Phosphorothioic acid, O,O-bis(2-methylpropyl) ester, sodium salt (1:1)

Vapour pressure

Administrative data

Endpoint:

vapour pressure

Type of information:

experimental study

Adequacy of study:

key study

Study period:

August 18, 2011 - July 7, 2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2012

Report date:

2012

Materials and methods

Test guideline

Test guideline 1

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 104 (Vapour Pressure Curve)

Deviations:

yes

Remarks:

open aluminum pans were used under nitrogen purge at 25 mL/min. This is a discrepancy from the OECD guideline. The OECD guideline calls for a plate instead of a pan.

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: ST-AN-25

Deviations:

no

Principles of method if other than guideline:

The vapor pressure of the test substance was determined by effusion method: isothermal thermogravimetry (TGA). The TGA method is based on the determination of accelerated evaporation rates for the test substance at elevated temperatures and ambient pressure. This method is suitable for substances with vapor pressures as low as 10E-10 Pa (10-12 mbar) and with purity as close as possible to 100% to avoid the misinterpretation of measured weight losses. The estimated repeatability is 10 to 30% and the estimated reproducibility is up to 50%. However, incorporating NIST traceable standard reference materials and open pans, the reproducibility and accuracy is much higher.

TGA experiments were conducted using a Q5000 TGA following ST-AN-25 procedure. Open aluminum pans were used under nitrogen purge at 25 mL/min. This is a discrepancy from the OECD Guideline. The OECD Guideline calls for a plate instead of a pan. The diameter of the pan is 6 mm. The sample weight of the benzoic acid and test substance is approx. 20 mg. This is enough material to keep the surface area consistent throughout the analyses.

Isotherms at appropriate temperatures were conducted until weight loss rate was stable. The instrument software was used to calculate the evaporation rate by taking the slope when weight loss rate is constant. The evaporation rate was then plotted against the literature vapor pressure values of benzoic acid in order to obtain a calibration equation for the instrument parameters. Other compounds of known vapor pressures were also analyzed against the benzoic acid calibration curve in order to validate the method.

GLP compliance:

no

Type of method:

effusion method: isothermal thermogravimetry

Test material

Test material information

Constituent 1

Reference substance name:

Sodium O,O-diisobutyl phosphorothioate

EC Number:

610-992-2

Cas Number:

53378-52-2

Molecular formula:

C8 H18 O3 P S . Na

IUPAC Name:

Sodium O,O-diisobutyl phosphorothioate

Test material form:

other: grease-like solid

Specific details on test material used for the study:

- Name of test material (as cited in study report): S10821; AERO® 6697 Promoter distilled
- Name: Sodium diisobutyl monothiophoshate
- CAS: 53378-52-2
- Molecular formula: C8H18O3PS.Na
- Molecular weight: 248.26
- Storage condition of test material: not indicated in the study report
- Batch no.: 20154-189-B
- Purity: 87.3%

Results and discussion

Vapour pressure

Vapour pressure 1

Temp.:

25 °C

Vapour pressure:

ca. 0.026 Pa

Vapour pressure 2

Temp.:

20 °C

Vapour pressure:

ca. 0.024 Pa

Any other information on results incl. tables

The vapor pressure equation with mm Hg units is:

Y = -708.72X - 1.325

where Y = log pressure (mmHg), and X = 1/K. The R² = 0.9992.

The converted vapor pressure equation to Pa pressure unit is:

Y = -708.15X + 0.7982

where Y = log Pressure (Pa), and X = 1/K. The R² = 0.9992

Experimental Evaporation Rates on the Test Substance and Calculated Vapor Pressure.

Evaporation Rate		Temperature		Calculated Vapor Pressure
Wt%/min	Log Wt%/min	°C	1/K	Log P (mmHg)	P (mmHg)
0.0000655	-4.1837587	50	0.003095	-3.5160	0.000305
0.0000745	-4.127843727	60	0.003002	-3.4570	0.000349
0.00009875	-4.005462896	80	0.002832	-3.3278	0.00047
0.0001242	-3.905878404	100	0.002680	-3.2226	0.000599
0.0001229	-3.910448117	100	0.002680	-3.2275	0.000592

Applicant's summary and conclusion

Conclusions:

The estimated vapor pressure of the test substance at 20 °C is 0.000181 mmHg (0.0241 Pa) and at 0.000199 mmHg (0.0265 Pa) at 25 °C. Both values were determined using a method similar to OECD 104 guideline.

Executive summary:

Using the isothermal thermogravimetric effusion method, the vapour pressure of the substance at 25°C has been determined as 0.0265 Pa.