Process for the preparation of 4,4-dimethyl-2-pentene

Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By alkyl transfer – e.g. – disproportionation – etc.

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585646, C07C 602

Patent

active

053960149

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to the field of organic synthesis. More particularly, it concerns a novel naphthalenic compound and its use as an intermediate product for the preparation of a prized perfuming ingredient.


Prior art

Published European patent application No. 405 427-A2 describes a series of naphthalenic compounds of formula ##STR4## wherein a) indexes m and n are identical and each defines an integer number equal to 0, symbols R.sup.1 and R.sup.2 are identical and represent each a hydrogen atom, or are different and represent each a hydrogen atom or a methyl radical, symbols R.sup.5 and R.sup.8 represent each a methyl radical, symbols R.sup.6 and R.sup.7, identical or different, represent each a hydrogen atom or a methyl radical, and either symbol R.sup.4 represents a methyl radical and symbol R.sup.3 a hydrogen atom or a methyl radical, or symbols R.sup.3 and R.sup.4 represent each a methylene radical belonging to a cycle as indicated by the dotted line, with the proviso that the following combinations are excluded: 0 or 1, symbol R.sup.2 represents a hydrogen atom or a methyl radical, symbols R.sup.1 and R.sup.3 represent each a hydrogen atom, symbol R.sup.4 represents a methyl radical and, either symbols R.sup.5 and R.sup.6 are identical (n=1) and represent each a methylene radical belonging to a cycle such as indicated by the dotted line, symbol R.sup.7 representing a hydrogen atom and symbol R.sup.8 a methyl radical, or symbol R.sup.5 represents a methyl radical and symbol R.sup.6 a hydrogen atom, symbols R.sup.7 and R.sup.8 being then identical (m=1) and representing each a methylene radical belonging to a cycle such as indicated by the dotted line.
These are compounds useful in perfumery, mainly as a result of their musky, amber and animal odor character. Amongst these compounds there is one preferentially used, owing to both the nature and the strength of its odor. It has in fact been ascertained that 5,6,7,8-tetrahydro-3,5,5,6,7,8,8-heptamethyl-2-naphthalenecarbaldehyde, as a result of its qualities, represents a prime perfuming ingredient.
In the above-mentioned European application, several synthetic methods for preparing this compound have been proposed but, considering its usefulness, it is not surprising to observe that its preparation has been the object of further reseach, which research has been aimed at improving the manufacturing costs.


DESCRIPTION OF THE INVENTION

The present invention is provided in this context. It brings in fact a novel solution of which there was no suggestion in the cited reference. It hinges on a critical element consisting of a useful intermediate of the synthesis of 5,6,7,8-tetrahydro-3,5,5,6,7,8,8-heptamethyl-2-naphthalenecarbaldehyde. Said intermediate is a hydrocarbon of formula ##STR5## or 1,1,2,3,4,4,6-heptamethyl-1,2,3,4-tetrahydronaphthalene (hereafter designated as "HpMT"), which can be converted into the desired aldehyde via a formylation reaction according to the following reaction scheme: ##STR6##
HpMT is a novel chemical entity which can be obtained, thanks to a process which is also the object of the invention, by reacting p-cymene and an olefin of formula ##STR7## wherein R.sup.1 and R.sup.2 represent distinct substituents and each defines a hydrogen atom or a methyl radical. This is a reaction which can be carried out by analogy with known methods [see, to this effect: patent application JP 82 40420 -cf. C.A. 97, 38653 f]. It is based on the principle illustrated by way of the following reaction scheme: ##STR8##
The reaction takes place in the presence of catalytic amounts of aluminium chloride, to which there is optionally added iodine [cf. U.S. Pat. No. 4,551,573].
The concentration of AlCl.sub.3 in the reaction mixture can vary in a fairly wide range of values; however, we observed that concentrations of the order of around 3-10 mole-%, relative to the quantity of olefin (III), made it possible to obtain the best yields. When concentrations below the lower limit indicated are used, the reaction proceeds too sl

REFERENCES:
patent: 4284818 (1981-08-01), Sato et al.
patent: 4551573 (1985-11-01), Cobb
patent: 4877910 (1989-10-01), Frank
patent: 4877916 (1989-10-01), Frank
Chemical Abstracts: 104704t, vol. 99, 1983.

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