Sciencemadness Discussion Board - Indigo: a ghetto synthesis

Indigo: a ghetto synthesis

MeshPL - 14-3-2017 at 14:16

So I was wondering if it was possible to synthesise indigo dye with as little equipment and reagents as I have.

What I have (and will likely be useful):
-benzene
-nitric, sulfuric, hydrochloric, phosphoric acid
-iron, aluminium
-chloroacetic acid
-some metals
-salt, sodium carbonate, NaOH
-bunch of others, less useful reagents...

The plan is:

-nitrate benzene:
Rather straightforward. I don't have a hotplate with stirrer or a condenser, but I can leave reaction standing for quite a long time, and I can stirr manually in a fume hood. I can also heat it just (and only) slightly. Our schools fume cupboard is quite efficient, so I don't worry too much about benzene fumes. Nitrobenzene will not be purified exept for phase separation.

-reduce nitrobenzene:

I could use Fe, Sn, Zn and Al, in HCL or (last 2) in NaOH. Which is the best one? The aniline will need to be separated by phase separation, perhaps salting it out will increase the yield.

-N-phenylglycine:
Rather doable:
http://www.prepchem.com/synthesis-n-phenylglycine/

-Indoxyl:
N-phenyl glycine will be boiled in phosphoric/sulfuric/polyphoshoric acid. It should than cyclize to form indoxyl.

-Indigo:
The solution from previous step will be dumped into water and possibly neutralised. The air will eventyally oxidise indoxyl to indigo, which is insoluble in water.

What do you guys think? I know, not a great plan. But maybe it will work. Shouldn't be the hardest thing ever. Maybe even easier than growing actual indigo plants... (wild ones are so rare here, where I live, that collecting them is not an option

)

[Edited on 14-3-2017 by MeshPL]

clearly_not_atara - 14-3-2017 at 14:40

Big problem I see there is the cyclization of N-phenylglycine. I'm doubtful this is going to happen the way you envision it. Pfegler used sodium amide to achieve this transformation:

https://en.wikipedia.org/wiki/Indigo_dye#/media/File:Indigo_...

Sodium amide is the trouble here. You can produce sodium oxide by heating sodium carbonate to about 900 C, but this is not practical for most people. Sodium oxide reacts with NH3 to NaNH2 + NaOH. Potassium however can be made by reducing potassium hydroxide with Mg, which is a sticky in "Chemistry in General" and is usually the amateur's favorite source of alkali metals. Metallic potassium reacts readily with ammonia.

If you have toluene, acetone, and copper (or manganese) available, I recommend using the Baeyer-Drewsen synthesis.

MeshPL - 14-3-2017 at 15:12

Oh, but how are you going to make o-nitrobenzaldehyde? I don't know for sure, but it is not easy to make. O-nitrobenzoic acid will often be the product of most method of oxidising o-nitrotoluene. And nitrating benzaldehyde is just not an option-I can't make pure enough benzaldehyde.

Cryolite. - 14-3-2017 at 15:39

Another possibility would be to synthesize a mixture of 2- and 4-chlorobenzoic acid by chlorinating toluene and oxidizing this with permanganate. This could then undergo an Ullmann-type arylation with glycine and copper iodide catalysis (see attached -- this seems to be selective for replacement of the ortho halogen). Now you have a mixture containing N-carboxymethylanthranilic acid-- this should form indoxyl by simple treatment with sodium hydroxide.

Attachment: ullman review.pdf (3MB)
This file has been downloaded 427 times

Attachment: tyrian purple.pdf (229kB)
This file has been downloaded 355 times

anewsoul - 14-3-2017 at 18:42

Quote: Originally posted by clearly_not_atara

If you have toluene, acetone, and copper (or manganese) available, I recommend using the Baeyer-Drewsen synthesis.

This reaction looks like it would be interesting. How would the conversion of 2-nitrotoluene to 2-nitrobenzaldehyde be done with MnO2 and H2SO4 though? I can't find any clear information on that. I guess I could take a shot in the dark at it.

JJay - 14-3-2017 at 18:47

Benzylic and allylic positions are susceptible to oxidative attack, especially by manganese-based oxidizers.

Texium - 14-3-2017 at 21:02

Quote: Originally posted by anewsoul

Quote: Originally posted by clearly_not_atara

If you have toluene, acetone, and copper (or manganese) available, I recommend using the Baeyer-Drewsen synthesis.

