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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Physical & Chemical properties

Dissociation constant

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Administrative data

Link to relevant study record(s)

Reference
Endpoint:
dissociation constant
Type of information:
other: expert statement
Adequacy of study:
key study
Study period:
2010-07-05
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: The dissociation constant of mmt was assessed based on the structural formula of mmt.
Qualifier:
no guideline followed
Principles of method if other than guideline:
Study of physical-chemical properties and molecular structure of mmt.
GLP compliance:
no
Remarks:
N.A.
Dissociating properties:
no
Remarks on result:
other: MMT does not dissociate
Conclusions:
Based on the structural formula of mmt it is not expected to dissociate.

Description of key information

mmt will not dissociate based on its structural formula. No dissociation constant can be calculated.

Key value for chemical safety assessment

Additional information

From its chemical formula it is clear that there are no functional acidic groups in mmt and it contains no H-bond donors or acceptors. There are no hydrogen atoms attached to oxygen in mmt and threfore if does not exhibit an acidic behaviour. Based on this data, dissociation will not occur under naturally relevant pH conditions. In addition, the substance is poorly soluble in water.

Typically, highly charged metal ions, such as Fe3+ or Cr3+ show acidic speciation in water, forming non-dissociated oxides and hydroxides, and resulting in acidic solutions. The higher a metal is charged, the bigger this effect. For Fe3+ and Cr3+ pKa values of 2.22 and 3.82 respectively are reported, whereas for Cu2+ and Zn2+ pKa values are 8.00 and 9.66 respectively. In mmt, where the manganese atom charge is +1 and the metal is surrounded by relatively large organic molecules this phenomenon does not play a role.

Although conceptually, mmt is described as containing Mn+ and Cyclopentadiene(Cp)-ions, in part to allow for the known aromatic character of the cyclopentadiene ring in mmt, the actual binding between ionic Mn and the Cp ring is not ionic in nature, consequently an aqueous solution of mmt does not contain ionic species.

As the carbonyl ligands in mmt have no acidic behavior, their binding to a mildly electrophylic atom does not change this behaviour.