Abstract: The present invention relates to a particularly economic overall method for producing menthol, specifically for producing optically active, essentially enantiomerically and diastereomerically pure L-menthol and racemic menthol, starting from the starting material citral which is available inexpensively on an industrial scale. The method has the following steps a.1) catalytic hydrogenation of neral and/or geranial to give citronellal, b.1) cyclization of citronellal to isopulegol in the presence of an acidic catalyst, c.1) purification of isopulegol by crystallization and d.1) catalytic hydrogenation of isopulegol to give menthol.

Abstract: The present invention relates to a particularly economic overall method for producing menthol, specifically for producing optically active, essentially enantiomerically and diastereomerically pure L-menthol and racemic menthol, starting from the starting material citral which is available inexpensively on an industrial scale. The method comprises the following steps a.1) catalytic hydrogenation of neral and/or geranial to give citronellal, b.1) cyclization of citronellal to isopulegol in the presence of an acidic catalyst, c.1) purification of isopulegol by crystallization and d.1) catalytic hydrogenation of isopulegol to give menthol.

Abstract: The present invention relates to a particularly economic overall method for producing menthol, specifically for producing optically active, essentially enantiomerically and diastereomerically pure L-menthol and racemic menthol, starting from the starting material citral which is available inexpensively on an industrial scale. The method comprises the following steps a) catalytic hydrogenation of neral and/or geranial to give citronellal, b) cyclization of citronellal to isopulegol in the presence of an acidic catalyst, c) purification of isopulegol by crystallization and d) catalytic hydrogenation of isopulegol to give menthol.

Abstract: The present invention relates to a method of working up an aluminum-containing reaction product from the production of isopulegol by cyclization of citronellal in the presence of complex compounds, comprising at least one ligand of the formula (I), where R1, R2, R3 are chosen from hydrogen, halogen, nitro, C1-C8-alkyl, C1-C8-alkoxy, di(C1-C4-alkyl)amino and aryl; R4, R5 are chosen from halogen, nitro, C1-C8-alkyl, C1-C8-alkoxy, di(C1-C4-alkyl)amino, aryl or heteroaryl; in which a) the reaction product is subjected to distillative separation to obtain an isopulegol-enriched top product and an isopulegol-depleted bottom product and b) the ligand of the formula (I) is separated off from the bottom product. Moreover, the invention relates to a method of producing isopulegol, and to a method of producing menthol.

Abstract: The present invention relates to a particularly economic overall method for producing menthol, specifically for producing optically active, essentially enantiomerically and diastereomerically pure L-menthol and racemic menthol, starting from the starting material citral which is available inexpensively on an industrial scale. The method comprises the following steps a.1) catalytic hydrogenation of neral and/or geranial to give citronellal, b.1) cyclization of citronellal to isopulegol in the presence of an acidic catalyst, c.1) purification of isopulegol by crystallization and d.1) catalytic hydrogenation of isopulegol to give menthol.

Abstract: The present invention relates to a method of working up an aluminum-containing reaction product from the production of isopulegol by cyclization of citronellal in the presence of complex compounds, comprising at least one ligand of the formula (I), where R1, R2, R3 are chosen from hydrogen, halogen, nitro, C1-C8-alkyl, C1-C8-alkoxy, di(C1-C4-alkyl)amino and aryl; R4, R5 are chosen from halogen, nitro, C1-C8-alkyl, C1-C8-alkoxy, di(C1-C4-alkyl)amino, aryl or heteroaryl; in which a) the reaction product is subjected to distillative separation to obtain an isopulegol-enriched top product and an isopulegol-depleted bottom product and b) the ligand of the formula (I) is separated off from the bottom product. Moreover, the invention relates to a method of producing isopulegol, and to a method of producing menthol.

Abstract: The present invention relates to diarylphenoxyaluminum compounds which are obtainable by reacting a bis(diarylphenol) ligand of the formula (I) with an alkylaluminum compound and/or a complex aluminum hydride. The invention moreover relates to the use of such diarylphenoxyaluminum compounds as catalysts. Moreover, the invention relates to a method of producing isopulegol by cyclization of citronellal in the presence of diarylphenoxyaluminum compounds as catalysts. The invention also relates to a method of producing menthol by cyclization of citronellal in the presence of diarylphenoxyaluminum compounds as catalysts and subsequent hydrogenation.

Abstract: The invention relates to a process for preparing optically active alkylsuccinic acid monoalkyl esters of the formula (I) where D and E are independently of one another H, C1-C10 alkyl, R is C1-C10 alkyl, aryl or alkylaryl.

Abstract: The present invention relates to a process for the preparation of isopulegol of formula (I): comprising the cyclization of citronellal of formula (II): in the presence of a tris(aryloxy)aluminum catalyst, wherein the cyclization is carried out in the presence of I. at least one acid and/or II. at least one compound selected from the group comprising carboxylic anhydrides, aldehydes, ketones and vinyl ethers.

Abstract: The present invention relates to a process for the preparation of isopulegol of formula (I): comprising the cyclization of citronellal of formula (II): in the presence of a tris(aryloxy)aluminum catalyst, wherein the cyclization is carried out in the presence of I. at least one acid and/or II. at least one compound selected from the group comprising carboxylic anhydrides, aldehydes, ketones and vinyl ethers.

Abstract: The present invention relates to diarylphenoxyaluminum compounds which are obtainable by reacting a bis(diarylphenol) ligand of the formula (I) with an alkylaluminum compound and/or a complex aluminum hydride. The invention moreover relates to the use of such diarylphenoxyaluminum compounds as catalysts. Moreover, the invention relates to a method of producing isopulegol by cyclization of citronellal in the presence of diarylphenoxyaluminum compounds as catalysts. The invention also relates to a method of producing menthol by cyclization of citronellal in the presence of diarylphenoxyaluminum compounds as catalysts and subsequent hydrogenation.

Abstract: The invention relates to a process for preparing optically active alkylsuccinic acid monoalkyl esters of the formula (I) where D and E are independently of one another H, C1-C10 alkyl, R is C1-C10 alkyl, aryl or alkylaryl.