Methanaminium, N-[4-[[4-(dimethylamino)phenyl]phenylmethylene]-2,5-cyclohexadien-1-ylidene]-N-methyl-, ethanedioate

Endpoint summary

Additional information

Many information about Malachite Green (MG) are available. In some cases the salification form tested is not specified, nevertheless the read across from a similar substance which has the same main component, with a different counter ion, can be considered as reliable; the possible counter-ions of Malachite Green do not signficantly impact the physicochemical properties of the substance.

 

APPEARANCE AND PHYSICOCHEMICAL STATE

MG oxalate is a green solid crystal with a metallic lustre.

During the Differential Thermal Analysis (DTA) an exothermic reaction was recorded with a heat release of about -95 J/g (onset: 153 °C). Directly before and after this exothermic reaction, endothermic reactions were detected. The melting point was stated at 145 °C, followed by decomposition at 153 °C (DyStarColours Distribution GmbH, 2005).

A melting point at 164 °C is reported in the C&L document prepared by Health and Safety Executive, UK (Health and Safety Executive, UK, 2005). In the report are indicated also a boiling point in the range of 172 – 175 °C and decomposition at 210 °C.

 

Thus, the substance undergoes decomposition at the same temperature of metling onset. Taking into account the outcomes from the DTA analysis, it is improbable that the substance may boil at 172 – 175 °C; it seems more plausible that at these temperatures the water/solvent may be released.

 

MG oxalate is manufactured as a powder characterized by a MMD of 94.2 – 121.1 µm. Particle size distribution showed that MG oxalate is characterized by particles too large to pass in bronchi and lungs (DyStarColours Distribution GmbH, 2011).

 

SOLUBILITY AND PARTITION COEFFICIENT

The affinity of MG oxalate with the n-octanol phase is low, demonstrated by LogKow of 0.8 (DyStarColours Distribution GmbH, 1998). Data collected from Bayer's studies and performed with different salification forms of MG are in a small range from -0.61 to 1.15. The estimated datum resulted higher than other values, because the neutral form is less hydrophilic than the corresponding salt forms.

 

Concerning the water solubility, the available data are all taken from review, handbook and secondary source, thus the reliability of results can be considered as comparable.

MG oxalate is expected to be completely dissociated in aquatic compartment: the ionic species and their stability is expected to be mainly pH dependent. In neutral/basic pH conditions, the MG tends to include a hydroxyl ion into the central carbon atom (breaking the double bond) and forms the MG carbinol. Speed of the reaction is proportional to the hydroxyl-ion concentration, thus the carbinol formation is expected faster in basic conditions.

 

PHYSICAL HAZARDS

MG does not ignite and propagate combustion; no chemical groups associated with oxidising properties are present in the molecule. Explosiveness test shows that substance has no impact sensitivity and an exothermic reaction occurs with onset at 153 °C. Regarding dust explosive risk, it only occurs in concentrations (≥ 100 g/m³) which are not relevant for handling in the dye facilities; these concentrations are only relevant for spray drying.

MG oxalate does not meet the criteria to be considered as flammable/explosive/oxidising.