18thTimeLucky - 18-11-2017 at 04:27
I am definitely not an experienced chemist in any form so I was wondering if I could have some quick help. I came across a few old bottles of food
dyes from an elderly friend of my mother. I saw they had propan-2-ol in them and I have been wanting to get my hands on some for a while. I could of
course buy propan-2-ol pretty cheap but, of course, where is the fun in that?
I decided distillation should be best for extracting the propan-2-ol? I have never done a distillation before but I recently got the equipment. Other
ingredients in the food dyes include sorbitol which is a sugar alcohol which should stay in the solution and the dyes themselves should also stay in
solution? Propan-2-ol has a boiling point of 82.6oC so as long as I keep the temperature below the boiling point of water this should work (83oC?). I
think I could then remove the leftover water contamination in the propan-2-ol with some anhydrous magnesium sulfate? I don't at the moment have any
magnesium sulfate on hand so would anhydrous copper sulfate do the same job?
The question basically is am I correct in my thoughts here or am I being silly and a more experience chemist could point me in the right direction for
an extraction method. Thank you for your time!
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LearnedAmateur - 18-11-2017 at 05:08
As long as those ingredients are the only ones present then yes, it should be as simple as that. Just be observant of any possible colour changes
and/or odours that may indicate decomposition of the dyes - if not already then you should become accustomed to the smell of iPrOH (it's half way
between ethanol and acetone in my opinion, an 'industrial' odour). I've distilled isopropyl alcohol and ethanol after using them to clean stuff, it's
pretty straightforward and difficult to mess up if you know what's in the mixture to begin with. You can use a variety of anhydrous metal salts to
dessicate, most of them love some water of crystallisation. Copper sulphate, in my opinion is better because it will turn blue when hydrated, not only
a useful indicator but you can actually use it to calculate how much water was in the sample for future reference.
[Edited on 18-11-2017 by LearnedAmateur]
happyfooddance - 18-11-2017 at 08:38
I know it might sound like a fun experiment, but think about how messy that will be to clean up! Without the alcohol the dyes will almost certainly be
less soluble; you might end up needing to use the ipOH you just distilled to clean your boiling flask. Not trying to discourage you, but this just
seems like more of an "intro to cleaning glassware" than an "intro to distillation".
18thTimeLucky - 18-11-2017 at 11:28
Thank you for the tips, I will probably go ahead with the distillation tommorow then as I have some free time. That is true, happyfooddance, I might
ruin my flask if I am not careful. Would anybody recommend something the dyes might be soluble in for afterwards clean-up? For instance, as it is
soluble in propan-2-ol then maybe it would be soluble in acetone, or maybe would an alcoholic drink have enough ethanol in it to dissolve the dyes? I
would like to avoid wasting some of the already probably small volume of distillate for cleaning my RBF. I would also appreciate any suggestions for
experiments a newbie to distillation could do. I was going to try distilling vinegar to form a more concentrated solution of ethanoic acid, but after
a hour long search through previous SM posts I realised it was not worth bothering with.
One other quick question too, I see some people using water or oil baths and others just plonking their RBF straight onto the hotplate surface. How
come some do one and others do the other, they must have their pros and cons? That is, if not using a bath is just because the person is being lazy.
(My hotplate is 400W if it makes a difference)
happyfooddance - 18-11-2017 at 11:38
An rbf isn't going to make hardly any contact with the hot-plate; Use an oil-bath or similar. Acetone would probably work great to clean up. Also,
remember to use boiling chips, that will be the difference between having to clean one piece of glass and having to clean 5, and the floor. Good luck,
and take your time.
unionised - 18-11-2017 at 14:07
It might be an idea to add something like glycerine to the mixture before distilling.
It has a high boiling point, so very little of it will distil over with the propanol.
However, with luck, it will dissolve the dyes and stuff so they won't be so hard to remove from the flask.