Recovery of bis(diarylphenol) ligands during the production of isopulegol

A method for producing isopulegol of formula (IV)

• comprising
• a) cyclizing citronellal of formula (V)
• in the presence of a catalyst obtained by reacting a bis(diarylphenol) ligand of formula (I)
• wherein
• Ar1, Ar2, Ar3, and Ar4
• are, independently of one another, a C6-C15-aryl radical or a C2-C15-heteroaryl radical, wherein said C6-C15-aryl radical and said C2-C15-heteroaryl radical is optionally substituted with up to 7 identical or different substituents selected from the group consisting of C1-C6-alkyl, C1-C6-perfluoroalkyl, C1-C6-alkoxy, C7-C12-aralkyl, halogen, SiR5aR6aR7a, optionally substituted C6-C10-aryl, NR8aR9a, SR10a, and NO2;
• R1, R2, R3, and R4
• are, independently of one another, hydrogen, C1-C6-alkyl, C1-C6-perfluoroalkyl, C1-C6-alkoxy, C7-C12-aralkyl, halogen, SiR5bR6bR6b, optionally substituted C6-C10-aryl, NR8bR9b, SR10b, or NO2, wherein R1 or R2 and/or R3 or R4 together with A optionally define an aromatic or nonaromatic cycle;
• and
• A is a straight-chain or branched and/or cyclic hydrocarbon radical having up to 25 carbon atoms, wherein said straight-chain or branched and/or cyclic hydrocarbon radical is optionally saturated or mono- or polyunsaturated and/or partially aromatic, optionally has one or more identical or different heteroatoms selected from the group consisting of O, S, and NR11 and/or one or more identical or different functional groups selected from the group consisting of C(O), S(O), and S(O)2, and is optionally substituted with one or more identical or different substituents selected from the group consisting of C1-C6-alkyl, C1-C6-perfluoroalkyl, C1-C6-alkoxy, C1-C10-acyloxy, C7-C12-aralkyl, halogen, —SiR5cR6cR7c, optionally substituted C6-C10-aryl, optionally substituted C2-C10-hetaryl, NR8cR9c, SR10c, NO2, C1-C12-acyl, and C1-C10-carboxyl, or
• is a C6-C15-aryl radical or a C2-C15-heteroaryl radical, wherein said C6-C15-aryl radical and said C2-C15-heteroaryl radical is optionally substituted with up to 5 substituents selected from the group consisting of C1-C6-alkyl, C1-C6-perfluoroalkyl, C1-C6-alkoxy, C7-C12-aralkyl, halogen, SiR5dR6dR7d, optionally substituted C6-C10-aryl, NR8dR9d, SR10d, and NO2, or
• is a functional group or a heteroatom selected from the group consisting of —O—,
• —S—, —N(R11)—, —S(O)—, —C(O)—, —S(O)2—, —P(R11)—, —(R11)P(O)—, and —Si(R12R13);
• wherein R5a, R6a, R7a, R8a, R9a, R10a, R5b, R6b, R7b, R8b, R9b, R10b, R5a, R6c, R7c, R8c, R9c, R10c, R5d, R6d, R7d, R8d, R9d, R10d, R11, R12, and R13 are in each case independently of one another selected from the group consisting of C1-C6-alkyl, C7-C12-aralkyl, and/or optionally substituted C6-C10-aryl, and wherein R8a and R9a, R8b and R9b, R8c and R9c, R8d and R9d, independently of one another, in each case optionally define a cyclic hydrocarbon radical having 2 to 8 carbon atoms which optionally has one or more identical or different heteroatoms selected from the group consisting of O, S, and NR11a, wherein R11a is as defined as R11;
• with an aluminum compound of formula (II):
• (R14)3-pAlHp (II)
• wherein
• Al is aluminum;
• R14 is a branched or unbranched alkyl radical having up to 5 carbon atoms;
• and
• p is 0 or an integer from 1 to 3;
• and/or
• with an aluminum compound of the formula (III):
• MAlH4 (III)
• wherein
• Al is aluminum;
• and
• M is lithium, sodium, or potassium;
• and
• β) recovering the bis(diarylphenol) ligand of formula (I) after the reaction has taken place by
• a) subjecting the reaction product obtained in α) to distillative separation to obtain an isopulegol-enriched top product and an isopulegol-depleted bottom product;
• b) bringing the isopulegol-depleted bottom product into close contact with an aqueous base to give an aluminum-containing aqueous phase and an organic phase comprising the majority of the ligands of formula (I);
• and
• c) separating off the ligand of formula (I) from the organic phase.