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Melting point / freezing point

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Endpoint:
melting point/freezing point
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Qualifier:
no guideline required
Principles of method if other than guideline:
No information is provided regarding the guideline followed
Melting / freezing pt.:
-45 °C
Endpoint:
melting point/freezing point
Type of information:
(Q)SAR
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a (Q)SAR model, with limited documentation / justification, but validity of model and reliability of prediction considered adequate based on a generally acknowledged source
Justification for type of information:
The original Joback methodology used a data set of 388 compounds to derive 41 chemical structure group descriptors via multiple linear regression (Joback, 1982).  The Joback adaptation in MPBPWIN is an extension of the original method to include the same groups as in the adapted Stein and Brown boiling point method (see Boiling Point).  In addition, MPBPWIN also uses melting point correction factors for specific structures. Appendix F contains a complete list the group descriptors and coefficient values.

 

The second estimation method (Gold and Ogle, 1969), simply relates melting point (Tm) to boiling point (Tb) as follows (both values in K):

 

 Tm  =  0.5839 Tb

 

MPBPWIN averages the adapted Joback and the Gold and Ogle estimates and reports the average estimate as well as both individual estimates.

 

MPBPWIN then goes one step further.  It reports a "suggested" melting point (MP) that is based upon the two individual estimates and several criteria.  First, MPBPWIN looks at the difference between the two estimates.  If the difference is small (< 30 K), the suggested MP is simply the average.  When this criteria fails (which occurs quite often), MPBPWIN examines the structure type and the magnitude of the difference.  It then decides which estimate is more likely to be accurate and "weights" the suggested MP accordingly.  For example, when MPBPWIN detects an amino-acid structure, it uses a 75% weighting factor for the higher estimate and 25% for the lower estimate to derive the suggested MP.  Weighting factors in MPBPWIN were approximated through observation of estimated versus experimental MP.
Qualifier:
no guideline required
Principles of method if other than guideline:
QSAR MpBpWIN
GLP compliance:
no
Melting / freezing pt.:
-31.6 °C

Description of key information

Value from Merck SDS is supported by QSAR prediction.

Key value for chemical safety assessment

Melting / freezing point at 101 325 Pa:
-45 °C

Additional information