Process for the manufacture of dihydrocitral

Details Process for the manufacture of dihydrocitral Process for the manufacture of dihydrocitral

1999-03-29

2001-02-20

Padmanabhan, Sreeni (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S450000, C568S449000, C568S467000, C568S488000, C568S490000, C568S492000

Reexamination Certificate

active

06191313

ABSTRACT:

FIELD OF THE INVENTION
The present invention is concerned with a novel process for the manufacture of dihydrocitral by a catalyzed rearrangement reaction.
BACKGROUND OF THE INVENTION
The &agr;,&bgr;-unsaturated aldehyde dihydrocitral (E/Z-3,7-dimethyl-2-octen-1-al) is a valuable intermediate.
&agr;,&bgr;-Unsaturated carbonyl compounds are generally important intermediates for the manufacture of odorants, vitamins and carotenoids (See, for example, Chem. Ztg. 97, 23-28 (1973) and Ch. VI (“Total Syntheses”) in “Carotenoids”, Ed. Otto Isler, published by Birkhäuser Basel and Stuttgart (1971)). Their production by acid-catalyzed rearrangement of &agr;-alkynols has already been described in the 1920s by K. H. Meyer and K. Schuster, Ber. deutsch. Chem. Ges. 55:819-823 (1922) and H. Rupe and E. Kambli, Helv. Chim. Acta 9:672 (1926). The isomerization of secondary or tertiary &agr;-alkynols to &agr;,&bgr;-unsaturated carbonyl compounds has also generally become known as the Meyer-Schuster or Rupe-Kambli rearrangement. In the case of the rearrangement of a carbonyl compound having a terminal alkynyl group there are obtained aldehydes, otherwise ketones are the rearrangement products:
wherein R
1
and R
2
each signify hydrogen or an aliphatic or aromatic residue.
Depending on the reaction conditions, the rearrangement of dihydrodehydrolinalyl acetate catalyzed by silver or copper ions yields, according to G. Saucy, et al. (Helv. Chim. Acta, 42:1945-1955 (1959)), a mixture of “allene acetate” (1 -acetoxy-3,7-dimethyl-octa-1,2-diene) and “diacetate” (1,1-diacetoxy-3,7-dimethyl-2-octene), which can then hydrolyze to dihydrocitral:
This rearrangement of dihydrodehydrolinalyl acetate is also known as the Saucy-Marbet rearrangement.
Compared with the synthesis of dihydrocitral starting from isoheptanoyl chloride, described by C. C. Price and J. A. Pappalardo, J.A.C.S. 72:2613-2614 (1950), the Saucy-Marbet rearrangement has the advantages of a higher yield, namely 80% in comparison to 20%, and the avoidance of lachrymatory intermediates. Moreover, the use of a silver- or copper-containing catalyst is disadvantageous.
Further known methods for the production of dihydrocitral are the rearrangement of 3-methyl-1-(3-methylbutoxy)-butta-1,3-diene, which is carried out in biphenyl at 350° C., according to Japanese Patent Publication (Kokai) 203025(1982)/Chem. Abs. 99, 5873r (1983), and the oxidation, which proceeds in 59% yield, of 3,7-dimethyl-oct-2-en-1-ol with silver carbonate on Celite® [Fetizon's reagent; B. C. L. Weedon and co-workers, J. Chem. Soc. Perkin Trans., 1:1457-1464 (1975)]. The high reaction temperature and, respectively, the use of a silver-containing catalyst are disadvantageous.
An interesting variant of the aforementioned Meyer-Schuster rearrangement has been described briefly by C. Y. Lorber and J. A. Osborn in Tetr. Lett., 37:853-856 (1996); this is the rearrangement of methylbutynol to prenal using, a molybdenum catalyst. In this case, methylbutynol is rearranged to prenal in ortho-dichlorobenzene as the solvent in the presence of the catalyst system molybdenyl acetylacetonate, dibutyl sulphoxide and 4-tert.butylbenzoic acid. Although the yield in this rearrangement is indicated to be 97%, the prenal was not isolated from the reaction mixture, but the stated yield was obtained by gas-chromatographical analysis of the crude product. Presumably, it was difficult to work up the reaction mixture in order to isolate prenal.
L. A. Kheifits and co-workers found that dehydrolinalool could be converted into citral only in 28% yield and into 2-hydroxymethyl-1-methyl-3-isopropenylcyclopent-1-ene in 12% yield at 170° C. in a reaction period of 14 hours when a molybdenum catalyst produced from molybdenum oxide and triphenylsilanol was used for the rearrangement (Tetr. Lett., 34:2981-2984 (1976)).
