Organotin Chemistry Information

Organotin compounds or stannanes are chemical compounds based on tin with hydrocarbon substituents. Organotin chemistry is part of the wider field of organometallic chemistry.^[1] The first organotin compound was diethyltin diiodide, discovered by Edward Frankland in 1849. An organotin compound is commercially applied as a hydrochloric acid scavenger (or heat stabilizer) in polyvinyl chloride and as a biocide. Tributyltin oxide has been extensively used as a wood preservative. Tributyltin compounds are used as marine anti-biofouling agents. Concerns over toxicity^[2] of these compounds (some reports describe biological effects to marine life at a concentration of 1 nanogram per liter) have led to a worldwide ban by the International Maritime Organization. n-Butyltin trichloride is used in the production of tin dioxide layers on glass bottles by chemical vapor deposition.

Preparation of organotin compounds

Organotin compounds can be synthesised by reaction of a Grignard reagent with tin halides for example tin tetrachloride. An example is the organic synthesis of tributyl-[(Z)-5-phenyl-2-penten-2-yl]stannane:^[3][4]

The Wurtz-like coupling of alkyl sodium compounds with tin halides yield tetraorganotin compounds. Another method is an exchange reaction of tin halides with organoaluminium compounds (AlR₃). Triorganotin halides can be prepared in the Kocheshkov redistribution reaction.

Reactions of organotin compounds

Important reactions involving organotin compounds are the Stille reaction (coupling reaction with sp2-hybridized organic halides catalyzed by palladium):

and organostannane additions (nucleophilic addition of an allyl-, allenyl-, or propargylstannanes to an aldehydes and imines)

Use and toxicity

• Tetraorganotins are very stable molecules with low toxicity and low biological activity. They are unusable as biocides, but they can be metabolized to toxic triorganotin compounds. They are used as starting materials for catalysts.
• Triorganotins are very toxic. Tri-n-alkyltins are phytotoxic and therefore cannot be used in agriculture. Depending on the organic groups, they can be powerful bactericides and fungicides. Tributyltins are used as industrial biocides, e.g. as antifungal agents in textiles and paper, wood pulp and paper mill systems, breweries, and industrial cooling systems. Tributyltins are also used in marine anti-fouling paint. Triphenyltins are used as active components of antifungal paints and agricultural fungicides. Other triorganotins are used as miticides and acaricides.
• Diorganotins have no antifungal activity, low toxicity, and low antibacterial activity, except for diphenyltins. They are used in polymer manufacturing, as PVC heat stabilizers, catalysts, in the manufacturing of polyurethane and silicone curing. DBT is however immunotoxic, and a recent paper suggests a link to auto-immune related diseases.^[5]
• Monoorganotins have no biocidal activity and their toxicity to mammals is very low. Methyltin, butyltin, octyltin and monoestertins are used as PVC heat stabilizers.
• Many different organotin complexes are being studied in anticancer therapy, observing that their cytotoxicity and selectivity towards cancer cell is higher than that of cisplatin.^[6]

Compounds

Organotin compounds are used commercially in a wide range of applications such as biocides, insecticides, chemical intermediates and as catalysts.

• Organotin compounds

• Tetrabutyltin starting material for the di- and tributyl compounds

• Tributyltin oxide, a colorless to pale yellow liquid used in wood preservation

• Triphenyltin acetate, an off-white crystalline solid, used as an insecticide and a fungicide

• Triphenyltin chloride, a white crystalline solid, used as a biocide and an intermediate in chemical synthesis

• Trimethyltin chloride also a biocide

• Triphenyltin hydroxide, an off-white powder, used as a fungicide and to sterilize insects

• Azocyclotin, a colorless crystalline solid, used as a long-acting acaricide for control of spider mites on plants

• Cyhexatin, a white crystalline solid, used as an acaricide and miticide

• Hexamethylditin used as an intermediate in chemical synthesis

• Tetraethyltin, boiling point 63–65° /12 mm is a catalyst ^[7]

• Tributyltin azide

Other classifications

Polystannanes are polymeric stannanes of the type (SnR₂)_n

Stannoles are the structural analogs of pyrrole. Unsaturated organostannanes also exist: stannenes are compounds of the type RRC=SnRR with a formal double bond (also see stannabenzene) and distannenes have a tin to tin double bond as in RRSn=SnRR. A stannyne contains a carbon to tin triple bond and a distannyne a triple bond between two tin atoms (RSnSnR) . Tin radicals are called stannyl radicals and tin carbenes stannylenes (RSn:) ^[8]

