Protic solvent
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2008-06-16T02:49:03Z
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In [[chemistry]] a '''protic solvent''' is a [[solvent]] that has a [[hydrogen]] atom bound to an [[oxygen]] as in a [[hydroxyl]] group or a [[nitrogen]] as in an [[amine]] group. More generally, any molecular solvent which contains dissociable H<sup>+</sup>, such as [[hydrogen fluoride]], is called a '''protic solvent'''. The molecules of such solvents can donate an H<sup>+</sup> (proton). Conversely, '''aprotic solvents''' cannot donate hydrogen.
Common characteristics of protic solvents:
* solvents display [[hydrogen bonding]]
* solvents have an [[acidic]] hydrogen (although they may be very weak acids)
* solvents are able to stabilize [[ion]]s
** [[cations]] by unshared [[free electron pair]]s
** [[anions]] by hydrogen bonding
Examples are [[water (molecule)|water]], [[methanol]], [[ethanol]], [[formic acid]], [[hydrogen fluoride]] and [[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 constant]]s and high [[Chemical polarity|polarity]].
Examples are [[dimethyl sulfoxide]], [[dimethylformamide]], [[dioxane]] and [[hexamethylphosphorotriamide]].
Polar protic solvents are favorable for S<sub>N</sub>1 reactions, while polar aprotic solvents are favorable for S<sub>N</sub>2 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 or [[n-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.
[[Category:Solvents]]
[[pt:Solvente prótico]]
[[sv:Protiskt lösningsmedel]]