Fungicides iron dithiocarbamates

The traditional copper fungicides are in fact inorganic copper coordination compounds The still most important group of organic protectant fungicides, the dithiocarbamates, are applied in the form of their metal-coordination compounds. Dimethyldithiocarbamate as the iron complex ferbam and the zinc complex ziram, ethylenebisthiocarbamate as the zinc complex zineb and the manganese complex maneb. 

Dithiocarbamates are normally prepared as alkali metal salts by the action of primary or secondary amines on CS2 in the presence of, say, NaOH. The zinc, manganese, and iron dithiocarbamates are extensively used as agricultural fungicides, and zinc salts as accelerators in the vulcanization of rubber. Alkali metal dithiocarbamates are usually hydrated and are dissociated in aqueous solution. When anhydrous, they are soluble in organic solvents in which they are associated. 

The first report of iron dithiocarbamate chemistry was in 1907, when Delepine (2) detailed the synthesis of the iron(III) tris(dithiocarbamate) complex [Fe(S2CN i-Bu2)3]. Later the dimethyldithiocarbamate complex [Fe(S2. CNMe2)3l (Ferbam) found widespread use as a fungicide (14). Iron(ll)... 

Dithiocarbamate fungicides consist of metal salts of dimethylthiocarbamate and ethylenebis-dithiocarbamate anions, as shown in Figure 17.5. These fungicides are named in accordance with the metal ion present. For example, the manganese salt of dimethyldithiocarbamate is called maneb, and the zinc and sodium salts are zineb and nabam, respectively. The iron salt of ethylenebisdithio-carbamate is called ferbam, and the zinc salt of this ion is called ziram. These salts are chelates (Section 2.3) in which two S atoms from the ethylenebisdithiocarbamate anion are bonded to the same metal ion in a ring structure. 

Give the names and structures of two dithiocarbamate fungicides. How are they used How are zinc and iron involved with these fungicides ... 

Penicillamine (D-(3,(3-dimethylcysteine) is an effective chelator of copper, mercury, zinc and lead which promotes the excretion of these metals in the urine. It is clinically used in patients with Wilson s disease, with rheumatoid arthritis and with heavy-metal intoxications. Ziram and ferbam are the zinc and the iron salts respectively of dimethyl-dithiocarbamic acid (Figure 20.44). They are widely used as selective fungicides in agriculture. Pyrithione (1 -hydroxy-2(l//)-pyridinethione), as its zinc salt is used in dermatology as antiseborrheic. 

Traces of zinc are naturally present in must and wine. Higher concentrations of this heavy metal may come from the vineyard, due to galvanized iron wire damaged by mechanical harvesting, or dithiocarbamate-based fungicides. Another source is winemaking equipment made of alloys, such as bronze pumps, hose connections, taps, etc. 

Derivatives of thiocarbamic acid are a family of very important fungicides used in many plant-care products. Manganese salts (maneb), zinc salts (zineb), sodium and iron salts have no action on aluminium, whatever their degree of dilution. On the other hand, copper salts of dithiocarbamic acid may attack aluminium. 

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