Isophthalic acid

Endpoint summary

Additional information

Appearance

At ambient temperature and pressure, isophthalic acid (IPA) is an organic solid. The high purity (>99.9%) form of IPA required for the manufacture of polyesters is commercially available as a white (colourless), crystalline powder (Park & Sheehan, 1996; Sheehan 1986).

 

Melting point

Isophthalic acid has been observed to melt at 345 to 348 degrees C at elevated pressure when heated in sealed tubes (Park & Sheehan, 1996; Sheehan, 1986). The melting point of isophthalic acid, measured under high pressure (3447379 Pa) to suppress its sublimation, was 348 degrees C (Martin et al., 1979). The vapour pressure line plotted for IPA reaches 760 mm (atmospheric pressure) at 384 degrees C, which would imply that IPA first melts at a lower temperature and then boils at 384 degrees C, however there are no reports that this sequence of changes of state has ever been observed. Under standard atmospheric conditions, IPA sublimes with a direct transition from the solid to vapour phase. Melting and boiling occur only under elevated pressure under artificial conditions.

 

Boiling point

Isophthalic acid is a solid. It sublimes at ca. 345 degrees C at atmospheric pressure without undergoing a transition to the liquid phase. Its boiling point cannot therefore be determined except under highly artificial physical conditions that have no practical relevance. A study to determine the boiling point of isophthalic acid is therefore scientifically unjustified.

 

Density

The crystal density of isophthalic acid is 1.53 g/cm³ at 25 degrees C. The specific gravity of isophthalic acid is 1.53 at 4 degrees C. (Sheehan, 2005; Park & Sheehan, 1996).

Granulometry

The particle size distribution of a sample of purified isophthalic acid typical of the Lead Registrant's commercial production was characterised by laser granulometry (dry measurement) as follows: D10, D50 and D90 = 13.60, 65.38 and 153.22 microns, respectively, on a percentage of volume basis. The volume mean diameter was 75.74 microns and the surface area (Sauter) mean diameter was 20.61 microns.

The data provided by the Lead Registrant are compatible with other, independently collated data contributed by members of the Isophthalic Acid Sub-Group of the Polyester Monomers Consortium (contributors anonymised, number of sources not known), whose collective particle size distribution data are described by the following envelope: 70% in the range 26 to 342 microns and 20% to 30% smaller than 50 microns.

Vapour pressure

Based on a mathematical relationship between temperature and vapour pressure for isophthalic acid, derived from published VP measurements at temperatures in the range 100 to 200 degrees C, the vapour pressure of IPA at 25 degrees C is estimated to be 0.000000024 mm Hg - equivalent to 0.00000320 Pa (Sheehan, 1986). The vapour pressure of isophthalic acid estimated using the MPBPVP v1.43 model of the US EPA is 0.00000347 Pa at 25 degrees C (Modified Grain method), and in close agreement with the estimate derived from the measured data set. The vapour pressure estimate for isophthalic acid is very low, compared to standard atmospheric pressure and IPA is therefore not likely to volatilise to the atmosphere.

 

Partition coefficient

The log octanol/water partition coefficient (log Kow) of isophthalic acid was estimated using the KOWWIN v1.67 QSAR model available from the US EPA. The estimated log Kow of isophthalic acid is 1.76. Additionally, KOWWIN provides a measured log Kow value of 1.66 for isophthalic acid, retrieved from the data base of experimental results used to construct the QSAR model.

 

The octanol/water partition coefficient of isophthalic acid has also been determined according to the shake-flask procedure, in a system buffered to pH 7. The mean log Kow obtained under these conditions was -2.34. This value implies a much higher relative solubility of IPA in the aqueous phase than the log Kow indicated by KOWWIN QSAR and by the experimentally determined value for IPA that has been used in the construction of the KOWWIN model. This is likely to have been caused by the presence of the buffer (composition not stated) used to maintain the test system at pH 7: IPA would have been converted under these conditions to salts with higher aqueous solubility than that of the free acid (Hatoum & Garthwaite, 1992).

 

Water solubility

The limit of solubility of isophthalic acid (IPA) in water at 25 degrees C is ca. 120 mg/L. IPA is therefore considered to be moderately soluble in water (Park & Sheehan, 1996; Roehrscheid, 2005).

 

Solubility in organic solvents

Limits of the solubility of isophthalic acid at 25 degrees C are published for five organic solvents: glacial acetic acid (0.23 %, w/w), methanol (2.5 % w/w), n-propanol (1.7% w/w) dimethylformamide (37 % w/w) and DMSO (64 % w/w) (Park & Sheehan, 1996).

 

Surface tension

In accordance with Column 2 adaptation statement of REACH Annex VII, information requirement 7.6, this study does not need to be conducted if, based on structure, surface activity is not expected and no surface-active properties would be predicted for this compound. Surface activity is not a desired property of the material.

 

Flash point

In accordance with Column 2 of REACH Annex XI, information requirement 7.9, this study does not need to be conducted based on the physical state of the molecule. According to ECHA guidance, flash point is only relevant to liquids and low melting solids.

 

Autoflammability

In accordance with Column 2 adaptation statement of REACH Annex VII, information requirement section 7.10, this study does not need to be conducted based on a structural assessment of the substance.

 

Flammability

A preliminary flammability screening test was performed by igniting a loosely-packed linear pile of IPA. Combustion propagated 200 mm along the pile in a time of 865 seconds. According to the UN Recommendations on the Transport of Dangerous Goods, isophthalic acid is therefore not classified as a readily combustible solid of Division 4.1 and further flammability testing is not required (Atwal & Tremain, 2010).

 

Explosiveness

According to theoretical considerations based on chemical structure, isophthalic acid does not to possess explosive or oxidising properties. Isophthalic acid is unlikely to undergo rapid decomposition accompanied by the evolution of gases or release of heat and therefore does not present a risk of explosion (Curl & Wright, 2010a).

 

Oxidising properties

According to theoretical considerations based on chemical structure, isophthalic acid does not possess oxidising properties. Isophthalic acid is unlikely to cause or contribute to the combustion of other material during transport, storage or use (Curl & Wright, 2010b).

 

pH

The pH of isophthalic acid in a saturated aqueous solution at 25 degrees C is 3.30 (Sheehan, 1986).

 

Dissociation constant

The pK1 and pK2 values for isophthalic acid in aqueous solution at 25 degrees C are 3.62 and 4.60, respectively (Park & Sheehan, 1996).

 

Viscosity

In accordance with Section 2 of REACH Annex XI, information requirement section 7.17, this study cannot be conducted on solid materials or gases. According to ECHA Chapter 7 guidance, viscosity measurement is only relevant to liquids.