Process for Preparing Hydroxycitronellal

This invention relates to a process for preparing hydroxycitronellal and, more particularly, to a process for preparing hydroxycitronellal by isomerizing a 7-hydroxygeranylamine compound (trans form), represented by formula (I) below, or a 7-hydroxynerylamine compound (cis form), represented by formula (II) below, to form a 7-hydroxyaldehydoenamine represented by formula (III) below, and then hydrolyzing the resulting enamine. ##STR1##

The formulae (I), (II), and (III), R.sub.1 and R.sub.2 each represents an alkyl group containing from 1 to 6 carbon atoms or a cycloalkyl group, or R.sub.1 and R.sub.2 may jointly form together with the adjacent nitrogen atom a 5- or 6-membered ring that may contain other heterocyclic atoms selected from nitrogen and oxygen.

Hydroxycitronellal is a compound useful as a perfume, and is now being produced on a large scale.

As a result of various investigations to prepare this hydroxycitronellal with industrial advantages, it has now been discovered that a 7-hydroxygeranylamine compound according to formula (I) or a 7-hydroxynerylamine compound according to formula (II) can be isomerized to form a 7-hydroxyaldehydoenamine according to formula (III) in high yield by a catalytic isomerization reaction using a catalyst composed of a divalent palladium compound and a phosphine compound.

Therefore, the present invention provides a novel process for preparing hydroxycitronellal with industrial advantages.

The 7-hydroxygeranylamine compound of formula (I) and the 7-hydroxynerylamine compound of formula (II) can be easily obtained by the conventional methods, for example, by the reaction of myrcene with dimethylamine in the presence of an alkali metal (see Japanese patent application (OPI) No. 70707/76), or the telomerization of isoprene with a secondary amine (see K. Takabe et al, Tetrahedron Letters, No. 39, pp 4009 (1972), or K. Takabe et al, Bulletin of the Chemical Society of Japan, Vol. 46, pp 218 (1973)), to form a corresponding geranylamine or nerylamine compound which is then hydrolyzed with sulfuric acid in the conventional manner.

The catalyst of the present invention is prepared from a divalent palladium compound, a trivalent organophosphorus compound, and an alkali metal phenoxide.

Examples of the divalent palladium compound include halides, nitrates, carboxylates, and chelate compounds (e.g., acetylacetonato salt) of divalent palladium.

The trivalent organophosphorous compound is a unidentate ligand represented by formula (IV) ##STR2## wherein A represents an alkyl group containing from 1 to 6 carbon atoms, a cycloalkyl group, or an aryl group, and B and C each represents an alkyl group containing from 1 to 6 carbon atoms, a cycloalkyl group, or an aryl group, or B and C may jointly form together with the adjacent phosphorus atom a 5- or 6-membered ring; or the organophosphorous compound may be a bidentate ligand such as an alkylenediphosphine, wherein two phosphorus atoms are connected to each other through a carbon chain containing from 1 to 4 carbon atoms, a diphosphine wherein two phosphorus atoms form a heterocyclic ring, or a 1,1'-bisphosphinoferrocene compound wherein two phosphorus atoms are connected to each other through a ferrocenyl group. Specific examples thereof include triphenylphosphine, diphenylisopropylphosphine, 3-methyl-1-phenylphosphorene, 1,3-bis-diphenylphosphinopropane, 1,4-bis-diphenylphosphinobutane, 1,1'-bis-diphenylphosphinoferrocene and so forth.

The alkali metal phenoxide is a compound derived from unsubstituted, mono-substituted, di-substituted, or tri-substituted phenol. Examples of useful substituents include a halogen atom, a trifluoromethyl group, an alkoxy group, a cyano group, an aldehydo group, an acetyl group, a nitro group, an alkylsulfoxide group, etc. Useful substituted phenols include, for example, o-, m- or p-chlorophenol, m- or p-cyanophenol, m- or p-nitrophenol, m- or p-hydroxybenzaldehyde, o-, m- or p-bromophenol, o-, m- or p-fluorophenol, o-, m- or p-trifluoromethylphenol, 2,3-dichlorophenol, 2,4-dichlorophenol, 2,5-dichlorophenol, 3,4-dichlorophenol, 3,5-dichlorophenol, 2,4-dinitrophenol, 3,4-dinitrophenol, 3,4-dicyanophenol, 3,5-dicyanophenol, 2,3-difluorophenol, 2,4-difluorophenol, 2,5-difluorophenol, 2,3-dibromophenol, 2,4-dibromophenol, 2,5-dibromophenol, 3,4-dibromophenol, 2,3-di(trifluoromethyl)phenol, 2,4-di(trifluoromethyl)phenol, 2,5-di(trifluoromethyl)phenol, 3,4-di(trifluoromethyl)phenol, 2-chloro-4-nitrophenol, 3-chloro-4-nitrophenol, 3-trifluoromethyl-4-nitrophenol, 3-cyano-4-chlorophenol, 3-hydroxy-4-nitrobenzaldehyde, 2-bromo-4-nitrophenol, 2,3,4-trichlorophenol, 2,3,5-trichlorophenol, 2,4,5-trichlorophenol, 3,4,5-trichlorophenol, 2,3,4-trifluorophenol, 2,3,5-tribromophenol, 3,4,5-tricyanophenol, and so forth.

