Patent GB-738676-A (GB)
Title: New 2-substituted benzthiazole compounds and silver halide emulsions containing them
IPC: G03C1/35
Filed: 1953-03-05
Abstract: The invention comprises compounds of the general formul <FORM:0738676/IV (b)/1> and <FORM:0738676/IV (b)/2> wherein R and R1 represent a thiol or acetylthiol group, M and M1 represent hydrogen or an alkali metal and Z and Z1 represent the non-metallic atoms necessary to complete a heterocyclic nucleus of the benzthiazole series.  The invention also includes the following processes for the preparation of the above compounds:-(a) compounds of formula I in which M is hydrogen and R represents the acetylthiol group are prepared by heating maleic anhydride and a 2-aminobenzthiazole and then heating the resulting amide of the formula <FORM:0738676/IV (b)/3> with thioacetic acid; (b) compounds of formula II in which M1 is hydrogen and R represents the acetylthiol group are prepared by heating a 2-aminobenzthiazole with a compound having the formula <FORM:0738676/IV (b)/4> (an acetylthiolsuccinic anhydride) in substantially equimolecular amounts; (c) compounds of formula I in which R represents a thiol group are prepared by hydrolysing the corresponding compound in which R represents the acetylthiol group in the presence of aqueous caustic alkali, or by hydrolysing a compound of the formula <FORM:0738676/IV (b)/5> wherein Z and M have the above significance and R2 represents an alkyl group, in the presence of concentrated ammonia and in each method, if necessary, acidifying the reaction product, or by condensing a compound of the formula <FORM:0738676/IV (b)/6> wherein Z and M have the above significance, with thioacetic acid in the presence of aqueous alkali, and, if necessary, acidifying the reaction product; and (d) compounds of formula II in which R1 represents a thiol group are prepared by hydrolysing the corresponding compound in which R1 represents the acetylthiol group in the presence of aqueous alkali or by hydrolysing a compound of the formula <FORM:0738676/IV (b)/7> in which Z1 and M1 have the above significance and R3 represents an alkyl group, in the presence of concentrated ammonia and in each method, if necessary, acidifying the reaction product.  The alkali metal salts of compounds of the general formul  I and II may also be prepared by neutralizing the corresponding free acids with an alkali, e.g. sodium or potassium hydroxide.  The benzthiazole radical in the compounds of the general formul  I and II may be derived from 2-amino-5-bromo-, 2-amino-6-bromo-, 2-amino-4-chloro-, 2-amino-6-chloro-, 2-amino-7-chloro-4-methoxy-, 2-amino-4-methoxy-, 2-amino - 5 - methoxy -, 2 - amino - 6 - methoxy -, 2 - amino - 6 - ethoxy -, 2 - amino - 6 - n - butoxy -, 2 - amino - 6 - isobutoxy -, 2 - amino - 4-methyl-and 2-amino-6-methyl-benzthiazole.  In the examples the following compounds are prepared:-2 - (a  - acetylthiol - b  - carboxypropionamide) substituted benzthiazole and 6-ethoxybenzthiazole, 2-(b -acetylthiol-b -carboxypropionamide) substituted benzthiazole and 6-ethoxybenzthiazole, 2-(b -carboxy-a -thiolpropionamido) substituted benzthiazole and 6-ethoxybenzthiazole, and 2-(b -carboxy-b -thiolpropionamido) substituted benzthiazole and 6-ethoxybenzthiazole.  The following intermediate amides formed by method (a) above are also prepared:-2-(b -carboxyacrylamido)-benzthiazole and -6-ethoxybenzthiazole.  Specification 738,675 is referred to. Acetylthiolsuccinic anhydride of the formula <FORM:0738676/IV (b)/8> is prepared by condensing thioacetic acid and maleic anhydride.