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Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Study period:
29 January 2004 to 10 February 2004
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
Deviations:
no
GLP compliance:
yes
Dissociating properties:
not determined
No.:
#1
Remarks on result:
not determinable

The test substance is not soluble in water. Six different organic solvents were evaluated for use as a co-solvent. The solvents evaluated were methanol, acetonitrile, 2 -propanol, methylsulfoxide, N,N-dimethylformamide and acetone. Aliquots of the test substance were weighed into glass beakers and a different solvent was added to each beaker. The contents of the beakers were swirled by hand to aid in dissolution. Methanol, acetonitrile, 2 -propanol, methylsulfoxide and acetone did not completely dissolve the test substance. The beakers with undissolved test substance were allowed to stand to let the solids settle. The clear and coloured supernatant was added dropwise to each of three aqueous environments to see if the test substance remained in solution. The three aqueous systems used were water, 0.1 M NaOH and 0.1 M HCl. Each time a drop of organic test substance solution was added to an aqueous system the test substance immediately fell out of solution. Of the solvents evaluated, only N,N-dimethylformamide completely dissolved the test substance. The test substance solution in N,N-dimethylformamide was added dropwise to each of three aqueous systems; water, 0.1 M NaOH and 0.1 M HCl. each time a drop of test substance solution was added to an aqueous system, the test substance immediately fell out of solution. All observations were made with the unaided human eye.

Conclusions:
Under the conditions of the test, the pKa of the test substance could not be determined.
Executive summary:

In a GLP compliant dissociation constant study conducted in line with OECD Guideline 112, the dissociation constant of butanoic acid, 4-[[4-[7-chloro-6-(1,1-dimethylethyl)-3H-pyrazolo [1,5-b][1,2,4]triazol-2-yl]phenyl]amino]-4-oxo-, tetradecyl ester was investigated. The pKa could not be determined because of the inability of the test substance to stay in solution.

Description of key information

Key study:- Foley (2004) 'pKa determination' conducted in line with OECD 112. The pKa of the test substance could not be determined due to the inability of the test substance to stay in solution.

Key value for chemical safety assessment

Additional information

The key study (Foley, 2004) was performed in compliance with GLP and to OECD Guideline 112 with a sufficient level of detail to assess the quality of the presented data. The study was performed to a good standard in line with an accepted, standardised guideline and was assigned a reliability score of 1 using the principles for assessing data quality as set out in Klimisch et al. (1997). The pKa of the test substance could not be determined due to the inability of the test substance to stay in solution.