Aprotische

Aprotic (aprotische in German) refers to solvents or reagents that do not donate hydrogen atoms in typical acid–base interactions, i.e., they lack O–H and N–H bonds. This contrasts with protic solvents, such as water or alcohols, which can donate protons and form strong hydrogen bonds. Aprotic solvents can be broadly categorized as polar aprotic and nonpolar aprotic, depending on their ability to stabilize ions.

Polar aprotic solvents have high dielectric constants and dissolve salts well, yet they do not donate hydrogen bonds. Common examples include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), acetonitrile, and acetone. Thf and diethyl ether are less polar but still categorized as aprotic. Nonpolar aprotic solvents, such as toluene, benzene, and hexane, lack strong ion-dissolving power but are useful in nonpolar reaction media or where strong nucleophiles are employed.

Applications and effects: In organic synthesis, polar aprotic solvents are favored for SN2 reactions because they solvate cations effectively while leaving the anions relatively free, increasing nucleophilicity. They are also used to stabilize organometallic reagents (e.g., Grignard reagents) under dry conditions. Solvent choice can influence reaction rates, selectivity, and reagent stability, with aprotic media often enabling higher reactivity of nucleophiles or reactive organometallic species.

Safety and handling: Many aprotic solvents are flammable or toxic and require proper ventilation and handling. Some, such as DMF and DMSO, have particular health considerations with prolonged exposure, so appropriate safety measures are recommended.