CH325834A - Process for the production of primary alcohols of the vitamin A series - Google Patents

Description

  

  <B> Process for the production of primary </B> alcohols <B> the </B> vitamin A series It is known that the structure of the system characterizing vitamin A. Yawed double bonds cause difficulties. Insofar as the syntheses in question proceed with elimination of water, optionally combined with allyl rearrangement, various isomers differing in the position of the double bonds can arise.



       These isomers are subdivided here into: called normal and iso compounds. In the following, normal compounds are to be understood as substances in which a system of conjugated double bonds corresponding to vitamin A (formula 1) is present. One such substance is, for example, f-Jonylidenethanol (Formula 2). Iso compounds are to be understood as meaning substances whose arrangement of the double bonds is different. than that of vitamin A. Such substances are z.

   B. the compounds of formulas 3 and 4.



  In the formation of such isomers, the explanation was sought for the relatively low yields of ss-Jonyliden-Essigsätire- ethyl ester or of vitamin A esters with the normal system of conjugated double bonds in the production of these substances from ss-.Tonon and Monobromessigsätire ethyl ester or from ss-.Tonylidene acetaldehyde and y-bromine #, niethyl-crotonic acid ethyl ester. It is known (see e.g.

   B. Swiss Patent No. 324432 of the applicant) that when converting certain acids, possibly consisting of normal and iso forms, into acid halides only or almost exclusively only normal acid halides are obtained. This is true. z. B. to in the preparation of the acid halides of the formula:
EMI0001.0037
    where n - 1. or 2 and Hlg represents a halogen atom.



  The present invention now relates to a method of making primary; Alcohols from the vitamin A series, based on acid halides of the formula given above.



  The process according to the invention is characterized in that acid halides of the formula
EMI0001.0043
      where n is 1 or 2 and Hlg is a halogen atom, to alcohols of the formula
EMI0002.0002
    be reduced by means of a metal hydride containing two metal atoms.



  Lithium aluminum hydride, sodium boron hydride or magnesium aluminum hydride, for example, are used as reducing agents. Of the acid halides, special acid chlorides or acid bromides are particularly suitable as starting materials. .



       Acid halides of ß-jonylideneacetic acid or of vitamin A acid leave the corresponding acids with. suitable halogenating agents such as phosphorus trichloride or thionyl chloride.



  It is also possible to use the acid halides mentioned in the Swiss patent. No. 324432 of the applicant described method. According to the process described there, certain ss hydroxy acids of the vitamin A series are converted into the acid halides with halogenating agents, such as phosphorus trichloride or thionyl chloride, with elimination of water.



  The reduction of acid halides to the corresponding primary alcohols is. known per se. The reduction process with lithium aluminum hydride or similar hydrides has already been described. However, the reduction of acid halides of the vitamin A series has not yet been described. It should also be mentioned that lithium aluminum hydride has already been proposed to reduce esters of vitamin A acid to vitamin A.

   The idea of using acid halides of the formula given above for the synthesis of primary alcohols of the vitamin A series zii, however, has not yet been described in the literature. <I> Example 1 </I> 25.3 g (= 0.1 mol) of j3-ionylidene acetic acid chloride were dissolved in absolute ether and, after cooling down to 0 C, an ethereal solution, which was likewise cooled to 0 C, was dropped Solution of 2.3 g of lithium aluminum hydride added.

   The reaction mixture was kept at this temperature for half an hour and then water was carefully added. The aqueous layer was separated, and the ethereal layer was subjected to distillation after drying with sodium sulfate. The residue consisted of 20 g (= 0.09 mol) of ß-Jonyliden- ethanol. The light ultraviolet absorption spectrum of a solution of the substance in ethanol showed: Maxima, at 2650 Å (e = 13200) and 2400 Å (e = 12900).

           Example <I>, 2 </I> In a manner similar to that in Example 1, vitamin A acid chloride was reduced to vitamin A in an ethereal solution at approximately 0 ° C. with lithilini aluminum hydride.

 

Claims (1)

PATENT CLAIM Process for the production of primary alcohols of the formula EMI0002.0060 where n is 1 or 2, characterized in that acid halides of the formula EMI0002.0062 in which Hlg represents a halogen atom, by means of a metal hydride containing two metal atoms are reduced. L'NTERANSPRÜ CH method according to claim, characterized in that the reduction is carried out at a temperature below 5 C.