posted 02-01-99 07:43 PM         

"In a 2L wide-necked Ehrlenmeyer flask with a 3" stirbar on a hotplate, added:
- 30 g Al pie plate cut up into 1" squares
- 1.6g HgCl2 in 850 mL MeOH

Let amalgamate for 10 minutes. Small bubbles were evident rising from
the Al, and the water turned grey. Began rapid stirring, and added:
- 62g ketone
- 57g MeAm-HCl
- 26g NaOH dissolved in 75 mL dH2O

Continued stirring. The pieces of Al tended to stop the stirbar, so
I had to babysit the reaction for the first couple of hours. This is
a real good argument for an overhead stirrer. Temperature was
maintained around 55 deg. C throughout.

At the 2 hour 45 minute mark, added another .5g HgCl2. There was still
a lot of undissolved Al, but the stirbar was at least starting to
behave itself a little better. At 4 hours, there was still a large
amount of unreacted Al. After 6 hours, turned off heat.

Prepared a solution of 180g NaOH in 1.6L H2O. Mag-stirred it strongly as I
slowly poured the reaction mixture into it. As I got to the bottom of the
flask, I noted a *lot* of unreacted aluminum. Maybe half at most reacted.
Damn. Too late now. Let solution stir for a couple of hours, and let stand
for 15 hours.

I was left with 3L of reddish liquid with most of the aluminum settled at
the bottom of the container. Divided liquid into 3 portions, and extracted
each portion 3x with 100 mL of toluene. Pooled toluene extracts and washed
4x with 200 mL dH2O, then with 2x 200 mL sat. NaCl solution.

Didn't bother to dry the toluene, but instead vac-distilled it off. Was
left with some dark red oil. Dissolved oil in 500 mL 3N HCl. A lot of
the oil went into solution. Washed with DCM, and was left with a nice
clean cider-colored aqueous solution.

Slowly basified with ~250 mL chilled conc. NaOH. The solution went from
cider colored to a cloudy reddish brown when the pH got closer to 9. Let
stir for a bit, then extracted with 3x30 mL DCM. Some emulsions formed, but
after shaking the funnel a bit and waiting most things separated out.

Was left with 120 mL dark reddish-black DCM/oil. Dried with Na2SO4.
Evaped some of the DCM off on a water bath, and put the remaining solution
into a 125 mL FB flask for and set up for vac-distillation. Drove off the
remaining DCM. Collected 14.7g of clear oil at 156-161 deg C. Bio-assay was
conclusive!!

SUMMARY
==========

Using methanol as a solvent is awesome!! - temperature control is no longer
an issue. Just keep the heat on low and it stays between 50-60 deg. Fuck
ice baths! Almost no tar was produced. Also, the toluene extraction does seem to pick up less tar compared to DCM (though there wasn't much anyway )

As per Bright Star's suggestion, I used only .75 molar equivalent of NaoH
per molar equivalent of MeAm-HCl. Things seemed to work fine, with the
added bonus of having less H2O in the mix.

The yields were pretty poor. Judging by the amount of unreacted Al left, I bet
if I had just let things go longer (6-8 more hours), more ketone would have been converted. Maybe stepping down to heavy duty foil would have sped things
up.

Total time spent using Buchner to filter Al sludge: 0.0 min! The NaOH
quench and the toluene extraction (and subsequent washings) left almost no
Al in the oil at all. Didn't filter a damn thing!! I assume the (fairly
minimal) emulsion that did form when extracting the honey from the aqueous
solution was caused by leftover Al. No big deal.

Big thanks to Ritter & Bright Star. Try it bees, you'll like it!"

PS: I put the book back under the tree. If this is your lab book, you'd
better go and get it!

posted 02-02-99 08:51 AM         

The reaction needs cooling!!!

The ketone -> imine condensation produces heat, and depending on the purity of your ketone, after an hour or so.. the temperature should steadily increase to reflux (if you are using MeOH) ....

