Investigation of the allantoin synthesis regularities

Allantoin is heterocyclic compound which is used in the modern cosmetic compositions and pharmaceutical products. The basic method of its production is the condensation of gly-oxylic acid and its derivatives with urea in the presence of acidic catalysts. In this paper, the method of allantoin synthesis by heterocyclization of glyoxylic acid and urea in the presence of phosphoric acid was proposed. This method allows obtaining pharmaceutical grade product with a high yield. Using of medium-strength acid as a catalyst reduces the possible negative impact on the environment compared to the strong acids which are used as similar catalysts. The synthesis consists of the following steps: the reaction mixture preparation, reaction mixture exposition, product isolation and purification. The resulting product was identified by IR, NMR spectroscopy and comparison with a commercial sample of allantoin. The influence of synthetic parameters on the product yield was studied. Allantoin yield remains at the same level in the temperature range 50-70 °C and reaches a maximum at T = 65 °C (67%). Further increasing of process temperature leads to the hard reduction of the main product yield. The variation of synthesis time allowed us to determine the necessary exposure time of reaction mixture (24 hours) in order to achieve maximum yield (67%). The influence of the reagents ratio on the allantoin yield was investigated. Using an excess of urea with respect to the glyoxylic acid (1:4) is necessary to increase the yield. Maximum yield is achieved by using a glyoxylic acid:phosphoric acid ratio 1:0.3. Further increasing the reaction catalyst amount mostly doesn't change allantoin yield.

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