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Vapour pressure

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Reference
Endpoint:
vapour pressure
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH
1. HYPOTHESIS FOR THE ANALOGUE APPROACH
The target substance fatty acids, tall oil, reaction products with acrylic acid, potassium salt (Diacid 1550 K-salt) is manufactured from reaction of fatty acids, tall oil, reaction products with acrylic acid (Diacid 1550) by neutralisation with potassium hydroxide.
The neutralisation is almost complete, but approx. 10% free acids is left, whereas the majority of acids is converted to the corresponding potassium salt. It is generally known, that mineral salts of organic acids (ionic compounds) do have a negligible vapour pressure and in this case even the organic acid does have a vapour pressure of only 0.000045 Pa (at 25 °C), as experimentally determined in a study with the source substance fatty acids, tall oil, reaction products with acrylic acid (Diacid 1550).

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
The target substance is manufactured from the source substance by neutralisation of its organic acid functions with potassium hydroxide. Thus, the purity is not relevant as identical, based on the organic moiety.
The source substance is liquid at ambient temperature (20 °C), whereas the target substance, the potassium salt, is solid, showing a melting point range from 80 to 134 °C, since approx. 80 - 90% of acid functions are neutralized only.

3. ANALOGUE APPROACH JUSTIFICATION
The target substance is the corresponding potassium salt of the source substance. The assumption that the vapour pressure of the potassium salt is lower than the one of the free acid is supported by the fact, that the source compound (acids) is liquid at room temperature, having a pour point of ca. -3 °C, whereas the potassium salt (solid at room temperature) shows a melting range of 80 - 134 °C. Thus, it can be reasonably assumed that the target substance does have an even lower vapour pressure than the free acid. However, as the potassium salt does contain approximately 10% remaining free acid, it is justified to use the vapour pressure of the free acid (0.000045 Pa at 25 °C) as a worst-case value for the potassium salt too. Further studies are scientifically not justifiable.

4. DATA MATRIX
The melting point of Diacid 1550 (liquid at room temperature) was determined according to OECD guideline 102 under GLP using the pour point method. The melting point was found to be -3 ±3 °C. The target substance, the corresponding potassium salt, was found having a melting point range of 80 - 134 °C.
Reason / purpose:
read-across source
GLP compliance:
yes (incl. certificate)
Temp.:
25 °C
Vapour pressure:
0 Pa
Remarks on result:
other: Mean value out of 10 runs
Conclusions:
The vapour pressure of Diacid 1550, the corresponding free acid to the tragte substance (potassium salt) is 0.000045 Pa at 25 °C. As ionic substances such as the target substance are known to have negligible vapour pressure and certainly higher than the corresponding acid, the value for the free acid is used as a surrogate for its potassium salt, considering that this value already is very low and that the neutralisation to form the potassium salt is not complete, resulting in approximately 10% of free acid being components in the UVCB substance tall oil, fatty acids, reaction products with acrylic acid, potassium salt.

Description of key information

The target substance fatty acids, tall oil, reaction products with acrylic acid, potassium salt (Diacid 1550 K-salt) is the corresponding potassium salt of the source substance. The assumption that the vapour pressure of the potassium salt is lower than the one of the free acid is supported by the fact, that the source compound (acids) is liquid at room temperature, having a pour point of ca. -3 °C, whereas the potassium salt (solid at room temperature) shows a melting range of 80 - 134 °C. Thus, it can be reasonably assumed that the target substance does have an even lower vapour pressure than the free acid. However, as the potassium salt does contain approximately 10% remaining free acid, it is justified to use the vapour pressure of the free acid (0.000045 Pa at 25 °C) as a worst-case value for the potassium salt too. Further studies are scientifically not justifiable.

Key value for chemical safety assessment

Vapour pressure:
0 Pa
at the temperature of:
25 °C

Additional information