Sciencemadness Discussion Board

Seperating 2-phenylpropionaldehyde from phenyl-2-propanone

OBLONG - 25-9-2016 at 05:47

Hello people of Sciencemadness, I was wondering how I would separate a mixture of 2-phenylpropionaldehyde and phenyl-2-propanone at an unknown ratio, meaning a bisulfite adduct probably cannot be used since it will react with the ketone as well. I read here that
Quote:

A good idea for separating a mixture of the two is to oxidize the mixture with a mild oxidant which won't affect the P2P, but which will oxidize the aldehyde to 2-phenylpropionic acid.

What oxidizer should I use, or are there any other methods for separation? Also, I am aware that phenyl-2-propanone is a commonly used precursor to methamphetamine, and I have no intention to synthesize any illegal substances, and since drug-related discussion isn't allowed on Sciencemadness, I apologise if I this post is breaking any rules, and the moderator is welcome to delete it. Thank you

[Edited on 25-9-2016 by OBLONG]

[Edited on 25-9-2016 by OBLONG]

Metacelsus - 25-9-2016 at 06:25

I'd expect them to be separable using column chromatography.
Also, if you're looking for mild oxidants, Fehling's (or Tollens') reagent will selectively oxidize the aldehyde.

OBLONG - 25-9-2016 at 06:43

Thanks you Metacelsus. I haven't heard of either Fehling's or Tollen's reagent, I'll try it out when I can.

[Edited on 25-9-2016 by OBLONG]

Darkstar - 25-9-2016 at 07:06

Quote: Originally posted by OBLONG  
Also, I am aware that phenyl-2-propanone is a commonly used precursor to methamphetamine, and I have no intention to synthesize any illegal substances, and since drug-related discussion isn't allowed on Sciencemadness, I apologise if I this post is breaking any rules, and the moderator is welcome to delete it.


If you're in the US, please be aware that simply possessing phenylacetone can get you into some serious trouble if you were ever caught. Unlike most meth precursors, which are just DEA List I or II, phenylacetone is a straight-up Schedule II controlled substance, making its mere possession without a DEA license illegal, regardless of intentions.

*Edit* - And just for future reference, drug-related discussion is allowed here as long as it's genuine and scientific in nature. It's low-effort spoon-feeding requests that are frowned upon here. Legitimate questions regarding the actual chemistry involved in the synthesis of illegal drugs, even when the end goal is ultimately to implement that chemistry, are perfectly acceptable as long as they are are asked in a scientific manner using proper chemical nomenclature. It helps to demonstrate that you have at least attempted to do some form of research on your own beforehand, though.

[Edited on 9-25-2016 by Darkstar]

OBLONG - 25-9-2016 at 17:43

Thanks Darkstar, I'm in Australia.

solo - 25-9-2016 at 18:21


There is a patent which talks about separating the adducts of aldehyde and ketones at a temp of somewhere in the 40˚C for one and above that for the other.....if i can remember where i have i will post it.....solo

OBLONG - 25-9-2016 at 22:08

That isn't going to work since the boiling points are just 6 degrees apart.

Protium-1 - 26-9-2016 at 00:24

OBLONG, solo actually mentioned that some as-yet-unspecified "adduct" of said compound had a 40°C bp difference, inherently your point about the 6°C bp difference of the base compounds you have in question is taken.

Also, judging by your disclaimer about appropriate discussions on this forum, I assume it is appropriate that you drop the 2-prefix from the aldehyde name, unless that is truly what you intend.

Besides the Tollen's reagent, you could use Potassium Permanganate or Potassium Dichromate (both of which are commonly available) to selectively oxidize the aldehyde to a carboxylic acid, leaving the ketone unreacted.
This is probably your best bet as it remains super easy to remove the carboxylic acid from the mixture with a mild Sodium Hydroxide solution, while the ketone remains dissolved in most organic solvents.

CuReUS - 26-9-2016 at 01:40

you could also use the pinnick oxidation to convert your aldehyde to acid without affecting the ketone
there is another way but its not that practical :(
if you can get some dimedone , you can form an adduct with phenylpropionaldehyde only
Quote:
Dimedone (5,5-dimethylcyclohexane-1,3-dione) reacts to form a crystalline derivative ONLY with aldehydes.

The condensation products of dimedone and aldehyde are called alkylidene dimethones. The alkylidene dimethones are almost insoluble in water, but can be crystallised from dilute ethanol.

Test Procedure.

Add 0.1 grams of the test-aldehyde to 5 mls of a 50/50% ethanol/water solution, add 2 mls of a 10% or saturated ethanolic solution of Dimedone.

If a precipitate does not form immediately, warm for 5 minutes; if the solution is still clear at the end of this period, add hot water until the mixture is just cloudy and cool to about 5 oC. Collect the crystalline precipitate by filtration.


https://the-hive.archive.erowid.org/forum/showflat.pl?Cat=&a...

[Edited on 26-9-2016 by CuReUS]

OBLONG - 26-9-2016 at 18:54

Sorry solo, I misunderstood. Protium-1, 2-phenylpropionaldehyde is the specific isomer I have. Also, thanks for pointing out that permanganate/dichromate doesn't oxodize the ketone. I'll try to oxidize the aldehyde with permanganate and sodium hydroxide, which from my understanding should form the salt that can then be vacuum filtered out, leaving just the ketone and any excess sodium hydroxide, potassium permanganate, and water.