FriendlyFinger (Hive Bee)
05-16-03 02:50
No 433439
      propiophenone to B-Methylstyrene ?  Bookmark   

What's the story with the synth below? Haven't seen much talk on the hive about it (Trans-Beta-Methylstyrene specifically). Does it work well? It looks easy except for the absolute ethanol, that makes me want to puke! So my question is how about substituing the ethanol for methanol and is it ok to use DCM instead of Ether? Fuck it, I'm going to try it anyway. Right now!

Synthesis of Propenylbenzenes from Propiophenones by Psychokitty

Reduction of the Ketone
"Dissolve the ketone (2 g) in ethanol (10 mL) in a 50 mL round bottom flask with a magnetic stirrer. Add NaBH4 (0.4 g) over a period of 15 min. The reaction may be mildly exothermic, so do not add the hydride reagent too fast. After stirring for 15 min, add 10 mL of water, heat to reflux for 5 min, and cool to room temperature (this destroys most of the excess sodium borohydride). Wash the reaction mixture into a separatory funnel with additional water (25 mL) and diethyl ether (50 mL). Shake, separate the organic layer and wash the aqueous layer again with ether (25 mL). Combine the organic layers, wash with water (25 mL), separate, and dry the organic layer over Na2SO4."

Dehydration of the Alcohol
"In a 50 mL round bottom flask, add 0.5 g of alcohol, a magnetic stirrer, and 25 mL of a 1.5 M solution of KHSO4. Set up a distillation apparatus on top of your round bottom flask (your lab notebook has a schematic for distillation set-ups) and distill off approximately 20 mL of liquid. This procedure not only drives the dehydration reaction to completion but it also purifies your product by steam distillation. Transfer the distillate to a separatory funnel, extract the aqueous phase twice with ether (2 tms 15 mL), dry the ether solution over Na2SO4, and evaporate the ether"

(Hive Addict)
05-16-03 03:09
No 433446
      similar  Bookmark   

I've read similar procedures, so it might be a valid method. Reduction of the C=O with NaBH4 is high yielding, but I have seen elsewhere that they used sodium acetate to dehydrate the alcohol. I can't remember in which article I read the procedure though.

The faster you run, the quicker you die.
(Hive Bee)
05-17-03 05:44
No 433651
      I've done a bit of reading and found that...  Bookmark   

I've done a bit of reading and found that NaBH4 is more reactive in Methanol than Ethanol. There must be something other than Absolute ethanol that I can use, even if the yields are a bit lower.

(Hive Addict)
05-17-03 12:02
No 433684
      You can reduce ketones or aldehydes with ...  Bookmark   

You can reduce ketones or aldehydes with sodium borohydride using MeOH as solvent with excellent results. Just dissolve the ketone in some MeOH and add, dropwise and with cooling, a aqueous solution of sodium borohydride. Use 0,3 mol sodium borohydride/mol ketone. Destroy the residual borohydride with some acid and extract the alcohol with DCM, toluene, ether or whatever.

(Hive Bee)
05-18-03 05:22
No 433823
      Music to my ears! Do you have any references...  Bookmark   

Music to my ears! Do you have any references of the top of your head? I'd like to learn more about it. Details. I'm a bit confused because I though it had to be anhydrous unless with an alkaline solution. I've been reading my Vogle's but alot of it is over my head right now.


Be joyful, though you've concided that facts!
(Chief Bee)
05-18-03 20:08
No 433972
      Sodium Borohydride Reductions of Ketones  Bookmark   

Stereochemistry and Mechanism of Hydride Reductions of Ketones
Tetrahedron 35, 449-462 (1979) (../rhodium/pdf /hydride.ketone.reduction-1.pdf)

Stereochemistry of Hydride Reductions
J. Am. Chem. Soc. 78, 2579-2582 (1956) (../rhodium/pdf /hydride.ketone.reduction-2.pdf)
(Hive Bee)
05-21-03 13:26
No 434529
      Thanks for the references, I understand it...  Bookmark   

Thanks for the references, I understand it better.

To 40g Propiophenone and 100ml MeOH in a 500ml RBF in an ice bath was added dropwise (3.4g NaBH4 in 60ml ice water) over 10 min keeping the temp between 23-30C. After another 10 min removed ice bath and let stir for 1 hour. Temp was still 1 or 2 deg higher than room temp.

Added 30ml of 2M HCl till neutrality and 2 layers appeared. Transfered to sep funnel and added 40ml DCM (should also have added water). Removed organic layer and extracted aqeous layer with 20ml then 10ml DCM. Combined these layers and washed once with water.  Was still murky. Filtered through Na2SO4 into a 250ml RBF with stir bar and distilled without vacuum. DCM came over at 37C?? then last few ml at 40C.

Added 1g KHSO4 to 45g (supposed 1-Phenyl-1-Propanol). Applied heat and vacuum to remove last bit of DCM. Whan oil bath was at 95C saw small bubbles then when at 120C saw water and oil distilling but only a little bit came over, then just kept dripping back and steaming. So used a bit of vacuum on and off. Didn't know what I was doing here! Took the bath up to 180C to see if any propenylbenzene existed, but sizzling water was getting bad.

Applied vacuum and eventually got about 40% visually of something that boiled around 175C. Smells good! But what happened to the rest? Is the stuff left in the reaction flask Propiophenone or unreacted alcohol? How do you tell, they both boil at 218C and 219C respectively (Merck index).

Was 1g KHSO4 enough? I used the example from PIKHAL page 698. 0.22mol KHSO4/mol alcohol. Is KHSO4 supposed to dissolve? The above synth posted by Psychokitty says 0.5g alcohol and 25ml of a 2.5M KHSO4 solution. That's about 5g KHSO4! Could that be right? Did I rush the reaction? Should I distill the water slowly and then turn up the heat with vacuum?

Don't get me wrong I'm not unhappy with what I did. I just don't know what I'm doing here and there.


Be joyful, though you've concided the facts