It's unclear exactly how it works and I haven't seen any references of people actually doing it, but I know that it requires a fresh and active form of MnO₂, such as that formed by comproportionation of MnSO₄ and KMnO₄. Pottery grade is not active enough for the reaction to work. I've been wanting to do the Baeyer-Drewsen synthesis for over a year now and I've looked into a lot of alternative routes for the oxidation, but I'm thinking I'll have to just bite the bullet and try using the MnO₂ route.

Also, nitrating benzaldehyde will not work anyway, because the aldehyde group is meta directing. You'll get m-nitrobenzaldehyde, and probably m-nitrobenzoic acid as well, from oxidation.

MeshPL - 15-3-2017 at 05:28

I don't know. I don't really have means to reflux reactions. I was wondering if it was possible to make indigo for me, but I guess I would need to check. However, I don't know whether to try or not. I'll see.

CuReUS - 15-3-2017 at 06:51

Quote: Originally posted by MeshPL

Oh, but how are you going to make o-nitrobenzaldehyde?

In two steps from methyl anthranilate :
1.oxidise the amine to nitro using oxone -http://www.sciencemadness.org/talk/files.php?pid=143874&...
2.reduce the ester to aldehyde using DIBAL
methyl anthranilate is available OTC as grape flavor or bird repellent -https://www.sciencemadness.org/whisper/viewthread.php?tid=19...

Texium - 15-3-2017 at 16:10

Quote: Originally posted by CuReUS

Quote: Originally posted by MeshPL

Oh, but how are you going to make o-nitrobenzaldehyde?

Yeah, methyl anthranilate is OTC, but unfortunately DIBAL is not...

CuReUS - 16-3-2017 at 06:18

Quote: Originally posted by zts16

Yeah, methyl anthranilate is OTC, but unfortunately DIBAL is not...

I know DIBAL isn't OTC,but that doesn't mean it can't be bought,since its not a watched chemical or anything.Fisher is selling it at $50/100ml and I am sure you can get it even cheaper from china

https://www.fishersci.com/shop/products/diisobutylaluminium-...

[Edited on 16-3-2017 by CuReUS]

clearly_not_atara - 16-3-2017 at 10:03

Quote: Originally posted by MeshPL

Oh, but how are you going to make o-nitrobenzaldehyde? I don't know for sure, but it is not easy to make. O-nitrobenzoic acid will often be the product of most method of oxidising o-nitrotoluene. And nitrating benzaldehyde is just not an option-I can't make pure enough benzaldehyde.

Are you saying that copper sulfate works on unsubstituted benzaldehyde but not the o-nitro version? I suppose that's possible, although I expect the electron-deficient arene to be less susceptible to oxidation a priori.

The selective conversion may be achieved with alkyl nitrites:

http://acta-arhiv.chem-soc.si/52/52-4-460.pdf

"To a 4 M methanolic solution of sodium methoxide (700 mL), 500 mL of toluene was added followed by immediate removal of the methanol by distillation. After cooling, pentane (300 mL) was added to the resulting suspension. The flask was equipped with an ethanol cooled condenser (–20 °C) and a mixture of 2-nitrotoluene (118 mL, 1 mol) and 2-propylnitrite (111 mL, 1 mol) was added slowly with vigorous stirring. The temperature of the reaction mixture was controlledby regulation of the rate of addition. After complete addition, the ethanol-cooled condenser was removed and a distillation head fitted. 600 mL of 36% HCl was added dropwise, following by controlled distillation of the solvent. Separation of the organic layer followed by its concentration in vacuo gave a solution of 2-nitrobenzaldehyde in 2-nitrotoluene."

I think this will do. Isopropyl nitrite is relatively easy to make. I believe the conversion proceeds by deprotonation of nitrotoluene, which is nitrosated to nitrobenzaldoxime, and this is hydrolysed to nitrobenzaldehyde. It should be possible to precipitate nitrobenzylhydroxysulfonate with bisulfite addition.

Electrochemical oxidation may be performed with cobalt sulphate in sulfuric acid:

http://link.springer.com/article/10.1007/BF00614970

[Edited on 16-3-2017 by clearly_not_atara]

[Edited on 16-3-2017 by clearly_not_atara]