Bordeaux mixture

Vapour pressure

Administrative data

Endpoint:

vapour pressure

Type of information:

(Q)SAR

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

accepted calculation method

Justification for type of information:

Bordeaux mixture is a multicomponent substance with variable amounts of water of crystallisation. An endothermic event seen to occur over the range 110 to 190°C in a melting/boiling point study (O'Connor and Mullee, 2003); Safepharm Project Number 1510/003) was attributed to the loss of water of crystallisation. Using the extrapolated onset of this endotherm (approximately 140°C), the vapour pressure associated with the entrained water was calculated by an integrated form of the modified Watson correction to be 614 Pa. (The Watson correction method is identified in REACH guidance as being suitable for substances with vapour pressures in the range 10E+05 Pa to 10E-05 Pa; Chapter R.7a: Endpoint specific guidance, Version 6.0 – July 2017). As an absolute worst case, therefore, this value of 614 Pa is reported as the vapour pressure of Bordeaux mixture in its hydrated state. For practical purposes, however, and given the high melting/boiling points of the remaining components of Bordeaux mixture, it is considered that the vapour pressure of the substance in the absence of water of crystallisation is too low to accurately measure experimentally.

Based on the above determination, it is concluded for the purposes of classification and risk assessment that the vapour pressure of Bordeaux mixture is very low and that the substance should be regarded as non-volatile.

Computer software was not used in this determination. See "Any other information on results" for a further discussion on the approach taken.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2017

Report date:

2017

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

other: The assessment carried out was intended to be compatible with Method A4 Vapour Pressure of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 104 of the OECD Guidelines for Testing of Chemicals, 23 March 2006.

Test material

Test material information

Constituent 1

Reference substance name:

calcium tetracopper(2+) dioxocopperbis(olate) hexahydroxide sulfate

EC Number:

910-853-9

Cas Number:

8011-63-0

Molecular formula:

Ca3Cu4H6O22S4.nH2O where n = 1 to 6

IUPAC Name:

calcium tetracopper(2+) dioxocopperbis(olate) hexahydroxide sulfate

Specific details on test material used for the study:

Bordeaux mixture is a reaction mass of calcium sulfate and tetracopper hexahydroxide sulfate(3:1) with a variable degree of hydration. The molecular formula is as follows:Cu4(OH6)SO4.3CaSO4.nH2O (where n = 1 to 6).

Results and discussion

Vapour pressure

Key result

Vapour pressure:

<= 614 Pa

Remarks on result:

other: The vapour pressure of Bordeaux mixture in its hydrated state was calculated by an integrated form of the modified Watson correction.

Remarks:

The vapour pressure of the dehydrated components would be extremely low at 25°C and would be difficult to measure accurately.

Any other information on results incl. tables

Based on data from the boiling point test of Safepharm Project Number 1510/003, the test item had an endothermic event over the range approximately 110 to 190 °C. This event was considered to be the temperature at which the test item was dehydrated (loss of water of crystallisation). Using the extrapolated onset of this endotherm (approximately 140°C), the vapour pressure was calculated by an integrated form of the modified Watson correction to be 614 Pa (0.0061 atm). This is in contrast to the vapour pressure of pure water at 25 °C of approximately 3169 Pa (0.031 atm). The vapour pressure of entrained water is significantly lower than the pure form, hence it requires a higher temperature to volatilize.

As the initial volatilization of the test item was due to loss of the hydrate and there were no definitive thermal events up to 400°C after this, further volatilisation of the test item required the assessment of the components in their dehydrated form. For example, the literature value for the melting point of calcium sulphate is 1460°C. Although a value for tetracopper hexahydroxide sulphate was not available, as a comparison copper (II) sulphate decomposesat 560°C; this suggests that tetracopper hexahydroxide sulphate wouldn’t boil significantly lower than this. However, hydroxides are known to decompose to their respective oxide, for example copper (II) hydroxide. Even so, decomposition would only liberate H2O which would merely contribute to the vaporised hydrate but only then at a higher temperature than140°C.

Therefore, it was considered that the vapour pressure of the dehydrated components would be extremely low at 25°C and would be difficult to measure accurately. The vapour pressure of the test item, as a worst case scenario, needed to be based on the hydrated form for which avalue of 614 Pa was calculated. Overall, the vapour pressure of the test item was considered to be ≤ 614 Pa.

Applicant's summary and conclusion

Conclusions:

The vapour pressure of the test item was considered to be ≤ 614 Pa.

Executive summary:

The vapour pressure of Bordeaux mixture in its hydrated state was calculated by an integrated form of the modified Watson correction to be 614 Pa (0.0061 atm). The vapour pressure of the dehydrated components would be extremely low at 25°C and would be difficult to measure accurately.