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

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

other: read across from analogue substance

Adequacy of study:

weight of evidence

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Data from literature; despite the experiment is well documented and scientifically acceptable, some details about the test material and test procedures are missing. Read across from a similar substance which has the same main component and with a different counter ion that does not influence the characteristics related to the specific end-point.

Principles of method if other than guideline:

A test tube with glass stopper containing 50 ml of 10 mg/l Malachite Green (MG) solution entirely enclosed by tinfoil was placed in a temperature-controlled reactor. The absorbance variation was measured by UV–vis spectrometer at regular time intervals and degradation intermediates were separated and identified by LC-ESI-MS and GC–MS.

GLP compliance:

not specified

Details on sampling:

SAMPLE PREPARATION FOR THE DEGRADATION PRODUCTS
The SPE cartridges (Waters Oasis MCX column, 6ml/150 mg) were equilibrated by 3 ml acetonitrile and 3 ml 2 % (V/V) formic acid solution. Next, 10 ml final reaction solutions were loaded through the cartridges at 0.2 ml/min. Subsequently, 2 ml 2 % (V/V) formic acid/acetonitrile solution and 6 ml acetonitrile were added in turn at 2 ml/min to perform washing process. Afterwards, 4 ml 5 % (V/V) ammonium acetate (5 mol/l, pH 7.0)/methanol solution was added at 1ml/min to complete the elution. Finally, the eluents were transferred into rotary evaporator flasks and evaporated at 40 °C until almost dry. The final product was prepared into 1 ml acetonitrile solution and analyzed by LC-ESI–MS.

Details on test conditions:

A test tube with glass stopper containing 50 ml of 10 mg/l MG solution entirely enclosed by tinfoil was placed in a temperature-controlled reactor. The absorbance variation was measured by UV–vis spectrometer at regular time intervals and degradation intermediates were separated and identified by LC-ESI-MS and GC–MS.

Duration:

40 h

Initial conc. measured:

10 mg/L

Preliminary study:

Hydrolysis: 18.80 % after 40 h (rate constant: 0.0192/h; R2= 0.9409)

Transformation products:

no

Details on hydrolysis and appearance of transformation product(s):

Results from LC–MS identification
Intermediates were detected as follows:
(1) 2.88 min, m/z = 329.4, MG; m/z = 347.3, MG leucocarbinol.
(2) 3.47 min, m/z = 315.4, MG− CH2; 329.4, MG.
(3) 4.37 min, m/z = 331.3, LMG.
(4) 4.80 min, m/z = 329.4, MG; m/z = 361.2, MG + 2OH.
These results conformed to the fact that MG, MG leucocarbinol and LMG can transform naturally to each other in water matrix.

Results from GC–MS identification
The TIC of hydrolysis differed.

% Recovery:

81.2

pH:

8

Duration:

40 h

Remarks on result:

other: see details in the sections above

Other kinetic parameters:

Rate constant kh was 0.0192/h (R2 = 0.9409)

Details on results:

After 40 h hydrolysis, 81.20 % of MG was still remaining. Hydrolysis was fit by first-order kinetics model and its apparent rate constant kh was 0.0192/h (R2 = 0.9409). The spectra variation shows no blue shift of the major peaks at about 315 nm, 425 nm, and 618 nm, but the peaks exhibit a slight decrease trend. Meanwhile a slight increase trend between 200 nm and 280 nm is observable, indicating the slight increase trend of benzene rings and conjugated structure with double bonds. This observation is consistent with the LC–MS results.
Based on the structure of MG, the triarylmethyl cation is stabilized by the conjugation that delocalizes the positive charge and Cl− is a good leaving group. Therefore, the hydrolysis mechanism should be SN1 mechanism and the reaction rate is unrelated to the concentration of the nucleophile H2O.
MG+Cl- → MG+ + Cl-
MG+ + H2O → MGOH + H+
The pH varied from 8.98 to 7.87 in the reaction process, which conformed to the presumption above.

