Hi y'all,
At this time i use a Zn2+ ammonia complex in water at pH 11. This well known complex dissociate when exposed to 140°C and releases free Zn2+ ions.
I need to find another complex of Zn2+ in water pH 11 that dissociate as easily at 150°C.
I thought of EDTA but it looks like the complex is stable at 150°C, so it is a no no.
Do someone know a chelating agent that gives the complex the properties i need ?
Zinc acetoacetate or zinc ethyl acetoacetate would be my first stab from the top of my head and shot from the hip.
Maltol is an inexpensive flavor agent which forms a 2:1 complex with Zn(II). It should be labile under the conditions you describe.
You may possibly want to consider masking the Zn2+ cation in aq. sol., with either ammonia, BAL (2,3-dimercapto-1-propanol), EDTA (ethylenediaminetetraacetate), gluconate, lactate, picolinate, or TETA (triethylenetetramine). For demasking, it is convenient that the equilibrium for the formation of the Zn(II) complex or pseudosalt in aq. sol. can be reversed, what can be possibly achieved by a drastic pH change (often a strong mineral acid is added), by somehow favouring the formation of stable alternative complexes or other predominantly nonionized compounds that capture the ligand, by oxidizing or promoting the thermal decomposition of the ligand, by extracting unbound ligand to another phase; or by conveniently changing the temperature (possibly increasing) to render the masked species unstable, owing to its effect on the stability constant (translated by Van 't Hoff equation). So, you may want to ponder alternative options for demasking the before masked Zn2+ cation, besides (just) increasing the temperature.
Thank you all for your answers.
To Carlos : unfortunaltely temperature will be the only parameter in this experiment that will be able to do the unmasking. But i do understand that maybe some intermediates could be triggered by temperature and then unmask the Zn2+. Thank you for the concept.
Zn(ClO4)2 or Zn(NO3)2 completely dissociate in water.
HOWEVER!!!!
I do not believe that: "This well known complex dissociate when exposed to 140°C and releases free Zn2+ ions" at pH 11. Zn2+ should undergo hydrolysis at pH 11.
Read
Critical evaluation of thermodynamics of complex formation of metal ions in aqueous solutions: VI. Hydrolysis and hydroxo-complexes of Zn2+ at 298.15 K
Yu Zhang, , Mamoun Muhammed
Hydrometallurgy
Volume 60, Issue 3, May 2001, Pages 215–236
How do you measure pH at 140C?
Keep in mind that the THE IONIC PRODUCT FOR WATER, Kw, increases with temperature
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