Bedlasky - 21-6-2019 at 11:52
Hi.
I tried blue bottle experiment, but I haven't any glucose in home. So I decided to make invert sugar solution. I added 10g of sugar in to 250ml of hot
water and add 2g of tartaric acid. After half an hour I added in to it 19g of KOH and dissolved it. Solution was immediately turning bright yellow. So
I pour it in to the drain and bought glucose candies (90% glucose + some citric acid, vitamin C, aroma and magnesium stearate). I dissolved in 250ml
of water four glucose candies (9,5g) and filtred it. After that I added 15g of KOH and dissolved it. Solution was very slightly yellow. Why were basic
solutions of sugars yellow?
Ozone - 22-6-2019 at 06:55
Hexose alkaline degradation products (HADP). Base catalyzed retro-aldol scission and subsequent self-condensation leads to a melange of conjugated
(colored) compounds. Some of these are sensitive to pH and have what the call an "indicator value."
How much you get is a matter of how basic the solution is, how hot it is, and how long it is maintained under the disruptive condition. It will happen
at rt if left long enough.
In this case, you'd start with equimolar glc and fru, the latter being a ketose, is more reactive (about 7x, in my experience; see anomalous
mutarotation). Fru will formed colored stuff when just acid at rt long-term, too (though this is a different mechanism, see caramelization and
hydroxymethylfurfural for more). This (with alkali) is probably why your invert darkened much more quickly than the simple glc candies.
O3