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Phosphonium saltA phosphonium salt is a salt containing the phosphonium (PH4+) ion such as phosphonium iodide (PH4+I−). More commonly, phosphonium refer to an organic derivative such as tetraphenylphosphonium chloride, (C6H5)4P+ Cl- and tetramethylphosphonium iodide, [P(CH3)4]+I−. Additional recommended knowledgeAlkyltriphenylphosphonium salts are widely used for the preparation of Wittig reagents for the Wittig reaction. Such salts are readily made by the reaction of triphenylphosphine with an alkyl halide:
The reaction works well if the alkyl group is methyl or an unhindered primary alkyl group (as shown), but it is usually poor with secondary alkyl halides. Tertiary alkyl groups cannot form the ylide. The phosphonium salt is a stable compound which can often be purified by recrystallisation from ethanol. To form the Wittig reagent (ylide), the phosphonium salt is suspended in a solvent such as diethyl ether or THF and a strong base such as phenyllithium or n-butyllithium is added. One study [1] demonstrates the use of benzyl alcohols as starting material for the synthesis of phosphonium acetates provided that the arene carries activating groups:
The phosphonium acetate group does not have an impact on the subsequent Wittig reaction. See alsoReferences |
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Phosphonium_salt". A list of authors is available in Wikipedia. |