Determination of dissociation and complex formation constans of N,N diethyldithio carbamic acid

SUMMARY In this study, first, the determination of the dissociation constant of N,N diethlydithio carbamic acid was made in an aqueous medium of ionic strength 1=1. OM with sodium perchlorate as an inert electrolyte at 25.0±0.2C° and second the step-wise stability constants with Cd(II) were determined. However, due to the decomposition of the acid in aqueous solution, an estimation of acid constant is not possible. Potentiometry has been the main technique used for studying the complex formation in the medium stated. Determination of the stability constants has been carried out at 25.0±0.2C° in %50 dioxane-water medium of ionic strength 1=0. 1M. The complex formation equilibria of N,N diethyldithio carbamate with Cd(II) have been carried out via the central ion measurements by means of a cadmium amalgam electrode. Potentimetric titrations were performed with four different values of C^ as 2.5; 5;0 and 7.5 mM. The e.m.f of the following galvanic cell was measured. (-)Cd(Hg) CM, M Cd(CI04)2 CL, M NaEt2DTC NaCI04 to 1=0. 1M in 50% dioxane Ag,AgCI ( + ) Before and during the titrations the solutions were deaereted and mixed by a stream of purified nitrogen. To obtain the correct vapour pressure, the nitrogen gas first bubbled through 0.1M NaCIC>4 solution. In the same manner it has been checked that the cadmium amalgam electrode obeys the Nernst's law. Measurements were arranged as titration where the solutions in the left hand half-cell were obtained by 42adding increasing volumes of a solution T in to a known volume v0(ml) solution S. The solutions S and T had the following compositions: S: CM, Cd(CI04)2 T: 2.0mM NaEt2DTC (0.1-3CM)M NaCI04 98.0mM NaCI04 The stability constant was evaluated by graphical method as described below: When no ligand is added, the e.m.f of the cell is given : El= ERE_E°- (RT/nF) lnCM Where C^ is the metal ion concentration. The e.m.f of the cell which contains NaEt2DTC is given by E2= ERE-E°- (RT/nF) ln[M] Where [M] is the free metal ion concentration. In the equation ERE; is the potential of reference half-cell. E° is the standard reduction potential of Cd(II). After the addition of the ligand,.E^ values must be subtracted from E2 value to find the real potential changes: EM= Ei-E2= (RT/nF) In (CM/[M]) X function, X=Cjy[/[M], was obtained by using above equation, as described before. Here, it's assumed that only the mononuclear complexes exist and the activity coefficients do not vary during the experiment. The ligand number, defined as n=(CL~[L]) /C^ equal to the slopes of the Cl versus C^ lines of constant Ej/[, and [L] to the intercepts. From the corresponding values of [L] and X([L]) obtained, the formation constant Pj 43value was determined by successive extrapolation to [L]=0 of the following function. (*j-i -Pj-i) [L] Xj 3~ \^ 3 (1 rs j =s N; X0 - X ; p0 = 1) Cd(II) ion forms two strong mononuclear complexes with Et2DTC in the medium used. The constants were found to be p!=(1.0±0.3)xl04 M-1, P2=(14.0±0.5)xl06 M-2. Errors given correspond to estimated errors from the graphical calculations. 44