04-30-03 16:05
No 430486
      Demethylation with aniline hydrochloride
(Rated as: excellent)

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 180-200C for several hours a significant but still only light demethylation occured.
With hydriodic acid (bp 132C) 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 "hemipinsure". no idea what this is
Toluinide 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 180-230C). 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.

[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 200C 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.


Comment by Lego: Pouring a 200C hot smelting in concentrated hydrochloric is no good idea crazy 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.

The candle that burns twice as bright burns half as long
05-03-03 07:44
No 431119
      Aromatic carboxylic acids to anilines
(Rated as: excellent)

The original article for the translation above can bee found at:
../rhodium/djvu /aniline.demethylation.djvu (../rhodium/djvu /aniline.demethylation.djvu)

Anilines are unfortunately not OTC (as far as Lego knows).
This article was found by Lego some time ago when investigating the potential of the Lossen degradation.

Journal of the American Chemical Society, 1953, 75, 2014-2015

Conversion of Aromatic Acids and their Derivatives to Amines

General Method: To 25-50 g of polyphosporic acid was added the carboxylic acid and slightly more than the theoretical amount of hydroxylamine sulfate or hydrochloride. The mixture was stirred mechanically and heated slowly on an oil-bath. When the chloride salt was hydrogen chlorie was evolved from the reaction mixture as the temperature approached 100. Upon further increase in temperature the reactants gradually entered solution. In the range 150-170 there was a rapid evolution of carbon dioxide and the mixture darkened considerably. When the frothing has ceased the mixture was poured onto crushed ice. The insoluble material was removed and the filtrate was neutralized with potassium hydroxide. The liberated amine, if liquid, was extracted with several portions of benzene. The combined extracts were dried over sodium hydroxide pellets and then treated with dry hydrogen chloride gas. The precipitated hydrochloride was collected and dried in a desiccator. If the amine was solid it was filtered from the basic solution directly and then dried. The yield of the crude amines obtained in this way are reported in Table I.

beta-Naphtylamine: To a mixutre of 1.7 g (0.24 mole) of hydroxylamine hydrochloride and 4.0 g (0.23 mole) of -naphtoic acid was added 50 g. of polyphosphoric acid. The mixture was stirred mechanically and the temperature was gradually raised. At 160C the evolution of carbon dioxide had ceased and the brown mixture was poured over 250 g. of crushed ice. Filtration of the resulting mixture yielded 0.7 g. of an orange colored solid, which displayed no definitite melting point. The filtrate was neutralized with potassium hydroxide and the precipitated amine was collected and dried. The yield was 2.7 g (82%) of light tan beta-naphtylamine, m.p. 107-109 (lit. 111-112).

Aniline from benzophenone: To a mixture of 2.1 g. (0.030 mole) of hydroxylamine hydrochloride dissolved in 20 g. of polyphosphoric acid was added 1.82 g. (0.010 mole) of benzophenone. The mixture was heated with constant stirring to 160-165 for ten minutes. The purple mixture was poured over 100 g. of crushed ice and the small amount of insoluble material was removed by filtration. The filtrate was made strongly basic with potassium hydroxide and then extracted thoroughly with benzene. The extracts were dried over sodium hydroxide and then saturated with dry hydrogen chloride. The precipitated aniline hydrochloride was collected and dried in a desiccator. The dry hydrochloride hat a light purple tinge and melted 188-191. The yield was 1.72 g. (66%).

Table I:

