Alkenylsodium

Using Alfin catalysts, butadiene polymers were already obtained in the 1940s. The Alfin catalytic system consists of three components (formed in statu nascendi from alkyl chloride, metallic sodium, alcohol and olefin) sodium salt of secondary alcohol (e.g. sodium isopropoxide), alkenylsodium (e.g. allyl-sodium) and finely dispersed sodium chloride (the name Alfin originates from a/cohol + olefin) [2,3], Since the molecular weight of polybutadiene obtained with Alfin catalysts is very high (it can reach a value of a few millions), 1,4-dihydronaphthalene is often added to the polymerisation system for the regulation of molecular weight [1],... 

The rate-determining step in the Na/NH3 reduction of alkynes is the protonation of the radical anion A. The next step, the reaction of the alkenyl radical C to the alkenyl-sodium intermediate B, determines the stereochemistry. The formation of B occurs such that the substituents of the C=C double bond are in trims positions. This trans-selectivity can be explained by product-development control in the formation of B or perhaps also by the preferred geometry of radical C provided it is nonlinear at the radical carbon. The alkenylsodium compound B is protonated with retention of configuration, since alkenylsodium compounds are configurationally stable (cf. Section 1.1.1). The Na/NH3 reduction of alkynes therefore represents a synthesis of fnms-alkencs. 

All of the above features show the specific character of the components of the Alfin reagent or catalyst. The method of preparing the reagent may be varied, but all three components must be present. These are as a rule an alkenylsodium compound, a secondary alkoxide, and a sodium halide. Of the first two salts the most effective have the shortest unbranched carbon chain. 

In the field of alkali metal organic derivatives, the study of allyl compounds is a comparatively recent development. Alkenylsodium and potassium deri-... 

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