Author Topic: Modified Benseker reduction  (Read 192 times)

Doc B

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Modified Benseker reduction
« on: October 16, 2012, 02:05:31 PM »
Hopefully the combined wisdom and experience of the vespiary will educate a fellow wasp, heretofore my enquiry. Have any of the brave and brilliant wasps attempted the modified Benseker reduction of the common benzyl alcohol to  the phenylalkane of desire?

Using the EN ligand, in place of the heavily scrutinised solvent more commonly known, to solvate electrons from the earth metals proceeds according to established convention. Clarity of the royal blue solution upon end point (expected 10min at STP) and isolation is perplexingly on the contrary though.
The clarification of the solution does not accrue, even upon allowing several hours and/or heating of the reaction. It only clears upon quenching with several volumes of water.
Of far more concern and heartbreak is that the only extract reportedly obtainable, from both residue and NP extraction/acidification are undesired salts. Aqueous washes of the NP solvent/residue have not remedied this, nor has; introducing the reactant as a salt, dissolution of the residue with dilute aqueous hydrochloric, basification, NP extraction, acidification by gaseous or aqueous proton donors.

My the vespiary guide a troubled but gracious and hopeful wasp.



Sedit

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Re: Modified Benseker reduction
« Reply #1 on: October 17, 2012, 04:07:29 AM »
What modification are you talking about?

You have to be much more specific when asking questions like this.
There once were some bees and you took all there stuff!
You pissed off the wasp now enough is enough!!!

Doc B

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Re: Modified Benseker reduction
« Reply #2 on: October 17, 2012, 01:44:34 PM »
I always get this response when asking this question, I still don't really comprehend what detail is lacking. Please therefore excuse me should I neglect or not address a specific detail of interest, I really would appreciate any assistance and encourage you to take advantage of my offer to any further specific details that may be of interest or relevance upon query. Just ask away but shoot straight, I'm easily confused when dealing with people whilst on day release from the lab.  ;D

The modification to the standard reaction is that there is an absence of polycyclical reactants and the solvated electrons are hypothetically going to react to deoxygenate the alcohol functional group of the target monocyclical aromatics alcohol bearing side chain transforming it to the subsequent aminoalkane side chain of the benzyl ring. Its application is much like the infamous reduction named after that crazy but endearing ozzy chemist, Auther Birch. While traditionally neither named reaction is described as being specifically for the purposes of deoxygenation of aromatics the functionality of there diversity to do so is fairly well know.

I have read, Sedit, that you've had some experience with formation of the closely related and more potent lithum bronze. Hopefully you'll be able to shed some light on my dark corner of existance.

jon

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Re: Modified Benseker reduction
« Reply #3 on: October 18, 2012, 09:11:23 AM »
i can show you a real world example li bronze in action,

see here
http://www.youtube.com/watch?v=BlPI4sfeKsk&feature=related

skip to 30:00

Doc B

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Re: Modified Benseker reduction
« Reply #4 on: October 21, 2012, 12:32:38 PM »
Thanks Jon. Is SnB really a Li bronze reaction though or does the Li just look bronze as its slowly dissolves into the ammonial naphtha? In the Benseker type reactions Li powder dissolves into the amine without cosolvent at STP. However if wire, ribbon or reclaimed battery anodes are used the amine needs to be heated to afford progressive dissolution of the metal. As it dissolves there is a bronzed look to both the as yet in dissolved metals surface and the solution, approaching complete dissolution the solution turns to the deep blue commonly described.

Sedit

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Re: Modified Benseker reduction
« Reply #5 on: October 22, 2012, 05:15:21 AM »
The bronze is just an extremely concentrated form of the blue solution. I floats on Non polar solvents like Ether and performs reactions just like the blue Ammonia solution would except stirring is much more essential.
There once were some bees and you took all there stuff!
You pissed off the wasp now enough is enough!!!

Doc B

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Re: Modified Benseker reduction
« Reply #6 on: October 22, 2012, 09:24:47 AM »
Thanks Sedit. I added some xylene to an amount of blue EDA/Li solution I had in a sealed flask for over a week and the color change to a more bronzed appearance was almost instant. Correct me if I'm wrong but would it because the addition of the xylene altered the solubility parameters of the blue solution pushing some of the anions out of the mix?

You may ask why did I have a ready to go flask of blue sitting around for over a week? Well besides  not having sorted out the issues of product isolation, I was interested in the stability of the solution. I also have been unsuccessful in synthesis of a suitable reactant. The OTC variety seems to be a waste of funds if I cant extract the product. A pot of it sitting around while Im scratching my head as to how to get it out coupled with the potential increase in unwanted attention that may follow the OTC reactant acquisition, just seemed a bit risky.

Sedit

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Re: Modified Benseker reduction
« Reply #7 on: October 23, 2012, 05:38:15 AM »
Yields are low but don't allow the bronze to just go to waste. Use the OTC product and grind it in a blender with dry Xylene then bubble NH3 gas into the blended mush. Dump in the correct ratio of bronze and while still feeding NH3 in to ensure a blanket of protective gas then turn the blender right back on.

Filter and then heat the Filtered Xylene on a low heat for sometime to drive off Ammonia gas. Once you have driven off the NH3, Saturate the solution using HCl. Filter the precipitate and test for the presence of Ammonium chloride with a small amount of NaOH solution on a sample. Odds are it will smell like Amine and nothing more.

Good luck, keep better notes then I would if I where to perform such an insane reaction because I would suck at remembering the exact yields after synthesizing something that supports attention deficit syndrome.

Disclaimer: Do not try this at home or at all... and if it offends you... just... don't.... Listen to it!
There once were some bees and you took all there stuff!
You pissed off the wasp now enough is enough!!!

Doc B

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Re: Modified Benseker reduction
« Reply #8 on: October 26, 2012, 01:21:51 AM »
Thanks again, Sedit. Using the ammonia gas to provide a protective and beneficially reactive environment is a great idea.

Might the extraction difficulties from EDA be due to the fact that both product and solvent are amines?