Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
Author: Subject: Alcohol and alkali hydroxide
experimenter
Harmless
*




Posts: 19
Registered: 7-11-2010
Member Is Offline

Mood: No Mood

[*] posted on 4-4-2011 at 07:13
Alcohol and alkali hydroxide


I have forgotten enclosed in a bottle 95% alcohol with some NaOH pellets. The pellets have dissolved and the solution turned into a yellow color. I evaporated a part of it and I was left with a yellow thick oil which doesn't burn as is, but burns when soaked in some paper (just as olive oil).

What could have happened in there? Did I produce some a substance with more than two carbons?
View user's profile View All Posts By User
ScienceSquirrel
International Hazard
*****




Posts: 1863
Registered: 18-6-2008
Location: Brittany
Member Is Offline

Mood: Dogs are pets but cats are little furry humans with four feet and self determination! :(

[*] posted on 4-4-2011 at 07:24


The main part of the mixture is an aqueous alcoholic solution of the alkali hydroxide. There is an equilibrium between the water, hydroxide, alcohol and alkoxide that depends on the amount of water, concentration of the alkoxide etc.
You can show that the solutuion is just alkali hydroxide by adding water to form an aqueous alcoholic solution of the alkali hydroxide.
Various mionor reactions take place as well, some of these will involve traces of impurities or denaturants such as methyl ethyl ketone added to reduce potability.
View user's profile View All Posts By User
experimenter
Harmless
*




Posts: 19
Registered: 7-11-2010
Member Is Offline

Mood: No Mood

[*] posted on 4-4-2011 at 08:42


Here is the solution, it has a dark yellow color:


Why, is alcoxide yellow?

Quote:

Various mionor reactions take place as well, some of these will involve traces of impurities or denaturants such as methyl ethyl ketone added to reduce potability.
The alcohol was clear (potable). I bought it much more expensive.
View user's profile View All Posts By User
ScienceSquirrel
International Hazard
*****




Posts: 1863
Registered: 18-6-2008
Location: Brittany
Member Is Offline

Mood: Dogs are pets but cats are little furry humans with four feet and self determination! :(

[*] posted on 4-4-2011 at 08:52


Pure solutions of alkoxides are colourless.
We used to make up base bath for cleaning equipment from potassium hydroxide and industrial methylated spirits.
They would start off clear and gradually go yellow and then brown, I would guess that some sort of oxidation condensation reactions occured.
A little coloured glop goes a long way, you might only have a few tens of mgs in there.
View user's profile View All Posts By User
experimenter
Harmless
*




Posts: 19
Registered: 7-11-2010
Member Is Offline

Mood: No Mood

[*] posted on 4-4-2011 at 09:00


Thanks for your time to explain.

Quote:

They would start off clear and gradually go yellow and then brown, I would guess that some sort of oxidation condensation reactions occured.
I suppose something like this is happening here too.

Quote:

A little coloured glop goes a long way, you might only have a few tens of mgs in there.
Yes, after evaporating it, only a small quantity of a yellow oil remains.
View user's profile View All Posts By User
vmelkon
International Hazard
*****




Posts: 669
Registered: 25-11-2011
Location: Canada
Member Is Offline

Mood: autoerotic asphyxiation

[*] posted on 19-2-2012 at 06:55
Ethanol + NaOH = yellow stuff


Hello,
I made some ethanol from sugar using baker's yeast.
Through distillation, I separated it from water.
My 3rd distillation, I collected vapors coming at about 78.5 °C which should mean the purity is near 95% wt ethanol.

I did notice that the color of the ethanol is not totally clear. It has a slight yellowness to it. I wasn't sure why. I have a decent distillation kit. I have used a vigreux column as well.

I took a 2 mL and added a little NaOH. I noticed it was getting cloudy. Since NaOH dissolved slowly (ambient temp is 10 °C), I left it in the PETE for 1 day. The next day, I noticed the bottom of the PETE was cracked and the liquid was extremely cloudy and very yellow.

I figured the NaOH reacted with the PETE plastic so I redid the experiment in borosilicate glass. I left it 1 day.

This time, it is not cloudy but I noticed colorless needle crystals floating in the ethanol. The bottom had a solid mass (I guess NaOH). AGAIN, THE WEIRD STUFF => a layer of colorless yellow liquid on top of the NaOH mass.

Is there an impurity in my ethanol? Any comments? Your experiences needed!
View user's profile View All Posts By User
smuv
International Hazard
*****




Posts: 842
Registered: 2-5-2007
Member Is Offline

Mood: Jingoistic

[*] posted on 19-2-2012 at 17:14


It is likely that the yellow color you see is due to the aldol condensation of aldehydes/ketone impurities in your ethanol. Re-distill your NaOH treated ethanol, it should now contain much less of these impurities (due to condensation to much less volatile products).



"Titanium tetrachloride…You sly temptress." --Walter Bishop
View user's profile View All Posts By User
Ephoton
National Hazard
****




Posts: 463
Registered: 21-7-2005
Member Is Offline

Mood: trying to figure out why I need a dark room retreat when I live in a forest of wattle.

[*] posted on 19-2-2012 at 18:47


yep smuvs hit the nail right on the head with that :)

plus maby products from acyloin condensation.
http://www.perfumerflavorist.com/flavor/research/4236701.htm...

This enzyme was first discovered in bakers yeast it is for the brake down of alcohols into aldehydes and ketones.
http://en.wikipedia.org/wiki/Alcohol_dehydrogenase

I think you will find that if you use a different yeast like a turbo yeast made for making alcohol rather
than bread you will have less aldehydes in your ethanol.




e3500 console login: root
bash-2.05#

View user's profile View All Posts By User
Nicodem
Super Moderator
Threads Merged
20-2-2012 at 10:18
vmelkon
International Hazard
*****




Posts: 669
Registered: 25-11-2011
Location: Canada
Member Is Offline

Mood: autoerotic asphyxiation

[*] posted on 4-3-2012 at 19:58


Thanks for the replies.

That alcohol dehydrogenase is fascinating, specially the evolution theory behind it.

The wikipedia sites says that acetaldehyde is produced (aldehyde) but I'm not sure which ketone is produced so I'm going to assume it would be propanone since it is the simplest ketone.

Now, if I apply what limited knowledge I have....

I also read the document at www.chem.missouri.edu/Chem2050/Dibenzylacetone.doc

so in my case, I suppose the product name is Diacetylacetone (Diacetylpropanone).
It is based on propanone except that the 2 end carbon atoms lose 2 hydrogens. Then connect a acetyl group to each of those carbons.

but I can't find anything about Diacetylacetone and Diacetylpropanone.
View user's profile View All Posts By User

  Go To Top