Ch_322a_3.018

Ch_322a_3.018 - Acids and Bases in Nonaqueous Solvents Most...

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Acids and Bases in Nonaqueous Solvents Most organic reactions are not run in water because of serious side reactions with water. Because of the "leveling effect" of water, very strong bases react immediately . Consider the following reaction: HC CH + Na NH 2 : : ethyne sodium amide HC C : Na + NH 3 : sodium ethynide ammonia + + - - pK a = 25 pK a = 38 This reaction cannot be run in water because of the immediate reaction of amide anion with water: H-O H + NH 2 : - fast pK a = 15.7 HO - + NH 3 : pK a = 38 (stronger acid) (weaker acid) (stronger base) (weaker base)
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Nonaqueous Solvents Reactions involving strong bases such as sodium amide are run in nonaqueous solvents such as ethers, hydrocarbons, or liquid ammonia (NH 3 , BP -33 o C). RC CH + Na NH 2 : : sodium amide RC C : Na + NH 3 : + + - - terminal alkyne liquid NH 3 -33 o C pK a = 25 pK a = 38 The solvent for a reaction must be compatible with the acid and base strengths of the reactants and products.
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Organometallic Reagents Most organometallic reagents
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Ch_322a_3.018 - Acids and Bases in Nonaqueous Solvents Most...

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