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intermediate, but a re-isomerization rate in the range 20-35% make the process unattractive from an industrial point of view. 

[0014] No satisfactory process is described, in particular for the rearrangement of ~-isophorone epoxide or a mixture of the ~-IPO first obtained by epoxidation and hydroxyiso› phorone. The process suggested in British patent 791 953 for the rearrangement of HIP to DH-KIP is laborious, as HIP must first be produced from ~-IPO by basic hydrolysis in a separate process step. The consecutive reaction with strong acids, as described in Isler et al., Helv. Chem. Acta, (1956), No. 237 page 2041, is as laborious as it is non-selective, as HIP must be provided as a pure substance and rearrangement to DH-KIP in the presence of strong acids entails the formation of trimethylphenols as by-products. A reaction time of 20 h is also a substantial disadvantage of this process. 

[0015] Hitherto, there has been no known process which allows DH-KIP to be produced using inexpensive, industri› ally efficient and accessible oxidizing agents and high prod› uct selectivity, in particular from a readily available mixture of ~-isophorone epoxide and hydroxyisophorone. This is the basis of the objects to be achieved by the invention. 

[0016] An object of the present invention is to produce dihydro-ketoisophorone (DH-KIP) from ~-isophorone with high selectivity and yield, suppressing in particular the re-isomerization of the educt to alpha-isophorone, to avoid having to separate alpha-IP from the product solution by expensive means and having to change the environment from acid (environment for epoxidation with organic per› carboxylic acids) to basic (prior art for the production of HIP from ~-IPO) and back to acid (prior art for rearrangement of HIP to DH-KIP). Furthermore a process is to be provided, which makes it possible to convert the mixture of ~-IPO and HIP obtained "in situ" directly to DH-KIP and to reduce considerably the long reaction times in the prior art. 

[0017] A further object of the invention is to provide a process for converting ~-isophorone epoxide to DH-KIP, ~-isophorone epoxide with its isomer hydroxyisophorone being produced from ~-isophorone in a first reaction step by reaction with an organic peracid. 

[0018] The above and other objects can be achieved in that ~-isophorone is brought into contact at moderate tempera› tures with an organic percarboxylic acid dissolved in an organic solvent, the organic solvent being at the same time the extracting agent used to extract the organic peracid as it is produced, and the ~-IPO thus obtained together with its isomer hydroxyisophorone which is present as a by-product in a concentration of 0.1-80 mol% (in relation to ~-IPO) is isomerized to DH-KIP by thermal isomerization in the presence of the organic carboxylic acid or by reaction in the presence of a salt as catalyst. 

[0019] According to the process, inexpensive raw mate› rials such as aqueous hydrogen peroxide, organic carboxylic acids and a solvent on the one hand and, in the simplest case, alkali- or earth alkali salts on the other, can be used, and as 

## SUMMARY OF THE INVENTION 

only the educt substrate ~-isophorone and hydrogen perox› ide are spent during the epoxidation process, the majority of the other raw materials can be recycled. The catalysts used for the isomerization of ~-IPO/HIP solutions can also be recycled and in this sense are not specific consumption materials. 

[0020] The first aspect of the invention relates to a new process for the production of dihydroketoisophorone by epoxidation of ~-isophorone (~-IP) by reaction with a per› acid in the form of its solution in a suitable solvent in the liquid phase, which is stable under reaction conditions, thus substantially avoiding separation into two phases which can occur if there is a high concentration of water in the reaction mixture, and obtaining a mixture of organic carboxylic acid, extracting agent (=solvent), ~-isophorone epoxide with hydroxyisophorone as the product solution. In the simplest form of the process according to the invention, the solvent used for oxidation is also the agent for extracting the corresponding peracid as it is produced from an aqueous hydrogen peroxide solution, carboxylic acid and sulfuric acid. 

[0021] The second aspect of the process according to the invention relates to the rearrangement of the ~-IPO formed "in situ", which, depending on the production process, may contain 0.1-80 mol% hydroxyisophorone, by direct thermal isomerization of the solution obtained from epoxidation or isomerization of the epoxidation solution obtained directly from the reaction in the presence of an additional catalyst salt, in the simplest case an alkali- or earth alkali salt or other suitable isomerization catalysts, or by isomerization of an epoxidation solution, the majority of which at least is first released from the carboxylic acid by extraction or distilla› tion. 

[0022] To achieve high selectivity, the reaction is carried out in two temperature stages. 

## DETAILED DESCRIPTION OF INVENTION 

[0023] In particular, the present invention is a process for the production of dihydroketoisophorone (2,2,6-trimethyl› cyclo-hexane-l,4-dione) 

[0024] by reacting ~-isophorone (3,5,5-trimethylcyclo› hex-3-en-1-one) 

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