CH628043A5 - PROCESS FOR THE PREPARATION OF A TERPENIC ETHER. - Google Patents

Description

The present invention further relates to a process for the preparation of mixtures of rose oxide containing preponderant amounts of its isomer eis, said process being characterized in that a methylene cyclic ether of formula is subjected to hydrogenation

(I)

in the presence of a catalyst consisting of Raney nickel or palladium to provide a mixture of eis- and trans- 2- [2-methylprop-

l-ene-l-yl] -4-methyltetrahydropyran, and that said mixture is then enriched in the eis isomer by treatment with an acid agent.

It has been found that, by the process defined by claims 1 to 8, isomeric mixtures are obtained, the content of rose cisoxide of which exceeds 80-85% by total weight of the mixture obtained. Although the concentration of the desired isomer does not reach the value indicated for the product obtained by Tyman and Willis, the process of the invention turns out to be more profitable, from the point of view of its industrial application, than that described by these authors, the price of the hydrogenation catalyst as well as that of the acid reactant being much lower than that of the SnCl2 — H2PtCl6 mixture. Furthermore, it has resulted that the particular isomeric mixtures obtained using the process of the invention constitute raw materials of excellent olfactory quality, any additional purification being therefore superfluous for most practical uses.

According to a special embodiment of the process of the invention, as defined by claim 1, an inorganic protic acid, such as for example sulfuric or phosphoric acid, an acid diatomaceous earth or a Lewis acid. BF3, in particular in its form of boron trifluoride etherate salt, is preferably used. Such a treatment is carried out in an atmosphere of inert gas, nitrogen or argon for example, at ambient temperature or at a temperature above this, and in the presence of an inert solvent, such as an aromatic hydrocarbon such as benzene or toluene, or an ether.

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628043

According to the invention as described in claim 8, Raney nickel is preferably used as hydrogenation catalyst. It has in fact been observed that such a catalyst makes it possible to reduce the methylene cyclic ether almost exclusively to a cis / trans isomeric mixture (4/6) of rose oxide, this product being accompanied by small amounts, of the order of 3 to 5%, of nerol oxide.

When the catalytic hydrogenation is carried out in the presence of a palladium catalyst, such as palladium on carbon, at 5 or 10%, or partially inactivated palladium according to Lindlar [see for example: “Helv. Chim. Acta ”, 35,446 (1952)], the mixture of rose oxide obtained, on the other hand, is accompanied by much larger amounts of nerol oxide, these amounts being able to go up to 20 or 30%. On the other hand, the cis / trans isomeric ratio of the mixture of rose oxide thus obtained appears more favorable; it contains in these cases approximately 65% of isis isomer.

The above-mentioned catalytic hydrogenation is carried out according to the usual conditions, at ambient temperature, or at a temperature slightly lower than this, and at ordinary pressure. Preferably, said hydrogenation is carried out by dissolving the rose dehydro-oxide (I) in an inert solvent, such as an alcohol such as methanol or ethanol.

The rose oxide present in the mixture obtained, accompanied by nerol oxide, can be separated from the latter by simple distillation, optionally using a Vigreux type column.

The next step is carried out by treating the isomeric mixture of rose oxide obtained with an acid agent in accordance with the conditions indicated above.

Rose dehydrooxide (I), used as a starting material in the above-mentioned process, can be prepared according to the process described in the above-mentioned literature [see “Tetrahedron Letters”, 51,4507 (1970)]. 3-methylbut-2-ene-1-al and 2-methylbut-1-ene-4-ol used to prepare rose dehydrooxide are commercial products.

The invention is illustrated in more detail by the following examples in which the temperatures are indicated in degrees centigrade and the abbreviations have the usual meaning in the art.

Example 1:

A. 5 g (0.033M) of rose dehydrooxide in 25 ml of ethanol were hydrogenated at 15 ° C in the presence of 0.250 g of Raney nickel previously washed with water and ethanol. After 3 h, absorption

5 of hydrogen was 755 ml. The reaction mixture was filtered and the clear filtrate evaporated to provide a residue which, by distillation using a Vigreux column, gave a fraction having Eb. 65-70 ° / 8 Torr. This consisted of 4.5 g of a mixture of eis- and rose transoxide in a respective weight ratio 10 of 4/6.

