No more mercury?

[Barium]

Our master searcher PolytheneSam found this patent

Patent US4273679

. It describes things to use to activate aluminum beside mercury. They reduced a few nitrogen containing functional groups to amines with this activated aluminum in good yields.

Aluminum can seemingly be activated with salts of more electro positive elements like iron.

E.g. 27g aluminum grains was stirred with 100 ml N(?) hydrochloric acid and 5 g ferrous sulphate for one hour at 60-80°C. The solution is removed by decantation and the metal is washed with water, then it is ready for use.

Could this be something to use in the MeNO2/MDP2P reductions?
Catalytic hydrogenation freak

[Rhodium]

That sounds like an excellent idea!

[PolytheneSam]

Now we need some people to test it.  I believe those alloys are also couples.  Maybe looking into the theory of the use of couples in reduction processes would help to find the best ones.

http://www.geocities.com/dritte123/PSPF.html

The hardest thing to explain is the obvious

[Osmium]

Hg works so well because of "overvoltage". You won't get that with most other metals. Their reducing power might still be good enough for some reactions, but not necessarily good enough for reductive aminations.

I'm not fat just horizontally disproportionate.

[hermanroempp]

No doubt, hydrogen shows the highest overvoltage on a mercury surface. This is because mercury is a liquid and so there is always a smooth surface with almost no "hot spots" for the development of hydrogen. Keep in mind that  hydrogen on a very smooth platinum surface shows also overvoltage, that's the reason why platinum electrodes (e.g. for measuring differences in potentials) are "platinized" with platinum black. But this phenomeneon is not only dedicated to mercury and platinum, many other other metals show this effect too.
To name a few in increasing order of overvoltage:
Ag < Ni < Cu < Pb < Hg
Of particular interest here are lead and copper. Copper is well known from the famous zinc/copper couple already used in some reductions, but what about an aluminium/copper or an aluminium/lead couple?
In galvanic applications the effect of overvoltage is increased by forming a colloidal layer around the electrodes (blocking of "hot spots"). Colloids used are gelatinous organic substances or chromium(III)oxyhydrates or the corresponding oxyhydrates of iron(II).
Fertile field for the experimenter...
Quidquid agis, prudenter agas et respice finem!

[SPISSHAK]

Really like this idea, we can all thank Sam for his contributions, I have a question about the electropositivity differences in these metals your'e precipitaing on the aluminum, what I wonder is how a less electropositive metal than aluminum is going to undergo metathesis reaction in it's salt form (i.e. sulfate) would'nt the sulfate anion preferentially bond to the more electropositive metal and not undergo this exchage giving the hetereodispersion discussed in that patent?

[Sunlight]

I've thought several times if just assing a bit of NaOH solution to the aluminium + ketone and amine solution could just work, may be it will be enough.
Anyway, seems that the copper idea is fine, copper carbonate is cheap and OTC, it can be converted easily in copper chloride. But how to initiate de rxn with Al, adding a bit of NaOH to the Al, then adding the CuCl2 solution, then amine and ketone ?

[Osmium]

No, I would add CuCl2 to Al and see what happens. If necessary you can add a few drops of HCl to expose the Al metal, but it should work without.
When you basify you will precipitate insoluble copper hydroxide. That happened once when I added the amine too early to an Al/Hg, converting the hg salt into something insoluble (some sort of amine complex, and Hg hydroxide). It still worked but needed much longer to amalgamate.
I'm not fat just horizontally disproportionate.

[Antoncho]

Addition of CuCl₂ will probably have the same effect as adding CuSO₄ and NaCl to Al in water - a vigorous effervescence of hydrogen - i mean, REALLY vigorous (as in "shoot thru the condenser onto the ceiling").

I always wondered about the mechanism of this rxn - does it have smth to do with copper's ability to bind Cl^- from aq. solutions, forming [CuCl₄]^2-?


Also - it was my impression (i'm probably wrong here?) that another role of mercury was to deactivate rather than activate aluminium, so it doesn't get dissolved too quickly. At least, in case of Na amalgam that is the case.



Antoncho

[Rhodium]

The Hg activates the Al towards reaction, but deactivates it towards hydrogen gas evolution.