Patent GB-630081-A (GB)
Title: Improvements in or relating to beta-(heterocyclic-thio)-carboxylic acids and method of preparing same
IPC: C07D279/04
Filed: 1946-09-04
Abstract: As modifiers for the polymerization of butadiene-1,3 hydrocarbons there may be used b -(heterocyclic-thio)-carboxylic acids (see Group IV (b)).ALSO:A modification of the parent Specification in that b -(heterocyclic-thio)-carboxylic acid compounds are obtained by treating a b -lactone with a mercaptan which has a mercapto group attached to a carbon atom in a heterocyclic ring, the said carbon atom being directly adjacent to a nitrogen atom of the heterocyclic ring.  The reaction may be represented by the following equation: <FORM:0630081/IV (b)/1> wherein A is a heterocyclic radicle containing nitrogen in the ring having its connecting valency on a carbon atom directly adjacent to a nitrogen atom in the heterocyclic ring, R is hydrogen or a substituent group and H is replaceable by a salt-forming group.  The reaction may be effected in the presence of an inert solvent such as benzene but is preferably performed by adding the b -lactone to an aqueous solution of the mercaptan made alkaline by the addition of an inorganic base such as an alkali metal or ammonium hydroxide, in this case the sodium salt of the b -(heterocyclic-thio)-carboxylic acid is formed and may be converted to the free acid by treatment with a mineral acid. Preferably equimolar quantities of reactants are employed and if an excess of b -lactone is used it will react with the salt of the acid formed as above to give polymeric thio acids as in Specification 635,347. Temperatures instanced are from - 20 DEG  to 200 DEG  C., preferably 0 DEG  to 50 DEG  C.  Mercaptans instanced are mercapto-thiazoles, -thiazolines, -oxazoles, -oxazolines, -imidazoles, -imidazolines, -thiodiazoles, -thiazines, -quinolines, -pyridenes and -pyrimidines and are preferably those in which the carbon atom which is directly attached to a nitrogen atom in the ring is also directly attached to a ring sulphur or oxygenation, e.g. 2-mercapto -thiazoles, -thiazolines, -oxazines and -thiazines.  The mercaptans may contain as additional groupings halogen, nitro, oxy, hydroxy, thio, cyano. acyl, acyloxy, keto, amino, carboxy or sulpho groups, although the use of mercaptans in which all hydrogen atoms except these attached to carbon atoms are present in mercapto groups is preferred because of the possibility of side reactions.  b -Propiolactone is the preferred lactone and other lactones listed correspond with those instanced in the parent Specification.  The b -substituted acids may be reacted with alcohols to produce esters or with ammonia and amines to form amides, and salts of the acids with polyvalent metals, e.g. zinc, cadmium, mercury, lead, calcium, barium and iron may be obtained by reacting the requisite mercaptan salt with the b -lactone or by reacting a water-soluble salt of the acid with a water soluble salt of the required metal.  In examples, b -propiolactone is added to a sodium hydroxide solution of (1) 2-mercapto-thiazoline to yield the sodium salt of b -(2-thiothiazolinyl)-propionic acid which, on neutralization with hydrochloric acid in (2) yields the corresponding free acid; (3) a mixture of 85 per cent by weight of 2-mercapto-4,5-dimethyl-thiazole and 15 per cent by weight of 2-mercapto-4-ethyl-thiazole to give on neutralization with hydrochloric acid a mixture of b -(2-thio-4,5-dimethyl-thiazyl)- and b -(2-thio-4-ethyl-thiazyl)-propionic acids; (4) 2-mercapto-benzothiazole to give b -(2-thio-benzothiazyl)-propionic acid on acidification; and (5) the lead salt of this acid on treatment with lead nitrate, and (6) 2-mercapto-4,6,6-trimethylthiazine to give b  - (2 - thio - 4,6,6 - trimethylthiazinyl)-propionic acid on acidification.  It is stated that 2-mercapto-4,5-dimethyl-, 2-mercapto-5-methyl-, p 2-mercapto-4-ethyl-, 2-mercapto - 4,5 - tetramethlyene -, 2 - mecapto - 4 - phenyl-and 2 - mercapto - 4 - methoxy - thiazoline may replace the thiazoline used in examples (1) and (2) to give the corresponding acids and 2 - mercapto - 4 - phenyl, 2-mercapto - 4 - methoxy, 2-mercapto - 4 - p-nitrophenyl- or 2 - mercapto - 4 - o - chlorophenyl-thiazole may replace the thiazoles used in example (3) to give the corresponding acids.  The 2-mercapto-4,6,6-trimethylthiazine used in example (6) is prepared by treating mesityl-oxide in aqueous hydrochloric acid solution with ammonium dithio-carbamate. Specification 649,028 also is referred to. In the Specification as open to inspection under Sect. 91 it is stated that any nitrogen containing heterocyclic mercaptan may be treated with a b -lactone to give the corresponding b -(heterocyclic-thio)-carboxylic acid compound.  This subject-matter does not appear in the Specification as accepted.ALSO:b -(Heterocyclic-thio)-carboxylic acids (for preparation see Group IV (b)) and their salts with polyvalent metals such as zinc, cadmium, mercury, lead, calcium, barium and iron are vulcanisation accelerators and activators.