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Author: Subject: Non-polar chromaphores
DraconicAcid
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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:
https://www.ebay.co.uk/i/272316052933?chn=ps&var=5711595...

wax-dyes-l640.jpg - 67kB




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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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[*] posted on 26-9-2021 at 13:36


Bringing this back up, can anyone tell me if diphenylhydrazones are stable towards base extraction and chromatography?

I've got a couple of yellow compounds (fluorenone and benzil), plus a few things that I can nitrate that will hopefully turn out yellow, but I want MOAR!

[Edited on 26-9-2021 by DraconicAcid]




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[*] posted on 26-9-2021 at 13:44


I can tell you that dinitrophenylhydrazones are not stable to bases.
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[*] posted on 26-9-2021 at 13:46


Quote: Originally posted by unionised  
I can tell you that dinitrophenylhydrazones are not stable to bases.


That's what I thought. Thanks.

On a related note- one can't directly nitrate aromatics with unsaturated substituents, such as styrene, stilbene, or cinnimaldehyde, right?

And another related note- anyone got a prep for making hippuric acid from benzoic acid/glycine that doesn't require a) benzoyl chloride or b) my kidneys?

[Edited on 26-9-2021 by DraconicAcid]




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[*] posted on 26-9-2021 at 14:32


What about live glowstick juice?

https://pubs.acs.org/doi/10.1021/acs.jchemed.8b00237




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[*] posted on 27-9-2021 at 03:23


Carotenes/carotenoids are colored and quite nonpolar. You can extract them from vegetables.

Besides chlorophyll/carotene which you mentioned, there's also things like lycopene and zeaxanthin.

[Edited on 2021-9-27 by Metacelsus]




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[*] posted on 27-9-2021 at 05:54


In my undergrad organic lab, we separated fluorene (white) and fluorenone (yellow)

While it’s certainly easier to separate multiple colored compounds, it’s good practice for the students to have one colorless compound in the mix so that they have to test each fraction by TLC to find where it came out.

[Edited on 9-27-2021 by Texium]




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[*] posted on 27-9-2021 at 07:25


Quote: Originally posted by Texium  
In my undergrad organic lab, we separated fluorene (white) and fluorenone (yellow)

While it’s certainly easier to separate multiple colored compounds, it’s good practice for the students to have one colorless compound in the mix so that they have to test each fraction by TLC to find where it came out.

[Edited on 9-27-2021 by Texium]


We have that lab later in the semester (they do the oxidation first, then the separation). Because we only have the one UV lamp, the lab manual tells them to identify the fluorene-containing fractions by the way they can see crystals growing on the tip of the column.




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[*] posted on 30-9-2021 at 06:45


The test mixture that we used to use included nitroacetophenone, nitroaniline, nitroanisole and a few others. There are a few colored substituted acetopheones, those work well. Also acetylferrocene and ferrocene are brightly colored, so they separate well, I TA'd the lab to make acetoferrocene a few times, and they are quite visible as brown compounds. Also, look at some organic soluable dyes, like methyl violet, methyl blue, and others.
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[*] posted on 30-9-2021 at 07:11


I have used ferrocene and acetylferrocene while TA'ing like Dr.Bob said. We got great separation with ferrocene eluting with hexane and acetylferrocene eluting with DCM
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