Ureas alkoxylation

Heating TCNE with an alcohol in the presence of a mild base such as urea causes replacement of either one (19) or two (20) cyano groups by alkoxyl. The products with ethanol are 1-ethoxy-1,2,2-tricyanoethylene [69155-32-4] and l,l-bisethoxy-2,2-dicyanoethylene [17618-65-4]. 

Scheme 55, Eq. 55a) [119]. A plausible mechanism is depicted in Scheme 55 and involves radical addition of the 2-tetrahydrofuryl radical to the aldehyde followed by a rapid reaction of the alkoxyl radical with Et3B. Triethylborane has a crucial role since by reacting with the alkoxyl radical it favors the formation of the condensation product relative to the -fragmentation process (back reaction). A similar reaction with tertiary amines, amides and urea is also possible (Eq. 55b) [120]. 

The alkoxylation process is easy to apply to PU foams having a low concentration of urethane and urea groups such as flexible and semiflexible foams, integral skin foams, PU elastomers and so on. Urea groups react in a similar way with urethane groups, with the formation of oxazolidones and amines by an intramolecular alcoholysis of urea groups (reaction 20.15). 

By reacting urea groups from rigid PU foam scraps with DEG, amines are formed. The amines are transformed into rigid polyols by alkoxylation of the resulting polyol mixture. The idealised reaction for glycolysis of a rigid PU foam is presented in reaction 20.17. 

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