2O; Ln=La, Ce, Pr, Nd, Yb and Zn(CH3SO3)2⋅nH2O; n –
number of crystal water. Number of crystal water was determined by thermo-
gravimetry, thermal decomposition products of these compounds in nitrogen and air
atmosphere were also investigated. The thermal decomposition products in air
atmosphere were characterized by infrared spectrometry, the content of metallic ion in
*
Author for correspondence: E-mail: hjiang78@hotmail.com
1388–6150/2004/ $ 20.00
Akadémiai Kiadó, Budapest
© 2004 Akadémiai Kiadó, Budapest
Kluwer Academic Publishers, Dordrecht

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these thermal decomposition products was determined by complexometric titration.
The effect of atmosphere on the thermal decomposition products was investigated.
Experimental
Materials and sample preparation
All reagents and oxides in this experiment are chemically pure.
Preparation of hydrated La(III), Pr(III), Nd(III), Yb(III) and Zn(II) methane-
sulfonates: metal oxides and methanesulfonic acid were, respectively, weighed in 1:6
mole ratio (ZnO and methanesulfonic acid in 1:2). Then CH3SO3H–H2O(V/V=1:1)
were added into reactor, oxides were added slowly with stirring for 1 h under the
condition of heating and reflux. After evaporation of the water, the solid was dried in
vacuum for 3 h at 100°C.
Preparation of hydrated Ce(III) methanesulfonate: CeO2 and CH3SO3H/H2O
(V/V=1:1) were added into reactor, the mole ratio of CeO2 and methanesulfonic acid
was 1:3. The mixture was stirred and refluxed for 4~5 h, hydrogen peroxide was
added slowly at the same time. After evaporation of the water, the solid was dried in
vacuum for 3 h at 100°C.
Methods
TG curves of methanesulfonates were obtained from 40 to 850°C (hydrated Yb methane-
sulfonate from 40 to 500°C) at the rate of 20°C min–1 in nitrogen and air atmosphere on
Pyris 1 TGA (Perkin Elmer). According to data of TG curves, methanesulfonates were
torrefied for 1 h at 800°C (hydrated Yb methanesulfonate at 500°C) in muffle in air
atmosphere. Infrared spectra of the thermal decomposition products were measured in
KBr pellets in the region of 2000~400 cm–1 using Spectrum GX FT-IR System
(Perkin Elmer). Then, the content of metallic ion in these thermal decomposition
products were determined complexometrically using EDTA as an agent.
Results and discussion
Calculation for number of crystal water
Value of n can be calculated according to the following formula:
M1
content of crystal water%=100
M2
where M1 – molecular mass of crystal water; M2 – molecular mass of hydrated
methanesulfonates.
In this experiment, we think the mass loss in the 40~300°C temperature range in
TG curves were due to the loss of crystal water, and so content of crystal water%
should equal to the mass loss. Then value of n can be determined.
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Characterization of the thermal decomposition products of hydrated
methanesulfonates
Thermogravimetry
Thermogravimetric data of hydrated methanesulfonates are showed in Table 1. It is
known from Table 1 that the final mass fraction are not all same in different atmo-
sphere. If we think oxides were obtained, calculated values of thermal decomposition
products in nitrogen and air atmosphere of hydrated Ce and Zn methanesulfonates ap-
proximate to their respective measured values, their products are respectively CeO2 [5]
and ZnO. In nitrogen atmosphere, the thermal decomposition products of hydrated Pr
methanesulfonate are mixtures of Pr2O3 and PrO2 [6], its measured value is just be-
tween two its two calculated values; the thermal decomposition products of hydrated
La and Nd methanesulfonates are, respectively, La2O3 and Nd2O3, their calculated val-
ues also approximate to their respective measured values. However, in air atmosphere,
if we also think so, calculated values of thermal decomposition products of hydrated
La, Pr and Nd methanesulfonates are largely different from their respective measured
values. Figure 1 clearly shows that the thermal decompositon of La(CH3SO3)3·nH2O is
very different at 800 degree celsius under the nitrogen and the air. The reason may be
that the thermal decomposition products vary in different atmosphere. Besides mea-
sured values thermal decomposition products in nitrogen and air atmosphere of hy-
drated Yb methanesulfonate are same. And so its products in nitrogen and air atmo-
sphere are also same, but not Yb2O3 or Yb2(SO4)3 according to its measured values. If
we want to know whether different atmosphere influence the thermal decomposition
products and what on earth the thermal decomposition products in nitrogen and air at-
mosphere of hydrated Yb methanesulfonate are, infrared spectrometry can be used to
investigate the thermal decomposition products of hydrated methanesulfonates in air
atmosphere.
