Undecanal

Vapour pressure

Link to relevant study record(s)

Reference

Endpoint:

vapour pressure

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2010-07-19 to 2010-10-20

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 104 (Vapour Pressure Curve)

Version / remarks:

May 23., 2006

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method A.4 (Vapour Pressure)

Version / remarks:

August 24., 2009

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

static method

Specific details on test material used for the study:

Expiry date 01. Dec. 2010
The test item was stored in a closed flask at room temperature under inert gas Ar.

Key result

Temp.:

20 °C

Vapour pressure:

38 Pa

Temp.:

25 °C

Vapour pressure:

48 Pa

Detailed measurements:

1. Determination - increasing temperature		2. Determination - decreasing temperature
Temp. in °C	Pressure in mbar	Temp. in °C	Pressure in mbar
19.6	0.4	67.1	3.4
30.1	0.6	57.7	2.6
27.2	0.6	42.0	2.0
38.1	0.8	34.2	1.7
43.8	1.0	30.7	1.6
51.4	1.4	24.5	1.6
55.5	1.7	18.8	1.4
63.1	2.6
67.2	2.9
69.7	3.5

Calculation of results:

From the measured values for the increasing and for the decreasing temperature, log P (in log Pa) and 1/T (in 1/K) were calculated. The measured and the calculated values were plotted (p against T and log P against 1/T).

The regression curve with slope B, intercept A and correlation r was calculated (graph log P vs. 1/T). From the values of these parameters, vapour pressures at 20.0 and at 25.0 °C were calculated using the following equation:

log P = B * (1/T) + A, T [K]

When plotting P / T pairs from increasing and decreasing temperature (see attached plot), values at increasing and at decreasing temperature show considerable differences. As the test item contains impurities (purity 92.8% main component), the vapour pressure at increasing temperature is more likely to represent the vapour pressure of the authentic test item, as substances with lower boiling point evaporate more quickly, but condense more slowly, leading to erroneous values in the decreasing series.

As a consequence, values of the first determination (increasing temperature) were used for determining the vapour pressure. The following regression equation was derived from a plot of log P [Pa; ordinate] versus 1/T [K; abscissa] (as shown in the attached illustration):

Y = -1849.217812 * X + 7.885771174; correlation coefficient r = -0.992512432, r^2 = 0.9851

Accordingly, the following values for the vapour pressure of the test item were calculated:

Vapour pressure at 20 °C:       38 Pa;

Vapour pressure at 25 °C:       48 Pa.

Discussion of results:

The vapour pressures at lower temperatures show variations between the values which were recorded at increasing and at decreasing temperatures. Regression was made over the values at increasing temperature only. If the values for decreasing temperatures were also taken into account, different ambient vapour pressures would have been calculated (75 Pa at 20 °C and 88 Pa at 25 °C). This difference was assessed as uncritical. The test item has a stated purity of 92.8 %, therefore, 7.2 % of other compounds may have increased the measured value for the vapour pressure and may be the reason for the diverging curves for increasing and decreasing temperature. Measurements of pure compounds (> 99.8 %) never show this divergence.

Therefore, the study is considered as valid.

Conclusions:

Using the static method according to OECD 104, vapour pressures of 38 Pa at 20 °C and 48 Pa at 25 °C were determined.

Executive summary:

The vapour pressure of the submission substance was determined compliant with GLP in a reliable study performed according to OECD 104.

Using the static method, vapour pressures of 38 Pa at 20 °C and 48 Pa at 25 °C were determined.

These values were calculated from the regression of 10 individual measurements. These measurements were performed in a temperature range of 20 - 70 °C.

The measured values for pressure P and temperature T were used to calculate pairs of log P and 1/T. These values were plotted and from the linear regression the vapour pressures for the ambient temperature range (20 and 25 °C) were determined.

Description of key information

The vapour pressure of n-undecanal is estimated to be 0.38 hPa at 20°C.

Key value for chemical safety assessment

Vapour pressure:

0.38 hPa

at the temperature of:

20 °C

Additional information

In the reliable key study (LAUS, 2010), the vapour pressure of the submission substance was determined compliant with GLP according to OECD 104.

Using the static method, vapour pressures of 38 Pa at 20 °C and 48 Pa at 25 °C were determined.

These values were calculated from the regression of 10 individual measurements. These measurements were performed in a temperature range of 20 - 70 °C.

The measured values for pressure P and temperature T were used to calculate pairs of log P and 1/T. These values were plotted and from the linear regression the vapour pressures for the ambient temperature range (20 and 25 °C) were determined.

From a supporting study (OXEA, 2009) an experimental result of 1 hPa at 20°C is available for the vapour pressure. This result was obtained using an older equipment implying considerable extrapolation to lower temperatures (experimental T-range: 90 to 150 °C) and thus it gives less exact values at low vapour pressures. It is therefore not in conflict with the reliable key study.