Author Topic: Another easy route to P-2-P´s  (Read 5498 times)

0 Members and 1 Guest are viewing this topic.

GC_MS

  • Guest
1-phenyl-2-propanone
« Reply #20 on: March 05, 2004, 11:01:00 AM »
I was a long time ago since I tested the procedure on Rh's page, and I am currently in the need of some phenyl-2-propanone analogues, I wanted to re-evaluate the applicability of the method.

Substances: 32.6 g 1-phenyl-2-nitropropene (recrystallized from toluene), 100 g tin(II) chloride dihydrate, water and hydrochloric acid.

I allowed hydrolysis of the ketoxime for ca 1.5 h at 85-90°C. The reaction mixture was steam distilled to yield a yellow oil. The distillate was extracted with DCM and the combined organic phases washed with water. It is claimed that this procedure yields a reasonably pure product. On this, a little bit of comment...  :)

For the most amongst us, this oil indeed is pure enough. However, when washing the organic phase with aqueous NaOH instead of water, a discoloured aqueous phase is noticed. Some chromatography showed me that there was some benzyl alcohol present. Also, the "purified" oil contained some benzaldehyde (ca 5%). Depending on what the purposes are of the P2P, benzaldehydes are an interfering factor (reductive amination).


stratosphere

  • Guest
i apologize if this is reduntant, but here is...
« Reply #21 on: March 06, 2004, 08:34:00 PM »
i apologize if this is reduntant, but here is a procedure using Fe/HCl to reduce 1-(o-Methoxyphenyl)-2-nitro-1-propene to o-methoxyphenylacetone.

http://www.orgsyn.org/orgsyn/prep.asp?prep=cv4p0573


armageddon

  • Guest
Fe versus Sn
« Reply #22 on: April 22, 2004, 02:40:00 PM »
Hi Stratosphere!

The advantages of the above method (compared to iron/HCl) are:

a) magnetic stirring is made possible

b) yields are slightly higher

c) it avoids messy cleaning up afterwards (no red rust)

d) not sure 'bout that, but I think Fe/HCl needs 5 hours?
   Sn/HCl only 2h...

e) iron salts cannot be "regenerated", the SnCl4-soln. from above rxn. is easily converted to SnCl2 again by
    electrolysis... ;)

There are other threads about Fe/HCl reductions, too - but I think Tin(2)chloride is the reducing agent of choice for making ketones (see a) to e))...

Greetz A


armageddon

  • Guest
improved purity / suggestion
« Reply #23 on: August 30, 2004, 10:53:00 AM »
To achieve less benzaldehyde contamination of final ketone, I suggest the following:

Suspend SnCl2 in EtOAc and stir to dissolve as much as possible, place in cooling bath. Dissolve nitropropene of choice in just enough EtOAc, and add that via addition funnel to the SnCl2 suspension at such a rate that the temp. doesn't exceed 30°C. When done, stir for 1 hour, then add H2O, and again stir for 1h (white oxime stannate precipitates). Remove the solvent using slight vacuum, then add HCl and reflux to hydrolyze the ketoxime to its ketone. Steam distill as usual.

(to be honest, I haven't tried this yet; but the thought behind it is to remove solvent before changing the oxime's structure - I believe the reason for the BA impurities is the presence of solvent other than water during hydrolysis. Experimental data will follow soon - promised...)

Greetz A


Barium

  • Guest
Ok
« Reply #24 on: August 30, 2004, 03:16:00 PM »
What is the reasoning behind the solvent-theory? Why would the solvent disturb the hydrolysis?
I do indeed encourage improvements and welcome any and all suggestions. I'm just curious.


armageddon

  • Guest
just some feeling in my stomach ;^)
« Reply #25 on: August 30, 2004, 03:50:00 PM »
The idea came to me when I thought about the hydrolysis being a reversible reaction, but the ketone (once it has formed) being rather stable towards further reduction (to benzaldehyde and nitroalkane), in contrast to the oxime.

And a substance being not in solution is not as reactive as a dissolved substance is, right? (I thought this was why solvents are used at all!)

Maybe the key lies just in keeping temp. low during nitrostyrene addition and using as little SnCl2 as possible (like 2.05 eq.) - but I have some strange feeling that the solvent plays an important role in the unwanted further reduction of oxime. Experiment will tell...

(unluckily I don't know any other possibility for removing benzylalcohol from product, besides shaking with dilute NaOH - I think this is the more annoying side product, and I don't know if a careful procedure will avoid its formation... - we'll see!  ;) )

Did I mention that despite aldehyde and OH impurities, your method still simply fuckin rocks, seen yield- and workwise?!!  8)


Greetz A


amine

  • Guest
already answered
« Reply #26 on: August 31, 2004, 05:43:00 PM »

armageddon

  • Guest
umm..
« Reply #27 on: August 31, 2004, 06:14:00 PM »
As stated above (the 11th post in this thread): no. Maybe you should read the whole thread?  ;)

Greetz A


dextro

  • Guest
right ammount of HCL
« Reply #28 on: September 22, 2004, 04:46:00 AM »
swim will try this with 115g SnCl in 150ml EtOAc and 40,75g p2np in EtOAc.
after addition of water and removal of the solvent:
WHAT IS THE RIGHT AMMOUNT OF HCL 36% ?
in the original post by barium 140ml conc. HCL was used, but in other threads the ammount was not exactly described.

Thx for help