Studies on Solvent Extraction of Some Substituted Dithiocar bamic Acids K. 1. Aspila, C. L. Chakrabarti,' and V. S. Sastri Department of Chemistry, Carleton University, Ottawa, Ontario, K 7s 5B6, Canada
Several authors ( I , 2) have reviewed complexation reactions of substituted dithiocarbamic acids. De et al. ( 3 ) have discussed solvent extraction d a t a on metal dithiocarbamate complexes. Recent studies in our laboratory have involved t h e use of solvent extraction technique in determining stability constants of metal dithiocarbamate complexes ( 4 , 5 ) . During the course of the studies on stability constants of metal dithiocarbamates by solvent extraction technique, d a t a on the solvent extraction characteristics of dithiocarbamic (DTCH) acid ligand were needed by us b u t could not be found in the literature. Hence, this research was undertaken in order to determine solvent extraction characterissubstituted dithiocarbamic acids, to detics of some N,Ntermine acid dissociation constants (K,) of these ligands, and also to determine any relationship between pK, and solvent extraction parameters, such as pH1/2 (the p H value for 50% extraction). A brief theoretical discussion is in order before discussing the experimental results. As an approximation, it will be assumed t h a t the chloroform phase contains only a monomeric D T C H acid and the aqueous phase contains the D T C H acid and D T C anion (DTC-). T h e dithiocarbamate species extracted into chloroform is assumed to be dithiocarbamic acid (DTCH). This assumption seems reasonable because i t is the covalent D T C H (the most logical choice) which should be extracted into the non-polar solvent chloroform. T h e greater the length of the alkyl chain of t h e D T C H molecule, the more soluble is the molecule in chloroform, leading to an increase in pH112 with an increase in t h e number of carbon atoms in the molecule. Basic Assumption: the only species extracted is DTCH. Two equilibria are therefore involved.
DTCH(aq)
DTC-(aq) + H + acid dissociation extraction DTCH(aq) F= DTCH(org\ T_
(1) (2)
T h e distribution ratio, D, can be expressed as follows:
T h e p H , K c (acid dissociation constant) and K D (partition coefficient for DTCH) are related to the distribution ratio, D, by Equation 4.
If H t
>>
K,, then
If H +
