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EC number: 266-442-3 | CAS number: 66669-53-2
- 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
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- Sediment toxicity
- Terrestrial toxicity
- Biological effects monitoring
- Biotransformation and kinetics
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- Toxicological Summary
- Toxicokinetics, metabolism and distribution
- Acute Toxicity
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- Specific investigations
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- Additional toxicological data

Dissociation constant
Administrative data
Link to relevant study record(s)
- Endpoint:
- dissociation constant
- Type of information:
- (Q)SAR
- Adequacy of study:
- key study
- Study period:
- 2012
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- other: Accepted calculation method
- Justification for type of information:
- QSAR prediction
- Guideline:
- other: REACH guidance on QSARs R.6, May 2008
- Principles of method if other than guideline:
- ACD 7.0 software program for estimating the dissociation constant (pKa) in water.The recommended method, “apparent constants, approximated”, was used for the estimation. The program was developed by Advanced Chemistry Development Inc.
90 Adelaide Street West, Toronto, Ontario, M5H 3V9, Canada (http://www.acdlabs.com); Copyright © 1994-2003; Build: 18 April 2003 - GLP compliance:
- no
- Dissociating properties:
- yes
- No.:
- #1
- pKa:
- 8.59
- Temp.:
- 25 °C
- Remarks on result:
- other: HL/H+L
- No.:
- #2
- pKa:
- 4.99
- Temp.:
- 25 °C
- Remarks on result:
- other: H2L/H+HL
- No.:
- #3
- pKa:
- 4.44
- Temp.:
- 25 °C
- Remarks on result:
- other: H3L/H+H2L
- No.:
- #4
- pKa:
- 3.99
- Temp.:
- 25 °C
- Remarks on result:
- other: H4L/H+H3L
- No.:
- #5
- pKa:
- 1.08
- Temp.:
- 25 °C
- Remarks on result:
- other: H5L/H+H4L
- Conclusions:
- As generally dissociating properties of salts cannot be estimated by the program, estimation results of the parent acid 2-phosphonobutane-1,2,4-tricarboxylic acid are taken into account for this endpoint. The dissociation constants for 2-phosphonobutane-1,2,4-tricarboxylic acid are estimated to be pKa1 of 8.59, pKa2 of 4.99, pKa3 of 4.44, pKa4 of 3.99 and pKa5 of 1.08.
- Executive summary:
As generally dissociating properties of salts cannot be estimated by the program, the dissociation constants of the parent acid 2-phosphonobutane-1,2,4-tricarboxylic acid were estimated by ACD/pKa DB included in ACD/labs 7.00 Release. According to the estimated results, this substance presents mainly as ionic form under environmentally relevant pH 5 - 9.
Reference
1. Defined endpoint: Dissociation constant (pKa) in water
2. Unambiguous algorithm: For 2-phosphonobutane-1,2,4-tricarboxylic acid the following fragments descriptors (parent compound) and one structure (parent compound) descripter were identified as reaction centres: R-P(=O)(OH)(O-), C(=O)(O)-R-CH2 -CH2 -CH3, R-P(=O)(OH)(OH), R-C(=O)-CH2 -CH2 -C(=O)(OH) and C(=O)(OH)-CH2 -P(=O)(OH)(O-).
3. Applicable domain: The identified reaction centers have been found as fragments in the Internal Reaction Centers Database with experimental equations. The substance only contains 28 atoms, which is much less than the limit of ACD/pKa DB of 255. The substance only contains five ionization centres with one fragment for each. The substance does not contain the atoms, what are not accepted by ACD/pKa DB. The fragment that occurs in the structure of 2-phosphonobutane-1,2,4-tricarboxylic acid applied by the program is verified by the user. The rules applied for the substance appears appropriate. An individual uncertainty for the investigated substance is not available.
4. Statistical characteristics: Each calculation from ACD/pKa DB is provided with its 95 % confidence interval and, when available, literature references with experimental results. The accuracy of calculations for simple structures is usually better than ±0.2 pKa units (for complex structures it is better than ±0.5 pKa units).
5. Mechanistic interpretation: The mechanistic basis of the model is the linear free energy relationship (LFER), which is an empirical correlation between the standard free energies of reaction or activation for two series of reactions, both subjected to the same variations in reactant structures or reaction conditions. As applied to the estimation of acid dissociation constants, the LFER is basically a substituent-effect approach.
6. Adequacy of prediction: The result for 2-phosphonobutane-1,2,4-tricarboxylic acid falls within the applicability domain described above and the estimation rulesapplied for the substance appears appropriate. Therefore the predicted value can be considered reliable yielding a useful result for further assessment.
Description of key information
As generally dissociating properties of salts cannot be estimated by the program, estimation results of the parent acid 2-phosphonobutane-1,2,4-tricarboxylic acid are taken into account for this endpoint. The dissociation constants for 2-phosphonobutane-1,2,4-tricarboxylic acid are estimated to be pKa1 of 8.59, pKa2 of 4.99, pKa3 of 4.44, pKa4 of 3.99 and pKa5 of 1.08 indicating that this substance presents mainly as ionic form under environmentally relevant pH 5 - 9.
Key value for chemical safety assessment
- pKa at 20°C:
- 8.59
Additional information
The calculation of the dissociation constants of 2-phosphonobutane-1,2,4-tricarboxylic acid in water was performed by software ACD ChemSketch ACD/Labs 7.00 Release, Product Version 7.05. Usually the resulting dissociation constants are calculated for 20°C.
2-phosphonobutane-1,2,4-tricarboxylic acid in water can release 5 protons step by step.
Each release is described by one equilibrium reaction or equilibrium constant (pKa):
1. pKa (HL = H+L) = 8.59 ± 0.50
2. pKa (H2L = H+HL) = 4.99 ± 0.14
3. pKa (H3L = H+H2L) = 4.44 ± 0.10
4. pKa (H4L = H+H3L) = 3.99 ± 0.21
5. pKa (H5L = H+H4L) = 1.08 ± 0.42
Depending on the pKa value, the acid dissociation constants indicate strong (pKs < 3.8), medium strong (pKs < 7.2) and weak (pKs < 16) acids.
The pKa values indicate neither very strong nor very weak acids.
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