Hexamethylphosphoramide solvent properties

The reaction involves the transfer of an electron from the alkali metal to naphthalene. The radical nature of the anion-radical has been established from electron spin resonance spectroscopy and the carbanion nature by their reaction with carbon dioxide to form the carboxylic acid derivative. The equilibrium in Eq. 5-65 depends on the electron affinity of the hydrocarbon and the donor properties of the solvent. Biphenyl is less useful than naphthalene since its equilibrium is far less toward the anion-radical than for naphthalene. Anthracene is also less useful even though it easily forms the anion-radical. The anthracene anion-radical is too stable to initiate polymerization. Polar solvents are needed to stabilize the anion-radical, primarily via solvation of the cation. Sodium naphthalene is formed quantitatively in tetrahy-drofuran (THF), but dilution with hydrocarbons results in precipitation of sodium and regeneration of naphthalene. For the less electropositive alkaline-earth metals, an even more polar solent than THF [e.g., hexamethylphosphoramide (HMPA)] is needed. 

Non-aqueous solvents such as dimethylsulfone do nof react with many reducing-(Hj) or oxidizing (Oj, Clj) gases. They offer a wide range of redox potentials (e.g., the polarization window of hexamethylphosphoramide is 5.5 V). Herman and Rairden (1976) reviewed the electrochemistry of lanthanides in non-aqueous solvents. Martinot (1978) reviewed the electrochemical properties of actinides in non-aqueous solvents and has reported the reduction behavior of in non-aqueous solvents (Martinot et al. 1990). 

Critical reviews on ylides, enamines, and nitrenes have been published. Brown has reported on the reactivity and selectivity of diborane and disiamylborane with a range of functional groups. The properties of hexamethylphosphoramide as a solvent and a reagent have been catalogued ... 

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