(Hive Bee)
08-30-02 16:16
No 350855
(Rated as: excellent)
The following refs are pretty much the same reaction over a progression of time.
JACS 85 2858 (1963)
JACS 86 5272 (1964)
JOC 34 3970 (1969)
JOC 35 261 (1970)
This reaction is Constant current i.e. easy and no special equipment because it is an indirect reduction, the lithium salt is reduced to lithium which does the work turns back into the salt which is reduced again. This is great since you only need a catalytic amount of Li salt which you can reuse.
In short:
To reduce benzene to the dihydro version, the following procedure was used:
An electrolysis cell 170 mm in length by 100 mm in diameter was fitted with two dry ice condensers with 2(2x5 cm) platinum electrodes. (Note none of these dimensions really mater just keep the current density the same and stick to platinum or platinised whatever as the electrode material.)
There is no cell divider for this reaction. (They do use a cell divider (asbestos) for some of their examples to further reduce the benzene to a single double bond. But Scooby thinks the undivided reaction reducing only one of the double bonds of benzene is the go for ephedrine. Maybe a Bee with more experience with this could clarify?)
Anyways the ratio:
To reduce 0.1 mol of your favourite substance add 0.8 mol of Lithium chloride and 900 mls of methylamine. The reaction temp is around -7 deg (refluxing methylamine). Apply 2.0 Amps for 7 hours (50 000C) the voltage they saw was 85 volts. Again this is a constant current reaction voltage doesn't matter your's will be different because your cell will different. Their electrodes were pretty far apart (170 mm) to reduce that crazy voltage bring your electrode closer together, this will also reduce the heat generated by the reaction. Then do a standard workup, the yields will be different since none of you are going to reduce benzene.
However they got 90+ % for their reductions.N-Methylimine reduction to N-Methylamines
There are two ways, either add your LiCl (0.4 mol) and ketone (0.05 mol) and methylamine (300 mls) and let it sit for 6 hours. (The addition order is important adding the methylamine last creates heat solvating the LiCl which inturn speeds up the imine formation.) Then zap it, at 2 Amps for 2 hours and 41 mins, (19,300C) Then workup.
The second way is to produce your imine first isolate it then add it to the above reaction, this time using 0.2 mole of LiCl and 200 mls of methylamine and zapping at 1 Amp for 1 hour and 15 mins (4500C) then working up.
The yields of the ketones used by the ref were 73,70,70 for 2-Heptanone, Cyclohexanone and Cyclopentanone respectively. Yields were higher for the isolated imine method but this could have been tweaked by removing water while forming the imine instead of after this would have led to a higher yield in the imine and subsequently a higher amine yield. They added an 80% pure imine (not all converted) in which they got a 77% yield of amine.
This reaction could be modified quite easily, I doubt you have to use methylamine as the solvent, probably any solvent that won't react with Lithium and can dissolve the LiCl salt. It does matter for the Imine reduction since the solvent is also the amine sorce, Which is kinda cool whatever end product you want just have the ketone swimming around in it before reduction.
Also instead of letting the MeNH2 evap off bubble it into a dil HCl solution for reuse.
I'll get the most important refs scanned in and to Rhodium.
(Stoni's sexual toy)
08-31-02 12:36
No 351047
> To reduce 0.1 mol of your favourite substance add 0.8 mol
> of Lithium chloride and 900 mls of methylamine.
If I had 900ml of liquid methylamine I'd use it for something else, I can guarantee you that much.
> The reaction temp is around -7 deg (refluxing
> methylamine). Apply 2.0 Amps for 7 hours (50 000C) the
> voltage they saw was 85 volts.
Ok, so 85V * 2A = 170W heat generated. Ouch. Good luck keeping that reaction at -7°C without losing all the MeNH2.
This reaction may sound easy, but I can assure you that it is not!
I'm not fat just horizontally disproportionate.
(Hive Addict)
08-31-02 13:29
No 351055
900g methylamine gas? 77% yield? Man electroreactions can be cool but this one is a waste of it's needed precursors. Take that 900g of liq.meno2 and build a hydrogenating apparatus ad see what you get!
Though it is a good addition to teh electrostuff
Yes, That pic really is me!
(Hive Bee)
09-01-02 04:07
No 351266
If I had 900ml of liquid methylamine I'd use it for something else, I can guarantee you that much.
Yes using methylamine as the solvent would be a little extravagant. But who said that you have to? Bee's who have been running Birch type reactions are using great substitutes. NH3 will work fine, basically as long as the solvent can dissolve and doesn't react with the Li metal and the salt, your in business. There are plenty of potential solvents that Chem Guy has found. ../rhodium /birch.n
Remember your dealing with an indirect electroreduction process, not a direct reduction. Meaning the thing your worrying about is making Li metal which does the rest, the electro set-up has nothing to do but recycle the Li salt. It plays no other part but that.
Ok, so 85V * 2A = 170W heat generated. Ouch. Good luck keeping that reaction at -7°C without losing all the MeNH2.
Yes that is pretty shitty. In fact I really have no idea why they used that particular set-up. I've seen industrial electrodes which were huge and they were closer together than these (they had then 150 mm apart, this was also the reason for using so much MeNH2). So to solve that problem just move them to about 1 cm apart, I suggest using platinised screens these are easy to obtain and won't interfere with stirring so much. You will probably have around 3 to 4 volts across the electrodes at that proximity. If the resistance is still to high add more LiCl to lower it, or maybe add a second supporting electrolyte.
I also wouldn't get to hung up on keeping the reaction temp at -7º C. I believe this had more to do with keep the methylamine in the flask than a critical temp. Since it is an electro reaction you can control the rate and time.
The one big mystery is the selectivity, would the reaction just reduce your imine or would it reduce everything? You can limit the time with the imine hopefully being target No 1 but if it is not, it isn't going to work with MDP2P/P2P's
(Distinctive Doe)
09-01-02 13:50
No 351462
If you can find an easy way to make methylamine it might bee ok. Like say a tube furnace with ammonia and methanol. With the appropriate catalyst and a large excess of methanol it should work.
Those who give up essential liberties for temporary safety deserve neither liberty nor safety
(Chef d'Equippe)
09-05-02 03:05
No 352960
Why bother with an exotic 'tube furnace' reaction for methylamine? Reducing nitromethane in an Al/Hg seems much simpler for methylamine production and inexpensive to boot.
GODISNOWHERE
Shoot Narcs, Not Drugs
(Hive Bee)
09-05-02 17:47
No 353255
Foxy2 is referring to the very nice ref Rhod supplied in the CBE on his site JACS vol 50 p1786-1789 (1928) producing a very obtainable yield of 30% MeNH2 form a tube furnace under normal atmospheric conditions. Using Thorium oxide as the catalyst it was run at 370 to 380 degrees. According to most of the US patents out there, quite a few types of metal oxide cataylsts (they were vague) have been used. Until they switched to the new and exciting zeolite catalysts which run at very high pressures.
Baal the tube furnace might be exotic for some, but for a lot of old timers, the tube furnace was standard procedure (PAA to P2P conversion). The tube setup was very capable of producing very large amounts of P2P I'm sure the same could be said for production of MeNH2.
Anyway why are we still on the Methylamine bus? I already said you don't need it. This procedure is flexible, and is most useful for kiddies sick and tired of buying Li batteries, they can now simply recycle their current birch type reaction reagents and end up with a more selective reaction. Plus they are now doing their bit for the environment!