Organic compounds are more soluble in water as ions

Organic compounds are more soluble in water as ions 

Most organic compounds are insoluble in water. But sometimes it s necessary to make them dissolve, perhaps by converting them to anions or cations. Water can solvate both cations and anions, unlike some of the solvents you will meet later. A good way of dissolving an organic acid is to put it in basic solution the base deprotonates the acid to give an anion. A simple example is aspirin whilst the acid itself is not very soluble in water, the sodium salt is much more soluble. The sodium salt forms with the weak base, sodium hydrogencarbonate. 

The sodium or calcium salt of normal aspirin is sold as soluble aspirin. But when the pH of a solution of aspirin s sodium salt is lowered, the amount of the normal acidic form present increases and the solubility decreases. In the acidic environment of the stomach (around pH 1-2), soluble aspirin will be converted back to the normal acidic form and precipitate out of solution. 

Water is special for many reasons, and it falls into a class of solvents we call polar protic solvents. We will discuss other solvents in this class, as well as polar aprotic solvents (such as acetone and DMF) and nonpolar solvents (such as toluene and hexane) in Chapter 12. 

In the same way, organic bases such as amines can be dissolved by lowering the pH. Codeine (7,8-didehydro-4,S-epoxy-3-methoxy-17-methyimorphinan-6-ol) is a commonly used painkiller. Codeine itself is not very soiubie in water but it does contain a basic nitrogen atom that can be protonated to give a more soiubie sait. It is usuaiiy encountered as a phosphate salt. The structure is complex, but that doesn t matter. 

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