Sodium O-ethyl dithiocarbonate

Endpoint summary

Additional information

Physical and chemical properties

 

SEX/sodium O-ethyl dithiocarbonate

 

1.Appearance

Slight yellow or Kelly free flowing powder or pellet with strong odour.

 

2.Odour

Disagreeable odour due to the presence of carbon disulphide.

 

3.Melting point

Using the EPI Suite Mpbwin (v.1.43) QSAR model, a Melting Point of 195.02 deg C (Weighted Value) was established.

4.Boiling point

Not applicable as it decomposes on heating.Using the EPI Suite Mpbwin (v.1.43) QSAR model, a Boiling Point of 462.37 deg C (estimated) was established.

5.Specific gravity

1.24

 

6.Vapour pressure

Non-volatile solid at 25°C. However, it decomposes to volatile compounds.

A QSAR method predicts the vapour pressure of this substance to be 5.26E-007 Pa at 25C.

 

7.Water solubility

3924.9 mg/l

1000000 mg/l

Substance is predicted by QSAR method (EPI Suite v 4.1/WATERNTv 1.01) to be soluble (3924.9 mg/l) with water.

Substance is predicted by QSAR method (EPI Suite v 4.1/WSKOW v1.42 ) to be very soluble ( 1000000 mg/l) with water.

8.Partition co-efficient

This parameter, logKow, is not applicable to substances that dissociate in aqueous solution.

A reliable QSAR method predicts a value for the partition co-efficient (logKow) of -2.24 for this substance.

 

9.Hydrolysis as a function of pH

Xanthates are known to hydrolyse very rapidly under acidic conditions, and to bestabilised by high pH conditions. Below pH 9 at 25°C sodium ethyl xanthate almost totally dissociates.

 

10.Adsorption/desorption

SEX adsorbs strongly to sulphide minerals but has less affinity for surfaces in general.

11.Dissociation constant

The high water solubility and ionic character identify sodium ethyl xanthate as a dissociable compound.

SEX reacts with water and there are three decomposition pathways of xanthates in aqueous solution:

 

A. Xanthates dissociate forming alkali metal cations and xanthate anions. Thesolution undergoes further hydrolysis to xanthic acid which decomposes intocarbon disulphide and alcohol.

 

ROCS₂Na + H₂O——→ROCS₂H + NaOH

ROCS₂H——→CS₂+ ROH

 

B. Xanthate is oxidised to dixanthogen. The extent of this reaction is very smalland dependent on the pH. Equilibrium is reached after about 5–10% of thexanthate is oxidised, and the reaction increases with a fall in the pH.

 

2ROCS^–₂+ H₂O + _O₂——→(ROCS₂)₂+ 2OH–

 

C. In neutral and alkaline media, xanthates decompose by hydrolyticdecomposition.

 

6ROCS^–₂+ 3H₂O——→6ROH + CO₃²– + 3CS₂+ 2CS³₂–

 

Further hydrolysis of sodium trithiocarbonate to sodium carbonate and hydrogen sulphide and carbon disulphide to carbon dioxide and hydrogen sulphide may occur. The reaction is catalysed by the alcohol formed from the xanthic acid and is self accelerating.

 

Reaction C is the main reaction in alkaline solution while A and B occur in acidic solutions. During use in mining processes, reaction C is the principal decomposition pathway and carbon disulphide the principal decomposition product. Part of the carbon disulphide formed may decompose further to carbonate and thiocarbonatesalts, some of it may evaporate and some may build up in the xanthate solution.Once the solubility of carbon disulphide is exceeded it forms a separate layer below the Reaction mass of SEX solution.

 

 12.Flammability

Not applicable to solid SEX which in the presence of moisture and/or heat decomposes to carbon disulphide, alcohol, sodium carbonate and trithiocarbonate.

Carbon disulphide (CAS number 75–15–0) is the major decomposition product and has a low autoignition point and is highly flammable.

 

Due to the decomposition of SEX when is heated this substance is not considered to exhibit flammability but the major decomposition product Carbon disulphide (CAS number 75–15–0) have to be considered.

 

Flammable (solid).

 

13.Combustion products

Sodium sulphide, sulphur dioxide, carbon dioxide and water are combustion productst hrough flammable intermediary decomposition products such as alcohol and carbon disulphide. The hazardous total combustion products are sodium sulphide and sulphur dioxide. Incomplete combustion can result in thio ethers and carbonyl sulphide.

 

14.Decomposition temperature

> 25°C

15.Decomposition products

SEX in the presence of moisture decomposes to carbon disulphide, alcohol, sodium carbonate and trithiocarbonate.

 

16.Autoignition temperature

99 oC at for Carbon disulphide

Not applicable to solid Reaction mass of SEX which in the presence of moisture and/orheatdecomposes to carbon disulphide,alcohol, sodium carbonate and trithiocarbonate.

Carbon disulphide (CAS number 75–15–0) is the major decomposition product and has a low autoignition point and is highly flammable.CS2 has an auto flammability temperature of 99 oC at ambient pressure

 

17.Reactivity

Hygroscopic and reacts with water to form alcohol,sodium carbonate,trithiocarbonate and carbon disulphide. Susceptible to oxidation and reacts with oxidising agents to form dixanthogens.

 

18.Particle size distribution

Pelletised

form

width 5 to 6 mm

length 5 to 15 mm

Powderrange 1 to 10μm

mean 5μm

 

19.Composition of commercial product

Composition varies depending on the source of import. The specifications weresupplied by three applicants and are given below.

 

Purity of the chemical90% minimum

Moisture3–7% maximum

Free alkalies0.2% maximum

Sodium thiosulphate2% maximum

Sodium sulphide and sodium thiocarbonateTrace

Sodium sulphate and other inorganic saltTrace to 7%

Other volatilesApprox 2%

 

20.Oxidizing properties

This product no has oxidizing properties.

An oxidizing substance is one that, while in itself not necessarily combustible, may cause or contribute to the combustion of other material.

Oxidising substances generally act by yielding oxygen; however, those that release active halogens can also react as oxidants.

Due to the absence of chemical groups associated with oxidizing properties or other structural alerts this substance is not considered to exhibit oxidizing properties.

 But xanthates are susceptible to oxidation and can reacts with oxidising agents to form dixanthogens.

 

 

Carbon disulphide

SEX in the presence of moisture and/or heat decomposes. Carbon disulphide (CAS number 75–15–0) is the major decomposition product and has a low autoignition point and is highly flammable. The pertinent characteristics of carbon disulphide are:

 

1 Molecular weight

76.14

 

2 Appearance

Clear, colourless or faintly yellow liquid at 20°C and 101.3 kPa

 

3 Odour

Sweet ethereal odour when pure. However carbon disulphide is usually foul

smelling and rarely encountered in the pure form.

 

4 Odour threshold

0.1 ppm (response in 100% of subjects)

0.2 ppm (response in 50% of subjects)

0.02 ppm (perception in humans).

 

5 Freezing point

–111.5°C

 

6 Boiling point

46.5°C at 760 mm Hg

 

7 Specific gravity

1.263 at 20°C

 

8 Vapour pressure

40 kPa at 20°C

 

.9 Relative vapour density

2.67 (air=1)

 

10 Water solubility

2.1 g/L at 20°C

 

11 Flash point

–30°C (closed cup)

 

12 Autoignition temperature

99°C

 

13 Explosive properties

1.3–50% (v/v) in air

 

14 Reactivity/stability

Reacts vigorously with oxidising agents

 

15 Conversion factors

1 mg/m3 = 0.321 ppm

1 ppm = 3.11 mg/m3