Patent GB-570974-A (GB)
Title: Improvements in or relating to the production of pyran derivatives
IPC: C07D309/28
Filed: 1943-11-19
Abstract: 5 : 6-Dihydropyran-3-carboxylic acid chloride is obtained by reaction of dihydropyran with phosgene, e.g. excess of phosgene may be dissolved in the dihydropyran at subatmospheric temperature, maintaining the solution at atmospheric or lower temperature until the reaction has occurred; the solution may then be warmed to expel hydrogen chloride and fractionally distilled to isolate the acid chloride.  The dihydropyran may be used in solution, e.g. in carbon tetrachloride, advantageously with exposure to irradiation from a mercury are lamp.  5 : 6-Dihydropyran-3-carbonyl compounds are obtained by interaction of above acid chloride with various reagents including ammonia, a primary or secondary amine, water, an alcohol, a phenol, an alkali, an aromatic hydrocarbon or a zinc alkyl. Specified alcohols are methyl, ethyl, n-propyl, ethylene glycol, propylene glycol, diethylene glycol and pentamethylene glycol, specified phenols are phenol, the xylenols and b -naphthol, specified amines are methylamines, ethylamines, aniline, substituted anilines, naphthylamines or substituted naphthylamines and specified aromatic hydrocarbons are benzene, toluene and naphthalene.  The anhydride may be obtained by reacting the acid chloride with the free acid or with an alkali metal salt thereof.  Thus, the compounds produced are of the general formula <FORM:0570974/IV/1> wherein R represents OH or OM (M being a monovalent metallic ion), NH2, NHX1, NX1X2 (X1 and X2 representing the same or different substituted or unsubstituted alkyl, aryl or aralkyl groups) alkyl, e.g. methyl, ethyl, n-propyl or isopropyl, or aryl, e.g. phenyl, tolyl or naphthyl which may be substituted, e.g. by hydroxyl, amino or nitro groups or halogen-atoms.  The products are in general intermediates, e.g. for dyestuffs, and the esters derived from high molecular weight alcohols are useful as solvents or plasticizers.  In examples: (1) an excess of gaseous phosgene is passed into dihydropyran at ordinary temperature and the solution set aside for 3 days, prior to dilution with water, neutralization with sodium carbonate and slight acidification with hydrochloric acid to obtain crystals of 5 : 6-dihydropyran-3-carboxylic acid; (2) an excess of gaseous phosgene is gradually introduced into dihydropyran cooled to 0-10 DEG  C., the resultant solution being set aside for 64 hours and gradually brought to atmospheric temperature prior to expulsion of excess phosgene and of hydrogen chloride by heating and fractional distillation to obtain the acid chloride; (3) an excess of gaseous phosgene is dissolved in dihydropyran cooled to 0 DEG  C. and the reaction-mixture set aside for 12 hours, the temperature rising gradually to 18 DEG  C. and unreacted phosgene and hydrogen chloride are removed by warming, followed by distillation to isolate the acid chloride; (4) the product of (2) is gradually added to a mixture of aniline and aqueous sodium hydroxide and the whole is heated to 80 DEG  C. and set aside to deposit the crude anilide; (5) the product of (2) is gradually added to a mixture of p-toluidine and aqueous sodium hydroxide at 50 DEG  C., whereupon the temperature is raised to 80 DEG  C. for 2 hours and the whole is cooled to deposit the corresponding crude p-toluidide; (6) the product of (2) is gradually added, while stirring, to a mixture of benzene and aqueous ammonia at 3 DEG  C., the temperature rising to 16 DEG  C. prior to heating at 70 DEG  C. for 2 hours and cooling to deposit the crude amide; (7) the product of (2) is added with stirring to a mixture of phenol and aqueous sodium hydroxide at 40-45 DEG  C., whereupon the temperature is raised to 65 DEG  C. for 1 hour before cooling, separating the ester layer and purifying by fractional distillation; (8) 5 : 6-dihydropyran-3-carboxylic acid chloride is added, with stirring, to water cooled below 35 DEG  C., the stirring being continued for 1 hour, whereupon the precipitated 3-carboxylic acid is recrystallized from water; (9) the product of (8), neutralized with aqueous sodium hydroxide, evaporated to dryness and ground, is mixed with the product of (2) and heated under reduced pressure at 110 DEG  C. for 3 hours prior to removal of unchanged acid chloride by distillation and extraction with carbon tetrachloride to obtain the acid anhydride; (10) the product of (2) is added gradually to methanol or ethanol, with stirring, the mixture being set aside for 1 hour before dilution with water and extraction with ether to obtain the methyl or ethyl ester; (11) 5 : 6 - dihydropyran - 3 - carboxylic acid chloride is added gradually, with stirring and cooling, to ethylene glycol monoethyl ether, water being added after an interval and the oil which separates being extracted with ether to obtain the glycol monoethyl ether ester; (12) dihydropyran carboxylic acid chloride is added gradually, with stirring and cooling, to pentamethylene glycol, stirring being continued for 2 hours before dilution with water, ether extraction and fractional distillation to obtain the pentamethylene glycol di - ester; the ethylene and diethylene glycol di-esters are similarly obtained when ethylene and diethylene glycols respectively are used; (13) the product of (2) is slowly added to a well-cooled, agitated mixture of 2-nitro-4-chlorophenol, pyridine and ether with stirring for 1 hour after the addition and filtering off pyridine hydrochloride prior to separating the ether phase and distilling the residue in vacuo to obtain the 2-nitro-4-chlorophenyl ester.