smartgene1
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why you cant use other metals like aluminium in the birch reduction
hey I want to know why you cant use other metals like aluminum in the birch reduction why it got to be a alkali metal or alkaline metal
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The Austrian Scientist
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The Birch reduction relies on the reaction between a Alkalimetal and
liquid ammonia. The mechanism is pretty complicated but other metals like Al dont have enough reducing power to form the MNH2 (M = Li, Na, K, Rb, Cs)
salt.
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smartgene1
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I read if you react ammonia with Al it produces hydrogen and I read that lithium just acts as a catalyst in the birch reaction and calcium in Benkeser
reaction. Al has a reduction potential of -1.66 that's more then zinc so I don't see why it wont have enough reducing power
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walruslover69
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I believe it is because Aluminium does not form a stable electride salt with ammonia. Ammonia doesn't effect the charge of the Aluminium ammonia
complex so it would be +3. that means it would need 3 solvated electrons to act as the anion. This sounds highly unstable and is probably the reason
it cannot be used.
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smartgene1
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Then would Calcium Hexammoniate, Ca(NH3)6 be a electride
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clearly_not_atara
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Calcium works, but the selectivity changes:
https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&am...
The acidity of the relevant cation is important -- too acidic, and the metal-ammine complex will deprotonate, neutralizing the electride. Al3+ is very
acidic, so a solution of aluminium ions in ammonia will probably give aluminium nitride.
[Edited on 04-20-1969 by clearly_not_atara]
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smartgene1
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Is the ammonia the reducing agent and is the metal the catalyst in the reaction or vice versa
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walruslover69
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The sodium forms a complex cation with the ammonia with the formula Na(Nh3)6+ the anion is a free solvated electron. It is this free electron that
does the reducing.
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