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Vapour pressure

Link to relevant study record(s)

Reference

Endpoint:

vapour pressure

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-01-25 to 2016-02-12

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 104 (Vapour Pressure Curve)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method A.4 (Vapour Pressure)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 830.7950 (Vapor Pressure)

Deviations:

no

GLP compliance:

yes

Type of method:

effusion method: by loss of weight or by trapping vaporisate

Key result

Test no.:

#1

Temp.:

20 °C

Vapour pressure:

1 Pa

Key result

Test no.:

#2

Temp.:

25 °C

Vapour pressure:

1.8 Pa

The weight loss curves of the test item Experiment 1 and 2 are shown in Figure 1 and Figure 2 (attached). In experiment 2 some mechanical artefacts are shown. Since the weight loss was obtained in an area without artefact, it had no impact on obtained results. The results of the isothermal TGA analysis with the test item and the vapour pressure at 20°C and 25°C are given in Table 1 and Table 2.

The plot of the log PT of the test item as function of the reciprocal temperatures is shown in Figure 3 (attached).

The equation of the curve was: log P_T = -4163 x 1/T + 14.22 (r = 0.998, n = 8).

 

Table 1 Results of the isothermal TGA analysis

Temperature [°C]	Weight loss [μg/min]	νT[g/cm^2/h]	log νT	log PT	PT [Pa]
40	5.408 5.807	6.46 x10^-4 6.93 x10^-4	-3.19 -3.16	0.91 0.95	8.1 8.8
50	12.28 12.21	1.47 x 10^-3 1.46 x 10-3	-2.83 -2.84	1.32 1.31	21 21
60	27.31 29.26	3.26 x 10^-3 3.49 x 10^-3	-2.49 -2.46	1.71 1.75	52 56
70	54.94 59.82	6.56 x 10^-3 7.14 x 10^-3	-2.18 -2.15	2.06 2.10	110 130

 

Table 2: Vapour pressure of the test item

Temperature [°C]	log PT	PT [Pa]	PT [mmHg]
20	0.01	1.0	7.8 x 10^-3
25	0.25	1.8	1.3 x 10^-2

Conclusions:

Vapour pressure values of 1.0 Pa at 20°C and 1.8 Pa at 25°C were determined for the substance using a relevant test method and in compliance with GLP. The result is considered to be reliable.

Description of key information

Vapour pressure [whole substance]: 1.0 Pa at 20°C, 1.8 Pa at 25°C (OECD 104)

Vapour pressure [Constituent 1a and Constituent 1b, cis and trans isomers]: 0.073 Pa at 25°C (QSAR)

Vapour pressure [Constituent 2]: 0.065 Pa at 25°C (QSAR)

Vapour pressure [methylsilanetriol]: 5.0E-02 Pa at 25°C (QSAR)

Vapour pressure [2-ethylhexyl 3-[dihydroxy(methyl)silyl]propanoate]: 3.3E-06 Pa at 25°C (QSAR)

Vapour pressure [2-Ethylhexyl propanoate]: 19 Pa at 25°C

Vapour pressure [methanol]: 12790 Pa at 20°C

Key value for chemical safety assessment

Vapour pressure:

1 Pa

at the temperature of:

20 °C

Additional information

Vapour pressure values of 1.0 Pa at 20°C and 1.8 Pa at 25°C were determined for the whole substance using an isothermal thermogravimetric effusion method in accordance with OECD Test Guideline 104 and in compliance with GLP. The result is considered to be reliable.

The submission substance is a multi-constituent substance, measured vapour pressure for the whole substance is preferred for the purpose of human health exposure assessment while for the purposes of environmental hazard and fate assessment; vapour pressures of the constituents have been predicted using a validated QSAR estimation method. The vapour pressures of the constituents are 0.073 Pa at 25°C for Constituents 1a and 1b (cis and trans isomers) and 0.065 Pa at 25°C for Constituent 2.

In contact with water, all the constituents of the substance hydrolyse either rapidly or very rapidly to form the corresponding silanol and other non-silanols hydrolysis products methanol and 2-ethylhexyl propanoate.

The vapour pressures of the silanol hydrolysis products have been estimated using the same validated QSAR estimation method. The predicted vapour pressure are 0.05 Pa at 25°C for methylsilanetriol and 3.3E-06 Pa at 25°C for 2-ethylhexyl-3-[dihydroxy(methyl)silyl]propanoate.

Methanol has a reported vapour pressure of 12790 Pa at 25°C (OECD 2004)

2-Ethylhexyl propanoate has an estimated vapour pressure value of 19 Pa at 25°C using a MPBPVPWIN v1.43. The model was not validated for 2-ethylhexyl propanoate, but since there are several related substances in the test set, the estimated value is considered to be valid and reliable.

Reference:

OECD (2004). SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1.