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EC number: 603-094-7
CAS number: 125904-11-2
The pKa values for phosphoric acid were 2.38 and 7.06 at 25 °C.
The pKa value for 4 -nitrophenol was 6.99 at 22.1 °C. The reference
substance data were in good agreement with the literature values.
The pKa estimate obtained for DBS in the preliminary trial was
5.41. The preliminary results also indicated that a relatively weak NaOH
solution would be required. Therefore, a 0.001 N NaOH solution was
prepared and standardized for use in the definitive trial.
The calculated pK value for DBS is summarized below:
Table 1: pK Values of DBS at 20 °C
(CV = 1.27%)
Antilog (-pKa) = 1.91 x 10-7
1 Results were generated using Excel 2000 in the full precision
mode. Manual calculations may differ
Table 2: Determination of dissociation constant
% ionised = volume/equivalence point volume
% unionised = 1 - % ionised
pKa = pH – log(% ionised/% unionised)
Equivalence point = change in pH/change in volume is greatest
In a study performed in line with OCED Guideline 112 and in compliance
with GLP, the pKa value of dibromostyrene was determined to be 6.72 (SD
= 0.0855, CV = 1.27%) at 20 ºC.
Dibromostyrene does not contain any ionisable groups (basic or acidic).
Evaluation of dibromostyrene (a representative structure of the reaction
mass) using PALLAS 220.127.116.11: pKalc (CompuDrug Chemistry Ltd.) software
indicated that dibromostyrene contains not dissociating groups.
In accordance with Annex XI, point 2 (Testing is not technically
feasible) and in accordance with the ECHA guidance document, Guidance on
information requirements and chemical safety assessment chapter R.7a:
Endpoint specific guidance (November 2012) v. 2.0, testing for
dissociating properties is technically not possible as a consequence of
the properties of the substance. The three main constituents of the
multi-constituent substance, dibromostyrene, monobromostyrene and
tribromostyrene, cannot dissociate due to a lack of relevant functional
groups; a study to determine the dissociation constant is therefore
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