The room temperature chemistries of isocyanates with zeolite NaX

Isocyanates and di-isocyanates are used in the production of various chemicals and materials, such as pesticides and polyurethane. However, since the disastrous accidental release of isocyanate in Bhopal in 1984 this class of toxic compounds has been under scrutiny, with growing interest in means to respond to isocyanate release. The susceptibility of isocyanates to nucleophilic substitution [D.P.N. Satchell, R.S. Satchell, Chem. Soc. Rev. 4 (1975) 231] and the known nucleophilicity of NaX [Yang, et al., Microporous Mesoporous Mater. 92 (2006) 56; Doetschman, et al., Microporous Mesoporous Mater. 92 (2006) 292; Kanyi, et al., Microporous Mesoporous Mater. 108 (2008) 103] led to this study of a spectrum of isocyanates representing cyclic and aromatic isocyanates, di-isocyanates, 1°, 2°, and 3° isocyanates, and alkyl chain isocyanates of various lengths. Additional experiments were done in order to understand the nature of a tightly bound chemical adduct product that forms in the isocyanate reactions with the zeolite.The isocyanate functional group was shown to be susceptible to nucleophilic attack by Faujasite NaX. A carbamate framework adduct, with the anionic nitrogen stabilized by the sodium cation is proposed. The product is very tightly bound to the zeolite. In two, but not all, isocyanates in which there are methyl protons β to the isocyanate moiety, an elimination reaction took place to form the α, β olefin, competing with the nucleophilic addition reaction. The types of chemistry occurring and the tenacity with which the products are retained, suggests that zeolites may have practical applications in hazardous materials cleanup or controlling isocyanate vapor release.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Isocyanates react additively with porous zeolite NaX. ► Isocyanate C to N electron transfer is stabilized by Ozeo- and Na+, respectively. ► Olefin elimination from the alkyl substituent accompanies some reactions. ► Non-olefinic products cannot be extracted from the zeolite.