As requested by Lugh in
Post 429397 (not existing)Chem. Ber. 49, 1371 (1916)140. Alfons Klemenc: About the demethylation of phenol ethers and acid esters with the hydrochlorides of aromactic bases. Preparation of anilides and its homologs.
Like hydrobromic and hydriodic acid hydrochloric acid in aqueous solution demethylates phenol ethers and acid esters usually only at elevated temperature. Surely with hydrochloric acid this reaction is the slowest. If working in an open vessel hydrochloric acids can demethylate few substances even if gaseous hydrogen chloride is passed in.
In a pipe bomb this reaction proceeds a bit faster because higher temperatures can be achieved but still insignificant. Therefore usually hydriodic acid is used which demethylates completely in an open vessel. The reason is not only the specific action but also the substances dissolve better in concentrated hydrochloric acid than in ordinary concentrated hydrochloric acid.
Pyrogallol trimethylether for example treated with a continous stream of gaseous hydrogen chloride for several days was only slightly demethylated. With concentrated hydrochloric acid in a pipe bomb heated to 180-200°C for several hours a significant but still only light demethylation occured.
With hydriodic acid (bp 132°C) a quantitative demethylation was observed in a short period.
Some time ago it was observed that aniline boiled with phenol ethers demethylated the ethers. In the later experiments it was shown that this reaction proceeds slowly.
weird ancient german sentence about the use of aniline hydrochloride.
In an open vessel anilin hydrochloride quickly demethylates pyrogallol trimethylether completely.
Several phenol ethers and phenolether carboxylic acidesters were analysed. All, but anisole which also shows other different properties, were completely demethylated. The acids respectively their esters yielded the corresponding anilides. To avoid the formation of the anilides dimethylaniline hydrochloride can also be used but its demethylating activity is severely decreased. It can only be used if the ester is easily saponificated like "hemipinsäure".
no idea what this isToluinide hydrochlorides have the same properties as aniline.
The general procedure is quite simple. 1 mole substance is mixed with 2-3 moles aniline hydrochloride (or its derivates) and is heated in an oilbath until the mixture melts (between 180-230°C). The beginning of the reaction can easily be recognized that the flame of a Bunsen burner turns green (methyl chloride) if it gets near the air condenser attached on the vessel. After 0.5 to 1 h the reaction is over and the still hot smelting is poured in concentrated hydrochloric acid. The further workup depends on the substance.
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[page 2, right paragraph]
It was shown that all phenol ethers were demethylated quickly and with hight yields.
As an example I state the demethylation of pyrogallol trimethylether.
1 Mol pyrogallol trimethylether was mixed with about 4 moles aniline hydrochloride and the clear smelting was heated to 200°C for 20 minutes. It was poured in concentrated hydrochloric acid and extracted with ether. Evaporation of the ether yielded a residue which was pure pyrogallol after recrystallization from benzene.
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Comment by Lego: Pouring a 200°C hot smelting in concentrated hydrochloric is no good idea
even with a fume hood and a gas mask. Aniline is slight soluble in water, the hydrochloride will dissolve better. When the mixture is treated concentrated acid in water the free phenol should precipitate from the mixture and the aniline will stay in solution. Rhodium's page and the Hive are full of alternative workups.