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Author: Subject: Non-polar chromaphores
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[*] posted on 17-6-2020 at 20:28
Non-polar chromaphores

So I'm looking into doing a demonstration or lab with chromatography, and want to find some nice, relatively simple organic compounds that are coloured (at least yellow), just so that they show up without using a shared UV lamp.

Nitro compounds can be counted on to be yellow, at least, but the nitro group is fairly polar, so I'm not sure how well different nitro compounds would resolve.

I suppose I could do the plant-based chlorophyll/carotene separation, but I'd prefer something where I can point out the molecules and say, "See- this one's obviously more polar, and that's why it's slower!"

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[*] posted on 17-6-2020 at 23:15

Oxazolones (aka azlactones) have colours ranging from yellow to orange and show up clearly without UV.

Fairly easy to synthesize if you have acetic anhydride or acetyl chloride, and hippuric acid.

I have performed TLC on them with 1:3 EtOAc:hexane to get mid-range Rf.
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[*] posted on 18-6-2020 at 01:32

There is also the sudan III and related dyes.

Search for oil soluble dyes in particular dyes for colouring candles. Though I suspect some may be pigments but they are only a few pounds for a few grams:

wax-dyes-l640.jpg - 67kB

i am wg48 but not on my usual pc hence the temp handle.

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[*] posted on 18-6-2020 at 04:28

Nitro compounds work fine for TLC or flash Chrom. if the rest of the molecule is hydrocarbon. Many more polar ones work fine also. You could separate nitroaromatics, like isomers of nitrotoluene, nitroanilsole, etc easily, with ethyl acetate and hexanes (or almost any mixture of hydrocarbons like heptane, butane, isooctane, distilled gasoline, etc). The only hydrocarbons that are not good for flash are aromatics, as they absorb UV, so hard to see the spots on the TLC without drying the plate well first. But you can also use dcm as the solvent, but that is harder for most people to get and not as easy to dispose of. In place of the ethyl acetate you can use ether or many other polar solvents, but ethyl acetate works well, and is not too hard to find.
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