I want to deprotonate a ligand, which contains three OH group. If I add a base, how would I know that the protonation had occurred? Is there any technique which confirmed that the deprotonation had occurred?
If the deprotonated version of the ligand can be isolated (presumably in salt form), then the absence of OH groups can easily be confirmed via FT-IR spectroscopy. However, if the deprotonated ligand cannot be isolated, you may use excess amount of base and after appropriate time, back titrate to find out the amount of unused base and calculate the extent of deprotonation. Alternatively, you may use metal hydrides and quantify the amount of hydrogen released to know the extent of deprotonation. A lot depends on the nature of your ligand and the reactions conditions though.
Use a routine acid-base titration and process your data with whatever free software to determine pKas of your compound. If you are Chem Knight you are supposed to know well this procedure.
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pKa of a free molecules is not the same as pKa of the same molecule which is in the complex.
Yahia Z Hamada What is very special in your papers " about protonation and de-protonations"? Protonation/deprotonation is an acid-base equilibrium, which is described in textbooks. Your " NaOH solid at any solution" does not make any sense. NaOH solid will be in equilibrium with NaOH in solution, if a solution is saturated with NaOH. The solubility of NaOH in water is 1000g/L (~25 M)
Dear Yahia,
Does it matter 25 or 17M? Molarity (M) is the concentration of a solution expressed as the number of moles of solute per liter of solution: Molarity (M) = (1000g/L)/40 = 25 (at 25C).
Could you provide please the reference of your most representative paper?
In addition to what other colleagues have already suggested correctly. It can also be followed by UV-Visible spectroscopy if the ligand and deprotonated species have different coloration. Even if the color changes are small.
If your compound are fluorescent active you can check by titration method. Also you can carry out the titration method in absorption spectroscopy.
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