Hydrates of carbonyl compounds

Buschmann, H.-J., H.-H. Fuldner, and W. Knoche, The Reversible Hydration of Carbonyl Compounds in Aqueous Solution. Part I. The Keto/Gem-Diol Equilibrium, Ber. Bunsenges. Phys. Chem., 85, 41- 44 (1980). 

The hydration of carbonyl compounds, along with hemiketal and ketal or hemicacetal and acetal formation, were studied in K. B. Wiberg, K. M. Morgan and H. Maltz, J. Am. Chem. Soc., 116, 11067 (1994). 

Fig. 12 Mechanisms for base-catalyzed, uncatalyzed, and acid-catalyzed hydration of carbonyl compounds.

Table 8 AG1 for hydration of carbonyl compounds by acid-catalyzed, base-catalyzed, and uncatalyzed mechanisms ...

As already mentioned, S-hydroxyketones may be present in the open-chain form or as an isomeric cyclic hemiketal, depending on their substitution pattern. For example, the polyhydroxylated S-hydroxyketone, which D-fructose can be considered to be, is present exclusively in the form of hemiketals (Figure 7.13). Responsible for this equilibrium position is the fact that the carbonyl group involved contains an electron-withdrawing group in both a positions (cf. our discussion of the substituent effects on the equilibrium position of the hydration of carbonyl compounds Section 7.2.1). 

Another interesting possibility for the second step involves the reversal of a carbonyl addition. Examples are the dehydration of a gem-dihydroxy compound (hydrate of carbonyl compound)... 

Hemihydrate A species formed by the condensation of two hydrates of carbonyl compounds to give a compound of general formula RCH(0H)-0-CHR(0H). 

Table 7.4. Equilibrium Constants for Hydration of Carbonyl Compounds...

---