The truth about Ferric Chloride (FeCl3)

[Mountain_Girl]

Up until recently, I (as well as a few other bees I'm sure) assumed that FeCl3 could be made by simply dumping some iron in hydrochloric acid and filtering off the resulting ppte/evaporating to crystallisation.
This is not the case.
In fact, the pale green solid that results is Ferrous Chloride, FeCl2 (in the form of one of its hydrates actually).
[Fe + 2HCl ^__> FeCl2 + H2]

In order to obtain FeCl3, the FeCl2 must be further oxidized with Cl2:
FeCl2 + 1/2Cl2 ^__> FeCl3
This can be accomplished by bubbling Cl2 through a warm FeCl2 soln.
(The soln. will go from green to dark brown and the FeCl3 obtained from crystallisation should be yellow/brown as the hexahydrate).

And yes, I know FeCl3 can be purchased without any trouble. This post is just for anybee like me who thought it might be interesting to make it myself (and who happens to have a chlorine generator handy from an attempted SOCL2 synth).

[Antoncho]

.......dissolved FeSO4 (farmhouse supply grade ), dumped in 1/2 eq. sulfuric acid, a 1/2 molar eq. H2O2 - the mixtr will still bee milky, but that don't matter - it's just that Fe₂(SO₄)₃ is very prone to hydrolysis and partially dissociates into Fe(OH)₃ and HSO4^-.

This can bee reacted w/an equimolar qtty of CaCl₂ - take a note that if you do it at like 90 C, the formed CaSO₄ will bee in its 'anhydrite' form - i.e., doesn't suck up the water and is much easier to filter.

Evap the water, preferrably under vacuum. I dunno if the hydrate can bee dried under ordinary excicator conditions, but converting it into unhydrous salt is quite tricky, it hydrolyses on heating. OTOH, CuCl2 is also said to bee susceptible to that, but the practice shows that it dehydrates fairly easily under a heat of an ordinary lamp - although some decomposition still ocurs.




Antoncho

[terbium]

Shouldn't need chlorine, even air should be strong enough to oxidize ferrous chloride to ferric.

[former_chemist]

Add enough HCl to bring the pH of the solution to 1 before evaporating.  The excess HCl prevents hydrolysis.  Removing the final water of hydration should be done in a stream of HCl or Cl₂ gas.  For most purposes a little hydrolysis won't hurt.

[neuromodulator]

I know this isn't the coolest question to be asking, but exactly what type of reaction is FeCl3 useful for anyway?

[Rhodium]

Ferric Chloride is a Lewis acid, and is therefore often used as a catalyst in for example Friedel-Craft reactions.

Entropy just isn't what it used to be.

[neuromodulator]

That's great then, because I have access to already made FeCl3 but not to AlCl3.  However, would it be necessary to then use say, for example, CH3Cl with FeCl3 or does FeCl3 also work with CH3Br or even CH3I? 

Keep in mind, I'm not planning to make any sort of specifically controlled substance either.  In fact, I'm just curious really, but that is certainly no crime either.

Thanks.

[Rhodium]

You generally don't need to have any matching Lewis acid catalysts for your alkyl/acyl halides in the friedel-craft reaction. Also, as no halogens are present in your product after the workup, you can simply consider them spectator ions...

There is however a difference between the center metallic cations, making AlCl3 a stronger catalyst than FeCl3 for example. ZnCl2 is even weaker.

Entropy just isn't what it used to be.

[hest]

I't my understanding that the FridelCraft alkylation is hard to control (your product is more reactve than your startingmaterial). Usual only FC acylations is posible to control. But I don't have any personal eksp.

[neuromodulator]

Alkyl groups are activating which can lead to runaway alkylations in certain instances, but ultimately it depends on what compound you are trying to alkylate as to whether or not acylation followed by reduction versus straight alkylation should be used.

[former_chemist]

The usual procedure involving FC uses an excess of the compound to be alkylated.  This still leads to a lot of side products. These are usually widely different in characteristics (BP/MP) from the desired product allowing easy separating by fractional distillation or fractional crystallization.