Ritter says keep the temp below 45C ... I think that is a bit excessive, but It does need to be kept below 60C (IMHO)...

But my tests are conclusive that the MeOH is the way to go. Work-up is a bit of a pain, but my results are consistantly in the ~65-70% range ... as opposed to ~40-50% using the EtOH or IPA.

posted 02-02-99 10:31 AM         

Bright Star: It looks like the student followed pretty closely Ritter's method (found on the "Al Amalgamation using Methanol as Solvent, dated 1-13-99 09:53 am)
There were no problems! From other tales,
boingo surmises that the dreaded red tar is
produced when things get too hot. There was
almost no tar at all, and according to the
notes, the reaction came close to 60 deg. C
a few times. Boingo agrees with the student
that he should have let the amalgamation run
longer for better yields.

posted 02-03-99 08:06 AM         

This has been a source of great debate.

It is my opinion .... and the opinion of a 'more educated' person than myself ....

That the HgCl2 is only there to destroy the Al2O3 layer on the exterior of the Al foil/flashing/turnings/whatever. If you read Shulgin's recipe' you'll see that his HgCl2 is washed away before the reaction is ever going.

The Al is placed in some water, and a catalytic amount of HgCl2 is dumped inside with it. The HgCl2 attacks the Al2O3 because 1. It has a higher electronegativity, 2. It has an empty d orbital, and 3. It can act as an electron-transfer-agant..... After the surface has become 'silvery' .... IE the appearence of elemental Al ....

The Al is washed several times with water, to REMOVE the HgCl2 (See Shulgin's MDMA synth) and then the Al(o) is allowed to react with the imine (after the condensation) to produce the amine.

So the bubbling you notice is O2. The reduction requires water ... thats where the H's come from. Too much water will hamper the reaction by blocking Al surface area.

Whats the majic concentration? I'd GUESS about what Os uses (or Ritter). About ~3 moles per one mole of ketone.

posted 02-03-99 09:05 AM         

At the beginning of the Amalgamation, IE When the HgCl2 and Al2O3 start to form bubbles, the bubbles are O2. When there is no HgCl2 present, IE when the Reduction is going on (the ketone, +MeAM.HCl, +Al(o)) the bubbles are a combination of H2 and O2.

posted 02-03-99 01:57 PM         

1. The amount of Hg needed is very small. Almost any amount will produce good results. The amount is also dependent on the surface area. The more surface, the more Hg is needed.

2. Adding Hg later during the reaction is pretty much useless, because in that basic reaction it is immediately converted into insoluble HgO/Hg(OH)2/whatever strange Hg(I)-amine-complex.

3. The Hg forms an amalgam with the Al. This is the silvery, shiny surface. The Hg destroys the protective layer of Al2O3, avoiding its reformation.

4. The Al is now "naked", trying to show its reactivity with water. But the Hg doesn't let it do that. The reason is a phenomenon called overvoltage (or something like that). This means that H2 can not readily form on a Hg surface. The same phenomenon is used industrially in NaCl electrolysis (for NaOH and Cl2 production) and in analytic electrochemistry. Read about it when you don't believe me.

5. When Al dissolves (no matter if H+ or OH-), it doesn't produce O2.

Al ---> Al(3+) + 3e(-)
Al + 3 H2O ---> 3/2 H2 + Al(OH)3 aka "sludge"

6. Those electrons given away by the Al usually would react with H+ or H2O forming H2. But the Hg doesn't allow H2 formation on its surface (at least not to a great extend). The Hg sucks the electrons away from the Al (or the Al pushes them towards the Hg, all a matter of definition) and transfers them to the imine floating close nearby, reducing the imine. That's the reason why stirring is needed: to bring new, not-yet reduced imine in contact with the Al/Hg amalgam. Once all the imine is reduced, reaction is over and the residual Al dissolves only slowly, now with H2 formation. This can be observed, at least with Al sheeting.

posted 02-04-99 10:27 AM         

I knew O wouldn't let me get away with that one...

