2-methylhydroquinone

Additional information on environmental fate and behaviour

Administrative data

Endpoint:

additional information on environmental fate and behaviour

Type of information:

experimental study

Adequacy of study:

key study

Study period:

19.05.2018 – 13.09.2018

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

study originally performed to examine hydrolysis of the test substance

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2018

Report date:

2018

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD Test No. 111: Hydrolysis as a Function of pH

Version / remarks:

2004

Deviations:

yes

Remarks:

transformation products were not identified

GLP compliance:

no

Remarks:

accredited by DAkkS

Test material

Test material information

Constituent 1

Reference substance name:

2-methylhydroquinone

EC Number:

202-443-7

EC Name:

2-methylhydroquinone

Cas Number:

95-71-6

Molecular formula:

C7H8O2

IUPAC Name:

2-methylbenzene-1,4-diol

Test material form:

solid: particulate/powder

Results and discussion

Any other information on results incl. tables

Although the test item methylhydroquinone does not possess functional groups being associated with hydrolysis, an abiotic degradation takes place in buffered aqueous test samples, apparently. During the tests a discoloration from colorless to yellowish-brown/dark brown was observed. In the subsequent liquid extraction using ethyl acetate the organic phase took over this yellow-brown discoloration whereas the aqueous phase maintained it and was only weakly discolored in turn. By concentration measurement of methylhydroquinone by means of GC-MS a decrease in concentration in time was determined. However, the GC-MS chromatograms showed no new additional and prominent signals. Hence, it was initially assumed that the degradation products are possibly not extractable using ethyl acetate. The subsequent performed GC-MS measurements of the aqueous phase were not successful. No sufficiently volatile substances could be detected.

ESI-MS analysis revealed for the sample (pH 7-buffer, over 24 h, 50°C) a clearly different mass spectrum in comparison to the one of methylhydroquinone. A multitude of fragment and fragment groups were detected in the m/z-area of 150 – 700. A main component could not be determined by means of spectra comparison. Also, an unambiguous identification of single compounds was not possible. The most obvious assumption for this outcome is a slow reaction or slow reactions with the buffer system. A complex reaction mixture with no identifiable products is the result. On the TLC-plate a grey track below the methylhydroquinone spot was observed.

In NMR-measurements also no conclusions could be drawn to possibly formed main degradation products. A multitude of further signals with low intensity could be observed in the shift range of aliphatic protons (0.5 - 2.5 ppm). Also, additional signals in the shift area of aromatic protons were observed.¹³C-NMR measurements did not provide further insights.

Applicant's summary and conclusion

Conclusions:

Methylhydroquinone is stable in aqueous solution at pH 4 at 20°C, 27°C and 50°C for at least 5 days.
Methylhydroquinone is not stable in aqueous solution at pH 7 and pH 9 at 20°C, 27°C and 50°C and degrades within 700 h to at least 50% of the intial concentration.

Executive summary:

The tests were performed to describe the abiotic degradation of methylhydroquinone considering the scenario of an unintended release into surface water. Test performed at different pH values and temperatures revealed a relative stability of methylhydroquinone at pH 4 and distinct temperature-dependent degradation kinetics at pH 7 and pH 9. For both pH values and all applied incubation temperatures the kinetic parameters k (velocity constant) and DT₅₀ (time to reach 50% of the initial concentration) were calculated. The performed tests to describe the occuring reactions lead to the hypothesis that the observed process is not a hydrolysis of methylhydroquinone but a slow reaction with the used buffer system leading to a complex reaction mixture with substances that could not be identified any further.