Speedy the Snowman
Harmless
Posts: 1
Registered: 28-7-2005
Member Is Offline
Mood: No Mood
|
|
Only HI reductions?
Why is it that only HI can be used in reduction of ephedrine to N-methylamphetamine, and not other hydrogen halides?
|
|
|
praseodym
Hazard to Others
Posts: 137
Registered: 25-7-2005
Location: Schwarzschild Radius
Member Is Offline
Mood: crazy
|
|
This is because HI, with its iodide ions, is a stronger reducing agent compared to HF, HCl and HBr.
To make it more clear, we need to look at how the enthalpy changes from halogen to halogen.
We need to compare the amount of heat evolved or absorbed when you convert a halide (like sodium chloride) into molecules of the halogen.
While comparing the halides, we need to look at the lattice enthalpy and the thermal energy needed to remove the electron.
Hence, fluoride ions are difficult to oxidise and it gets easier as you go down the Group towards iodide ions. Looked at another way, fluoride ions
aren't good reducing agents, but iodide ions are. (I trust that you understand the theory behind oxidation and reduction.)
Fluorine is a very powerful oxidising agent because it very readily forms its negative ion in solution. That means that it will be energetically
difficult to reverse the process.
By contrast, iodine is relatively reluctant to form its negative ion in solution. That means that it will be relatively easy to persuade it to revert
to iodine molecules again.
|
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
