zooligan (Hive Addict)
09-19-01 09:47
No 215156
      NaCNBH3 description --> yield improvement??  Bookmark   

This is from a catalog description of NaCNBH3:

"Used in organic synthesis as a highly selective reducing agent. Sodium Cyanoborohydride selectively reduces aldehydes, ketones and oximes in acidic media at pH 3-4 not affecting other functinal groups as amides, ethers, nitriles, nitro compounds and epoxides in various reaction conditions."

Can the TSII method be modified to change the pH of the rxn media to the range specified above?  Could this improve yields?  There has been discussion here about making the pre-NaCNBH3-addition media neutral with GAA, but no one has discussed bringing the pH down to 3-4.

Ideas?  Comments?


"And if we don't get some cool rules ourselves, pronto, then we'll just be bogus too!"
(Hive Bee)
09-20-01 01:25
No 215480
      Re: NaCNBH3 description --> yield improvement??  Bookmark   

The only time my lab monkey was forced to perform a cyano reduction he kept the ph at 5 by addition of HCL as needed.

A two neck flask with thermometer well was used. One neck was fitted with a vacuum/inlet adaptor with stopcock and the other with an pressure equalized addition funnel with hcl solution with a loose stopper. The thermo well was fitted with an electronic ph probe. The pre-chilled contents were mixed then ph adjusted and the reaction was begun as per instructions from rhodiums' site. The cyano was added slowly as instructed and once addition is complete a vacuum is drawn on the flask and a slow stream of n2 is allowed through the inlet adaptor by turning the stopcock and allowed to escape through the pressure equalizing tube on the addition funnel. The styrofoam cooler under the flask is now filled with dry ice/sat. nacl/h20 solution while the reaction is stirred magnetically overnight or twelve hours which ever is longer.

In making mda ala cyano anhy. silica gel and pre dried AA helps yields subatantially either from a failed reaction or a difference in yield by bout 20%. A long cooled/reaction with no oxygen present in the flask to oxidise the cyano while mixing will result in 75-80% or higher. Performic drawn mdp2p reduces with a higher yield from minor cleaning than benzo mdp2p unless you vacuum filter with celite and high quality filter paper and double vacuum distill your mdp2p. But either way if you take the time and loving care and proper equipment/chems/technique that is required and don't be hasty you will score high every time with success.
(Hive Addict)
09-20-01 05:21
No 215543
      Re: NaCNBH3 description --> yield improvement??  Bookmark   

Interesting.  So lower pH does seem to help.  I haven't heard of such radical temp control on this rxn --  d.i./sat.NaCl is pretty chilly (exact temp??). 

Also, are we talking vac dessicated aa or oven-dried?  Does it matter?  Would dried MgSO4 work in place of silica gel, or would it have to be removed before the addition of the cyano?

"And if we don't get some cool rules ourselves, pronto, then we'll just be bogus too!"
(Hive Bee)
09-20-01 08:09
No 215599
      Re: NaCNBH3 description --> yield improvement??  Bookmark   

Well cooling to that extreme is not absolutely nessecary but cooling does inprove yields for the mdma and mda routes. Was referring to AA dried in a precision heated vacuum dessicator. Of course a cookie sheet in the oven at 150-200 degrees for a few hours should work also. The idea is to have your reagents and solvents as dry as possible for mda. The silica is intended to stay during the reaction to absorb excess water created by the reaction so that an excess does not interfere with the amination.

 Dunno about the epsoms there but my monkey has used it in an al/hg with aa once to make mda ala al/hg to keep any water from fouling the reaction and no problems erupted... But can't say for sure I never reqally studied that reaction that well to understand all the side reactions and whatnot to tell what impurities would come about from the reaction of any contents or impurities in them.

Thats a question for one of the moderators. Besides whatever happened to Unobtanium?
(Chief Bee)
09-20-01 08:11
No 215601
      Re: NaCNBH3 description --> yield improvement??  Bookmark   

Heating ammonium acetate to that high temperatures might convert it to acetamide. It should be dried in a desiccator.
(Hive Bee)
09-20-01 08:21
No 215603
      Re: NaCNBH3 description --> yield improvement??  Bookmark   

Oh dunno how cold it was but pinky's thermometer didn't read that low. It was contracted all the way down in the bulb and it reads down to 0c with the last line but going by scale from the bulb to the oc line I'd say about -5 or so...heehehe was actually a lil too cold it took for ever to get the damn AA to disolve in the methanol.

It ended up looking like a snow dome in the flask half way through. All the acetate coming out of solution and sticking to the stir bar and creating a ring around the top of the flask. It was cool looking at what loked like a sheet of ice around the edge of a vortex in the alcohol. But you know them damn monkeys they never do anything right always overdoing everyting.
(Hive Bee)
09-21-01 11:03
No 215990
      Re: NaCNBH3 description --> yield improvement??  Bookmark   

90% is possible under the right conditions and high purity reagents when making MDMA. MDA though, is another story. Pinky has only seen yields at 78% being the highest with MDA.

When your doing a 200g+ reaction and your using a magnetic mixer or overhead mixer that is capable of mixing 10-55gal volumes then the level of dissolved O2 in the solution will cause extremely low yields. Trust me Pinky thought that a non O2 aptmosphere was not nessecary but he was wrong when he ended up with a 20% return, which was improved when he just followed the writeups directions and didn't cut out steps. Nobody says you have to use N2 hell use H2 if your feeling lucky. Better yet, go to your local grocer and buy a couple helium filled rubber balloons and slip one over the  neck of your falsk squeeze all the helium out of it in to the flask and quickly slip the second ofer the neck in place. you may want to get a large one and let half the helium out carefully to allow room for any gasses created by your reaction.
(Hive Bee)
08-22-02 14:26
No 347824
      swim gets ammonium acetate (from chem company)and ...  Bookmark   

swim gets ammonium acetate (from chem company)and it doesn't say there is any water in it (assay 98.9% swim thinks)  are other bees using a different kind with more water?

and why does cooling help the cyano/amm acetate/md-p2p/methanol mix (for mda)?

What is a dessicator and how does it work? (can swim make one)
(Hive Bee)
08-22-02 14:34
No 347832
      Ammonium acetate and dessicators  Bookmark   

Ammonium acetate is very hygroscopic, which means it absorbs moisture from the air.  When you buy anhydrous grade (more expensive than regular) from a good chem supply, it comes airtight and with a dessicator bag inside, like those bags in the pockets of leather jackets.  These bags absorb the moisture in the bottle, so the stuff stays fairly anhydrous.  If you have regular Amm. Acetate, you should use a dessicator to dry it out as best you can.  A dessicator is basically a usually airtight container that you put whatever it is you are dessicating in.  You put the stuff in a tray and then underneath it you put drying agent.  You can also use vacuum to evaporate the air from the container.  A good desiccator can be bought for cheap from any online chemistry/biology equipment supplier.
(Hive Addict)
08-27-02 12:00
No 349720
      Damn you guys must have been bored as fuck ...  Bookmark   

Damn you guys must have been bored as fuck digging up this old post. I don' know what makes the cyano yield better at lower temps but the tip was picked up somewhere and was handed to an apprentice and he got excellent yields using dryice/ acetone bath I posted the results for him. I think iw has someting to do with its selectivity being narrowed at lower temps but I really don't know.

Yes, That pic really is me!