- Protic solvent
chemistrya protic solvent is a solventthat has a hydrogenatom bound to an oxygenas in a hydroxylgroup or a nitrogenas in an aminegroup. More generally, any molecular solvent which contains dissociable H+, such as hydrogen fluoride, is called a protic solvent. The molecules of such solvents can donate an H+ (proton). Conversely, aprotic solvents cannot donate hydrogen.
Common characteristics of protic solvents:
* solvents display
* solvents have an
acidichydrogen (although they may be very weak acids)
* solvents are able to stabilize
cationsby unshared free electron pairs
anionsby hydrogen bonding
Examples are water,
methanol, ethanol, formic acid, hydrogen fluorideand ammonia.
Polar aprotic solvents are solvents that share ion dissolving power with protic solvents but lack an acidic hydrogen. These solvents generally have high
dielectric constants and high polarity.
dimethyl sulfoxide, dimethylformamide, dioxaneand hexamethylphosphorotriamide, tetrahydrofuran.
Polar protic solvents are favorable for SN1 reactions, while polar aprotic solvents are favorable for SN2 reactions. Apart from solvent effects, polar aprotic solvents may also be essential for reactions which use strong bases, such as reactions involving
Grignard reagents or n-butyl lithium. If a protic solvent were to be used, the reagent would be consumed by a side reaction with the solvent.
*Loudon, G. Mark. Organic Chemistry 4th ed. New York: Oxford University Press. 2002. pg 317.
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