Acetone and 2-Butanone as Solvents

Both acetone and 2-butanone (known in industry as methyl ethyl ketone (MEK) are excellent solvents for a variety of organic compounds. These polar solvents dissolve polar solutes because like dissolves like. Acetone is especially effective in dissolving protic solutes such as alcohols and carboxylic acids because the carbonyl group acts as a hydrogen bond acceptor for these compounds. 

The lone pair electrons of the carbonyl group act as hydrogen bond acceptors. 

Acetone is an aptotic solvent (Section 10.3) because it does not have hydrogen atoms that can form hydrogen bonds to nucleophiles. The electron pairs of the carbonyl oxygen atom can solvate cations, but not anions. Consequently, anions have greater nucleophihcity in acetone than in protic solvents such as ethanol. 

The boiling points of 3-hydroxy-2-pentanone and 5-hydroxy-2-pentanone are 147 and 210 °C, respectively. Suggest a reason for this difference. 

As a consequence, the extent of intermolecular hydrogen bonding is decreased. Decreased intermolecular hydrogen bonding allows molecules to escape more readily and lowers the boiling point. The probability of an intramolecular hydrogen bond in 5-hydroxy-2-pentanone is far less than in 3-hydrox-yl-2-pentanone because a seven-membered ring would be required. 

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