Infrared spectrometry
It was reported [7] that thermal decomposition products of hydrated La(III), Nd(III)
and Er(III) methanesulfonates in air atmosphere were, respectively, (LaO)2SO4,
Fig. 1 TG curves of La(CH3SO3)3⋅nH2O in nitrogen and air atmosphere
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TIAN et al.: HYDRATED METHANESULFONATES
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(NdO)2SO4 and (ErO)2SO4, their calculated values approximated to their respective
measured values. But definite experimental supports have been still lacking. In order
to investigate whether above products can be obtained in air atmosphere, hydrated
methanesulfonates were torrefied in muffle at 800°C (hydrated Yb methanesulfonate
at 500°C) for 1 h in air atmosphere, infrared spectra of their thermal decomposition
products are shown in Fig. 2.
Fig. 2 Infrared spectra of thermal decomposition products of {Ln(CH3SO3)3⋅nH2O;
Ln=La, Ce, Pr, Nd and Yb} and Zn(CH3SO3)2⋅nH2O at 800°C
{Yb(CH3SO3)3⋅nH2O at 500°C} in muffle in air atmosphere
It can be seen from Fig. 2 that besides the infrared spectra of the thermal
decomposition product of hydrated Ce and Zn methanesulfonates, stretching vibration
v(O=S=O) (at 1190 and 1110 cm–1) and stretching vibration v(O–S–O) (at 1065
and 995 cm–1) are found in thermal decomposition products of hydrated La, Pr, Nd and
Yb methanesulfonates. This means that the thermal decomposition products of the four
RE methanesulfonates in air atmosphere are not simple oxides but compounds
containing sulfate radial group. In view of reference [7], it can be though that thermal
decomposition products of hydrated La, Pr, Nd and Yb methanesulfonates in air
atmosphere are respectively (LaO)2SO4, (PrO)2SO4, (NdO)2SO4 and (YbO)2SO4. In
this way, calculated values of hydrated La, Pr and Nd methanesulfonates approximate
to their respective measured values. This also means that above products can be surely
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obtained in air atmosphere. Because the thermal decomposition products in nitrogen
and air atmosphere of hydrated Yb methanesulfonates are same, its thermal
decomposition product in nitrogen atmosphere is also (YbO)2SO4.
Complexometric titration for the content of metallic ion in thermal decomposition
products in air atmosphere
Here, only thermal decomposition product in air atmosphere of hydrated La methane-
sulfonate is taken as an example for explanation. The content of La in the thermal
decomposition product in air atmosphere of hydrated La methanesulfonate was
determined by complexometric titration using standard EDTA solution. The result is
68.94% which approximate to the content of La in (LaO)2SO4, 68.45%. This also
means that the thermal decomposition product of hydrated La methanesulfonate in air
atmosphere is surely (LaO)2SO4. The content of metallic ion in thermal decomposition
products of the other five methanesulfonates in air atmosphere can also be determined
in the same way.
Discussion on decomposition process
Egashira et al. [8] have studied thermal decomposition in static air of
{Ln(CF3SO3)3⋅9H2O; Ln=La–Lu} systematically. They thought that thermal
decomposition process in static air Ln(CF3SO3)3 can be shown as follows:
Ln(CF3SO3)3 → LnF3+3SO2+CO2+CF3OCF3
The final residual products are LnF3. However, it can be seen obviously from
this experiment that the thermal decomposition products in air atmosphere of
{Ln(CH3SO3)3⋅nH2O; Ln=La, Ce, Pr, Nd and Yb} and Zn(CH3SO3)2⋅nH2O are quite
different from that of Ln(CF3SO3)3. Possible decomposition processes in air
atmosphere of Ln(CH3SO3)3 and Zn(CH3SO3)2 can be shown as follows:
2Ln(CH3SO3)3+3O2 → (LnO)2SO4+5SO2+6CO2+6H2O Ln=La, Pr, Nd and Yb;
4Ce(CH3SO3)3+19O2 → 4CeO2+12SO2+12CO2+18H2O
Zn(CH3SO3)2+3O2 → ZnO+2SO2+2CO2+3H2O
Conclusions
Thermal decomposition products of hydrated La(III), Ce(III), Pr(III), Nd(III), Yb(III) and
Zn(II) methanesulfonates in nitrogen and air atmosphere are studied in this paper.
According to the results of thermogravimetry, infrared spectrometry and complexometric
titration, thermal decomposition products of hydrated La(III), Pr(III) and Nd(III)
methanesulfonates vary in nitrogen and air atmosphere: in nitrogen atmosphere, thermal
decomposition products of hydrated Pr(III) methanesulfonate is mixtures of Pr2O3 and
PrO2, that of hydrated La(III) and Nd(III) methanesulfonates are, respectively, La2O3 and
Nd2O3; in air atmosphere, thermal decomposition products of hydrated La(III), Pr(III)
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and Nd(III) methanesulfonates in air atmosphere are, respectively, (LaO)2SO4,
(PrO)2SO4 and (NdO)2SO4. The thermal decomposition products of hydrated Ce(III)
methanesulfonate in nitrogen and air atmosphere are all CeO2. The thermal
decomposition products in nitrogen and air atmosphere of hydrated Yb(III)
methanesulfonate are all (YbO)2SO4. The thermal decomposition products in nitrogen
and air atmosphere of hydrated Zn(II) methanesulfonate are all ZnO.
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