Conclusions:

Hydrolysis: 18.80 % after 40 h (rate constant: 0.0192/h; R2= 0.9409)
MG, MG leucocarbinol and LMG can transform naturally to each other in water matrix.

Executive summary:

A test tube with glass stopper containing 50 ml of 10 mg/l Malachite Green (MG) solution entirely enclosed by tinfoil was placed in a temperature-controlled reactor. The absorbance variation was measured by UV–vis spectrometer at regular time intervals and degradation intermediates were separated and identified by LC-ESI-MS and GC–MS.

After 40 h hydrolysis, 81.20 % of MG was still remaining. Hydrolysis was fit by first-order kinetics model and its apparent rate constant kh was 0.0192/h (R2 = 0.9409). The spectra variation shows no blue shift of the major peaks at about 315 nm, 425 nm, and 618 nm, but the peaks exhibit a slight decrease trend. Meanwhile a slight increase trend between 200 nm and 280 nm is observable, indicating the slight increase trend of benzene rings and conjugated structure with double bonds. This observation is consistent with the LC–MS results. Based on the structure of MG, the triarylmethyl cation is stabilized by the conjugation that delocalizes the positive charge and Cl− is a good leaving group. Therefore, the hydrolysis mechanism should be SN1 mechanism and the reaction rate is unrelated to the concentration of the nucleophile H2O. The pH varied from 8.98 to 7.87 in the reaction process, which conformed to the presumption above.

Results from LC–MS conformed to the fact that MG, MG leucocarbinol and LMG can transform naturally to each other in water matrix.

Conclusion

Hydrolysis: 18.80 % after 40 h (rate constant: 0.0192/h; R²= 0.9409)

MG, MG leucocarbinol and LMG can transform naturally to each other in water matrix.

Reference 2

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: Data from literature; despite the global experiment is well documented and scientifically acceptable, the hydrolysis determination part of study miss of some information and details.

Principles of method if other than guideline:

Data taken from an experiment of photodegradation. Hydrolysis experiments were performed using 250 ml amber glass bottles, which were kept in the dark during the tests and the substance decrease from the initial concentration was measured.

GLP compliance:

not specified

Radiolabelling:

no

Preliminary study:

A 45 % decrease in initial MG concentration was observed in 145 hours, showing that a part of MG degradation is due to hydrolysis.

Transformation products:

no

Remarks on result:

other: see details in the sections

Remarks on result:

other: see details in the sections

Conclusions:

A 45 % decrease in initial MG concentration was observed in 145 hours, showing that a part of MG degradation is due to hydrolysis.

Executive summary:

Data obtained in combination with an experiment of photodegradation (see 5.1.3 phototransformation in water).

Hydrolysis experiments were performed using 250 ml amber glass bottles, which were kept in the dark during the tests and the substance decrease from the initial concentration was measured.

A 45 % decrease in initial Malachite Green Oxalate (MGO) concentration was observed in 145 hrs, showing that a part of MGO degradation is due to hydrolysis.

Description of key information

Malachite Green Oxalate (MGO), hydrolysis t1/2 (45%) ca. 145h in dark conditions, ambient temperature

 

Additional information

A 45 % decrease in initial Malachite Green Oxalate (MGO) concentration was observed in 145 hours under dark conditions, showing that an important part of MGO degradation is due to hydrolysis (Pérez-Estrada et al., 2008).

Further data, obtained in combination with an experiment of photodegradation, showed that MG hydrolysis reaction after 40 h was 18.80 %; hydrolysis was fit by first-order kinetics model and its apparent rate constant kh was 0.0192/h (R2 = 0.9409). Based on the structure of MG, the triarylmethyl cation is expected to be stabilized by the conjugation that delocalizes the positive charge and a good leaving group. Therefore, the hydrolysis mechanism should be S_N1 mechanism and the reaction rate is unrelated to the concentration of the nucleophile H₂O. The pH varied from 8.98 to 7.87 in the reaction process. Results from LC–MS confirmed to the fact that MG, MG leucocarbinol and Leucomalachite Green can transform naturally to each other in water matrix (Yong et al., 2015).