B. 45 g of an isomeric mixture of rose oxide, obtained according to the process indicated above under letter A, in 200 ml of toluene were mixed at 25 ° C with 5 ml of boron trifluoride etherate. The operation is carried out under an atmosphere

15 of nitrogen. 3 hours were enough to reach the desired balance. The mixture was then poured onto ice to which an NaHCO 3 solution was added, then, once separated, the organic phase was washed until neutral, dried and concentrated. By fractional distillation of the residue obtained, 39 g of a 20 Eb fraction were obtained. 65-70 ° / 8 Torr. This fraction consisted of an isomeric mixture of eis and rose transoxide, the content of the eis isomer of 85% (yield = 86.5%).

By replacing Raney nickel in the above process with palladium on carbon, or a catalyst of the so-called Lindlar type, a similar course of the reaction was observed. However, the hydrogenation mixture obtained contained amounts of up to 30% of nerol oxide. The mixture of rose oxide isolated by means of fractional distillation of the mixture obtained consisted of approximately 65% of isis isomer.

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Example 2:

45 g of rose transoxide, obtained from the 4/6 mixture of rose transoxide eiset as prepared in Example 1, under letter A, by fractional distillation using a column with a rotating band: 35 Eb . 68-69 ° / 8 Torr; ng> = 1.4591; àf = 0.8770,

were treated, in accordance with the method indicated under letter B of Example 1, with boron trifluoride etherate using the quantities and the reaction conditions indicated in said example. An isomeric mixture of eis and 40-rose transoxide was thus obtained, the eis isomer content of which was about 85%.

Claims (8)

628043 2 1. Process for the preparation of an isomeric mixture of trans-2- [2-methylprop-1-en-1-yl] -4-methyltetrahydropyran eiset having a content of cyclic isomer eis greater than or equal to 5 80- 85% by weight, characterized in that the trans-2- [2-methylprop-1-ene-1-yl] -4-methyltetrahydropyran, or any cis-trans mixture whose content in said trans isomer is greater is subjected or equal to 15-20% by weight, to treatment with an acid agent. 2. Method according to claim 1, characterized in that the acid agent is a mineral protic acid. 3. Method according to claim 2, characterized in that the mineral protic acid is phosphoric acid. 4. Method according to claim 1, characterized in that the acid agent is selected from Lewis acids. 15 5. Method according to claim 4, characterized in that the Lewis acid is BF3. 6. Method according to claim 5, characterized in that the BF3 is in the form of boron trifluoride etherate. 7. Method according to claims 4 to 6, characterized in that 2o the acid treatment is carried out in the presence of an inert organic solvent, such as an aromatic hydrocarbon. 8. Process for the preparation of an isomeric mixture of 2- [2-methylprop-1-en-1-yl] -4-methyltetrahydropyran with a high content of cyclanic isomer and by hydrogenation of a methylene cyclic ether of formula for providing a mixture of eis- and trans-2- [2-methylprop-1-ene-1-yl] -4-methyltetrahydropyran, and enriching said mixture with the eis isomer by treatment with an acid agent . 2- [2-methylprop-1-ene-1-yl] -4-methyltetrahydropyran, a terpene ether of formula (I) 30 characterized in that said hydrogenation is carried out in the presence of a catalyst consisting of Raney nickel or palladium better known under the name of rose oxide, is a compound highly appreciated in the perfume industry. Since its discovery in 1960 (see Swiss patent N ° 395406), numerous scientific publications have reported on new syntheses for its preparation. It has also appeared in use that the cyclanic isomer eis was of major interest, hence the need to develop manufacturing processes which can make it possible to obtain said isomer, or even a mixture containing predominant proportions of that -this. Most of the known methods provide for the use of acyclic intermediates or the introduction of the 2-isobutenyl substituent on the pyrannic ring previously formed. A new synthetic approach, starting from 3-methylbut-2-ene-1-al and 2-methylbut-1-en-4-ol, had been formulated by J.P.H. Tyman and B.J. Willis [see “Tetrahedron Letters”, 51.4507 (1970)], said method can be illustrated as follows: According to the authors cited above, the reduction of the methylene intermediate, or rose dehydroxide, was carried out by hydrogenation in homogeneous phase in the presence of tin II chloride and hexachloroplatinic acid. A mixture consisting of approximately 91% of the isis isomer and 9% of the trans isomer was thus obtained. Unfortunately, such a method encounters, in its industrial application, a major economic difficulty: the price of the hydrogenation catalyst is indeed very high. The present invention provides a new and advantageous solution to the problem posed. It has in fact been discovered that it is now possible, thanks to the process as defined by claim 1, to obtain mixtures of rose oxide containing predominant amounts of its isomer isis.