Synthesis, Properties and Dimerization Study of Isocyanic Acid

In an 1830 publication J. Liebig and F. Wöhler [1] first reported on the preparation of isocyanic acid, which later was improved by A. Baeyer [2]. The preparation and properties of HNCO and some of its derivatives have been described in the literature [3, 4]. The polymerization of HNCO leads to a mixture of cyanuric acid (trimer of HNCO) and cyamelide [3, 5]. Cyanuric acid is a commercially available substance [3, 6]. However, there has been some doubt regarding the thermal stability of HNCO and possible formation of dimers or other oligomers with the formula (HNCO)n [7]. Isocyanic acid forms very strong hydrogen bonds, therefore the formation of dimers is possible. These dimers should have bands in the same region as the ÿ1 fundamental of monomeric HNCO [8]. Owing to a formal analogy between isomeric cyanic acid: