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Physical & Chemical properties

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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
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.