Nov. 7, 2002  3  US 2002/0165414 Al  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  DETAILED DESCRIPTION OF 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.  [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)  0  0  0 