Kinetics and mechanism of the titanium tetrachloride-catalysed cyclotrimerisation of aryl cyanates

Abstract

Aryl cyanates are converted cleanly at 25 "C to 1,3.5-triazines by catalytic amounts of titanium tetrachloride in dichloromethane. Based on I R spectroscopic, kinetic and product analysis, a mechanism is proposed involving rate-limiting nucleophilic attack of the cyanate nitrogen on the cyanato carbon of a cyanate-titanium tetrachloride complex. Subsequent steps are fast, with no evidence for dimeric or acyclic trimeric intermediates; it is suggested that these steps involve a series of fast stereoselective reactions of nitrillium ion intermediates.

Acceleration effect of ionic liquids on polycyclotrimerization of dicyanate esters

“…The band at 2320 сm -1 , attributed to a cyanate-catalyst complex, was formed rapidly on mixing before gradually disappearing at the end of the reaction. Therefore, the band around 2300-2320 сm -1 was ascribed to a simple cyanateLewis acid complex [32][33][34]. Likewise, in our investigation, we proposed a mechanism involving a cyanate-ionic liquid complex.…”

“…A strong band at 2320 сm -1 indeed appeared upon addition of 1-5 equiv. of TiCl 4 to bisphenol A dicyanate ester; no 'free' cyanate was detectable in these cases [32]. The band at 2320 сm -1 , attributed to a cyanate-catalyst complex, was formed rapidly on mixing before gradually disappearing at the end of the reaction.…”

“…In summary, the higher the [OMIm] [BF 4 ] content, the higher the O-C≡N conversion (α c ) reached after heating at 150°C for 6 h, and the shorter the time to reach complete conversion during post-curing process. 4 ] contents was calculated using FTIR data, and both sets of values obtained from FTIR and DSC data matched pretty well (see Table 2 4 , could be used as catalysts for polycyclotrimerization of dicyanate esters [32]. Martin and coworkers [33,34] reported the appearance of bands around 2300 сm -1 when dicyanates were treated with an excess of Lewis acid.…”

A novel nanocomposite of NH2‐MIL‐125 modified bismaleimide‐triazine resin with excellent dielectric properties

“…Recently, NH 2 ‐MIL‐125 becomes a popular material in the fields of adsorption, separation and photocatalysis 25–27 . Based on studies by Osei‐Owusu et al 28 and Cunningham et al, 29 active hydrogen compounds and titanium ions can definitely act as curing catalysts for cyanate esters, which is beneficial to catalyze the curing reaction of cyanate esters. And the amino group is prone to react with the C═C of bismaleimide through Michael addition reaction, 30 indicating NH 2 ‐MIL‐125 could affect the crosslinking structures of BT resin.…”

Structural analysis and dielectric property of novel conjugated polycyanurates

“…Simon and Gillham proposed a clotrimerization reaction and kinetic model of dicyanate ester, which has considered all possible reaction paths and intermediates. Brownhill and coworkers reported the TiCl 4 ‐catalyzed polymerization of cyanate esters and proposed a four‐step reaction process model. The results show that the transition metal coordinates with the nitrogen, enhancing the electrophilicity of the nitrile group for addition of another cyanate group on to it.…”