Organotin compounds

Organotin compounds (organotin compounds, OZV, organotin) is the collective name for organometallic compounds with one or more tin-carbon bonds, which can be described with the general formula R _n SnX _m . Here “R” is a hydrocarbon group and X is any other group such as a halogen , hydrogen or a hydroxyl group (OH).

history

The first organotin compound was produced in 1848 by Edward Frankland , who, by reacting ethyl iodide with elemental tin, obtained a clear, colorless liquid, diethyltin diiodide :

${\displaystyle \mathrm {Sn+\ 2\ IC_{2}H_{5}\ {\xrightarrow[{}]{}}\ \ I_{2}Sn(C_{2}H_{5})_{2}\ } }$

But it was not until almost 100 years later that the industrial use of organotin compounds began when it was discovered that diorganotin compounds in particular can be used to stabilize polyvinyl chloride (PVC) against thermal and photochemical degradation. In Germany, triphenyltin acetate was first used as a pesticide in 1950 .

Manufacturing

Organotin compounds can be produced in various ways. Tin (IV) halides, such as tin tetrachloride , react when reacting with organometallic compounds such as Grignard compounds to form the corresponding organotin:

${\displaystyle \mathrm {SnCl_{4}+\ 4\ MR\ {\xrightarrow[{}]{}}\ \ SnR_{4}\ +4MCl\ \ M=MgCl,Li,Al\ \ R=} {\text{ organischer Rest}}}$

Another possibility is the Wurtz reaction , in which tin tetrachloride reacts with alkyl halides in the presence of elemental sodium :

${\displaystyle \mathrm {SnCl_{4}+\ 4\ ClR\ {\xrightarrow[{-8NaCl}]{+8Na}}\ \ SnR_{4}\ \ M=MgCl,Li,Al\ \ R=} {\text{ organischer Rest}}}$

Organotin halides are mostly obtained from tetraorganotin compounds by electrophilic substitution:

${\displaystyle \mathrm {SnR_{4}+\ XY\ {\xrightarrow[{}]{}}\ \ R_{3}SnX+\ RY\ R={\text{ organischer Rest}},\ XY=SnCl_{4},HCl,HBr,I_{2},Br_{2},Cl_{2}} }$

Mixtures of organotin compounds can be prepared by further alkylating partially halogenated organotin compounds:

${\displaystyle \mathrm {SnR_{2}Cl_{2}+\ 2\ LiR'\ {\xrightarrow[{}]{}}\ \ SnR_{2}R'_{2}\ +2LiCl\ \ R,R'={\text{ organische Reste}}} }$

Organotin compounds often react with one another by comproportioning :

${\displaystyle \mathrm {Sn(CH_{3})_{4}+\ Cl_{2}SnBu_{2}\ {\xrightarrow[{}]{}}\ \ (H_{3}C)_{3}Sn(Bu)Cl\ \ Bu={\text{Butylgruppe}}} }$

Alkyl tin hydrides can be obtained by reacting organotin halides with reducing agents such as lithium aluminum hydride :

${\displaystyle \mathrm {2\ R_{3}SnCl+\ LiAlH_{4}\ {\xrightarrow[{}]{}}\ \ 2\ R_{3}SnH+\ LiAlH_{2}Cl_{2}\ R=} {\text{ organischer Rest}}}$

These react with alkenes and alkynes via an addition reaction :

${\displaystyle \mathrm {R_{3}SnH+\ H_{2}C=CHR\ {\xrightarrow[{}]{}}\ \ R_{3}Sn-CH_{2}-CHR\ \ R=} {\text{ organischer Rest}}}$

use

Organotin compounds can be used as biocides in wood preservatives , as plastic additives and in catalysts . Of the 40,000 tons of organotin compounds produced annually worldwide at the end of the 1990s, about

• 76% as stabilizers for PVC
• 10% as biocides in underwater paints
• 8% as agricultural fungicides and
• 5% as catalysts in the production of polyurethane foams and silicones

used. Organotin compounds have the advantage that they have a relatively low level of plant toxicity ( phytotoxicity ) and that they quickly transform into harmless compounds in the environment. Due to their ecotoxicity and effects on human health, the use of organotin compounds is largely prohibited in the EU (see section Toxic properties ) .

In 1999 around 75,000 tons of organotin compounds were used worldwide. The following quantities were used in Europe:

metric tons	2002	2007
PVC stabilizers	15000	16000
Catalysts	1300-1600	~ 2000
Other uses
• Glass coating	760-800	760-800
• Biocides in anti-fouling paints	1250	sinking
• synthesis	<150	~ 500
• biocides (other)	<100	sinking
• pesticides	100	unknown
total	~ 19000	~ 21000

Organotin compounds are used in organic synthesis in a whole series of reactions, such as in the production of organolithium compounds or for dehalogenation reactions.

Toxic properties

The toxic properties of organotin compounds vary with the number and type of organic substituents (R), most are now classified as toxic and must therefore be handled with appropriate care. The toxic effect is particularly targeted at the kidneys , the central nervous system , liver , adrenal glands , thymus , spleen , urinary bladder , testes and epididymis .

