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Physical & Chemical properties

Dissociation constant

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Description of key information

Using benzenesulfonic acid and N-[3-(dimethylamino)propyl]benzenesulfonamide as model compounds the dissociation constants of C.I. Direct Blue 264 were estimated by ACD/pKa DB included in ACD/labs 7.00 Release. According to the estimated results, the sulfonic acid side chain is mainly present in the deprotonated/dissociated form under environmentally relevant pH 5-9. Whereas the dimethylaminopropyl sulfonamide side chain is primarily protonated at the tertiary nitrogen under environmentally relevant pH 5-9.

Key value for chemical safety assessment

pKa at 20°C:
9.19

Additional information

C.I. Direct Blue 264 is an UVCB substance consisting of phthalocyanine copper complexes. All constituents have copper phthalocyanine as basic structure. They carry further different numbers (1-4) of two different types of side chains (sulfonic acid and dimethylaminopropyl sulfonamide).

As the entire molecule of C.I. Direct Blue 264 was too large for the calculation the dissociation constants for benzenesulfonic acid and N-[3-(dimethylamino)propyl]benzenesulfonamide acting as model compounds for the side chains (sulfonic acid and dimethylaminopropyl sulfonamide) were estimated. The side chains of C.I. Direct Blue 264 are assumed to display the only dissociable regions within the molecule and thus can be used to describe the dissociation behaviour of the entire molecule.

The following dissociation constants were estimated for the side chains:

 

Sulfonic acid side chain:

pKa (HL/H+L) = -0.60 ± 0.50

 

Dimethylaminopropyl sulfonamide side chain:

pKa (HL/H+L) = 11.42 ± 0.40

pKa (H2L/H+HL) = 9.19 ± 0.40

pKa (H3L/H+H2L) = -8.63 ± 0.70

 

Using benzenesulfonic acid and N-[3-(dimethylamino)propyl]benzenesulfonamide as model compounds the dissociation constants of C.I. Direct Blue 264 were estimated by ACD/pKa DB included in ACD/labs 7.00 Release. According to the estimated results, the sulfonic acid side chain is mainly present in the deprotonated/dissociated form under environmentally relevant pH 5-9. Whereas the dimethylaminopropyl sulfonamide side chain is primarily protonated at the tertiary nitrogen under environmentally relevant pH 5-9.