Allantoin: synthesis and chemical properties

The availability and multifunctionality of allantoin makes it extremely attractive to unlock the synthetic potential on the basis thereof, especially for the needs of the pharmaceutical industry. Numerous publications on the allantoin chemistry are scarce, nonsystematic in nature and do not allow a deep understanding of the methods for its preparation and its chemical properties. In order to close this gap, the present review integrates the systematic data on the methods for the allantoin synthesis and the study of its chemical properties as well as the areas of allantoin practical application. In the present work, the methods most widely used in preparative practice to produce allantoin from the carbonyl compounds and urea are considered, and the ways of transformation of a number of nitrogen-containing heterocycles under the influence of various reagents leading to the target product are presented. The main chemical properties of allantoin are shown in hydrolysis reactions, complexation with organic and inorganic substrates, interactions with nucleophilic reagents, in chemoluminescence processes. In some cases, when the unconventional methods for the allantoin synthesis are given and allantoin transformations are considered, the mechanisms of the formation of final compounds are shown. A systematic material on the preparation methods and the chemical properties of allantoin can serve as a reliable navigator for those specialists who aim at manufacturing of allantoin-based practically important substances. Based on the integrated data it is pointed out that allantoin can be successfully used as a basic azaheterocycle to manufacture a wide range of new compounds, including bioactive ones.