CHAPTER-II

CHEMISTRY OF

DITHIOCARBAMATES

16

CHAPTER - II

CHEMISTRY OF DITHIO CARBAMATES

INTRODUCTION:

The development of the concept of co-

ordination theory by the Switzerland Noble prize

awardee, Werner1 in 1893 revolutionized the

approach to the structure of inorganic compounds

and permeated the entire area of coordination

chemistry. Since then number of ligands have been

introduced in inorganic analysis because of their

selectivity and sensitivity and dimethyl glyoxime

is an example of such organic reagents which is

highly selective for Ni(II)2.

Organic analytical reagents are found to be

advantageous over inorganic reagents for their

reactivity, sensitivity and selectivity and

voluminous literature is available on their use3-

5.The separation of metal ions is simple and more

effective with the organic reagents and hence they

have several applications in gravimetric, titrimetric

and spectrophotometric determinations and also as

17

masking and demasking agents in certain

extractive seperations of metals6-9

.

The simplest way of synthesis of these compounds

is as follows:

Ammonium salt of

dithio carbamic acid

N-substituted dithiocarbamic acids,

RNHCSSH or R2NCSSH are formed as their

substituted ammonium salts by the reaction of CS2

with a primary or secondary amine, usually in

alcoholic10

or aqueous solution11

.

The dithio carbamates were developed in

the early history of organo sulphur chemistry.

They are half amides of dithiocarbamic acid and

these amine compounds of dithio carbamates are

prepared by using alkali metal hydroxides12

.

R-NH2 + CS2 + NaOH RNHCSSNa + H2O

18

The sodium or ammonium salts of dithio

carbamates are sufficiently stable than the

corresponding carbamic acids. Sodium salts of

dithiocarbamates are white crystalline solids freely

soluble in water. These salts are stable for a long

period, but the solutions of dithiocarbamates are to

be prepared freshly whenever required. Most of the

heavy metal compounds of the dithiocarbamates

are colored facilitating spectrophotometric studies

in visible or near UV region. They are prepared

simply by the addition of a solution of the heavy

metal ion as its chloride, sulphate, etc., to a

solution of an ammonium or alkali metal salt of the

dithiocarbamic acid13

.

Heavy metal thio

compounds are sparingly soluble in organic

solvents such as chloroform, carbon tetrachloride

and ethyl ether.

Dithiocarbamates are decomposed in acid

solutions and the breakdown of dithiocarbamic

acid into amine and CS2 in the presence of mineral

acids has been used as the basis for quantitative

estimation of dithiocarbamates14

.

19

The CS2 liberated can be estimated by

iodometry as the amount of CS2 liberated is

directly proportional to the concentration of

dithiocarbamate. The detailed study15-18

of various

dithiocarbamates and their derivatives through

infrared spectra confirms the contribution of

various forms equally to the structure. The

significant among several canonical forms for the

dithicarbamates in their metal complexes,

M(S2CNR2)n are as follows :

STRUCTURES:

In the following structures, M is a metal

atom. Although all these forms contribute equally

to the structures of all N,N-dialkyl dithiocarbamic

acid derivatives the canonical form I(a) arises from

the mesomeric electron releasing tendency of the

R2N group. By this electron drift into the sulphur

atoms not only the electron donor capacity

20

increases but the formation tendency of the strong

complexes with the heavy metals also enriches

with reducing tendency of forming dative π-bonds

between the metal and sulphur atoms.

A Number of organic compounds have

been used in spectrophotometric analysis of metal

ions among which dithiocarbamates occupy one of

the prominent positions19

. The abundant

applications of dithiocarbamtes and their

substituted compounds in inorganic analysis are

mainly because of the ease of replacement of

hydrogen from -SH group. A coordinate bond will

be formed through S to form strongly colored

complexes with a number of metals. The strong

metal binding properties of the dithiocarbamates

were recognized by Delepine20

.

21

USES OF DITHIO CARBAMATES IN

VARIOUS FIELDS:

The nitrogen derivatives of dithiocarbamic

acids have got wide applications in the field of

medicine and agriculture because of their

biological activity. The first observation of the

activity of dithio carbamates against human

pathogenic fungi has been ascribed to Hall of

Baker and Baker Co., in 1938. Ferbam, the iron

salt of dimethyl dithio carbamic acid as a first

fungicide, ziram, zinc salt of sodium dimethyl

dithio carbamate as a vegetable fungicide are

particularly effective against the anthracnose

disease. Vapum (sodium methyl dithio carbamate)

is in the market as a soil fungicide, insecticide and

herbicide. The synthesis and anti microbial activity

of piperidine and morpholine dithio carbamates

have also been reported. Another interesting

development has been the discovery of their value

in drugs for the correction of chronic alcoholism.