In preparing the catalyst of the present invention, molar ratios of respective ingredients are important; for example, it is preferable to add from 1 to 2 mols of the trivalent organophosphorous compound per mol of divalent palladium compound, and, after dissolving in a solvent to prepare a homogeneous solution, to add thereto from 1 to 5 mols of the alkali metal phenoxide in a nigrogen stream while cooling to a temperature of from 0.degree. C. to 10.degree. C. As the solvent to be used, hydrocarbon series solvents or ether series solvents are preferable.

The catalyst prepared as described above has an extremely high activity. For example, the catalyst prepared from 1 mol of the palladium compound can isomerize about 5,000 mols of the 7-hydroxygeranylamine compound of formula (I) or the 7-hydroxynerlyamine compound of formula (II).

In practicing the present invention, the palladium compound is preferably used in such amount that the molar ratio of the compound of formula (I) or (II) to the palladium compound is from 1,000/l to 5,000/l. When used in such amount, the catalyst causes the isomerization providing the 7-hydroxyaldehydoenamine (III) in a yield as high as 80 to 95%. The isomerization reaction is generally carried out at a temperature of about 140.degree. C. to 180.degree. C. for about 5 to 20 hours, but it is the most optimum from the economical viewpoint to carry out the reaction at 150.degree. C. for 15 hours.

After completion of the isomerization reaction, addition of a dilute solution of a mineral acid, such as hydrochloric acid, sulfuric acid, phosphoric acid, etc., or an organic acid, such as acetic acid, etc. causes separation of hydroxycitronellal as a result of decomposition of (III). The thus formed oily layer is separated and, after extraction of the aqueous layer with an organic solvent such as benzene or the like, the oily layer and the extract are combined, followed by purification by distillation, to obtain hydroxycitronellal.

Alternatively, highly pure hydroxycitronellal can be obtained by adding, after completion of the isomerization reaction, a small amount of water or methanol to the reaction solution to deactivate the catalyst, distillating to isolate the 7-hydroxyaldehydoenamine (III), and treating the resulting enamine (III) with a dilute acid as described above.

The present invention will now be described in more detail by the following non-limiting examples.

100 g (441 mmols) of 7-hydroxygeranyldiethylamine was added to a catalyst prepared by treating 30 mg (0.113 mmol) of palladium nitrate, 59 mg (0.226 mmol) of triphenylphosphine and 66 mg (0.565 mmol) of sodium phenoxide in 10 ml of tetrahydrofuran, and heated to 150.degree. C. for 15 hours to react. Then, after deactivating the catalyst by adding a small amount of water, the reaction mixture as produced was subjected to distillation under reduced pressure to obtain 91 g of 7-hydroxycitronellal diethyleneamine boiling at 95.degree. C./1 mmHg. Addition of 2 N sulfuric acid to the resulting 7-hydroxycitronellaldiethyleneamine up to a weakly acidic level caused separation of 7-hydroxycitronellal. After distillation of the product, there was obtained 59 g (yield: 78%) of 7-hydroxycitronellal boiling at 95.degree. C./1 mmHg.

Table 1 shows results obtained in the same manner as in Example 1, except using 0.1 mmol of the palladium compounds as listed in Table 1 in place of the palladium nitrate used in Example 1, and using 12.5 g (55 mmols) of 7-hydroxygeranyldiethylamine.

Table 2 shows results obtained in the same manner as in Example 1, except using the organophosphorous compounds listed in Table 2 in place of the triphenylphosphine used in Example 1, and using 12.5 g (55 mmols) of 7-hydroxygeranyldiethylamine.

Table 3 shows results obtained in the same manner as in Example 1, except using 0.5 mmol of the alkali metal phenoxides listed in Table 3 in place of the sodium phenoxide used in Example 1, and using 12.5 g (55 mmols) of 7-hydroxygeranyldiethylamine.

Proceeding in the same manner as in Example 1, except using 7-hydroxyneryldiethylamine in place of the 7-hydroxygeranyldiethylamine used in Example 1, 65 g (yield: 86%) of 7-hydroxycitronellal was obtained.

Table 4 shows results obtained in the same manner as in Example 1, except using the 7-hydroxygeranylamine listed in Table 4 in place of 7-hydroxygeranyldiethylamine used in Example 1.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.