- Protic solvent
In
chemistry a protic solvent is asolvent that has ahydrogen atom bound to anoxygen as in ahydroxyl group or anitrogen as in anamine group. More generally, any molecular solvent which contains dissociable H+, such ashydrogen 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
hydrogen bonding
* solvents have anacidic hydrogen (although they may be very weak acids)
* solvents are able to stabilizeion s
**cations by unsharedfree electron pair s
**anions by hydrogen bondingExamples are water,
methanol ,ethanol ,formic acid ,hydrogen fluoride andammonia .Polar aprotic solvents are solvents that share ion dissolving power with protic solvents but lack an acidic hydrogen. These solvents generally have high
dielectric constant s and high polarity.Examples are
dimethyl sulfoxide ,dimethylformamide ,dioxane andhexamethylphosphorotriamide ,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 reagent s orn-butyl lithium . If a protic solvent were to be used, the reagent would be consumed by a side reaction with the solvent.References
*Loudon, G. Mark. Organic Chemistry 4th ed. New York: Oxford University Press. 2002. pg 317.
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