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Physical & Chemical properties

Dissociation constant

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dissociation constant
Type of information:
experimental study
Adequacy of study:
supporting study
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
equivalent or similar to guideline
OECD Guideline 112 (Dissociation Constants in Water)
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
Test item name: Ethylene Glycol Dibenzoate
Purity: 100%
Appearance: White solid crystal powder
Batch No.: 6OLJG
CAS: 94-49-5
Expiration date: Nov. 20, 2023

Determination the max absorbance wavelength of the sample solution of various pH solutions, the max absorbance wavelength was 198.5 nm and 231.5 nm at acidic conditions, the max absorbance wavelength was 224.5 nm and 226.5 nm at alkaline conditions, the UV spectrum varied greatly between acidic and alkaline conditions.
Larger differences (0.73384) of absorbance between pH 10 and 11, the further tests were needed to figure out which kind of reaction had happened, dissociation or hydrolysis.
The pH of a test item solutions in alkaline conditions (original pH value was 12.35) was adjusted to acidic (final pH value was 1.58). Contrast its UV spectrogram with that of the acidic solution (original pH value was 1.65) and find that both of UV spectrograms shapes and absorbance value of characteristic absorption peak changed significantly. The results
indicated that the reaction was not reversible, so the no dissociation reaction had taken place but hydrolysis reaction.

The test item did not dissociate in water, instead it reacts and forms two different substances under alkaline conditions (see attached reaction).
No dissociation constant can be derived, therefore.
Executive summary:

The dissociation constants in water test of Ethylene Glycol Dibenzoate was determined by UV—VIS spectrophotometer. The study was designed to be compatible with the Principles of OECD Guidelines for Testing of Chemicals No.112 ‘Dissociation Constants in Water’.
The test results indicated that no dissociation reaction to the test item in water had taken place. No dissociation constants can be derived for it. 
Ethylene Glycol Dibenzoate does not contain groups that can dissociate in water. The UV spectrums varied greatly between acidic and alkaline conditions, because Ethylene Glycol Dibenzoate broke down in alkaline solution.

dissociation constant
Data waiving:
study technically not feasible
Justification for data waiving:
the study does not need to be conducted because the substance has no ionic structure

Description of key information

The endpoint is waived since the chemical structure of the test substance does not contain groups that can dissociate. This is supported by the findings of the study performed according to OECD 112.

Key value for chemical safety assessment

Additional information