DraconicAcid
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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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DrDevice
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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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wg48temp9
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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...
I am wg48 but not on my usual pc hence the temp handle.
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Dr.Bob
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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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DraconicAcid
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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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unionised
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I can tell you that dinitrophenylhydrazones are not stable to bases.
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DraconicAcid
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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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mayko
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What about live glowstick juice?
https://pubs.acs.org/doi/10.1021/acs.jchemed.8b00237
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Metacelsus
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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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Texium
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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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DraconicAcid
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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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Dr.Bob
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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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walruslover69
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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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DraconicAcid
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| Quote: Originally posted by DraconicAcid |
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? |
Getting back to this....would refluxing methyl benzoate and sodium glycinate in methanol work for making hippuric acid?
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Boffis
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@ Draconic acid, looking at von Richter, he lists a series methods for hippuric acid but not the reaction you propose. My fear is that sodium
glycinate would simply act as a base and hydrolysis the methyl benzoate, it might be better with methyl glycinate ester and melting them together
without solvent. On the other hand the reactants are cheap and readiy available so it might be worth a try.
Von Richter mentions the reaction of chloroacetic acid with benzamide and benzaldehyde-sodium glycinate followed by oxidation of the Schiff base. I
presume you are trying to avoid the use of benzoyl chloride.
Just had a look at OrgSynth.org website and there is a reference under the hippuric acid synthesis to the reaction of benzoic acid and glycine.
Unfortunately the ref is in one those early yearbooks (Jahresbuch für Chemie) and I couldn't find it on the Munich digital library web site but I
have found it before online so it is out there... somwhere! Perhaps on Galica
[Edited on 5-1-2025 by Boffis]
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AvBaeyer
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@Draconic Acid:
I have been able to make hippuric acid derivatives via two pathways:
1. Activation of benzoic acid with carbonyldiimidazole (CDI) followed by reaction with ethyl glycinate hydrochloride. The liberated imidazole from the
reaction with CDI provides enough base for the acylation reaction to proceed. Yields are in the 70% range of ethyl hippurate. Both CDI and ethyl
glycinate HCl are easily available in the US. The addition of 4-dimethylaminopyridine (DMAP) leads to somewhat higher yields and faster reaction.
2. Activation of benzoic acid with p-toluenesulfonyl chloride / triethylamine (2-2.5 molar equiv.) at ice bath temperature followed by addition of
ethyl glycinate HCl. This reaction is somewhat touchy but does work well if temperature is minded. There are several good references to
carboxylic-sulfonyl mixed anhydrides which are are quite informative.
I have also investigated at a cursory level the in-situ formation of anhydrides by the reaction of CDI with excess carboxylic acids. This is known
chemistry, but I have only run a couple of reactions. Conceivably, carboxylic anhydrides could be obtained by the reaction of excess carboxylic acid
with p-toluenesulfonyl chloride and excess base.
AvB
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