Disodium hydroxy(sulfonato)acetate

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

september 2012 - november 2012

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: performance of the study was not inspected

Qualifier:

according to guideline

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

GLP compliance:

yes

Specific details on test material used for the study:

Name: BLANCOLEN HP Disodiumhydroxy(sulfonato)acetate
Batch no.: 09102303
Designation in Test Facility: 12092101G

Dissociating properties:

yes

No.:

#1

Remarks on result:

other: determination not possible

Main Test 1

The intercept of the linear fit of the Kohlrausch correlation represents the limit conductivity

of the test item (conductivity in unlimited dilution): 234.71 S*cm2*Mol-1.

Concentration.	Molar Conductivity.	Limit Conductivity	Degree of Dissociation
Mol/L	S*cm^2*Mol^-1	S*cm^2*Mol^-1	α
6.249E-04	225.62255	234.71	0.9612900
1.250E-03	221.62215	234.71	0.9442458
2.500E-03	215.62155	234.71	0.9186796
5.000E-03	207.82077	234.71	0.8854435
9.999E-03	197.61975	234.71	0.8419809

With the calculatedα,K_Dwas determined.

Degree of Dissociation	Dissociation Constant	- log (Dissociation Constant)
α	KD	pKD
0.9612900	0.014918	1.8262782
0.9442458	0.019988	1.6992407
0.9186796	0.025943	1.5859748
0.8854435	0.034216	1.4657714
0.8419809	0.044859	1.3481484

 

The mean of the measured values would be 1.59, standard deviation is 0.19 (RSD=11.9%), but the values showed a decreasing tendency with increasing concentration.

Main Test 2

The intercept of the linear fit of the Kohlrausch correlation represents the limit conductivity of the test item (conductivity in unlimited dilution): 233.92 S*cm²*Mol^-1.

Concentration.	Molar Conductivity.	Limit Conductivity	Degree of Dissociation
Mol/L	S*cm^2*Mol^-1	S*cm^2*Mol^-1	α
6.249E-04	224.34243	233.92	0.9590727
1.250E-03	221.62215	233.92	0.9474434
2.500E-03	215.62155	233.92	0.9217906
5.000E-03	208.02079	233.92	0.8892971
9.999E-03	197.41973	233.92	0.8439771

With the calculatedα,K_Dwas determined

Degree of Dissociation	Dissociation Constant	- log (Dissociation Constant)
α	KD	pKD
0.9590727	0.014045	1.8524738
0.9474434	0.021347	1.6706541
0.9217906	0.027158	1.5660978
0.8892971	0.035716	1.4471389
0.8439771	0.045649	1.3405704

The mean of the measured values would be 1.58, standard deviation is 0.20 (RSD=12.6%), but the values showed a decreasing tendency with increasing concentration.

Conclusions:

A dissociation constant could not be determined according to the OECD 112 guideline.

Executive summary:

The conductometric approach for the determination of the dissociation constant was chosen

on behalf of the properties of the test item. A titrimetric determination was not possible

as no point of equivalence could be observed neither by titration with acid nor with base. A

photometric determination was not possible as the UV/Vis spectrum did not change with

the pH.

The evaluation of the conductometric method showed a linear Kohlrausch correlation, indicating

that the test item is a strong electrolyte, but the calculated values, derived with

equation 2, showed a downward tendency. For a valid evaluation the calculated values

would show an asymptotic approximation with decreasing test item concentration (as it is

the case for e.g. acetic acid). The limit value determined in such a manner is then called

dissociation constant KD, its negative common logarithm is called pKD. For the test item,

such a limit value could not be determined. Therefore, the conductometric method yields

no reliable result, but confirms that the test item BLANCOLEN HP

Disodiumhydroxy(sulfonato)acetate is a strong electrolyte. With the conductometric

method it is not possible to distinguish if the sodium ions are dissociated either from the

carbonic acid or the sulfonic acid group. In conclusion it is not possible to determine a

dissociation constant following the OECD 112 guideline, neither using the titrimetric nor

the photometric nor the conductometric method.

As the test item is a sodium salt of a strong acid containing vincinal chemical groups with

high electronegativities it can be concluded that the test item would be virtually completely

ionised at environmentally relevant pH’s.

From the result of the titrimetric tests - no point of equivalence could be determined - it can

be further concluded that the anionic derivatives of the substance do not exhibit

noteworthy basic properties.

Description of key information

The test item behaves like a strong electrolyte (like a salt), which means that it dissociates quite completely.
It is not suspected to exhibit noteworthy basic properties.
Determination of a dissociation constant according to the OECD guideline 112 was not possible.

Additional information

In conclusion it is not possible to determine a dissociation constant following the OECD 112 guideline, neither using the titrimetric nor the photometric nor the conductometric method.