Use of organotin compounds in agriculture
Author: Bipasa Sarkar
Division of Agricultural Chemicals, ICAR-Indian Agricultural Research Institute, New Delhi-110012.
Organotin (IV) compounds are characterized by the presence of at least one covalent C-Sn bond. The compounds contain tetravalent Sn centres and based upon the number of alkyl (R) or aryl (Ar) moieties, they are classified as mono-, di-, tri- and tetraorganotins. The anion is usually fluoride, chloride, oxide, hydroxide, a carboxylate or a thiolate (Sarkar, 2012). Organotin compounds have variety of applications in agriculture and human health, though in recent years these have been circumscribed by environmental considerations. Their biological properties make them suitable to be use as antifouling paints on ships, in wood preservatives and as agricultural pesticides. The unique properties of organotin compounds as biocidal agents make them worthy of study in agriculture. The advantage of organotin compounds are the high fungicidal activity and the toxicity to insect pests (Lewis and Hedges, 1959). In the early 1950s, Vander Kerk and Lujten, systematically discovered the high fungicidal activity of tributyl- and triphnyl-tin compounds (Vander Kerk and Luijten, 1954). However, later in the early 1960s, the first organotin compound to reach commercialization in agriculture were triphenyltin acetate (Brestan, Hoechst A.G) and triphenyltin hydroxide (Duter, Phlips Duphar N.V), both of which were widely used to combat a number of fungal diseases in various crops such as potato blight, leaf spot on sugar beet and celery, rice blast as well as coffee leaf rust. Subsequently several organotin based compounds were commercially used as pesticide in Agriculture. For an example, a third triphenyltin compound, the chloride (fentin chloride: Brestanol) was also commercially used in agriculture by Hoechst. Similarly, Dow, USA developed the tricyclohexyltin hydroxide (cyhexatin: Plictran) which was highly effective in the control of phytophagous mites. Subsequently, two further organotin miticides were introduced e.g. bis(trineophy1tin) oxide (fenbutatin oxide: Vendex or Torque) by Shell, USA and tricyclohexyltin- 1,2,4-triazole (azocyclotin: Peropal) by Bayer, USA. The efficiency of fungicidal property was also influenced by the nature of the organic group present in organotin compounds. For an example, the fungicidal activity of a group of Ph3SnX compounds was highest when X= NCO or NCS. Apart from the use as fungicide, organotin compounds have several other pesticidal properties. The trimethyl- and triethyl-tin derivatives had high toxicity to insects and mammals, the tripropyltins to gram-negative bacteria, and the tributyltins to the gram positive bacteria and fungi (Sijpesteijn et al, 1969). The tricyclohexyl- and trineophyl- tin compounds are effective acaricides. The nonpermanent nature of the toxicity of the organotin compounds is of great potential interest for two reasons. Firstly, these compounds ultimately decompose under the action of light and air into harmless inorganic tin and there is therefore no danger of the residual contamination of soil, water etc so that crops either cannot grow or, if they do, contain undesirable amounts of toxic substances. As a consequence, elemental tin disappears from living matter. Secondly, it is toxic to fungi and other pests when applied but later decompose into inorganic tin within a few days and leave only harmless residues on the crops when harvested. On the debit side, few organotin compounds such as crude trialkyltin, are found to be the only compound of this group which are toxic to both fungi and plants. Therefore, the challenge is to develop new organotin compounds which will be selectively toxic to the pests and not to the plants. Although, it was demonstrated that fungicidal and phytotoxicity did not always run parallel (Sarkar et al, 2010, 2011). It is noteworthy to say that the aim of a scientist should be to reduce the phytotoxic nature of organotin compound to make them suitable for agricultural use by proper formulation. Perhaps more promising still is the possibility of preparing functionally substituted organotin compounds.
Sarkar B (2012) Synthesis of new organotin (IV) derivatives of thio-semicarbazides and S, N, O containing related legends, characterization and studies on the biocidals properties of the new compounds with special reference to the agricultural applications. Ph.D. thesis. North Bengal University, West Bengal.
Lewis WR and Hedges ES (1959) Applications of Organotin Compounds. Metal Organic Compounds, Advances in chemistry, ACS, Washington, DC. Chapter 17, 23: 190–203,
Vander Kerk GJM, Luijten JGA (1954) Investigations on organo-tin compounds. III the biocidal properties of organo-tin compounds J. Appl. Chem. 4: 314-319.
Sijpesteijn AK, Luijten JGA, Vander Kerk GJM. (1969) in: ‘ Fungicides, An Advanced Treatise’, Ed. Torgeson DC, Academic Press, New York, Vol. 2 p.331.
Sarkar B, Choudhury AK, Roy A, Biesemans M, Willem R, Ng SW and Tiekink ERT (2010). Synthesis, characterization, crystal structure analysis, and anti-fungal and phytotoxicity activities of diorganotin compounds derived from dihalo-substituted [(2-hydroxyphenyl) methylideneamino] thiourea. Applied Organometallic Chemistry. 24:842-852.
Sarkar B, Choudhury B, Sen Sarma M , Kamruddin SK, Choudhury AK and Roy A. (2011). Potentiality of organotin (IV) compounds in the control of foliar blight disease of wheat (Triticum aestivum) caused by Bipolaris sorokiniana. Archives of Phytopathology and Plant Protection 44: 1754-1769.
About Author / Additional Info:
I am working as a Research Associate in the Division of Agricultural Chemicals, ICAR-Indian Agricultural Research Institute, New-Delhi-110012