Patent GB-648672-A (GB)
Title: Improvements in or relating to beta-thio carboxylic acid compounds and method of preparing same
Filed: 1946-09-04
Abstract: b -Thio carboxylic acids or metal salts thereof are obtained by reacting a saturated aliphatic b -lactone with an aliphatic, alicyclic or aromatic mercaptan in which all hydrogen atoms except those attached to carbon are present in mercapto groups and in which the carbon atoms connected to mercapto groups are otherwise directly attached only to carbon or hydrogen atoms or with a metal salt of such a mercaptan.  Inert solvents such as benzene may be used as reaction media although higher yields are obtained when polar solvents such as alcohol or water are employed.  In the preferred reaction equimolar quantities of reactants are used, the b -lactone being added to a mercaptan salt obtained by dissolving the mercaptan in an equimolar quantity of an inorganic base such as an alkali metal or ammonium hydroxide.  On acidification after such a reaction the free b -thio carboxylic acid is obtained.  The salt of the b -thio carboxylic acid may react with excess b -lactone as in Specification 635,347, although this reaction is not appreciable so long as unreacted mercaptan salt is present. Temperatures specified are 0 DEG to 100 DEG  C., preferably 0 DEG  to 50 DEG  C., e.g. 20 DEG  to 50 DEG  C., and may be between - 20 DEG  and 200 DEG  C. Mercaptans may contain radicles attached to the mercaptan groups which are exclusively of hydrocarbon structure or which may be substituted by, e.g., halogen, oxygen, sulphur and nitrogen containing groups such as chloro, bromo, iodo, nitro, oxy, keto, thio, or cyano groups when these groups are attached to carbon atoms other than those to which mercapto groups are attached. Amongst mercaptans specified the following may be mentioned: ethyl-, isopropyl-, tert.-butyl-, 2-ethyl-hexyl-, octadecyl- and allyl-mercaptans, 1,2-ethane-dithiol, thiophenol, thionaphthols, dithiohydroquinone, cyclohexyl and benzyl mercaptans, b -chloro ethyl mercaptan, o-chloro-thiophenol, p-nitro-thiophenol, b -phenoxyethyl mercaptan and esters, nitriles and N-dialkyl amides of thioglycollic acid, thiolactic and thiosalicylic acid, e.g. ethyl thioglycollate and thiohydracrylate. b -Propiolactone is the preferred lactone, others specified including b -butyro-, b -isovalero-, b -n-capro-, a -butyl-b -propio- and b -methyl-b -valero lactones.  In examples, b -propiolactone is reacted in aqueous sodium hydroxide solution with (1) tert.-butyl mercaptan; (2) n-hexyl mercaptan; (4) thiophenol and dithioresorcinol; (5) ethyl thiohydracrylate to produce on acidification (1) b -(tert. - butyl - thio) - propionic; (2) b  - (n - hexyl-thio)-propionic; (4) b -thiophenoxy propionic and thioresorcinol-b -dipropionic; and (5) b -thiodipropionic acids, it also being stated in (2) that ethyl, isopropyl, 2-ethyl hexyl, lauryl or octadecyl mercaptans may be treated as in (1) and (2) to produce the corresponding acid; in (3) thiophenol and b -propiolactone are heated to yield b -thiophenoxy propionic acid; and in (6) b -propiolactone is reacted with ethyl thiohydracrylate in aqueous sodium hydroxide solution, the intial product being refluxed with additional sodium hydroxide to hydrolyse the ester to yield S-carboxymethyl thiohydroacrylic acid on acidification.  In the Specification as open to inspection under Sect. 91 it is stated generally that b -lactones may be reacted with mercaptans either as such or in the form of their salts to produce the corresponding b -thiocarboxylic acid compound, and other mercaptans and b -lactones are specified.  Heterocyclic mercaptans, e.g. mercapto-furans, -thiophenes and -pyrenes are mentioned and b -lactones mentioned include those of b -hydroxy-monocarboxylic acids containing cycloalkyl, aryl and aralkyl substituents such as b -cyclohexyl-b -, b -phenyl-b - and b -benzyl-b -propiolactone, lactones of unsaturated b -hydroxy carboxylic acids, mono-b -lactones and dilactones of dicarboxylic acids, e.g. a ,a -dimethyl-b -propiolactone-b -carboxylic acid and the b - -dilactone of citrylidene malonic acid nitrogen, sulphur and halogen substituted lactones specified include those containing nitro, amino and hydroxy groups or ether linkages such as a -nitrophenyl-b -propiolactone, b -(-o nitro - m - chlorophenyl) - b  - propiolactone and a -hydroxy-b -phenyl-b -propiolactone.  Specification 649,028 is referred to.