Patent GB-803765-A (GB)
Title: A process for the manufacture of unsaturated ketones
IPC: C07C47/20
Filed: 1956-09-06
Abstract: A process for the manufacture of unsaturated ketones comprises treating a 3-methyl-3-[41-methylpenten - (31) - yl] - allyl halide or a 11-, 21-, 31- or 51-methyl derivative thereof with an alkali-metal salt of a nitronic acid, condensing the resulting aldehyde with acetone in an alkaline medium and cyclising the condensation product by treatment with an acidic agent.  The first step of the process may be carried out in the presence of anhydrous or aqueous diluents such as mono- or polyhydric alcohols, e.g. ethanol, isopropanol, tertiary butanol, ethylene glycol, diethylene glycol, the ketone to be used in the next step, i.e. acetone, water-soluble ethers, e.g. diethylene-glycol ethyl butyl ether, dioxane or tetra-hydro-furane, dialkyl amides, e.g. dimethyl-formamide, acetals, e.g. methylol or acetonitrile.  Nitronic acids mentioned for use in the form of alkali metal salts include methane-, ethane-, propane-(1)- and propane-(2)-nitronic acids which may be prepared from the corresponding nitro compound and an alkali-metal hydroxide or alkoxide.  As alkaline medium there may be used an alkali-metal hydroxide or carbonate or an alkaline earth metal hydroxide.  The process may be carried out by dissolving the halide in acetone, adding an aqueous solution of the alkali metal salt of the nitronic acid, e.g. the sodium salt of propane-(2)-nitronic acid which may be formed in situ and after completion of the first stage of the reaction adding aqueous alkali, e.g. caustic soda solution.  Ketones having structures analogous to a -ionone are obtained usually if syrupy phosphoric acid at room temperature or slightly higher temperature or boron trifluoride at a temperature below zero is employed to effect cyclisation and when concentrated sulphuric acid is employed structures analogous to b -ionone predominate.  In examples: a -ionone is prepared by reacting 1-bromo-3,7-dimethyl-octadiene-(2,6) in acetone with the product obtained by dissolving 2-nitro-propane in aqueous potassium hydroxide and adding caustic soda to effect condensation between the aldehyde formed and the acetone to obtain 6 6,10-dimethylundecatrien-(3,5,9)-one-(2) and treating the latter in benzene solution with boron trifluoride (1); b -ionone is prepared by a similar process in which the intermediate compound is cyclised by treatment with concentrated sulphuric acid in the presence of glacial acetic acid and petroleum ether (2); b -ionone is prepared by a similar process using 1-bromo-3,7-dimethyl-octadiene-(2,6) as starting material (3); and a -irone is obtained by using 1-bromo-3,6,7-trimethyl-octadiene-(2,6) as starting material in a process similar to (1) with the formation intermediately of 6,9,10-trimethyl-undecatrien-(3,5,9)-one-(2).  Semi-carbazones of the intermediates and final products are mentioned.  In similar processes 1-chloro- or 1-bromo-3,7-dimethylnonadiene-(2,6) is converted to 6,10-dimethyl-dodecatrien-(3,5,9)-one-(2) which is converted by treatment with syrupy phosphoric acid at room temperature or a slightly higher temperature or with boron trifluoride at a temperature below zero to 4-[21,61-dimethyl-61-ethyl - cyclohexen - (21) - yl] - buten - (3) - one-(2) or with concentrated sulphuric acid to 4-21,61 - dimethyl - 61 - ethyl - cyclohexen - (11)-yl] - buten - (3) - one - (2). Specifications 643,353, 666,881 and 666,993 are referred to.