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Physical & Chemical properties

Melting point / freezing point

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Reference
Endpoint:
melting point/freezing point
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study performed according well-known techniques but not under GLP
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 102 (Melting point / Melting Range)
Principles of method if other than guideline:
Both Thermal Gravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) had been performed in order to obtain complementary information and allowing differentiation between endothermic and exothermic events which have no associated weight loss (e.g., melting and crystallization) and those which involve a weight loss (e.g., degradation).
For Differential Thermal Analysis (DTA), sample was heated from 20°C to 350°C in a closed glass crucible with a heating rate of 3.0 K/min.
For Thermal Gravimetric Analysis (TGA), sample was heated from 20°C to 240°C under inert atmosphere in a open Aluminium Oxide crucible with a heating rate of 3.0 K/min.
GLP compliance:
not specified
Type of method:
thermal analysis
Sublimation:
yes
Subl. temp.:
> 160 °C
Remarks on result:
other: at atmospheric pressure

2 endothermic phenomena have been observed belowin DTA:

-         The first endothermic reaction started at 98 ºC (with a peak at 100 ºC) and has been attributed to loss of water of di-hydrated oxalic acid; this is has been proven via TGA showing a weight loss of 29% corresponding to water content of di-hydrated oxalic acid

-         The second endothermic reaction started atand up to; TGA proved the loss of total remain weight (71%) corresponding to full decomposition of oxalic acid giving off gases and corresponding to sublimation

Conclusions:
The apparent melting point of di-hydrated oxalic acid is caused by loss of crystal water starting at 98°C with a maximum at 100°C. The anhydrous form of oxalic acid starts sublimation around 160°C.

Description of key information

Key value for chemical safety assessment

Melting / freezing point at 101 325 Pa:
160 °C

Additional information

The substance sublimates at temperature around 160 ºC