[Akutni]

Hello
The maleic acid is said to be isomerated into the fumaric acid via partial addition of H+ or Br• which allow the molecule to rotate and leave it afterwards. Shouldn't the products be malic acid or dibromo derivative respectively as well? How is it ensured these don't form? What are different conditions in isomerization and hydration of maleic acid? The same about isomerization and bromination?

My guess would be the insolubility of the fumaric acid, which once formed reacts only slowly due to its forming an insoluble solid phase. I can imagine hydration being reversible, but that would mean that we could never make malic acid from maleic acid via hydration as it would always fall to the insoluble fumaric acid. But the double hydration of maleic anhydride is said to be a way to produce malic acid? What are the different conditions in isomerization and  hydration? And is radical addition of bromine reversible as the radical bromination isomerization seems suspicious to me as well?

Thank you for your answers.

[rolnor]

I dont get this, you can brominate fumaric acid? A electron deficient double bond as in maleic acis is probably impossible to protonate and hydrate, the conditions for normal alkenes are very harch


https://www.oc-praktikum.de/nop/en/instructions/pdf/3002_en.pdf

[Akutni]

I dont get this, you can brominate fumaric acid? A electron deficient double bond as in maleic acis is probably impossible to protonate and hydrate, the conditions for normal alkenes are very harch


https://www.oc-praktikum.de/nop/en/instructions/pdf/3002_en.pdf

If H+ didn't add, I don't know how the isomerization would work. But the Wikipedia states "Reversible addition (of H+) leads to free rotation about the central C-C bond and formation of the more stable and less soluble fumaric acid."
It means the H+ eventually really adds and if so, why couldn't OH¯ add afterwards (plus OH¯ would actually prefer electron deficient substrate)?

[rolnor]

Yes, sorry I saw that now, you use low pH for the isomerization. And your question is reasonable. Maybe the conjugation with the two carbonyls makes the double bond so stable it will not hydrate? Maybe you do have the hydrate as an intermediate and this looses water again to form the fumaric acid, again, because the double bond can conjugate? The maleic anhydride is probably so easy to hydrolyse that the isomerisation does not take place at this pH.