From the above remarks it is evident that the previously known processes for the catalyzed rearrangement of &agr;-alkynols to &agr;,&bgr;-unsaturated aldehydes, e.g., dehydrolinalool to citral, have serious disadvantages, which presumably would also apply to the analogous rearrangement of dihydrodehydrolinalool to clihydrocitral.
SUMMARY OF THE INVENTION
The process in accordance with the invention is a process for the manufacture of dihydrocitral by the catalyzed rearrangement of dihydrodehydrolinalool to dihydrocitral, which process comprises carrying out the rearrangement in the presence of a molybdenum compound of the general formula
MoO
2
X
2
  I
wherein X signifies an acetylacetonate or halide ion, and a dialkyl or diaryl sulphoxide as the catalyst system, in the presence of an organic acid having a pK value in the range of about 4.0 to about 6.5 and in an aprotic organic solvent.
The components are added together and mixed. The reaction mixture is heated to a temperature at which the catalytic rearrangement occurs, to provide a resulting mixture. Dihydrocitral can then be obtained from the resulting mixture.
DETAILED DESCRIPTION OF THE INVENTION
The process of the present invention surprisingly achieves a substantial yield of dihydrocitral using a catalyst system which includes the known molybdenum compound molybdenyl acetylacetonate [also known as dioxomolybdenum(VI) acetylacetonate] or a molybdenyl halide.
The molybdenum compound of formula I, i.e., molybdenyl acetylacetonate (conventionally denoted as MoO
2
acac
2
) or a molybdenyl halide of the formula MoO
2
(Hal)
2
[X=Hal], wherein Hal signifies chlorine or bromine, is in each case a readily obtainable known compound. The molybdenyl halide is preferably molybdenyl chloride, MoO
2
Cl
2
. However, the preferred molybdenum compound of formula I is molybdenyl acetylacetonate.
The dialkyl or diaryl sulphoxide likewise present in the catalyst system is especially a dialkyl sulphoxide, the alkyl groups of which are each straight-chain or branched and contain up to 8 carbon atoms, or a diaryl sulphoxide, the aryl groups of which in each case are optionally substituted phenyl groups. In the latter case, the substituents which may be present are especially C
1-4
-alkyl groups, with the phenyl groups being in each case mono- or multiply-substituted by alkyl. Examples of both types of sulphoxides are dimethyl sulphoxide and dibutyl sulphoxide and, respectively, diphenyl sulphoxide and di(p-tolyl) sulphoxide. Dimethyl sulphoxide is preferably used as the sulphoxide.
As organic acids having a pK value in the range of about 4.0 to about 6.5 there come into consideration, inter alia, optionally halogenated, saturated and unsaturated aliphatic carboxylic acids, e.g., acetic acid (pK value 4.74), propionic acid (4.87), chloropropionic acid (3.98), pivalic acid (5.01) and acrylic acid (4.25); alkanedicarboxylic acids, e.g., adipic acid (4.40); aryl-substituted alkanecarboxylic acids, e.g., phenylacetic acid (4.25); as well as aromatic carboxylic acids, e.g., benzoic acid (4.19) and 4-tert.butyl-benzoic acid (6.50). An organic acid having, a pK value in the range of about 4.25 to about 6.5, especially acrylic acid having the pK value 4.25, is preferably used.
As solvents there can be used in the scope of the present invention in general apolar aprotic organic solvents, especially aliphatic, cyclic and aromatic hydrocarbons, such as, for example, C
7-10
-alkanes, C
5-7
-cycloalkanes, benzene, toluene and naphthalene as well as mixtures of such solvents with one another, e.g., paraffin oil (a mixture of saturated aliphatic hydrocarbons), and polar aprotic organic solvents, especially aliphatic and cyclic esters with up to about 6 carbon atoms, such as, for example, ethyl acetate and butyl acetate and, respectively, ethylene carbonate, propylene carbonate and butyrolactone. Toluene is an especially preferred solvent.
The rearrangement is conveniently effected at temperatures in the range of about 80° C. to about 140° C., preferably at temperatures of about 90° C. to about 120° C.
The amount of molybdenum compound of formula I is conveniently about 0.1-8 mol % based on the amount of dihydrodehydrolinal

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