Sodium 3-amino-2,4,6-triiodobernzoate

Dissociation constant

Administrative data

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

13 October 2002

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2003

Report date:

2003

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Schering project “Ecotoxicological Evaluation of Starting Materials, Intermediates and Drug Substances”. The project is part of the “Freiwillige Selbstverpflichtung der deutschen chemischen Industrie für die Erfassung und Bewertung von Stoffen” (voluntary self commitment of the German chemical industry to catalogue and evaluate chemicals) as promoted by the VCI (Verband der Chemischen Industrie).The guidance provided by the VCI calls for valid data with respect to the aim of the project, namely to gain of information on the behavior or the persistence and fate of such compounds in the environment.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Sodium 3-amino-2,4,6-triiodobernzoate

EC Number:

614-015-0

Cas Number:

67031-56-5

Molecular formula:

C7-H3-I3-N-O2.Na

IUPAC Name:

Sodium 3-amino-2,4,6-triiodobernzoate

Test material form:

solid: bulk

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: WBF, Bergkamen, Schering AG; Batch number 60707022

Results and discussion

Dissociating properties:

yes

Dissociation constant

Dissociation constant 1

No.:

#1

pKa:

>= 1.53 - <= 1.93

Temp.:

25 °C

Remarks on result:

other:

Remarks:

Photometric titration

Dissociation constant 2

No.:

#2

pKa:

< -1

Temp.:

25 °C

Remarks on result:

other:

Remarks:

Hammett Equ.:

Any other information on results incl. tables

 The pKa-values were obtained in aqueous solution with a photometric method at different wavelengths.

 

Wavelengths (nm)	pKa2– Exp.1	pKa2– Exp.1
230	1.48	1.58
250	1.93	1.77
330	1.70	1.93

 

Averaging the results of the two experiments obtained at different wavelengths gives the

following mean pKa – value (with 95% confidence interval):pKa₁= 1.73 ± 0.2, s = 0.18.

 

In addition the pKa values were calculated using the following Hammett equations (Ref.1) and the computer program ACD/pKa (Ref.2).

 

Benzoic acid: pKa = 4.2 – Σσ

Anilinium ion: pKa = 4.58 – 2.88⋅Σσ

 

The results of the two methods are summarized in the table below.

 

 Results of pKa calculation

	Hammett Equ.	ACD/pKa
-COOH	1.3	1.51
-NH3^+	-1.1	-1.41

 

Therefore, the pKa value of the protonated anilin group can be estimated to be:pKa₂< -1.

Applicant's summary and conclusion

Conclusions:

The acid dissociation constant of the carboxylic group of the test substance was determined at 25 °C with a photometric titration method as pKa1= 1.7 ± 0.2, using Photometric titration and pKa2< -1 using the Hammett Equation.

Executive summary:

The acid dissociation constant of the carboxylic group of the test substance was determined at 25 °C with a photometric titration method. The pKa value of the protonated anilin group was estimated using a Hammett equation and a calculation with the computer program ACD/pKa. The following pKa values were obtained:

 

Photometric titration: pKa₁= 1.7 ± 0.2

Hammett Equ.: pKa₂< -1