The archetypal solvolysis reaction is the reaction with water, i.e., hydrolysis, Equation 5. However, solvolysis is a general reaction, involving bond breaking by the solvent. Thus, the reaction with ammonia is ammonolysis, Equation 6, the reaction with acetic acid is acetolysis, Equation 7, and the reaction with an alcohol is alcoholysis, Equation 8 where Et = C₂H₅. In each case the same general reaction takes place yielding the cation associated with the solvent.

(5)

(6)

(7)

(8)

Where more than one reaction could occur the reaction involving the solvent can often compete with the desired reaction.

If it is desired to synthesis the Lewis acid-base complex between diethylether (Et₂O) and boron trifluoride (BF₃) it is important to choose a solvent that will not compete with the complex formation. For example, pyridine is a poor choice because the nitrogen donor is a stronger Lewis base than the diethylether, Equation 9, and thus no reaction would occur between diethylether and boron trifluoride. In contrast, since acetonitrile (MeCN) is a poor Lewis base, then the reaction will occur.

(9)

If the synthesis of GeCl₆^2- from germanium tetrachloride (GeCl₄) and a source of chloride anion, then water would be a poor choice of solvent since hydrolysis of GeCl₄ would result. Liquid hydrogen chloride would be equally poor solvent since strong Cl^-...H-Cl hydrogen bonding would stabilize the chloride anion and preclude reaction. In contrast, nitromethane (CH₃NO₂) would be a polar enough solvent to solvate the GeCl₄, but it will be displaced by the chloride anion, which would be only weakly solvated.

The attempted formation of nitronium perchlorate from nitric acid and perchloric acid, Equation 11, in water will result in the decomposition of the NO₂⁺ cation, Equation 12. However, if the reaction is carried out in a stronger acid, i.e., sulfuric acid, the NO₂⁺ cation is stable, and the resulting salt can be recystallized, Equation 11.

(11)

(12)

In a similar manner, the weak basic character of water means the equilibrium reaction, Equation 13, has a very small equilibrium constant, K. However, if the reaction is carried out in a strongly basic solvent such as ammonia the uride anion is stabilized, Equation 14, and can be precipitated by cation exchange.

(13)

(14)

The following observations may be explained by a consideration of the solvation ability of the solvent.

(15)

(16)

Since silver nitrate and barium nitrate are soluble in both solvents, the differences must be due to differences in the solubility of the chlorides in each solvent. A consideration of the relative stability of solid silver chloride versus the solvated species (Figure 2) shows that the enthalpy of solvation in water is less than the lattice energy. Thus, if silver chloride were present as Ag⁺ and Cl^- in water it would spontaneously precipitate. In contrast, the enthalpy of solvation in ammonia is greater than the lattice energy, thus solid AgCl will dissolve readily in liquid ammonia. The reason for the extra stabilization from the specific solvation of the silver cation by the ammonia, i.e., the formation of the covalent complex [Ag(NH₃)₂]⁺.

Figure 2: Enthalpy of solvation of silver chloride in water and ammonia in comparison to the lattice energy.

As may be seen from Figure 3, the opposite effect occurs for barium chloride. Here the enthalpy of solvation in ammonia is less than the lattice energy. Thus, if barium chloride were present as Ba²⁺ and Cl^- in ammonia it would spontaneously precipitate. In contrast, the enthalpy of solvation in water is greater than the lattice energy, thus solid BaCl₂ will dissolve readily in water. The stabilization of Ba²⁺(aq) occurs because water will have a larger sphere of non-specific solvation as a consequence of having two lone pairs, allowing interaction with the Ba²⁺ as well as other water molecules (Figure 4).

Figure 3: Enthalpy of solvation of barium chloride in water and ammonia in comparison to the lattice energy.

Figure 4: Schematic representation of the extended water solvation (aquation) sphere about Ba²⁺ cation.