In simplified terms, organotin compounds for substances used in industry can be summarized as follows:

• Tetra-organotin compounds, R ₄ Sn, are very stable, have practically no biocidal effect and are almost non-toxic. However, many of them decompose or are converted into the toxic triorganotin compounds in an organism by metabolic processes.
• Tri-organotin compounds, R ₃ SnX, represent the most toxic group of organotin compounds. Trialkyltin compounds with a linear organic residue cannot be used as agricultural biocides due to their high level of plant toxicity (phytotoxicity).
  The group of tri-organotin compounds includes tributyltin hydride , which was used as a biocidal component in antifouling paints for ship hulls, as well as tributyltin oxide (TBTO) and tributyltin chloride (TBTC).
• With the exception of diphenyl compounds, diorganotin compounds, R ₂ SnX ₂ , have only a low level of antibacterial and toxic activity.
• Mono-organotin compounds, RSnX ₃ , are not biocidal and have low toxicity towards mammals.

The use of organotin compounds is declining due to their ecotoxicity. For example , tributyltin oxide (TBTO) , which was previously used as an antifouling agent in ship paints, is banned (with restrictions) in many countries due to its high level of ecotoxicity . In the EU, the use of phenyltin compounds in agriculture as fungicides has been banned since 1998 and as algicides and molluscicides in anti-fouling paints since 2003. Due to their effect on humans and animals, trisubstituted organotin compounds ( tributyltin , triphenyltin, etc.) have been banned in consumer products in Germany since June 2010. Disubstituted organotin compounds (e.g. dimethyltin and dibutyltin and dioctyltin compounds, etc.) since January 2012.

Occurrence in the environment

Organotin compounds can be found in the environment around the world, some of which were created through natural processes ( biomethylation ), while the other was released into the environment through production and use. Organotin compounds were u. a. detected in house dust and harbor sediments.

literature

• Dietrich Klingmüller, Burkard Watermann (Hrsg.): TBT - organotin compounds - a scientific inventory. (PDF; 2.1 MB) Federal Environment Agency Berlin, March 2003, ISSN  0722-186X .

Individual evidence

1. ↑ ^{a b c d e} Bernard Jousseaume: Organometallic Synthesis and Chemistry of Tin and Lead Compounds . In: Mikrochimica acta . tape 109 , no. 1-4 , 1992, pp. 5–12 , doi : 10.1007 / BF01243203 (English).
2. ^ Günter G. Graf: Tin, Tin Alloys, and Tin Compounds. In: Ullmann's Encyclopedia of Industrial Chemistry, Fifth Completely Revised Edition . Volume A27. VCH Verlagsgesellschaft mbH, Weinheim 1996, ISBN 3-527-20127-0 , p. 49-81 .
3. ^ Production and use of tin orgainic compounds. In: nabu.de. Retrieved September 26, 2015 . Text document  
4. ↑ Impact Assessment of Potential Restrictions on the Marketing and Use of Certain Organotin Compounds ( Memento of the original from September 27, 2015 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. European Commission report (PDF file)  
5. ↑ Dietmar Seyferth, Michael A. Weiner: The Preparation of Organolithium Compounds by the Transmetalation Reaction. I. vinyl lithium. In: Journal of the American Chemical Society . 83, 1961, p. 3583, doi: 10.1021 / ja01478a010 .
6. ↑ methyl tin compounds . In: DFG (Ed.): The MAK Collection for Occupational Health and Safety . 2014, p.  3-9 , doi : 10.1002 / 3527600418.mb744031metd0056 .
7. ↑ ^{a b c} phenyltin compounds [MAK Value Documentation in German language, 2010] . In: The MAK Collection for Occupational Health and Safety . January 31, 2012, doi : 10.1002 / 3527600418.mb240668verd0048 .
8. ^ Australian Government - Department of the Environment, Water, Heritage and the Arts : Substance Fact Sheet - Organo-tin compounds .
9. ↑ Heinz Rüdel, Jürgen Steinhanses, Josef Müller, Christa Schröter-Kermani: Retrospective Monitoring of Organotin Compounds in Biological Samples from the North and Baltic Seas - Are the Application Restrictions Successful? Environmental sciences and pollutant research 21 (3), pp. 282-291 (2009), ISSN  0934-3504 .
10. ↑ Safety in maritime traffic: ban on organotin compounds on ships ( online ).
11. ↑ DECISION OF THE COMMISSION of 28 May 2009 amending Council Directive 76/769 / EEC with regard to restrictions on the placing on the market and use of organotin compounds in order to adapt its Annex I to technical progress ((2009/425 / EC). Official Journal of the European Union L138, pp. 11–13, June 4, 2009 ( PDF (PDF) ).
12. ↑ Glossary: ​​Entry organic tin compounds . (No longer available online.) In: Oekotest. Archived from the original on September 5, 2014 ; Retrieved September 5, 2014 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  
13. ↑ Glossary: ​​Entry organic tin compounds . (No longer available online.) In: Oekotest. Archived from the original on September 5, 2014 ; Retrieved September 5, 2014 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  
14. ↑ Jörg Thumulla, Wolf Hagenau: Organotin compounds in PVC floors and house dust . In: Environment, Buildings & Health; Proceedings of the 6th AGÖF specialist congress 2001; Springe-Eldagsen 2001, ISBN 3-930576-03-1 ( PDF ).
15. ↑ Romana Brandsch, Karl-Ernst Nowak, Norbert Binder, Bernd Jastorff: Investigations into the sustainability of the remediation of tributyltin-contaminated harbor sediment by land deposits . Environmental sciences and pollutant research 14 (3), pp. 138-144 (2002), ISSN  0934-3504 .