Medical brain notes 14

  INTRODUCTION In general, aromatic primary amino moiety ( i.e ., Ar-NH 2 ), as present in a host of sulphadrugs  viz ., succinyl sulphathiazole, sulphamethoxazole, sulphaphenazole and other potent pharmaceutical substances, for instance sodium or calcium aminosalicylate, isocarboxazid, primaquine phosphate, procainamide hydro-chloride, procaine hydrochloride and dapsone react with sodium nitrite in an acidic medium to yield the corresponding diazonium salts as expressed below : It is interesting to observe here that the above reaction is absolutely quantitative under experimental parameters. Therefore, it forms the basis for the estimation of pharmaceutical substances essentially contain-ing a free primary amino function as already illustrated earlier.   THEORY Nitrous acid is formed by the interaction of sodium nitrite and hydrochloric acid as follows : NaNO 2  + HCl   ------ à  NaCl + HNO 2   The end-point in the sodium nitrite titration is det...

  ASSAY METHODS A number of pharmaceutical substances can be assayed by official methods employing sodium nitrite titrations. A few typical examples are described below to get an indepth knowledge about sodium nitrite titrations.   1. PREPARATION OF 0.1 M SODIUM NITRITE SOLUTION   Materials Required :  Sodium nitrite : 7.5 g.   Procedure :  Weigh accurately 7.5 g of sodium nitrite and add sufficient DW to produce 1 litre in a   1000 ml volumetric flask.   2. STANDARDIZATION OF 0.1 M SODIUM NITRITE SOLUTIOlN WITH SULPHANILAMIDE   Materials Required :  Sulphanilamide (previously dried at 105°C for 3 hours) : 0.5 g ; hydrochloric acid (  − ~ 11.5 N) : 20 ml ; 0.1 M sodium nitrite.   Theory :  The nitrous acid, generated on the introduction of sodium nitrite solution into the acidic   reaction mixture, reacts with the primary amino group of sulphanilamide quantitatively, resulting into the formation of an unstable nitrite...