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Diss Factsheets

Physical & Chemical properties

Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Study period:
Initiation: September 24, 2013 Completion May 20, 2014
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 (incl. QA statement)
Dissociating properties:
yes
No.:
#1
pKa:
6.936
Temp.:
25 °C
Remarks on result:
other: Calculated (Albert & Serjeant)
No.:
#2
pKa:
6.904
Temp.:
25 °C
Remarks on result:
other: calculated (Albert & Serjeant)
No.:
#3
pKa:
6.974
Temp.:
25 °C
Remarks on result:
other: calculated(Albert & Serjeant)

 Test  Result
 Test  OECD Test No. 112
 Method  Potentiometric titration
 Test Item and purity  100%
 Test temperature  25 ±0.5 °C
 Final calculated mean pKa 6.94 (calculation method) 
 Standard deviation  ±0.04 (n = 3)
Additional comments 

Graphical approach gave an average

pKa of 6.77

 

Conclusions:
Based on measurements and observations it was concluded that tall oil, maleated contained acid groups with a pKa of 6.94 ±0.04 at 25 °C. The agreement between the replicate measurements falls within the ±0.1 log units specified in OECD Method 112.
The measured pKa is consistent with the reported chemical structure of the test material which is predominantly long chain fatty acids augmented with maleate groups. The acid groups are expected to be predominantly carboxylic acids.
Executive summary:

The dissociation constant was determined for test item EnvaMul 600 according to OECD method 112.

The potentiometric titration was first conducted using a 0.01M solution of sodium hydroxide with 100 mL of continuously-stirred sample. The pH was measured using a Corning Model 10 pH meter and an Analytical Solutions Inc. pH probe. After each addition of titrant, pH measurements were taken to give at least 10 measurements over the entire pH range.

The titration was continued until the solution cleared, and was stopped once the pH had reached about 9 and no further changes were observed. The point at which the solution transitioned from cloudy (acids in protonated form and largely insoluble) to clear (acids in conjugate base form and soluble) was noted.

The solution was then back-titrated using 0.01N hydrochloric acid back down to a pH of about 4. Again, the transition from clear to cloudy was noted.

This process was repeated twice more with fresh preparations of test item, for a total of three replicates.

The final pKa was calculated using at least ten useable points on the sodium hydroxide titration curve using the formulae described by Albert and Serjeant. A commercially available spreadsheet program was used for the calculations and plotting of the titration curve. The pH readings fell in the 4 to 9 range so no correction for {H+ } or {OH-} was required.

Based on measurements and observations it was concluded that tall oil, maleated contained acid groups with a pKa of 6.94 ±0.04 at 25 °C. The agreement between the replicate measurements falls within the ±0.1 log units specified in OECD Method 112.

The measured pKa is consistent with the reported chemical structure of the test material which is predominantly long chain fatty acids augmented with maleate groups. The acid groups are expected to be predominantly carboxylic acids.

Description of key information

Based on measurements and observations it was concluded that tall oil, maleated contained acid groups with a pKa of 6.94 ±0.04 at 25 °C. The agreement between the replicate measurements falls within the ±0.1 log units specified in OECD Method 112.

Key value for chemical safety assessment

pKa at 20°C:
6.94

Additional information