Ma. Mohamed et Sa. Halawy, KINETIC AND MECHANISTIC STUDY OF THE NONISOTHERMAL DECOMPOSITION OF MANGANESE(II) ACETATE TETRAHYDRATE, Thermochimica acta, 242, 1994, pp. 173-186
The non-isothermal decomposition of manganese(II) acetate tetrahydrate
was studied between ambient temperature and 500 degrees C by means of
thermogravimetry (TG), derivative thermogravimetry (DTG), differentia
l thermal analysis (DTA) and differential scanning calorimetry (DSC).
The dehydration process was found to take place in two consecutive ste
ps. The first step commences early (approximate to 20 degrees C) while
the second step is accompanied by melting (at 120 degrees C) with the
evolution of acetic acid. Careful investigation of the course of the
decomposition revealed that two reaction intermediates are formed. The
first was identified as acetyl manganese acetate, Mn(CH3COO)(2) . COC
H3, at approximate to 120 degrees C, which is believed to form during
the second dehydration step. The second intermediate compound was iden
tified as manganese acetate hydroxide, Mn(CH3COO)(2) . OH, formed near
155 degrees C in an exothermic process. This is followed by the decom
position of the hydroxide intermediate to form MnO as a solid product,
with possible melting. Then, catalytic decomposition of the anion tak
es place, with the formation of initial gaseous products on the surfac
e of MnO. In air, however, Mn3O4 is formed as a residual solid product
. IR spectroscopy, X-ray diffractometry and scanning electron microsco
py (SEM) were used to identify and investigate the solid decomposition
products. Gas chromatography (GC) was used to identify the volatile g
aseous products as acetone, acetic acid, CO, CO2 and trace amounts of
acetaldehyde. Methane and isobutene were formed at high temperatures,
i.e. at 290 degrees C. The kinetic parameters (activation energy Delta
E, and frequency factor ln A), and the thermodynamic parameters (enth
alpy change Delta H, heat capacity C-p, and the entropy change Delta S
), were calculated for the dehydration and the decomposition processes
.