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Pyridine hydrochloride is a classical reagent for cleavage of aryl methyl ethers at 200-220o. It is also used in the demethylation of 4,5-dimethyl-7-methoxy-1-tetralone.
William G. Dauben.; Gerhard J. Fonken. Trofimov. Isomerization of Isospirostans to Furostenols with Pyridine Hydrochloride as the Catalyst. J. Am. Chem. Soc. 1954, 76, (18), 4618-4619.
T. S. Hamilton.; Roger Adams. Reduction Of Pyridine Hydrochloride And Pyridonium Salts By Means Of Hydrogen And Platinum-Oxide Platinum Black. XVIII1. J. Am. Chem. Soc. 1928, 50, (8), 2260-2263.
Classical reagent for cleavage of aryl methyl ethers at 200-220 o : Ber ., 75, 445 (1942), avoiding the strongly acidic or basic conditions of some alternative methods; see, e.g.: J. Org. Chem., 27, 4660 (1962):
Demethylation of methyl aryl ethers can also be carried out under solvent-free conditions with microwave irradiation: J. Chem. Res. (Synop.), 394 (1999).
Epoxides at ambient temperature in chloroform give chlorohydrins: Synth. Commun., 11, 287 (1981).
In DMF, has been used for the conversion of alkyl tosylates to chlorides at room temperature: J. Am. Chem. Soc., 80, 2726 (1958).
Cleaves N-trityl groups from histidine residues in peptide synthesis: Tetrahedron Lett., 28, 6031 (1987).
Mild acid catalyst, e.g. in the formation of acetals with ethylene glycol: J. Org. Chem., 31, 26 (1966), or 1,3-propanediol: Bull. Soc. Chim. Fr., 2287 (1972); and in the Fischer indole synthesis for acid-sensitive substrates: Synthesis, 645 (1977).
Hazard Statements: H302-H315-H319-H335
Harmful if swallowed. Causes skin irritation. Causes serious eye irritation. May cause respiratory irritation.
Precautionary Statements: P261-P280a-P305+P351+P338-P304+P340-P405-P501a
Avoid breathing dust/fume/gas/mist/vapours/spray. Wear protective gloves and eye/face protection. IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. IF INHALED: Remove to fresh air and keep at rest in a position comfortable for breathing. Store locked up. Dispose of contents/container in accordance with local/regional/national/international regulations.