Molecular organization of reactants in the kinetics and catalysis of liquid phase reactions: X. Synergism in the combined catalysis of urethane formation by organotin compounds and tertiary amines

On the Versatility of Urethane/Urea Bonds: Reversibility, Blocked Isocyanate, and Non-isocyanate Polyurethane

“…Several studies demonstrated that for both amine 58 or tin 59 catalysis systems, increasing the catalyst concentration beyond a certain level does not accelerate the reaction further. Synergism between tin and amine catalyst systems has been depicted by Tarasov et al 28 for addition of butanol on mchlorophenyl isocyanate, by Sojecki and co-worker 60,61 for the TDI-macrodiols reactions or by Frisch and Rumao 49 (Table 3).…”

“…The n−π* transition of CO absorbs at 282−283 nm. Tondeur et al 28,52,53 studied cyclopentanol−phenylisocyanate kinetics of reaction by calculating the conversion ratio according to eq 10: (10) where A 282 stands for absorbance at 282 nm and ε NCO and ε ure stand for the extinction coefficients of phenylisocyanate and urethane, respectively. When heat is applied to blocked isocyanate adducts, the urethane linkage scission leads to an endothermic transition in the DSC curve, possibly preceded by a sharp transition that corresponds to the adduct melting.…”

“…Many groups studied the association states of the reactants mainly in the case of alcohol–isocyanate reaction, particularly Baker, − Entelis et al, , Ephraim, Oberth and Bruenner and Saunders and Frisch . Different parameters (hydrogen bonding, dielectric constant, or basicities of species) were proposed to explain such effects with more or less incomplete data explanation.…”

Chemical reactivity and solution structure: on the way to a paradigm shift?

“…A series of nucleophilic addition reactions with known mechanism (e.g., reactions of alcohols with isocyanates) are featured by a reaction order (with respect to nucleophile) that may vary considerably for the same reaction depending on reaction conditions. In attempts aiming at understanding this unusual kinetics Tiger et al [127][128][129][130][131][132][133][134][135][136][137] have been developing an original concept which is now supported by extensive experimental and computational studies. They hypothesised that experimentally determined concentration dependencies of reaction rate constants (apparent reaction order) in associated solutions are not directly related to the reaction mechanism but rather reect the solution structure.…”

“…The situation becomes even more complex if one considers that the solution domains (supramers) may react on their surfaces (see above the section on Tiger's theory [129][130][131][132][133][134][135][136][137] of reactivity of H-bonded pseudo-polymeric fractal clusters). The solute molecules located on the surface of a supramer inevitably have asymmetric environment thus creating conditions for preferential attack from one of the faces hence for stereoselectivity.…”