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Diss Factsheets
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EC number: 255-288-2 | CAS number: 41272-40-6
- 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:
- migrated information: read-across from supporting substance (structural analogue or surrogate)
- Adequacy of study:
- key study
- Reliability:
- 2 (reliable with restrictions)
- Rationale for reliability incl. deficiencies:
- other: Data from reviews Read across from a similar substance which has the same main component and with a different counter ion that doesn't influence the characteristics related to the specific end-point
- Reason / purpose for cross-reference:
- reference to same study
- Principles of method if other than guideline:
- Colourimetry method. The speed at which the equilibrium (I <--> II) was attained was measured at various pH values, and the degree of ionization, at each pH value, was calculated only after equilibrium had been established. Ionization constants were calculated from the degrees of ionization of the bases at equilibrium at various pH values, by means of the law of mass action.
- Dissociating properties:
- yes
- pKa:
- ca. 6.9
- Temp.:
- 25 °C
- Conclusions:
- The basic triphenylmethane dyes can exist in the form of coloured cations (as in the acid salts) or as undissociated bases, the carbinols. The percentage of the dye in the cationic state is therefore dependent on the hydrogenion concentration of the system, and the greater the hydrogen-ion concentration, the greater the dissociation into the cationic form. Experiments with such dyes are complicated by two of their inherent properties. First, the equilibrium between the cation and the carbinol often requires an appreciable time to become established; and secondly, the carbinol form is relatively insoluble. At certain hydrogen-ion concentrations the carbinol form began to precipitate. In these circumstances a true equilibrium could not be established.
pK = 6.9 - Executive summary:
Data was reported in two review, in which are reported different aspects of the original study (Goldrace and Phillips, 1949).
Data is referred to Malachite Green (MG); read across between chloride, oxalate and acetate salts form of MG have the same main component and have a different counter ion that doesn't influence the characteristics related to the specific end-point.
Resuts:
The ionisation constant (pK) of MG is 6.90. It is 100% ionised at pH 4.0, 50% at pH 6.9, 25% at 7.4 and 0% at pH 10.1
Conclusion:
The basic triphenylmethane dyes can exist in the form of coloured cations (as in the acid salts) or as undissociated bases, the carbinols. The percentage of the dye in the cationic state is therefore dependent on the hydrogenion concentration of the system, and the greater the hydrogen-ion concentration, the greater the dissociation into the cationic form. Experiments with such dyes are complicated by two of their inherent properties. First, the equilibrium between the cation and the carbinol often requires an appreciable time to become established; and secondly, the carbinol form is relatively insoluble. At certain hydrogen-ion concentrations the carbinol form began to precipitate. In these circumstances a true equilibrium could not be established. Malachite Green it is 100% ionised at pH 4.0, 50% at pH 6.9, 25% at 7.4 and 0% at pH 10.1
Reference
Effect of pH on degree of ionization; (α) Malachite Green 27 x 10-6M at 25°C
pH | Extinction coefficient (E) (red filter) | Degree of ionization (α) | logα/ (1 α) | pK |
4.00 | 0.113 | 1.00 | - | - |
6.09 | 0.097 | 0.86 | 0.80 | 6.89 |
6.60 | 0.075 | 0.66 | 0.30 | 6.90 |
6.78 | 0.060 | 0.53 | 0.06 | 6.84 |
6.97 | 0.052 | 0.46 | - 0.07 | 6.90 |
7.10 | 0.044 | 0.39 | - 0.20 | 6.90 |
7.42 | 0.026 | 0.23 | - 0.52 | 6.90 |
10.1 | 0.000 | 0.00 | - | - |
T1/2 = time required for degree of ionization to fall half-way from 100% to its equilibrium value, at a pH value equal to the pK.
MG (4:4'-bisdimethylaminotriphenyl-carbinol) | 2.7 x 106M | pK: 6.90 | T1/2 hours: 2.1 |
Rate of disappearance of the coloured ion of Malachite Green
Concentration: 1.3 x 10-5M at pH 7.90 (20°C)
Time, mins | Extinction coefficient (red filter) | k x 103 |
2 | 0.424 | - |
12 | 0.386 | - |
22 | 0.362 | 6.4 |
32 | 0.341 | 6.0 |
42 | 0.320 | 6.4 |
52 | 0.300 | 6.4 |
∞ | 0.100 | - |
Description of key information
Key value for chemical safety assessment
Additional information
The dissociation constant (pKa) of Malachite Green has been considered and derived from the solvolytic reaction indicated by Goldacre in 1949. MG is 100% ionised at pH 4.0, 50% at pH 6.9, 25% at 7.4 and 0% at pH 10.1
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