Patent GB-571265-A (GB)
Title: Improvements in or relating to chlorine-containing pyran derivatives
IPC: C07D309/08
Filed: 1943-11-19
Abstract: Tetrahydro- or dihydro-g -pyran is chlorinated by reaction with elemental chlorine, optionally in the presence of a solvent, e.g. carbon tetrachloride.  Chlorine may be passed into liquid tetrahydropyran maintained at 50-70 DEG  C., advantageously with the use of a catalyst, such as ferric chloride, aluminium chloride, stannic chloride, antimony pentachloride, iron turnings or, according to the first Provisional Specification, iodine, or using actinic radiation, whereas dihydropyran is preferably reacted with chlorine at approximately 0 DEG  C., avoiding the use of catalysts. In recovering the chlorination-products, the reaction mixture may be distilled in vacuo and further fractionated; in general, trichlorohydropyran fractions distil at 75-95 DEG  C./8 mm. while tetrachloro derivatives distil at 100-120 DEG  C./4 mm.  By treating tetrahydropyran or dihydropyran with chlorine until approximately 2 gram-atoms of chlorine have combined per gram-molecule of hydropyran and distilling the reaction mixture at ordinary pressure 3-chloro-5 : 6-dihydropyran is obtained, which in turn may be reacted with chlorine in the optional presence of a solvent to yield products containing three or more chlorine atoms.  2 - Hydroxy - 3 - chloro - tetrahydropyran is obtained by treating the crude reaction-product containing approximately 2 gram-atoms of chlorine per molecule with water at ordinary temperature, a carbonate of an alkali or alkaline earth metal advantageously being present.  The corresponding ether is also obtained as a by-product.  In examples: (1) chlorine is passed slowly into dihydropyran in carbon tetrachloride, cooled to 0 DEG  C. until evolution of hydrogen chloride commences, whereupon the product is distilled at ordinary pressure; the distillate boiling at 141-2 DEG  C. comprises 3-chloro-5 : 6-dihydropyran; (2) chlorine is introduced into the product of (1) at ordinary temperatures until evolution of hydrogenchloride commences and the product is then distilled at ordinary pressure to yield at 212 DEG  C. a stable liquid which solidifies and is redistilled to yield 2 : 3 : 3-trichlorotetrahydropyran; (3) chlorine is passed slowly into a solution at 0 DEG  C. of dihydropyran in carbon tetrachloride containing some antimony pentachloride until 3 atoms of chlorine per molecule have combined the residue is distilled at 20 mm. pressure to yield a product of boiling-range 120-155 DEG  C. which is re-distilled at 8 mm. to yield fractions boiling at 58-65 DEG  C., 68-100 DEG  C. and 100-110 DEG  C.; the solid portion of the third fraction is recrystallised from ethyl alcohol as 2 : 2 : 3 : 3-tetrachlorotetrahydropyran, and re-fractionation of the middle range yields essentially a mixture of isomeric trichlorotetrahydropyrans; (4) chlorine is passed slowly into tetrahydropyran at 65-70 DEG  C. until the increase in weight corresponds to the substitution of 3 atoms of chlorine per molecule, and the product is distilled in vacuo at 22 mm. to give the fractions, (a) up to 100 DEG  C., (b) 100-140 DEG  C., (c) 110-140 DEG  C. and a residue, the fraction (b) comprising a mixture of trichlorotetrahydropyrane and fraction (c) the tetrachlorotetrahydropyran of (3); (5) the crude reaction-product obtained by chlorinating dihydropyran at 0 DEG  C. until 2 atoms of chlorine per molecule have been absorbed is agitated for 10 hours with an aqueous suspension of calcium carbonate and the aqueous layer is extracted with ether to obtain 2-hydroxy-3-chloro-tetrahydropyran, the oily layer containing the corresponding ether, which is isolated by distillation in vacuo; (6) chlorine is passed for 4 hours into dihydropyran at ordinary temperature containing 0.1 per cent anhydrous ferric chloride to obtain a dichloro derivative; (7) chlorine is passed into dihydropyran at 0-5 DEG  C. until an appropriate gain in weight is obtained, whereupon the product is distilled at 11 mm. to yield 3 fractions, that boiling at 74 DEG  C. comprising 2 : 3-dichlorotetrahydropyran; (8) the isolated product of (7) is stirred for 3 hours at 0-10 DEG  C. with an aqueous solution of sodium carbonate and the solution is extracted with ether to yield 2-hydroxy-3-chlorotetrahydropyran.  Specifications 570,160 and 571,266 are referred to.