Sodium sulfide (Na2(Sx))

Endpoint summary

Additional information

Sodium polysulfide is available as a solid but also as a 25% solution in water. Therefore the phys-chem properties are available for the solid and the liquid form.

Overview of physico- chemical properties

Parameter	Guidelines(	Result	Comment
Freezing/Melting temperature	EC A.1 OECD 102	Liquid: - 6.2°C
		Solid: 230°C – 278°C
Boiling temperature	EC A.2 OECD 103	Liquid: Waiving	Statement
		Solid: Decomposition before boiling.
Density	EC A.3 OECD 109	Liquid: D20/4 : 1.2034
		Solid: 2.124
Particle size distribution (granulometry)	ISO 2591- 1	Liquid: Waiving
		Solid:Particle size distribution shows that the size of approx. 78 % of test substance particles is > 1 mm, the D10 is approx. 600µm and D50 and D90 are both above 1000 µm.
Vapour pressure	EC A.4OECD 104	Liquid: Waiving	Statement
		Solid: 2 x 10- 10 Pa	At 20°C by effusion method
Partition coefficient	EC A.8	Liquid and solid: Waiving	Statement
	OECD 117
Water solubility	EC A.6OECD 105	Liquid: Waiving	Statement
		Solid: Miscible
Surface tension	EC A.5	Liquid and solid: Waiving	Statement
	OECD 115
Flash- point	EC A.9	Liquid and solid: Waiving	Statement
	ISO 2719
	ASTMD 93
Auto flammability	EC A.15	Liquid: Waiving	Statement
	EC A.16
		Solid: Self ignitable,at an ambient temperature of about 170 °C to 200 °C
Flammability	EC A.10	Liquid: Waiving	Statement
		Solid: Not highly flammable
Explosive properties	EC A.14	Liquid: Waiving	Statement
		Solid: Not explosive
Oxidizing properties	EC A.21	Liquid and solid: Waiving	Statement
Stability in organic solvents and identity of relevant degradation products		Liquid and solid: Waiving	Statement
Dissociation constant	OECD 112	Liquid: The dissociation constant of sodium polysulfide solution (at 23 °C) was determined as:  pKb1 = 9.56 and pKb2 = 7.02
Viscosity	OECD 114	Liquid: The kinematic viscosity of sodium polysulfide solution at 20 °C is 2.16 mm2 s- 1

Aqueous Na2Sx solutions are only stable at pH > 10. At lower pH values they are decomposed to H2S and S. At physiological pH values, hydrogen sulfide in the non-dissociated form (H2S) and the hydrogen sulfide anion (HS-) will be present in almost equimolar proportion, whereas only very small amounts of the sulfide anion (S2-) will be present. In conclusion, under physiological conditions, inorganic sulfides or hydrogen sulfides as well as H2S will dissociate to the respective species relevant to the pH of the physiological medium, irrespective the nature of the “sulfide”, which is why read-across between these substances and H2S is considered to be feasible without any restrictions.

Literature study that shows there is no reference in the literature indicating the release or regeneration of sodium polysulfide, the monomer used for the manufacture of liquid polysulfide polymers, after the polysulfide polymer has been formed.

This substance is not produced nor transported as an aerosol nor as a gas under pressure. In addition, it is not expected that it has pyrophoric properties and reacts with water. Instead it is very well soluble in water.