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Preparation of Polymerizable Isocyanate Esters Disclosure Number: IPCOM000028164D
Publication Date: 2004-Apr-29
Document File: 2 page(s) / 57K

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Preparation of Polymerizable Isocyanate Esters

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Preparation of Polymerizable Isocyanate Esters

Isocyanates are known precursors for urethanes, a class of chemicals widely used in paints, foams, adhesives, elastomers, and many other materials. Isocyanates previously have been made from processes that require environmentally and toxicologically unfavorable starting materials, such as phosgene or substituted oxazolines. Isocyanates have also been made from urethanes via thermal elimination processes where elevated temperatures, e.g., above 300°C, are required or from processes that employ toxic materials, such as certain catalysts.

More recently, isocyanates have been made from corresponding urethanes or carbamates via less vigorous thermal elimination reactions. For example, U.S. Patent 5,990,345 (Lohmann et al.) describes a process for preparing unsaturated ester isocyanates from the reaction of the corresponding carbamates and trialkyl silyl halide. Subsequent thermal elimination of alkoxy silane leads to the formation of the isocyanate. The silylation step alone takes about 6 hours at 50°C, followed by 8 hours at 100°C for the thermal elimination of alkyloxy (aryloxy) trimethylsilane. This reaction seems to be feasible only when bulky alkyl or aryl carbamates are used. Elimination of alkoxy silane from carbamates with smaller alkyl groups, such as methyl and ethyl, is extremely difficult to carry out.

Alper et al. (in U.S. Patent 5,457,229 and in Chem. Communications, [1998], 2575-2576) has described processes for preparing mono-, di-, and tri-isocyanates (both aromatic and aliphatic) from the reaction of alkyl (aryl) urethanes and BCl3, BBr3, BI3 or chlorocatecholborane. Both publications provide details on how to make mono-, di-, and tri- aromatic and alkyl isocyanates, however they are silent regarding the tolerance of their procedures towards the presence of functional groups such as esters, amides, olefins, α,β-unsaturation, etc., that might be present on the starting urethane.

We report here two different process routes via which alkyl and aryl urethanes (i.e., carbamates) can be smoothly transformed into isocyanates even if functionalities such as unsaturated esters or acyl...