Keras - 31-5-2022 at 03:12
Folks,
about one month ago, I made a haloform reaction using 10% bleach and MEK (Methyl Ethyl Ketone), the goal being to get propionic acid in addition to
chloroform, propionic acid I intend to make esters from.
After a few hours, I found the separation to be unsatisfactory, so I covered the beaker with cling film and left it in a cool and dark place to rest.
When I returned to it last Sunday, the solution of what I assumed to be sodium propionate had turned from colourless to whisky amber.
Does anyone have a clue as to why that dark tinge?
clearly_not_atara - 31-5-2022 at 07:51
Leftover MEK undergoing aldol condensations could produce some colored byproducts?
Fantasma4500 - 31-5-2022 at 08:09
i recall large rolls of cling film appears purple, could this be explanation maybe? its possible that this film attains the color due to atmospheric
reactions or maybe reactions in the processing plant- maybe its a refraction thing
https://gyazo.com/249f87e99a0377ad4285dcacc720daa5
maybe try to react the cling film with all reagents involved in the experiment? sometimes you get fancy colors out of nowhere. nitration acids with
duct tape produces something that goes both orange and bright yellow depending on pH
could be the MEK has some additive- or the bleach, bought or homemade?
Keras - 31-5-2022 at 21:38
This is not a refraction thing, since the cling film covers the top of the beaker only, and the solution is – lol – at the bottom 
The bleach was not home made, but I had previously used it to make chloroform from
acetone and it worked fine. The MEK was purchased from laboratoriumdiscounter.nl, which I trust. Probably Atara is right, leftover MEK
self-condensing over a long period, unless propionate can react with chloroform.
I performed the reaction in a 2 L beaker that I transferred into 2 x 1L later on. Fact is, the two beakers look the same: one contains the lower layer
of chloroform, and the other does not, but whatever took place took place in both. Anyways. I will try to boil the solution to reduce the volume of
water, then add hydrochloric acid and salt it out. Might not be as efficient as boiling everything to dryness before adding hydrochloric acid, but I
hope this way the impurities will remain in the aqueous layer.
Thanks a bunch for your suggestions!