Ametryn

Boiling point

Description of key information

Boiling point (1 atm, OECD 103) = 346 °C

Key value for chemical safety assessment

Boiling point at 101 325 Pa:

346 °C

Additional information

Two GLP studies are available. M. Meinerling (2006) study has been chosen as Key study while R .Das (2000) as Supporting study.

R .Das (2000) reports discoloration of the sample prior to boiling as evidence of decomposition, and this appears to be confirmed by the DSC in air showing a weak exotherm beginning at 124°C, and then a stronger exotherm beginning at 248°C without any endotherm to indicate boiling. R .Das (2000) reports also that, under nitrogen, only a single exotherm is seen, beginning at 277°C.

In comparison, M. Meinerling (2006) reports repeatable results of boiling at 346°C using the capillary method. This is supported by a DSC under nitrogen from the vapour pressure test (H. Smeykal (2006)) showing a clear endothermic melt from 84.4°C (peak at 87.05°C), followed by a second endotherm beginning ~350°C (peak ~373°C). From ~373°C to ~384°C the curve rises back to about the same level as before the second endotherm, before falling again in the jagged way often seen after the sample has been lost. It is not clear whether this final rise indicates an exothermic event, or merely the waning of an endothermic boiling resulting in the loss of the sample.

The most likely cause of this apparent discrepancy in the information is that the substance used in R .Das (2000) study is less pure than the one used in M. Meinerling (2006), or contains a trace amount of a contaminant that catalyses its thermal degradation. The M. Meinerling (2006) study was chosen as the key study as the DSC from the H. Smeykal (2006) vapour pressure report appears to be consistent with the boiling point findings. Additional evidences of thermal stability of the substance is given in the study by M. Bailey (2006).