Patent GB-477774-A (GB)
Title: Process for the manufacture of polyene carboxylic acids
IPC: C07C57/03
Filed: 1936-07-02
Abstract: Aliphatic polyene carboxylic acid esters are prepared by reducing an acyl derivative of an oxalo compound of an unsaturated aliphatic carboxylic acid ester in which the oxalo radicle is connected with a carbon atom standing in a -position to a doubly-bound carbon atom, and then splitting off the acyl radicle from the resulting dihydro compound in the form of the acid, whereby a further double bond is formed.  The products may be saponified to the free acid.  As reducing agents, aluminium amalgam or zinc dust are preferably used, whilst the splitting off of the acyl radicle may be effected either by treating the dihydro compound with alkali or by heat treatment. According to the examples: (1) a -acetoxy-muconic acid diethyl ester is reduced with aluminium amalgam to a -acetoxy-a : d -dihydromuconic acid diethyl ester, heated with methyl alcoholic caustic potash to give trans-trans-muconic acid diethyl ester and then with water to form the acid; (2) b  : b <1>-dimethylacrylic acid methyl ester is condensed with oxalic acid diethyl ester in the presence of potassium ethylate and the product heated with acetic anhydride yielding a -acetoxy-g -methyl-muconic acid methylethyl ester; reduction followed by caustic potash treatment produces trans - trans - b  - methylmuconic acid; the latter is also obtained by using as starting material a  - hydroxy - b  - methyl - muconic acid ethyl ester, which is prepared by condensing a  : b -pentene acid ethyl ester with oxalic acid diethyl ester in the presence of potassium alcoholate, and subjecting it to acetylation, reduction and saponification; (3) a - acetoxy - hexatrien - dicarboxylic acid diethyl ester is reduced and the resulting 1 - acetoxyhexadien - 2 : 4 - dicarboxylic acid - 1 : 6 - diethyl ester saponified to form hexatrien-1 : 6-dicarboxylic acid; the product is purified by conversion into its dimethyl ester followed by saponification; (4) 3-methylhexatrien-1 : 6-dicarboxylic acid is prepared by condensing g -methylsorbinic acid ethyl ester with oxalic acid diethyl ester, esterifying the oxalo compound with acetic anhydride, reducing with aluminium amalgam and saponifying with caustic potash; (5) a mixed methyl, ethyl and isopropyl ester of oxalo-octatrien-carboxylic acid is first prepared by treating octatriencarboxylic acid methyl ester with oxalic acid diethyl ester in the presence of potassium isopropylate and separating the products chromatographically; by acetylation, reduction and treatment with methyl alcoholic caustic potash, octatrien - 1 : 8 - dicarboxylic acid dimethyl ester is obtained, which is converted into the acid by boiling with aqueous caustic potash; (6) hexadien - 1 : 3 - carboxylic acid -1-ethyl ester is condensed with oxalic acid diethyl ester in a potassium ethylate solution and the resulting oxalo compound subjected to acetylation, reduction and saponification, whereby 2-methylhexatrien-dicarboxylic acid-1 : 6 is obtained; the starting material is prepared by heating bromacetic acid ethyl ester and pentene-2-al-1 with zinc borings in benzene and heating the resulting 2-hydroxyhexene - 3 - carboxylic acid - 1 - ethyl ester with potassium bisulphate to split off water; (7) 1 - methylhexadien - 1 : 3 - carboxylic acid-1-ethyl ester is condensed with oxalic acid diethyl ester in potassium alcoholate solution, the oxalo compound so obtained then acetylated and reduced, and the acetoxy-dihydro product boiled with aqueous caustic potash to give 1 : 5-dimethylhexatrien-dicarboxylic acid-1 : 6; the starting material is obtained by heating a -bromopropionic acid ethyl ester with a -pentenal and zinc borings in dry benzene and splitting off water from the product by heating with potassium bisulphate; (8) decatetraenic acid ethyl ester is condensed with oxalic acid diethyl ester in presence of potassium ethylate and the oxalo product, after chromatographic separation, is acetylated, reduced and saponified with methanolic caustic potash, yielding decapentaen - 1 : 10 - dicarboxylic acid dimethyl ester, from which the acid is obtained by boiling with aqueous caustic potash; (9) oxalo-tetradecahexaenic acid diethyl ester is acetylated with acetic anhydride and the resulting a -acetoxytetradecaheptaen-dicarboxylic acid diethyl ester reduced with aluminium amalgam until the spectroscopic absorption bands of the starting material just disappear; the 1-acetoxy-tetradecahexaen - 2 : 4 : 6 : 8 : 10 : 12-dicarboxylic acid - 1 : 4 - diethyl ester so formed is then treated in pyridine solution with sodium ethylate and the product chromatographed with aluminium oxide whereby tetradecaheptaen-1 : 3 : 5 : 7 : 9 : 11 : 13 - dicarboxylic acid - 1 : 14 - diethyl ester is obtained, from which the acid is prepared by saponification; the starting material is produced by heating crotonaldehyde with a mixture of pyridine and glacial acetic acid, condensing the resulting dodecapentaen-2 : 4 : 6 : 8 : 10 - al - 1 (the yield of which may be increased by condensing the octatrienal also formed with more crotonaldehyde) with malonic acid in pyridine solution containing a little piperidine, separating the tetradecahexaen-2 : 4 : 6 : 8 : 10 : 12 - carboxylic acid - 1 from the accompanying tridecahexaen - 1 : 3 : 5 : 7 : 9 : 11-dicarboxylic acid - 1 : 1, converting it into its methyl ester with diazomethane, condensing it with oxalic acid diethyl ester in potassium alcoholate solution, and subjecting the product to chromatographic purification.