Kocheshkov rearrangement

The Kocheshkov rearrangement (also: Kozeschkow rearrangement, uncommon Kotscheschkow rearrangement ) is a disproportionation reaction in organotin compounds named after the Russian chemist Xenofont Alexandrowitsch Kotscheschkow (1894–1978) .

Overview

Kotscheschkow found that the reaction of tin (VI) halides, such as tin (IV) chloride or tin (IV) bromide with organotin compounds of the SnR ₄ type (with R = alkyl - or aryl -) leads to a Comproportioning comes, the product of which is essentially dependent on the stoichiometric ratio of the two reactants.

For example, tetraalkyl or tetraaryl tin compounds with tin tetrahalides will relatively readily exchange one or two organic groups:

${\displaystyle \mathrm {3\ SnR_{4}\ +\ SnX_{4}\ \rightarrow \ 4\ SnXR_{3}} }$

${\displaystyle \mathrm {SnR_{4}\ +\ SnX_{4}\ \rightarrow \ 2\ SnX_{2}R_{2}} }$

${\displaystyle \mathrm {R={-}CH_{3},\ {-}C_{2}H_{5},\ {-}n{-}C_{3}H_{7},\ {-}Phenyl;\ \ X=Cl,Br} }$

The cleavage of a further organic moiety is only organotin compounds having unsaturated radicals such as tetraphenyltin or tetravinyltin boabachtet. In the case of alkyl tin compounds, however, the third organic residue is not transferred.

${\displaystyle \mathrm {SnR_{4}\ +\ 3\ SnX_{4}\ \rightarrow \ 4\ SnX_{3}R} }$

${\displaystyle \mathrm {R={-}Phenyl,{-}CH=CH_{2};\ \ X=Cl,Br} }$

Likewise, when alkyl or aryl tin halides are reacted with organotin compounds, comproportionation occurs:

${\displaystyle \mathrm {2\ SnR_{4}\ +\ SnX_{3}R\ \rightarrow \ 3\ SnXR_{3}} }$

${\displaystyle \mathrm {SnR_{4}\ +\ SnX_{2}R_{2}\ \rightarrow \ 2\ SnXR_{3}} }$

${\displaystyle \mathrm {SnR_{4}\ +2\ SnX_{3}R\ \rightarrow \ 3\ SnX_{2}R_{2}} }$

${\displaystyle \mathrm {R={-}CH_{3},\ {-}C_{2}H_{5},\ {-}n{-}C_{3}H_{7},\ {-}Phenyl;\ \ X=Cl,Br} }$

mechanism

Kocheschkow assumed that the reaction always proceeds in the following sub-steps:

${\displaystyle \mathrm {SnAr_{4}\ +\ SnCl_{4}\ \rightarrow \ 4\ SnCl_{2}Ar_{2}\ \ \ Ar=C_{6}H_{5}} }$

${\displaystyle \mathrm {SnCl_{2}Ar_{2}\ +\ SnX_{4}\ \rightarrow \ 2\ SnCl_{3}Ar} }$

${\displaystyle \mathrm {SnCl_{2}Ar_{2}\ +\ SnR_{4}\ \rightarrow \ 2\ SnClAr_{3}} }$

Wilhelm Neumann was able to show through studies that the formation of the compounds of the SnX ₂ R _{2 type} from tetraalkyltin and tin tetrahalide compounds takes place in a two-step process. First, a ligand is transferred immediately and the mixed tin alkyl halides are formed:

${\displaystyle \mathrm {SnEt_{4}\ +\ SnCl_{4}\ {\xrightarrow {0-20\,{}^{\circ }C}}\ SnClEt_{3}+\ SnCl_{3}Et\ \ \ \ Et=C_{2}H_{5}} }$

The second step of comproportioning then takes place at higher temperatures over several hours:

${\displaystyle \mathrm {SnClEt_{3}+\ SnCl_{3}Et\ {\xrightarrow[{2-3h}]{0-20\,{}^{\circ }C}}\ 2\ SnCl_{2}Et_{2}} }$

If the reaction is carried out with an excess of tin tetrachloride, further monoalkyl trihalide is formed with the trialkyl monohalide

${\displaystyle \mathrm {SnClEt_{3}+\ SnCl_{4}\ {\xrightarrow {\ }}SnCl_{2}Et_{2}+\ SnCl_{3}Et} }$

Thus - contrary to the observations of Kotscheschkow - besides a third dialkyl dihalide also two thirds monoalkyl trihalide are formed:

${\displaystyle \mathrm {SnEt_{4}+\ 2\ SnCl_{4}\ {\xrightarrow {\ }}SnCl_{2}Et_{2}+\ 2\ SnCl_{3}Et} }$

Individual evidence

1. ↑ ^{a b} KA Kozeschkow: Investigations on organometallic compounds, Part I: A new class of aryl tin compounds: Phenyl-trihalogenostannanes . In: Reports of the German Chemical Society . tape 62 , no. 4 , April 3, 1929, pp. 996-999 , doi : 10.1002 / cber.19290620438 .
2. ↑ ^{a b c} KA Kozeschkow: Investigations on organometallic compounds, Part II: The reaction between organotin compounds of the fat series and tetrahalides of tin . In: Reports of the German Chemical Society . tape 66 , no. 11 , November 8, 1933, pp. 1661-1665 , doi : 10.1002 / cber.19330661109 .
3. ↑ KA Kozeschkow, MM Nadj: . Studies on organometallic compounds IV msgs .: About aromatic Stannonsäuren and some of their reactions . In: Reports of the German Chemical Society . tape 67 , no. 5 , May 9, 1934, pp. 717-721 , doi : 10.1002 / cber.19340670502 .
4. ↑ ^{a b} KA Kozeschkow, MM Nadj, AP Alexandrow: Investigations on organometallic compounds, VII. Communication: Simplified method for the preparation of triaryl tin halides . In: Reports of the German Chemical Society . tape 67 , no. 8 , August 8, 1934, p. 1348-1349 , doi : 10.1002 / cber.19340670810 .
5. ↑ Dietmar Seyferth, FGA Stone: Vinyl Derivatives of the Metals. I. Synthesis of Vinyltin Compounds . In: Journal of the American Chemical Society . tape 79 , no. 3 , February 1957, p. 515-517 , doi : 10.1021 / ja01560a003 (English).
6. ↑ WP Neumann after work with G. Burkhardt E. Heymann F. Kleiner K. König H. Niermann J. Pedain R. Schick R. Sommer H. Weller: News from the chemistry of organotin compounds . In: Angewandte Chemie . tape 75 , no. 5 , March 7, 1963, pp. 225-235 , doi : 10.1002 / anie.19630750502 .
7. ^ Wilhelm P. Neumann, Gottfried Burkhardt: Organozinnverbindungen, IV. The comproportionation of tin alkyls with tin halides and the preparation of alkyl tin trihalides . In: Justus Liebig's Annals of Chemistry . tape 663 , no. 1 , April 26, 1963, p. 11-21 , doi : 10.1002 / jlac.19636630105 .