Patent GB-796906-A (GB)
Title: Esters of cyclic hemi-acetals and their preparation
IPC: C08K5/151
Filed: 1956-06-22
Abstract: Alkanoic esters of cyclic hemi-acetals are produced by intimately contacting gaseous oxygen with a cyclic hydrocarbon mixed with an anhydride of an alkanic acid having 2 to 4 carbon atoms, or of mixed acids having 2 to 4 carbon atoms, in the presence of a free-radical producing initiator, at a temperature of from 20 DEG  to 150 DEG  C., the proportion of anhydride ranging from 0.5 to 8 mols. per mol. of hydrocarbon, the hydrocarbon containing from 5 to 6 carbon atoms in an alicyclic ring and being selected from alkylcycloalkanes, cycloalkenes and benzocycloalkanes.  The esters which have the structure: <FORM:0796906/IV (b)/1> where n is 1 or 2, and the starred carbon atom is ternary or quaternary.  Typical alkylcycloalkanes are methylcyclopentane, methylcyclohexane, the dimethylcyclopentanes and the dimethylcyclohexanes.  Typical cycloalkenes are cyclopentene, cyclohexene, 3 - methylcyclopentene, 3-methylcyclohexene, the dimethylcyclohexenes and dicyclopentadiene.  Suitable benzocycloalkanes are indene, tetrahydronaphthalene and 9,10-dihydroanthracene.  The anhydride used may be acetic, propionic, butyric or isobutyric anhydrides.  Mixed anhydrides such as acetic butyric anhydride can also be used.  Suitable free-radical initiators are peroxides, such as the acyl peroxides, alkyl and cycloalkyl peroxides, alkyl and cycloalkyl hydroperoxides, peroxy acids and salts, e.g. <FORM:0796906/IV (b)/2> wherein R1 is an alkyl group containing no more than 3 carbon atoms, and R2 is either an hydrogen atom or a methyl radical, and wherein at least one R2 is hydrogen, are novel compounds.  The net result of the above-described reaction is shown schematically as follows: <FORM:0796906/IV (b)/3> the persulphates; azo compounds such as N,N1 - azobis - (a  - isobutyronitrile), and ultraviolet light.  The oxygen may be pure or mixed with an inert gas, as in air.  The process may be carried out batchwise or continuously, and in either case it is desirable to separate the ester from unreacted materials, e.g. by fractional distillation, as soon as the conversion reaches about 10 per cent. The products are useful solvents and may be used to make lacquers or pastes from vinyl polymers which may be brushed or sprayed on to textile fabrics and paper.  The ester products may also be hydrolysed to form difunctional compounds.  Thus, 2-oxa-3-cycloheptenyl alkanoates may be hydrolysed to adipaldehyde; 2-oxa-3-methylcyclohexyl alkanoates may be hydrolysed to 5-hydroxycaproaldehyde; 3 : 4-benzo-2-oxacycloheptyl alkanoates may be hydrolysed to 4-(o-hydroxyphenyl)-butyraldehyde; 2-oxa-3-cycloheptenyl acetate is converted to hexamethylene diamine by reductive amination under anhydrous conditions using a platinum or nickel catalyst; 2-(1-oxa-1,2-dihydronaphthyl) acetate is hydrolysed in aqueous acid under conventional oxidizing conditions to form b -(o-hydroxyphenyl)-acrylic acid which spontaneously esterifies intramolecularly to form coumarin; 2-oxa-3-cyclohexenyl acetate is chlorinated to give 2-oxa-3,4 - dichloro - cyclohexenyl acetate which is hydrolysed under oxidizing conditions to 2-chloro-glutaric acid which is converted by reaction with ammonia to the diammonium salt of glutamic acid and hence to glutamic acid.  In examples: (1) 2-oxa-3-cycloheptenyl acetate is formed by bubbling oxygen through a mixture of cyclohexene, acetic anhydride and N,N1 - azobis - (a  - isobutyronitrile) at 85-90 DEG  C. for 40 hours; the product is reduced with lithium aluminium hydride to 1,6-hexane-diol, it discolours dilute aqueous potassium permanganate giving glutaric acid among the products, and on reaction with 2,4-dinitrophenyl hydrazine in ethanol, or with hydroxylamine hydrochloride in sodium hydroxide, it gives the 2,4-dinitrophenyl hydrazone, or dioxime, respectively, of adipaldehyde; (2) to (5) show the effect of varying conditions on the oxidation of cyclohexene as in (1); (6) to (8) as in (2) to (5) using U.V. light as initiator; (9) 3-methylcyclohexene is reacted with oxygen and acetic anhydride using U.V. light as initiator to give 2-oxa-1-methyl-3-cycloheptenyl acetate and/or 2-oxa-5-methyl-3-cycloheptenyl acetate; (10) cyclohexene is reacted with oxygen and propionic anhydride to give 2-oxa-3-cycloheptenyl propionate; (11) cyclopentene is converted as in (6) to 2-oxa-3-cyclohexenyl acetate; (12) dicyclopentadiene is reacted as in (6) to give an acetate of undetermined structure; (13) methylcyclohexane is converted as in (6) to 2 - oxa - 1 - methylcycloheptyl acetate; (14) tetrahydronaphthalene is converted as in (6) to bicyclo - [5,4,0] - 2 - oxa - 8,10,1 - hendecatrien-3yl acetate.ALSO:Polyvinyl chloride and copolymers of vinyl chloride with vinyl acetate or vinylidene chloride are dissolved and plasticized by alkanoic esters of cyclic hemi-acetals.  (For details of preparation see Group IV (b)).  Examples describe the use of the following esters: (1) 2-oxa-3-cycloheptenyl acetate; (9) 2-oxa-1-methyl-3-cycloheptenyl acetate and 2-oxa-5-methyl-3-cycloheptenyl acetate; (10) 2-oxa-3-cycloheptenyl acetate; (11) 2-oxa-3-cyclohexenyl acetate; (13) 2-oxa-1-methylcycloheptenyl acetate; (14) bicyclo-[5,4,0]-2-oxa-8,10,1-hendecatrien-3-yl acetate.  The compositions may be used as lacquers or pastes to be brushed or sprayed on toe textile fabrics and paper.