Hypercoordinated stannanes

Unlike their carbon analogues, tin compounds can also be coordinated to five and even six atoms instead of the regular four. These hypercoordinated compounds usually have electronegative substituents for stabilization. Lithium pentaorganostannates were first detected and characterized in solution in 1986,^[9] while in the subsequent year a six-coordinated tetraorganotin compound was reported.^[10] In 2007 a crystal structure of room-temperature stable (in argon) all-carbon pentaorganostannane was reported as the lithium salt with this structure:^[11]

In this distorted trigonal bipyramidal structure the carbon to tin bond lengths (2.26Å apical, 2.17Å equatorial) are larger than regular C-Sn bonds (2.14Å) reflecting its hypervalent nature.

See also

References

1. ^ Sander H.L. Thoonen, Berth-Jan Deelman, Gerard van Koten (2004). "Synthetic aspects of tetraorganotins and organotin(IV) halides". Journal of Organometallic Chemistry (689): 2145–2157. http://dspace-test.library.uu.nl/keur/chem/2005-0426-063436/13093.pdf.
2. ^ Gajda, M.; Jancso, A. (2010). "Organotins, formation, use, speciation and toxicology". Metal ions in life sciences (Cambridge: RSC publishing) 7, Organometallics in environment and toxicology. ISBN 9781847551771.
3. ^ Martin J. Stoermer, John T. Pinhey (1998). "Tributyl-[(Z)-5-phenyl-2-penten-2-yl]stannane". Molecules 3: M67. http://www.mdpi.org/molbank/m0067.htm.
4. ^ A Grignard reagent is prepared from magnesium turnings and (Z)-2-bromo-5-phenyl-2-pentene in dry tetrahydrofuran and titrated with tributyltin chloride until the solution decolourises. The resulting solution is stirred at room temperature for 1 hour and the solvent is removed in a rotavapor. Diethyl ether is added and the ether extract is washed with brine and filtered and the ether evaporates in a rotavapor. The crude product is kugelrohr distilled to yield tributyl-[(Z)-5-phenyl-2-penten-2-yl]stannane as a colourless oil.
5. ^ C Gumy et al. (2008). "Dibutyltin Disrupts Glucocorticoid Receptor Function and Impairs Glucocorticoid-Induced Suppression of Cytokine Production". PLoS ONE 3: e3545. doi:10.1371/journal.pone.0003545.
6. ^ S. Gómez-Ruiz et al. (2008). "Study of the cytotoxic activity of di and triphenyltin(IV) carboxylate complexes". Journal of Inorganic Biochemistry 102 (12): 2087. doi:10.1016/j.jinorgbio.2008.07.009. PMID 18760840.
7. ^ Organic Syntheses, Coll. Vol. 4, p.881 (1963); Vol. 36, p.86 (1956). Link
8. ^ Organotin chemistry 2004 Alwyn George Davies ISBN-10: 3-527-31023-1
9. ^ Reich, Hans J.; Phillips, Nancy H. (1986). "Lithium-Metalloid Exchange Reactions. Observation of Lithium Pentaalkyl/aryl Tin Ate Complexes". J. Am. Chem. Soc. 108: 2102. doi:10.1021/ja00268a067.
10. ^ V. G. Kumar Das, Lo Kong Mun, Chen Wei, and Thomas C. W. Mak (1987). "Synthesis, Spectroscopic Study, and X-ray Crystal Structure of Bis[3-(2-pyridyl)-2-thienyl-C,N]diphenyltin(IV): The First Example of a Six-Coordinate Tetraorganotin Compound". Organometallics 6: 10. doi:10.1021/om00144a003.
11. ^ Masaichi Saito, Sanae Imaizumi, Tomoyuki Tajima, Kazuya Ishimura, and Shigeru Nagase (2007). "Synthesis and Structure of Pentaorganostannate Having Five Carbon Substituents". J. Am. Chem. Soc. 129: 10974–10975. doi:10.1021/ja072478.

External links

• National Pollutant Inventory Fact Sheet for organotins
• Industry information site
• Organotin chemistry in synthesis
• EU bans certain organotin compounds in consumer products

Categories: Organotin compounds | Persistent organic pollutants

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