[tr][td]Reactant[/td][td] Isolated or expected product[/td][td] Yield[/td][td] M.p., C.[/td][td] Reported m.p., C[/td][/tr]
[tr][td]alpha-Naphtoic acid[/td][td] alpha-Naphtylamine[/td][td] 82[/td][td] 107-109[/td][td] 111-112[/td][/tr]
[tr][td]beta-Naphtoic acid[/td][td] beta-Naphtylamine[/td][td] 80[/td][td] 43-45[/td][td] 50[/td][/tr]
[tr][td]Benzoic acid[/td][td] aniniline hydrochloride[/td][td] 66[/td][td] 190-192[/td][td] 198[/td][/tr]
[tr][td]m-Toluic acid[/td][td] m-toluidine hydrochloride[/td][td] 76[/td][td] 223-225[/td][td] 228[/td][/tr]
[tr][td]p-Toluic acid[/td][td] p-toluidine hydrochloride[/td][td] 72[/td][td] 238-239[/td][td] 243[/td][/tr]
[tr][td]o-Bromobezoic acid[/td][td] o-Bromoaniline hydrochloride[/td][td] 53a[/td][td] [/td][td][/td] [/tr]
[tr][td]m-Bromobezoic acid[/td][td] m-Bromoaniline hydrochloride[/td][td] 46a[/td][td] [/td][td][/td][/tr]
[tr][td]p-Bromobezoic acid[/td][td] p-Bromoaniline hydrochloride[/td][td] 43a[/td][td] [/td][td][/td][/tr]
[tr][td]p-Chlorobenzoic acid[/td][td] p-Chloroaniline[/td][td] 32[/td][td] 69-70[/td][td] 70-71[/td][/tr]
[tr][td]Salicyl acid[/td][td] Benzoxazolone[/td][td] 33b[/td][td] 137-138[/td][td] 138[/td][/tr]
[tr][td]o-Phenylbenzoic acid[/td][td] Phenanthridone[/td][td] 40[/td][td] 292[/td][td] 293[/td][/tr]
[tr][td]m-Nitrobenzoic acid[/td][td] m-Nitroaniline[/td][td] 53[/td][td] 109-110[/td][td] 112[/td][/tr]
[tr][td]o-Nitrobenzoic acid[/td][td] o-Nitroaniline[/td][td] 0[/td][td] [/td][td][/td][/tr]
[tr][td]p-Nitrobenzoic acid[/td][td] p-Nitroaniline[/td][td] 0[/td][td] [/td][td][/td][/tr]
[tr][td]Valeric acid[/td][td] n-Butylamine[/td][td] 0[/td][td] [/td][td][/td][/tr]
[tr][td]Caprylic acid[/td][td] n-Heptylamine[/td][td] 0[/td][td] [/td][td][/td][/tr]
[tr][td]Ethyl benzoate[/td][td] Aniniline hydrochloride[/td][td] 68[/td][td] 190-193[/td][td] 198[/td][/tr]
[tr][td]Benzamide[/td][td] Aniniline hydrochloride[/td][td] 43[/td][td] 190-193[/td][td] 198[/td][/tr]
[tr][td]Benzoyl chloride[/td][td] Aniniline hydrochloride[/td][td] 51[/td][td] 189-192[/td][td] 198[/td][/tr]
[tr][td]Benzonitrile[/td][td] Aniniline hydrochloride[/td][td] 20[/td][td] 190-192[/td][td] 198[/td][/tr]
[tr][td]p-Chlorobenzamide[/td][td] p-Chloroaniline[/td][td] 0[/td][td] [/td][td][/td][/tr]
[tr][td]Benzanilide[/td][td] Aniline hydrochloride[/td][td] 76[/td][td] 188-191[/td][td] 198[/td][/tr]
[tr][td]p,p'-Dichlorobenzanilide[/td][td] p-Chloroaniline[/td][td] 48[/td][td] 66-70[/td][td] 70-71[/td][/tr]
[tr][td]p,p'-Dichlorobenzophenone oxime[/td][td] p-Chloroaniline[/td][td] 40[/td][td] 65-68[/td][td] 70-71[/td][/tr]
[tr][td]p,p'-Dichlorobenzophenone[/td][td] p-Chloroaniline[/td][td] 15[/td][td] 69-70[/td][td] 70-71[/td][/tr]
[tr][td]Benzophenone[/td][td] Aniline hydrochloride[/td][td] 66[/td][td] 188-191[/td][td] 198[/td][/tr]
[tr][td]N-Methyl-p-chlorobenzamide[/td][td] p-Chloroaniline, methylamine[/td][td] 0[/td][td] [/td][td][/td][/tr]
[tr][td]N-Methylbenzamide[/td][td] Aniline, methylamine[/td][td] 0[/td][td] [/td][td][/td][/tr]

Error: Table contains the text "<b>" between [tr] and the next [td] markup tag in the table row "[tr]<b>[td]Reactant[/td][td]Isolated or expected product[/td][td]Yield[/td][td]M.p., C.[/td][td]Reported m.p., C[/td]</b>[/tr]".
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(a) Identity confirmed by conversion to acetyl derivative
(b) Recrystallized once from water

Comment by Lego: The depressed melting points indicate impure product but in this case this should bee no trouble as the aniline is used in excess.

Preparation of polyphosphoric acid:
Post 398338 (Aurelius: "repost", Methods Discourse)

The candle that burns twice as bright burns half as long