Patent GB-722938-A (GB)
Title: Improvements in or relating to a method of preparing cyclohexene-4-carboxylic acids
Filed: 1952-07-02
Abstract: A cyclohexene-4-carboxylic acid is prepared by a process which comprises reacting a b -lactone having at least one hydrogen atom on the a -carbon atom, or a polymer of said b -lactone with an acyclic, phenyl-substituted acyclic or alicyclic conjugated polyene at a temperature in the range of 100 DEG  to 250 DEG  C.  Among the b -lactones mentioned are b -propiolactone, b -n-valerolactone, a  - methyl - b  - propiolactone, b  - phenyl - b  - propiolactone, b  - chloroethyl - b  - propiolactone, a  - benzyl - b  - propiolactone, and b -lactone polymers. Conjugated polymers mentioned include butadiene-1,3, isoprene, 2-methylpentadiene-1,3, piperylene, 3-methyl-pentadiene-1,3, 2-neopentyl-butadiene-1,3, 2-phenylbutadiene-1,3, 2-chloro-, 2-bromo- and 2-fluoro-1,3-butadienes, hexadiene-2,4, hexatriene-1,3,5, 2-methyl- and 1,6-diphenyl-1,3,5-hexatrienes, myrcene and allo-ocimene, cyclopentadiene, 1,2,6,6-tetramethyl-cyclo-hexadiene, methylene - cyclopentadiene, 5 - isopropyl - 2 - methyl - 1,3 - cyclohexadiene and 6,6 - dimethyl fulvene.  b -Lactone polymers are prepared by heating the b -lactone either alone or with an acid, base or metal salt catalyst.  The reaction between the b -lactone or polymer thereof and the conjugated polyene is preferably carried out in a pressure reaction.  A polymerization inhibitor such as tertiary-butyl alcohol or hydroquinone may be employed.  Alkaline materials such as alkali metal hydroxides and carbonates, acidic materials and metal salts may be used as catalysts.  In examples: cyclohexene-4-carboxylic acid is obtained by heating b -propiolactone and butadiene-1,3 in the presence of potassium carbonate and hydroquinone in a stainless steel autoclave (I); a mixture of methylcyclohexene - 4 - carboxylic acids, believed to be mainly the 1-methyl isomer, is obtained when a mixture of b -propiolactone and isoprene is pumped into a heated autoclave containing potassium carbonate and hydroquinone (II); 3,6-endomethylene cyclohexene-4-carboxylic acid is obtained from dicyclopentadiene and b -propiolactone in a process similar to (I) (III); cyclohexene-4-carboxylic acid is obtained by heating a b -propiolactone polymer, obtained by heating the lactone with copper acetate, with butadiene in the presence of hydroquinone in an autoclave (IV); and a mixture of isomeric methyl cyclohexene-4-carboxylic acids is obtained by passing b -propiolactone into a heated autoclave containing potassium carbonate and hydroquinone (V).  5-Methylcyclohexene is obtained if b -butyrolactone is substituted for b -propiolactone.  The cyclohexene-4-carboxylic acids are insecticides and fungicides and may be converted to aliphatic dicarboxylic acids by alkaline isomerization and cleavage of the cyclohexene ring.  The cyclohexene ring may also be split by oxidation to give tricarboxylic acids and may be reduced to give cyclohexane carboxylic acids useful as selective herbicides.  Esters of the dicarboxylic acids are plasticizers for synthetic acids and rubbers and additives for lubricating oils.ALSO:Cyclohexene - 4 - carboxylic acids (see Group IV (b)) are insecticides and fungicides.  Cyclohexane carboxylic acids are selective herbicides.