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EC number: 476-160-4
CAS number: 54807-34-0
A result of 9.19 pKa was determined for the read-across substance 5,5-dimethylhydantoin (DMH) from e.m.f measurements on the cell H2/Acid-base solution/saturated KCl/HgCl/Hg.Due to the degradability of 5,5-dimethylhydantoin, sodium salt (NaDMH) it wasn't possible to conduct a Dissociation Constant study according to OECD Method 112. Instead a Dissociation Constant prediction was carried out using specialist prediction software.The structure of the submission material could not be inputted completely into the predictive software as the software is unable to process metallic elements. The structure was therefore inputted with a hydrogen atom replacing the sodium atom. As the substance degrades rapidly to its parent material in the presence of water, this would be the structure of the test item when in contact with water.Predicted pKa's were as follows:Functional Group 1: 8.93 ± 0.10Functional Group 2: 16.33 ± 0.40Functional Group 2: -1.13 ± 0.40
Both reports have been assigned a
reliability rating of 2 however the decision was taken to assign the
read-across study as the key study for the following reasons: It is
recognized that in water, 5,5 -dimethylhydantoin, sodium salt (NaDMH)
dissociates rapidly and becomes converted to the substance
dimethylhydantoin (DMH).This process of protonation of NaDMH by water to
form DMH occurs relatively easily in the presence of water or any other
similar proton-donating substance.The half-life for this transformation
is considered to be relatively short. It was not possible to conduct
either a full study or a dissociation constant prediction on the
registerable substance due to the degrgadability of the test material
and limitations with the prediction software. As a result the prediction
was based on the structure of the test item when in contact with water,
this being the parent material 5,5 -dimethylhydantoin (DMH). Furthermore
as the justification for using read-across material is that 5,5
-dimethylhydantoin, sodium salt dissociates to 5,5 -dimethylhydantoin
and that an experimental result was able to be obtained on the
read-across material, it was considered that the read-across study
should be the key study of interest.
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