Then why does Shulgin (and I) wash it clean? I've gotten great results (in those crazy dreams, of course) doing this very thing?
Once when I let it sit (dry) inbetween washings, the Al got VERY hot, and oxidized quickly .... IE I didn't think the Hg played a part here ... The Al(o) reacted on contact with O2 in the air.

I hate the fact that Hg Salts have to be used... but putting them as far as possible from the 'product' is a priority to me. So if I can wash away 99.9% of the salt in the first step, and have it work right, all the better.

I do not argue with you here Os ... I have discussed this subject with several of my professors ... they all seem to concur that the Hg Salt does nothing more than destroy the outer Al2O3 layer, in an Al/Hg amalgamation. They seem to think that Hg is unable to 'transfer' electrons. But of course, I can't really ask them about a direct procedure ... heh ....

By the simple fact that it likes to form a +2 charge ... It likes to give up electrons ... not accept them and transfer them.

So, in responce to your neat rebutal
1. Agreed.
2. Agreed.
3. I'm thinking its the Al(O) you see... not the Al-Hg complex.
4. It is indeed naked. I'm going to have to think about that one.... Hg electrodes have been used for years as anti-oxidation weapons...
5. You're probably right with that one... The bubbles are probably the first H2's coming off....
6. Agreed in part.
7. Completely agree.

I just worked out an area/molecule ratio in the hopes of proving you wrong, about the Hg coating on the surface of the Al ... but As it turns out I was wrong in my assumption. .5g of HgCl2 is more .. WAY MORE than enough to completely coat 40g of Al pie plate.

posted 02-05-99 11:48 AM         

Entropy brought Peace to this argument... Sounds like an oxymoron to me!!!

That makes sense ... the Hg 'bonds' to the surface .. I didn't think of that...

So the excess, HgCl2 IS washed away. That makes me feel better.

Semtex -> If it didn't go over 55-60C then I'd say your ketone was a bit impure .. but at least you noticed a temp increase so something happened! Do the work-up and the acid/base extraction and you should be fine!!!

posted 02-05-99 01:28 PM         

When you amalgamate the Al, most if not all of the Hg is reduced to the elemental state, the metal. So unless you are using way too much HgCl2, there is no need to wash the Al/Hg, because all of the Hg will already be reduced (Hg metal doesn't dissolve in water, so washing it is useless) and bonded to the Al. I have seen a ref. (forgot where) which used an Al to Hg ratio of 7:1 (!) for Al(wire)/Hg preparation! They indeed washed their amalgam, but our ratio is much lower. When I did that reaction, I never bothered to weight the Hg salt. I took a spatula and added some, sometimes a little more, sometimes a little less. It always worked with excellent results, in x00g (ketone) reacions. I simply was too lazy to wash all that Al, so I added the Hg(whatever salt) to the Al already in the solvent used for this reaction.

In doing such big reactions, I found it advantageous to use sheet metal, because the reaction was very easy to control when performed in a 3 necked 6L or bigger flask with heating mantle (refluxing) and overhead stirring. No boiling over (although those flasks were usually 2/3 full!), no bad smells, nothing ever happened.

Another point which proves that the Hg indeed forms an alloy with the Al: I never saw elemental Hg during the reaction, only when the reaction was over and almost all Al (95% or more) had dissolved did tiny drops of Hg appear on the bottom of the reaction flask, usually during the sludge decantation/extraction step.

posted 02-05-99 10:30 PM         

And with reference to the washing...as i stated, washing rids excess HgCL2...the salt...i never said anything about removing elemental or amalgamated Hg. It doesn't take a whole lot of salt to amalgamate all that AL...but exactly how much I dont know...so we add excess to compensate. If you dont wash it out in the beginning, you eventually wind up doing it later...its a mute point!

And I never denied or inferred the amalgum was composed of anything besides elemental Hg, even though that was never stated...i thought that was a given.