Definition
ChEBI: A polymeric complex of zinc with the ethylene bis(dithiocarbamate) anionic ligand. Formerly used as an agricultural fungicide for the control of downy mildews and rusts, its use is no longer permitted in the US or the EU.
Uses
Agricultural fungicide.
General Description
An off-white powder. Used as a fungicide.
Reactivity Profile
ZINEB(12122-67-7) is a zinc salt of a dithiocarbamic acid. May generate flammable gases with aldehydes, nitrides, and hydrides. Incompatible with acids, peroxides, and acid halides.
Air & Water Reactions
Decomposes gradually, accelerated by exposure to air, moisture, and heat. Insoluble in water. Thio and dithiocarbamates slowly decompose in aqueous solution to form carbon disulfide and methylamine or other amines. Such decompositions are accelerated by acids.
Fire Hazard
Flash point data for this chemical are not available, but ZINEB is probably combustible.
Chemical Properties
Light-tan solid. Insoluble in water; soluble
in pyridine; decomposes on heating.
Production Methods
The production of zineb involves a two-step chemical synthesis process. First, ethylenediamine is reacted with carbon disulphide and aqueous ammonia in the presence of a stabiliser such as sodium pyrosulphite, sodium sulphite, or sodium hydrosulphite. This reaction yields an intermediate compound known as "ambis." In the second step, ambis is reacted with zinc chloride in the presence of a catalyst, commonly bismuth molybdate, nickel on alumina or cobalt-based catalysts, to produce zineb.
Hazard
Toxic by inhalation and ingestion; irritant
to eyes and mucous membranes. Questionable carcinogen.
Mechanism of action
Non-specific with protective action. Multi-site activity. It disrupts fungal enzyme activity by reacting with metal-containing enzymes, particularly those involved in spore germination and fungal growth.
Metabolic pathway
Zineb and other alkylenebis( dithiocarbamate) fungicides are degraded
and metabolised via a common pathway. The primary degradation
reaction of zineb in water, soil, plants and animals involves the initial
dissociation of the metal complex and decomposition to numerous degradation
products including ethylenethiourea (ETU) and ethyleneurea (EU)
as major products (Scheme 1).
Purification Methods
Crystallise this herbicide several times from hot toluene or from hot CHCl3 by addition of EtOH. It is a skin irritant. [Beilstein 4 III 149, 4 IV 234.]
Degradation
[14C-ethylene]Zineb(1) was decomposed mainly to ETU (2) in an aqueous
suspension after 14 days via the 5,6-dihydro-3H-imidazo[2,1-c]-1,2,4-
dithiazole-3-thione (3) intermediate (Vonk, 1976). In dilute alkaline solution
and in the presence of light, heat and moisture, zineb decomposed
rapidly to compound 3 (Marshall, 1978). ETU (2) in aqueous solutions
was further converted into 2-imidazoline (4) and EU (5) (kaars Sijpesteijn
and Vonk, 1974). Zineb decomposed in sterile marine culture medium to
yield ETU (2) and compound 3. In the presence of copper, an additional
degradation product, ethylene diisothiocyanate (6), was also observed
(Hunter and Evans, 1991).
Toxicity evaluation
Zineb has a low mammalian toxicity however, it may cause adverse reproduction/developement effects if ingested. It is moderately toxic to most fauna and flora.
