Friend reaction

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The Freund reaction is a reaction from organic chemistry and was discovered in 1881 by the Galician chemist August Freund (1835-1892). It is used for the synthesis of cyclopropane ( trimethylene ) and its derivatives and is similar to the intramolecular Wurtz synthesis .

Overview reaction

Freund first experimented with 1,3-dibromopropane and sodium, from which he was able to obtain cyclopropane:

Overview reaction

1,3-Dichloro- and 1,3-diiodopropane react in the same way as 1,3-dibromopropane. By analyzing the product, which Freund called trimethylene, and a process of elimination, he was able to establish the correct structure of cyclopropane, so that Freund became known for his cyclopropane synthesis.

modification

Gustavson reaction

In the Gustavson reaction, zinc dust is used in the cyclization reaction instead of sodium .

Hass Cyclopropane Process

In order to further distance the Wurtz synthesis and improve the yields, in 1931 Henry Bohn Hass (1902–1987) modified the reaction by using zinc dust , dilute alcohol and a catalytic amount of sodium iodide .

mechanism

The mechanism is similar to the mechanism of the Wurtz synthesis. This can proceed both free-radical and via anionic intermediates. Based on the reaction between 1,3-dibromopropane 1 and sodium, the not yet fully proven mechanism of the Freund reaction should be explained:

mechanism

In the first step, sodium attacks the C-Br bond with its free electron, so that sodium bromide is split off and a bromopropyl radical 2 remains. With more sodium, a sodium salt 3 is formed , consisting of halogenated carbanion and sodium cation . The negatively charged carbon atom of the anion nucleophilically attacks the carbon on which the bromine atom is located. Meanwhile, the bromine attacks the sodium cation with one of its free electron pair bonds, taking along the electron pair bond to the carbon atom. As a result of this ring closure, cyclopropane 4 is formed .

Individual evidence

  1. ^ A b Zerong Wang: Comprehensive Organic Name Reactions and Reagents . John Wiley & Sons, 2009, ISBN 978-0-471-70450-8 , pp. 1123-1125 .
  2. ↑ HF Ebel, A. Lüttringhaus, Houben-Weyl: Methods of Organic Chemistry . 4th edition. Thieme, Stuttgart 1970, ISBN 3-13-212904-6 , p. 492 .
  3. ↑ a b August Freund: About trimethylene . In: Journal for Practical Chemistry . tape 26 , no. 1 , 1882, p. 367-377 , doi : 10.1002 / prac.18820260125 .
  4. ↑ August Freund: About trimethylene . In: Monthly magazine for chemistry . tape 3 , no. 1 , 1881, p. 625-635 , doi : 10.1007 / BF01516828 .
  5. ^ Zerong Wang: Comprehensive Organic Name Reactions and Reagents . John Wiley & Sons, 2009, ISBN 978-0-471-70450-8 , pp. 3094-3099 .