Indole from pyrrole

[PolytheneSam]

Has anyone heard of a proceedure like this?

Indole is obtained by disolving pyrrole in 10 p.c. sulphuric acid, allowing the mixture to stand 1-2 hours, and then distilling in steam after adding excess of sodium hydroxide.  Diethyl indole prepared by this process is a viscid ill-smelling oil, boiling at 270º-310º C (D. R. P. 125489).
Pyrrole may also be converted into indole by dissolving in dilute hydrochloric acid, adding slight excess of ammonia, filtering, extracting the filtrate twice with ether, and heating the tripyrroline obtained in the extract to above 300º C, when indole and pyrrole result (Ber. 1894, 476).

Dictionary of Applied Chemistry Vol 1, E. Thorpe 1921

http://www.geocities.com/dritte123/PSPF.html

[Rhodium]

Sounds really strange - Where does the benzene ring come from? A ring-opened pyrrole, followed by some kind of cycloaddition to an unchanged pyrrole molecule?

[PolytheneSam]

That's all I found on it.  After I found it I tried looking for more references mainly in other chemical encyclopedias.  The book I found it in says dictionary on it, but its in several volumes like encyclopedias and has encyclopedia-like articles in it.  The word dictionary must of had a different meaning back in 1921.  D. R. P. 125489 looks like an old German patent.  Maybe I can get a copy of that.  I can order the Berichte reference.  They used to have journals back to the 1800's in one chemistry library about 20 years ago, but now put most of them in storage, probably to make room for new ones.
I also looked in a lot of patent subclasses on indoles (ie. 548/469 etc.) and tryptamines before and never saw anything like it.

http://www.ibiblio.org/patents/class/CLASS548.html

http://www.geocities.com/dritte123/PSPF.html

[Lilienthal]

That's not synthetic chemistry, that's pyrolysis (or pyrrolysis...).

[Rhodium]

Hahaha! Lol! Pyrrolysis!!  

[PolytheneSam]

The word pyrrole comes from the Greek word for fire-red.  Here's patent number 125489 from the Kaiser's patent office.

http://briefcase.yahoo.com/bc/beefiles2001/lst?&.dir=/Pyrrole+to+Indole&.src=bc&.view=l&.last=1

http://www.geocities.com/dritte123/PSPF.html

[PolytheneSam]

I need help with understanding (and translating) this Berichte article from 1894.  The German looks different from more recent German.  It says something about pyrrole being converted into tripyrrole and under some conditions it can be converted into carbazole and under other conditions, ie. high temperature, it can be converted into indole.

http://briefcase.yahoo.com/bc/beefiles2001/lst?.dir=/BerVol27p476-480&.order=&.view=l&.src=bc&.done=http%3a//briefcase.yahoo.com/bc/beefiles2001/lst%3f.dir=/BerVol27p476-480%26.src=bc%26.view=l

After looking up a couple words I can read the German patent fairly well (link below).  I did have one native German speaker look at it because I was confused about injecting steam after the copper vessel had been heated above 200º C.  The boiling point of water is 100º C and steam distillation seems to be done around 100º C.

http://briefcase.yahoo.com/bc/beefiles2001/lst?.dir=/Pyrrole+to+Indole&.order=&.view=l&.src=bc&.done=http%3a//briefcase.yahoo.com/bc/beefiles2001/lst%3f.dir=/Pyrrole%2bto%2bIndole%26.src=bc%26.view=l

http://www.geocities.com/dritte123/PSPF.html
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[terbium]

Steam distillation with superheated steam will work.

[PolytheneSam]

>Steam distillation with superheated steam will work.

That's what I figured they were doing, but the bp of indole at 1 atm is 253º C and the patent says the temperature gradually rises to 300º C.  Why not just distill out the indole without the steam?  Maybe the steam facilitates the reaction.

Also, from Ber. Vol 27 page 476.

Bekanntlich geht der Verharzung des Pyrrols durch Salzsäure oder Schwefelsäure, wenn man nicht mit ganz concentrirter Säure arbeitet, zunächst vollständige Lösung voraus, die bei Verwendung verdünnter Säuren sogar ohne Gefahr durch vorsichtigen Erwärmen beschleunigt werden kann.

This looks like it says concentrated acid converts pyrrole into a resin, whereas dilute acid converts pyrrole to tripyrrole and careful heating can accelarate the process.  Tripyrrole isn't specifically mentioned.  I assume the resin isn't it, or is it?  freetranslation.com gives this.

As you know the Verharzung of the Pyrrols precedes by salt acid or sulfur acid if one does not work concentrirter acid with entirely, first of all complete solution, that can be accelerated in use of thinned acids even without danger by careful heating.

   

http://www.geocities.com/dritte123/PSPF.html
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[PolytheneSam]

I got the first page of this article in some OCR software.  It has trouble recognizing all the text, but I can correct it.  Maybe I'll try some OCR and see what freetranslation.com comes up with.
http://www.geocities.com/dritte123/PSPF.html
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[uemura]

To aid this thread, Uemura translated the patent GE125489 into english. The German is a bit 'antiquated', some sentences go over a full para. Uemura did a split here and there.

Procedure for Preparation of Indoles from Pyrrols

In 1888 (Ber. 21, page 3429) the conversion of the isopropylpyrrol into an indole - the Pr3B3 [1] - di-isopropylindole has been observed. Later (Ber. 27, 1894, page 477) the transformation of the pyrrole into Indole was successful. The yields, especially in this one, are however not very satisfactory.

However, indole can be prepared from pyrrole - also the homologous of the indoles from the corresponding homologous of the pyrrols, quicker and with better yields, if the condensed[2] pyrrols made by dissolving pyrrols in acid are heated with alkali.

The best procedure is, dissolve the pyrrols in medium concentrated H2SO4 of HCl (see Ber 27, 477). Then saturate the clear solution with alkali in excess, then add solid alkali in excess. Now destill in a metal vessel with a water steam, regulating the destillation that the vessel heats up strongly using moderate water steam. Doing so, the alkali solution gets more and more concentrated, the temperature increases and finally one has to deal with an alkali fusion [3]

Examples:
I. 10grms Pyrrole are dissolved in 200ccm diluted H2SO4 (1:10) and the solution stands for 1 to 2 hours. Then 100grms NaOH are added and destilled from a copper vessel by introducing a moderate water steam [4]. The temperature increases slowly up to 300DegC. At about 200DegC Indole comes over, the main amount between 270-280 DegC. Yield: about 11grms indole-picrate. Using KOH reduces the temperatures by about 20DegC.

II. 5g Ethylpyrrole, produced from ethanol and pyrrole, with a bp of 163-165 DegC are dissolved in 50ml diluted H2SO4 (1:4). The solution was kept standing for 4 hours. After this time has elapsed, a solution of 50grsm NaOH in about 50ml H2O is added und the solution is destilled in a copper vessel by introducing a moderate water steam. At about 200DegC the Indole comes over, the main amount at about 270-310DegC. The Diethylindole is a tough oil with a faecal[5] odor which couldn't be cristallised. It can be dissolved in conc. HCl and re-precipitates by diluting with water. Yield of crude product about 4grms.

[.1] No clue what Pr3B3 might mean.
[.2] 'kondensiert' may also mean precipitated.
[.3] melted alkali.
[.4] no temp specified. May bee however a super hot water steam?
[.5] 'stinks like shit'

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