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'
Carpe Diem