[zsinger]

All,
Actually had a dream about this last night (thats how you know I am currently in the lab too much).  I am about to perform a tin and/or iron reduction in HCl (aq.), and something just hit me like a ton of bricks…….I planned on using iron, which is the single electron donor (SED) in this particular reaction as is tin in the synonymous said reaction.  If I decide on Fe, I MUST use an overhead stirrer I'm thinking, as the stirrer magnet and the iron could interact in a way that I am totally unaware of.  I postulate that the iron must be in the most contact possible with reactant, but heating to 100 C should take care of that kinetically.  Any sage answers are appreciated.  I consulted March's Advanced Organic Chemistry-7th Edition, and it does not mention anything about the stirrer.  Thanks.
                           -Zack 

[discodermolide]

You mean that the stirrer magnet turning the iron in one direction may lead to optical induction?

Always use a mechanical stirrer if you can, they are much more efficient.

[zsinger]

Never heard of that Disco……thanks….I think ill pick the Sn route instead to avoid this problem.  Not much more expensive .
        -Z

[Dan]

You can use a magnetic stirrer, I've done it before with Fe and also CrO₂.

As long as the phases move relative to one another it is OK - one phase can be stationary.

Results are fine on small scale, if you are doing anything large I would definitely use an mechanical overhead stirrer if you have one.

Not much more expensive

Did you factor in the cost of disposing the toxic Sn(IV) waste?

[zsinger]

Yes, I got a toxic waste pickup quote.  Still far cheaper than buying an overhead stirrer, as I really found them to be bulky (yet more efficient) to the point where I would sacrifice yield to not use them.  They often required another whole stand just to support, not to mention the clamps galore.  My magnetic stirrer is extremely powerful.
            -Zack

[discodermolide]

I assume you do not work in a process research lab. If you ever do anything on scale there is no substitute for an overhead stirrer. Try stirring 50-100L with your magnet.

[organosurf]

An iron stirrer can react with the conc HCl. Wount affect resolution though. For dissolving metal reductions, how about trying Aluminum ?? Its the ultimate electron donor ( 3e- ) Zinc is 2e-, Fe is 1e-.
Aluminum reacts with specific acids at specific concentrations. No one mentions using Aluminum.
Using Al / Hg, is non-ecofriendly and raises eyebrows
There is mention using Zn / Glacial Acetic acid also. I tried Al / NaOH, very exothermic, H2(g) evolved, but it seems its lousy for appreciable metal surface reductions.
The Gallium / Al is only for research / PhD acquiring, not practical day to day use. eg for fuel cell use.
All reductions involve mostly expensive metal catalysts with a myriad of fancy sounding "ligands" but at mild working conditions; cheap metals but at harsh conditions.

[zsinger]

Disco,
I am still a lab rat on the way to a PhD.  We are not allowed to remove any lab ware out of our area, at the risk of being expelled from school for theft, and possibly reported to authorities.  I hate those darn overheads, but yes, I know they are much better.
                -Z