4. DESCRIPTION OF THE INVENTION : Background information and objective :
This invention relates to a new indigenous process for the improvement in the preparation of Mancozeb, a complex compound of zinc with manganese ethylene bis dithiocarbamate. Mancozeb is a fungicide sold mainly under the trade name Dithane M-45, a WDP formulation containing 75 % (m/m) a.i., used for control of several fungus and bacterial diseases of plants such as potato / tomato blight, black spot of roses, cereal rusts etc. Mancozeb is manufactured in the country with an imported technology whose details are not known to us. Production of Mancozeb using imported technology in 1994-95 was 4128 MT as against a total installed capacity of 4000 MT. The import figure of this chemical during the year was 141 MT. This thus necessitated to develop an indigenous process for this fungicide for meeting its increasing demand at home, which has been projected at 6200 MT in 1996-97 and also because of its high potentiality for export to several countries.
Process :
In accordance with the present invention, there is provided a new indigenous improved process for the preparation of Mancozeb, a complex compound of zinc with manganese ethylene bis dithiocarbamate in good yield and purity. Nabam (Disodium ethylene bis dithiocarbamate), an intermediate for Mancozeb was first prepared by reacting carbon disulphide, ethylene diamine and sodium hydroxide in appropriate ratio and in aqueous medium with constant agitation for a specific period ranging from 2-8 hours and temperature ranging from 20-50 ° C . After recovering excess carbon disulphide if any, the reaction mixture containing Nabam (a.i.. 90 % ) was treated with manganese and zinc salt solutions in

appropriate proportions (8:1 to 12:1) with constant mechanical stirring for specific period ranging from 2-8 hours and temperature ranging from 20-80 C. The Mancozeb precipitated out was isolated from the mother liquor in good yield (80 %) and purity (a.i., 85 %).
Techno-economics :
The market price of Mancozeb is Rs. 140/Kg (Formulation). The cost of production based on this process (Lab. scale) is Rs. 78/Kg (Technical). This cost is likely to reduce by Rs. 4/Kg as one of the starting material i.e. carbon disulphide can be recovered to the extent of 15 % for reuse. Further cost reduction can be made by recovering and utilizing the by product, sodium sulphate.

5. CLAIMS:
We claim
1. A new indigenous improved process for the preparation of Mancozeb, a complex
compound of zinc with manganese ethylene bis dithiocarbamate in good yield ( 80 %)
and purity (a.i. content 85 % ) by reacting aqueous solutions of Nabam (Disodium
ethylene bis dithiocarbamate) a.i. 90% such as herein described with manganese and
zinc salts in molar proportions ranging from 8:1 to 12:1 with constant agitation for a
period ranging from 2-8 hours and at temperature ranging from 20-80 °C.
2. The process as claimed in Claim 1 wherein the intermediate Nabam (a.i. 90%) is
formed by reacting carbon disulphide, ethylene diamine and sodium hydroxide in
aqueous solution under constant agitation for a period ranging from 2-8 hours and at
temperature ranging from 20-50 °C.
3. The process as claimed in Claim 1 wherein the reaction is carried out in aqueous
medium under constant agitation for a period preferably ranging from 2-4 hours and
at temperature ranging from 20-40 °C.
4. The process as claimed in Claim 1 wherein the molar concentration of manganese and
zinc salts is maintained preferably in the range 8:1 to 10:1.
5. The process as claimed in Claim 2 wherein the reaction is carried out with constant
agitation preferably for a period ranging from 4-6 hours and at temperature ranging
from 20-35 °C.