Formic acid

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Meets generally accepted scientific standards and is described in sufficient detail.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1997

Report date:

1997

Materials and methods

Objective of study:

other: rate of formic acid dissociation at physiological pH

Principles of method if other than guideline:

Calculation of the chemical behavior of potassium diformate and formic acid solutions from titer curves.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Reference substance 001

Constituent 2

Reference substance name:

Potassium formate(1:2)

EC Number:

243-934-6

EC Name:

Potassium formate(1:2)

Cas Number:

20642-05-1

Molecular formula:

CH2O2.1/2K

IUPAC Name:

potassium formate(1:2)

Details on test material:

Test substance: Potassium diformate

Test animals

Species:

other: calculation

Results and discussion

Any other information on results incl. tables

Potassium formate is expected to form the following equilibriums in  aqueous solutions: 

1)   HCOOH-HCOOK         <-->         HCOOH  +  HCOOK  [equation 1]

2)         HCOOH                <-->              HCOO-  +  H+     [equation 2] 

2)         HCOOK          <-->         HCOO-  +  K+     [equation 3]     

Mapping the pH as function of dilution and titer curve allowed to estimate the buffer effect of the diformate system (equation 1) 

and to  calculate the concentration profile of diformate, formic acid and formate  as function of concentration in water solutions. 

The calculations indicate that in aqueous solutions

i) at pH <4 and at concentrations >0.1% the equilibrium in equation 1 is  in favor of potassium diformate.

ii) at pH of 4 to 5, and at dilution down to 0.001%, most of the formic acid content is released from potassium formate.

iii) further dilution and increase of pH above 5, the concentrations of  formic acid and diformate decrease rapidly, leaving only formate left at 

pH 7 and above. No diformate exists above pH 7.

Applicant's summary and conclusion

Executive summary:

Formic acid is in equilibrium with its salts in aqueous solutions. No diformate or formic acid exists above pH 7, only formate is left.

The pKa for the dissociation of potassium diformate into formic acid and potassium formate (equation 1) is approx. 4.3

HCOOH-HCOOK        <-->       HCOOH + HCOOK               [equation 1]

The pKa for formic acid is approx. 3.75 (equation 2).

HCOOH                <-->        HCOO- + H+                      [equation 2]