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EC number: 604-721-7 | CAS number: 150114-71-9
- Life Cycle description
- Uses advised against
- Endpoint summary
- Appearance / physical state / colour
- Melting point / freezing point
- Boiling point
- Density
- Particle size distribution (Granulometry)
- Vapour pressure
- Partition coefficient
- Water solubility
- Solubility in organic solvents / fat solubility
- Surface tension
- Flash point
- Auto flammability
- Flammability
- Explosiveness
- Oxidising properties
- Oxidation reduction potential
- Stability in organic solvents and identity of relevant degradation products
- Storage stability and reactivity towards container material
- Stability: thermal, sunlight, metals
- pH
- Dissociation constant
- Viscosity
- Additional physico-chemical information
- Additional physico-chemical properties of nanomaterials
- Nanomaterial agglomeration / aggregation
- Nanomaterial crystalline phase
- Nanomaterial crystallite and grain size
- Nanomaterial aspect ratio / shape
- Nanomaterial specific surface area
- Nanomaterial Zeta potential
- Nanomaterial surface chemistry
- Nanomaterial dustiness
- Nanomaterial porosity
- Nanomaterial pour density
- Nanomaterial photocatalytic activity
- Nanomaterial radical formation potential
- Nanomaterial catalytic activity
- Endpoint summary
- Stability
- Biodegradation
- Bioaccumulation
- Transport and distribution
- Environmental data
- Additional information on environmental fate and behaviour
- Ecotoxicological Summary
- Aquatic toxicity
- Endpoint summary
- Short-term toxicity to fish
- Long-term toxicity to fish
- Short-term toxicity to aquatic invertebrates
- Long-term toxicity to aquatic invertebrates
- Toxicity to aquatic algae and cyanobacteria
- Toxicity to aquatic plants other than algae
- Toxicity to microorganisms
- Endocrine disrupter testing in aquatic vertebrates – in vivo
- Toxicity to other aquatic organisms
- Sediment toxicity
- Terrestrial toxicity
- Biological effects monitoring
- Biotransformation and kinetics
- Additional ecotoxological information
- Toxicological Summary
- Toxicokinetics, metabolism and distribution
- Acute Toxicity
- Irritation / corrosion
- Sensitisation
- Repeated dose toxicity
- Genetic toxicity
- Carcinogenicity
- Toxicity to reproduction
- Specific investigations
- Exposure related observations in humans
- Toxic effects on livestock and pets
- Additional toxicological data
Dissociation constant
Administrative data
Link to relevant study record(s)
- Endpoint:
- dissociation constant
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Study period:
- 19 June 2001 to 25 June 2001
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- guideline study
- Qualifier:
- according to guideline
- Guideline:
- OECD Guideline 112 (Dissociation Constants in Water)
- Deviations:
- no
- GLP compliance:
- yes
- Specific details on test material used for the study:
- Purity: 99.5%
- Dissociating properties:
- yes
- No.:
- #1
- pKa:
- 2.56
- Temp.:
- 20 °C
- Conclusions:
- Under the conditions of the study, the acid dissociation constant (pKa) for the test material was found to be 2.56 ± 0.03.
- Executive summary:
The dissociation constant of the test material was determined using UV-Visible spectrophotometry in a study which was conducted under GLP conditions and in accordance with the standardised guideline OECD 112.
During the study a scan of the test material in 0.1 N HCl (test material present as the molecular species) was overlaid with a scan of the test material in 0.01 N KOH (test material present as the ionised species). From these initial scans, an analytical wavelength (wavelength where the greatest difference between the absorbances of the molecular and ionised species was observed) of 272.1 nm was chosen.
The test material was prepared at constant concentration in nine buffer solutions of pH where the compound was only partially ionised. The pH measurements for the nine test material solutions were 2.06, 2.22, 2.23, 2.56, 2.57, 2.87, 3.16, 3.30 and 3.40. The absorbance of these solutions was measured at 272.1 nm, and an average pKa value for the test material of 2.56 ± 0.03 was calculated.
Reference
Isolation of Ionic Species and Determination of Analytical Wavelength
The absorbance scan for the test material solution in 0.01 N and 0.1 N KOH showed absorbances differences at the peaks of <1 % indicating that in 0.01 N KOH the test material was fully (>99 %) dissociated or ionised.
A large absorbance difference was noted between the UV-Visible scan of the test material in 0.01 N HCl and the scan in 0.1 N HCl, indicating that isolation of the two species was incomplete. A test material solution was then prepared in 1 N HCl and the resulting scan showed absorbances differences at the peaks of <1 % when compared to the scan of the test material solution prepared in 0.1 N HCl. This indicated that the test material was predominantly (>99 %) present as the molecular species in 0.1 N HCl.
UV-Visible Scans from the test material prepared in 0.01 N KOH and 0.1 N HCl were then overlaid and an analytical wavelength of 272.1 nm was selected for further analyses.
Preliminary and Definitive Dissociation Constant Determination
All measurements were made at 20 °C. The absorbance of the test material prepared in 0.01 N KOH was 0.1851 (Ai) and absorbance of the test material prepared in 0.1 N HCl (Am) was 0.9859.
The preliminary pKa determination showed an approximate value of 2.6.
Absorbance, pH and calculated pKa values for the definitive determination are shown in Table 1.
The acid dissociation constant (pKa) for the test material was found to be 2.56 ± 0.03.
Table 1: Values of Measured pH and Absorbance at 20 °C for Nine Buffer Solutions containing Test Material, and Calculated pKa
pH of test material solution |
Measured absorbance at 272.1 nm |
pKa (calculated from equation 2) |
2.06 |
0.8039 |
2.59 |
2.22 |
0.7441 |
2.58 |
2.23 |
0.7414 |
2.59 |
2.56 |
0.5798 |
2.55 |
2.57 |
0.5759 |
2.55 |
2.87 |
0.4377 |
2.53 |
3.16 |
0.3471 |
2.56 |
3.30 |
0.3105 |
2.57 |
3.40 |
0.2869 |
2.56 |
Description of key information
pKa = 2.56 ± 0.03, OECD 112 using UV-Visible spectrophotometry, Cathie (2001)
Key value for chemical safety assessment
- pKa at 20°C:
- 2.56
Additional information
The dissociation constant of the test material was determined using UV-Visible spectrophotometry in a study which was conducted under GLP conditions and in accordance with the standardised guideline OECD 112. The study was assigned a reliability score of 1 in line with the criteria of Klimisch et al. (1997).
During the study a scan of the test material in 0.1 N HCl (test material present as the molecular species) was overlaid with a scan of the test material in 0.01 N KOH (test material present as the ionised species). From these initial scans, an analytical wavelength (wavelength where the greatest difference between the absorbances of the molecular and ionised species was observed) of 272.1 nm was chosen.
The test material was prepared at constant concentration in nine buffer solutions of pH where the compound was only partially ionised. The pH measurements for the nine test material solutions were 2.06, 2.22, 2.23, 2.56, 2.57, 2.87, 3.16, 3.30 and 3.40. The absorbance of these solutions was measured at 272.1 nm, and an average pKa value for the test material of 2.56 ± 0.03 was calculated.
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