Sciencemadness Discussion Board

Ketones to Alcohols?

Volitox Ignis - 12-2-2016 at 16:01

I am looking for a possible way to convert various ketones to their respective alcohols. I have decided to start with the conversion of acetone to isopropanol,since that would probably be the most straightforward conversion. The question is: How would one convert ketones to alcohols?

MrMario - 12-2-2016 at 17:11

Full information about this topic on:
http://www.chemguide.co.uk/organicprops/carbonyls/reduction....

You can use LiAlH4 or NaBH4 to get the alcohol.
Ketones will form secondary alcohols, while aldehydes form primary alcohols.:)

UC235 - 12-2-2016 at 20:24

LiAlH4 and NaBH4 are powerful, fast acting reducing agents that convert ketones into secondary alcohols. They are also outrageously expensive and wholly unavailable to the amateur and especially in the case of LiAlH4 represent a significant fire hazard.

Catalytic hydrogenation with Pd/C and the Meerwin-Pondorf-Verley reduction are the two amateur-friendly ketone reductions that I can think of off the top of my head.

Trying to make isopropanol from acetone is ridiculous. A lot of work is going to go into the reaction and workup, so at least pick an interesting substrate.

Volitox Ignis - 13-2-2016 at 23:20

Quote: Originally posted by UC235  
LiAlH4 and NaBH4 are powerful, fast acting reducing agents that convert ketones into secondary alcohols. They are also outrageously expensive and wholly unavailable to the amateur and especially in the case of LiAlH4 represent a significant fire hazard.

Catalytic hydrogenation with Pd/C and the Meerwin-Pondorf-Verley reduction are the two amateur-friendly ketone reductions that I can think of off the top of my head.

Trying to make isopropanol from acetone is ridiculous. A lot of work is going to go into the reaction and workup, so at least pick an interesting substrate.

The Wikipedia article of Sodium Borohydride says that it can be prepared from sodium hydride (Which in turn is prepared from sodium and hydrogen) and powdered borosilicate glass at over 100C (Not too high). Unless there is something else that is required,I don't see how sodium borohydride is not an amateur-friendly chemical. The fire hazard can,in theory,be avoided by carrying the entire synthesis out under a nitrogen atmosphere.


[Edited on 14-2-2016 by Volitox Ignis]

ParadoxChem126 - 14-2-2016 at 12:30

And how exactly would you plan to prepare sodium hydride? Messing with molten sodium and gaseous hydrogen at several hundred degrees is no trivial matter. As far as I'm aware, no easy amateur method of making sodium borohydride has been found. It is thus considered a rather rare and exclusive reagent.

Like UC235 said, there are much easier alternatives. If you are already willing to work with hydrogen, then consider the Pd/C reduction.

Ozone - 14-2-2016 at 13:49

Ideas:

Electrochemical:
http://pubs.rsc.org/en/content/articlelanding/1969/tf/tf9696...
http://cecri.csircentral.net/1585/1/84-1988.pdf

Dithionite:
http://www.sciencemadness.org/talk/files.php?pid=109817&...
https://www.researchgate.net/publication/30473593_Reduction_... (everything looks OTC).

Fermentation (via dehydrogenase):
http://www.ncbi.nlm.nih.gov/pubmed/22686835

There are many ways to do this (the reduction of a ketone to a 2° alcohol isn't a very large jump).

O3




zed - 14-2-2016 at 16:40

Ketones are not easily reduced. Even more recalcitrant are Carboxylic acids and Amides.

NaBH4 is a godsend....but it ain't cheap. And, it isn't really easy to make.

byko3y - 14-2-2016 at 20:29

Quote: Originally posted by zed  
NaBH4 is a godsend....but it ain't cheap. And, it isn't really easy to make.
It was sent by satan. You need to completely rely on industry to produce it. And if you can't buy it or NaH - you can't obtain it. Even if you have trimethylborate and can purchase sodium hydride - sodium hydride is dangerous to work with and has limited shelf life. While making sodium hydride without safety measures and relatively expensive equipment most likely will lead to injury or low yields.
Purchase of sodium borohydride always raizes suspision. No amateur chemist wants to draw attention.

Dithionite is indeed godsend, it is cheap and very easy to obtain, non-flammable and not toxic (at least a final reagent), resistant to water hydrolysis, yields are close to quantitative with 3-4 excess of reagent if done properly (which is similar to NaBH4).
Electrolytic reduction is tricky and strongly depends on substrate.
Pd/C is not very amateur-friendly, because it's easy to poison the catalyst by using a rubber and palladium is expensive.
But what I really want to emphasize is that ketones are easily reduced using 2-propanol and any MPV catalyst, as already mentioned. I haven't done it myself, but I'm sure the reason why amateurs prefer not to use this method is because of need for (i-PrO)3Al catalyst, which was used by the original researchers and which is not the only catalyst you can use. Even a simple NaOMe can work as a reducing agent sometimes (for steroidal ketones reduction).

Ozone - 14-2-2016 at 21:27

Good point. That reminds me of a few reactions I did a while back. We were having reasonable yields via transfer hydrogenation with iPrOH or formic acid via catalysis with copper chromite. But, these were done at high T (170+ °C) in a stirred reactor under autogenous pressure. IIRC, you must beware of dehydration reactions leading to olefins that massively increase the internal pressure. Cleaning out the hood (and you pants) because of rupture-disc failure was par for the course during catalyst development.

Nice general review:

http://ejournal.undip.ac.id/index.php/bcrec/article/view/798...

O3

byko3y - 14-2-2016 at 21:42

This shit can kill you.

zed - 16-2-2016 at 19:36

Well, the fact that the OP wanted to convert Acetone to 2-Propanol doesn't help. Kinda swimming against the current.

Generally speaking, the conversion of 2-Propanol to Acetone, isn't hard. It is standard MPV.

Just use the 2-Propanol to reduce some other ketone, by distilling out the acetone, as formed.


Don't know if Ethanol or Methanol could be used in the MPV, to reduce Acetone to 2-Propanol.

I can't remember the question coming up before. But, it is something to think on.

[Edited on 17-2-2016 by zed]

Volitox Ignis - 20-2-2016 at 15:16

Quote: Originally posted by zed  
Well, the fact that the OP wanted to convert Acetone to 2-Propanol doesn't help. Kinda swimming against the current.

Generally speaking, the conversion of 2-Propanol to Acetone, isn't hard. It is standard MPV.

Just use the 2-Propanol to reduce some other ketone, by distilling out the acetone, as formed.


Don't know if Ethanol or Methanol could be used in the MPV, to reduce Acetone to 2-Propanol.

I can't remember the question coming up before. But, it is something to think on.

[Edited on 17-2-2016 by zed]

Sorry for not posting for a long time. I don't think that you can use methanol or ethanol for the conversion of acetone to isopropanol,as it would result in Aldol Condensation products, though that would be a good project for some other time.

[Edited on 20-2-2016 by Volitox Ignis]