Recently Gordon research conference of 2006 on

metals in medicine demonstrated metal dithio

22

carbamates as potential anticancer drugs. A large

volume of biological literature has been built up on

the dithiocarbamates and a number of views have

been published on their activity as fungicides21.

Tertramethyl thiuram disulphide is one such

compound that has greater medicinal value in

controlling various dermatophytes, treating scabies

and correcting chronic alcoholism and because of

its importance it is used as an ingredient in various

soaps and lotions. Much useful research on

insecticidal, acaricidal, fungicidal, bactericidal and

microbicidal activity of these dithiocarbamates has

been published. Similarly these compounds have

played a major role in rubber chemistry as

vulcanization accelerators and anti-oxidants.

Dithiocarbamates play a major role in

analytical chemistry also due to their metal binding

property and chelating tendency and these are

effective in the treatment of effluents arising from

refineries of non ferrous metals22,23

.

Dithiocarbamates are used in the spectrophoto-

metric analysis of metal ions and also in different

23

techniques such as amperometry, pH metry and

catalytic polarography. The application of PDTC

as an analytical reagent has been mostly used in

different techniques such as amperometry24

, pH

metry25,26

, spectrophotometry27-37

and catalytic

polarography38

.

Kinetic and mechanistic studies of metal-

DTC complexes in addition to their analytical

determination by electro analytical methods have

been well documented39-41

. The use of DTC is

mainly for preconcentration of metal ions from

water samples and the metal ions after

preconcentration are determined by atomic

absorption spectrophotometry, pulse polarography,

derivative spectrophotometry and radiochemical

methods42-44

. The complexing ability of DTC is

directly related to the presence of 2 donor sulphur

atoms and stability with its cyclic nature45-51

.

Complexes of Cu(II), Co(II) and Ni(II)

were prepared along with 1,4-piperaizine-bis-

dithiocarbamate sodium salt and analysed by

24

conductivity measurements, magnetic

susceptibilities, thermal analysis and spectroscopic

studies52

. Sadafkhan etal53

have reported the

preparation of a ligand, bis(2,2-dithiopiperazinato-

2,2-diamino diethyl amine) Na2L2 and its transition

metal complexes of the type M2(L2)2 where

M=Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II),

Cd(II) and Hg(II). Some organotin complexes with

Sn were prepared54

as bis(2,2-dithiopiperazinato-

2,2-diamino diethyl amine) and characterized by

UV-visible spectroscopy, NMR spectroscopy and

thermo gravimetric analysis. Oi-Wah Lau and

Sing-Yiu Ho55

have developed a method for the

determination of Fe, Co, Ni, Cu, Hg and Pb in

water by energy – dispersive X-Ray fluorescence

spectrometry after subjecting them to pre

concentration as their piperazino-1,4-bis

(dithiocarbamate) complexes.

The synthesis of tetra dentate piperazine

ligand done56

lead to the determination of the

structures of the ligand N,N1 – bis (2-pyridyl

methyl) piperazine with the transition metal ions

25

Cu++

, Co++

, Mn++

and Cd++

. Adam Hulanicki57

presented a detailed report of complexation

reactions of dithiocarbamates and the properties of

metal-dithiocarbamates were presented as a

function of the nature of the substituents in the

ligand molecule. Complexes of Co(II), Zn(II) and

Cd(II) were prepared by using 1-ethoxy carbonyl-

piperazine -4-carbo dithioate and analysed for their

structure by spectrophotometry58

. Tombeux and

his co-workers59

obtained the spectra of N,N1-bis

(dithiocarboxy) piperazine complexed with

Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and

Cd(II) and conducted their studies. Since the

research on dithiocarbamates has been revealing

some promising new avenues in all fields of

sciences including inorganic analysis, the inclusion

of all these references is beyond the scope of this

dissertation.

In view of the importance of

dithiocarbamates, a simple and sensitive extractive

spectrophotometric technique for the determination

of micro quantities of Cu, Ni, Co, Fe and Mn have

26

been developed in the present work using

piperazine dithiocarbamate (PDTC).

Advantages of PDTC as analytical reagent:

1. The preparation of the reagent is simple,

easy and time required is less than 45

minutes.

2. The metal complexes of the ligand are

stable because of the contribution of

resonance hybrid structures.

3. The compound possesses high electric

dipole moment.

4. The electron releasing tendency of N-group

into sulphur atom increases the electron

donor capacity of PDTC to give strong

complexes with number of metal ions.

27

5. Water of crystallization is not known in

PDTC metal complexes and hence are

easily extractable into organic solvents.

28

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