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Physical & Chemical properties

Water solubility

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Reference
Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline followed
Principles of method if other than guideline:
Examination of the temperature dependences of the solubility of cobalt sulfamates in water and constructed two-component phase diagrams in the system Co(SO3NH2)2 * xH2O.
GLP compliance:
not specified
Type of method:
other: water solubility determination in a Pyrex reactor
Key result
Water solubility:
530 g/L
Conc. based on:
test mat. (dissolved fraction)
Incubation duration:
>= 2 - <= 8 h
Temp.:
25 °C
Remarks on result:
other: no data for pH value and loading
Water solubility:
470 g/L
Conc. based on:
test mat. (dissolved fraction)
Incubation duration:
>= 2 - <= 8 h
Temp.:
8.3 °C
Remarks on result:
other: no data for pH value and loading
Water solubility:
494 g/L
Conc. based on:
test mat. (dissolved fraction)
Incubation duration:
>= 2 - <= 8 h
Temp.:
19.3 °C
Remarks on result:
other: no data for pH value and loading
Water solubility:
530 g/L
Conc. based on:
element
Remarks:
Co
Incubation duration:
>= 2 - <= 8 h
Temp.:
25 °C
Remarks on result:
other: no data for pH value and loading
Water solubility:
541 g/L
Conc. based on:
element
Remarks:
Co
Incubation duration:
>= 2 - <= 8 h
Temp.:
28 °C
Remarks on result:
other: no data for pH value and loading
Water solubility:
552 g/L
Conc. based on:
element
Remarks:
Co
Incubation duration:
>= 2 - <= 8 h
Temp.:
31.1 °C
Remarks on result:
other: no data for pH value and loading

The solubility of Co(SO3NH2)2 showed strong temperature dependence in the binary system Co(SO3NH2)2-H2O:

- 47.0 wt% = 470 g/L at 8.3 °C

- 49.4 wt% = 494 g/L at 19.3 °C

- 53.0 wt% = 530 g/L at 25.0 °C

- 54.1 wt% = 541 g/L at 28.0 °C

- 55.2 wt% = 552 g/L at 31.1 °C

Bottom Phase

Analysis of bottom phases according to the lever rule (Schreinemakers’ method of wet residues) shows that cobalt sulfamates form several crystal hydrates (containing 4, 3.5, 3, and 2 water molecules).

Most probable bottom phase composition in the Co(SO3NH2)2 -H2O system

- 49 wt% of  α-Co(SO3NH2)2 * 4 H2O + β-Co(SO3NH2)2 * 4 H2O at 10.4 °C

- 54.2 wt% of  β-Co(SO3NH2)2 * 4 H2O + γ-Co(SO3NH2)2 * 4 H2O at 27.1 °C

Cobalt sulfamate crystal hydrate with four water moleclules shows tautomerism with the formation of α, β, γ modifications of Co(SO3NH2)2* 4 H2O. Slow isohydric crystallization at room temperature makes it posiible to obtain Co(SO3NH2)2* 4 H2O in the form of large (up to 5-10mm) transparent dark pink prismatic single crystals with a refraction index of Nav = 1.517. Cobalt sulfamate crystal hydrate with four water molecules, which is very unstable in air, is gradually eroded to form light pinkt powders by gradual passing from Co(SO3NH2)2* 3.5 H2O to the most stable in air crystal hydrate Co(SO3NH2)2* 3 H2O. The results of a thermographic study (Q-1500D derivatograph) of crystalline samples of Co(SO3NH2)2* 4 H2O at a heating rate of 10 °C/min showed that cobalt sulfamates lose crystal water in several steps.

Co(SO3NH2)2* 4 H2O - 0.5 H2O = Co(SO3NH2)2 - 3.5 H2O,

Co(SO3NH2)2* 3.5 H2O - 0.5 H2O = Co(SO3NH2)2 - 3 H2O,

Co(SO3NH2)2* 3 H2O - 0.5 H2O = Co(SO3NH2)2 - 2 H2O

Then, long before the onset of sulfamate ion decomposition, cobalt sulfamate successively loses the third and the fourth H2O molecules, forming anhydrous crystals. These are the processes responsible for removal of supersaturation in the course of vacuum-thermal crystallization.

CONCLUSIONS

(1) The solubility of Co(SO3NH2)2 show strong temperature dependences, and the compound exhibit tautomerism.

(2) The formation of tautomeric modifications of sulfamates is associated with multistage transformations from the zwitterionic form H2NSO3-(δ+1) to the open form H2NSO3- .

Conclusions:
The solubility of Co(SO3NH2)2 is dependant on temperature in the binary system Co(SO3NH2)2-H2O: 530 g/L at 25.0 °C
The water solubility of cobalt(II) sulfamate at 19.3°C is 494 g/L. At 8.3°C the water solubility is determined to 470 g/L and at 25°C at 530 g/L. No temperature dependence observed (< 3%/°C).

Description of key information

Key value for chemical safety assessment

Water solubility:
494 g/L
at the temperature of:
19.3 °C

Additional information