Kinetics of Uncatalyzed Reactions of 2,4′- and 4,4′-Diphenylmethane-Diisocyanate with Primary and Secondary Alcohols

Abstract

The kinetics of the uncatalyzed reaction of an industrially important 50/50 blend of isomers of 4,4′‐diphenylmethane‐diisocyanate (4,4‐MDI) and 2,4′‐diphenylmethane‐diisocyanate (2,4′‐MDI) with primary and secondary alcohols was studied using high‐performance liquid chromatography coupled with photodiode array detector. The alcohols such as 1‐propanol, 2‐propanol, 1‐hexanol, 2‐hexanol, 3‐hexanol, 1‐methoxy‐2‐propanol, and 3‐methoxy‐1‐propanol were used in high molar excess to diisocyanate in toluene at 80°C, and pseudo–first‐order dependences on the concentrations of 4,4′‐MDI and 2,4′‐MDI were found. Appropriate treatments of the kinetic data allowed us to determine the corresponding pseudo–first‐order rate constants. According to the kinetic results, the reactivity of the isocyanate group in the para‐position is about four to six times higher than that of the ortho‐positioned isocyanate group, depending on the reacting alcohol. Furthermore, the substitution effect, i.e., change in the reactivity of the free isocyanate group after the other has been reacted, was found for both 4,4′‐MDI and 2,4′‐MDI isomers. The differences in the reactivities of the isocyanate groups of 2,4′‐MDI and 4,4′‐MDI isomers before and after one of two isocyanate groups has been reacted are explained in terms of partial positive charges on the corresponding carbonyl carbon atom calculated by high‐level quantum chemical calculations. In addition, the UV‐spectral properties of the products obtained by quenching the reaction mixture with methanol are also discussed in light of practical implications.

Reactions of 2,6‐Toluene Diisocyanate with Alcohols: Kinetic Studies in the Absence and Presence of Catalysts

“…Alcohols containing ether groups such as DEGME and 3‐MeO show decreased reactivity towards 2,6‐TDI. Similar observations were found for the reaction of 4,4‘‐ diphenylmethane‐diisocyanate (4,4‘‐MDI) and 2,4‐TDI with DEGME and 3‐MeO. Furthermore, secondary alcohols, most likely due to a steric effect, were observed to react ca.…”

“…As seen in Figure , under the applied chromatographic conditions, all of the products formed in the reaction are well separated, thus making quantification of these compounds possible. Furthermore, both in this study and in our previous reports,, the UV‐Vis properties of aromatic carbamates are found to be strongly independent of the reacting alcohols; that is, the molar absorption coefficient is the same for each product formed by methanol quenching. Hence, the corresponding molar fraction for the products can easily be calculated as shown in the Experimental section.…”

“…However, to answer this question adequately, the experimental conditions under which the kinetics of these reactions are studied should be very similar. Fortunately, our previous kinetic studies on the uncatalysed reaction of 4,4’‐MDI and 2,4‐MDI with alcohols, most of which were also applied in this study, were performed under the same experimental conditions, allowing a direct comparison of the reactivity of these alcohols towards these different aromatic diisocyanates. The relative reactivities of the alcohols (r) were evaluated relative to that of 1‐propanol as the reference as shown by eq.…”

Uncatalyzed urethane forming reaction of 1,3-xylylene diisocyanate with aliphatic alcohols of varying chain lengths and polyols

“…The products of the methanol-quenched reactions are denoted as XDI_1,3, XDI_1,3R, and XDI_1R,3R. In order to calculate the relative concentrations of the products, i.e., the corresponding molar fractions (X i ), the peak areas obtained from HPLC-PDA measurements at λ = 210 nm were used similarly to those reported in our previous works [17,18]. The molar fractions of the unreacted (X XDI_1,3 ), the one-substituted (X XDI_1,3R , one of two isocyanate groups has reacted) and the two-substituted (X XDI_1R,3R , both isocyanate groups has reacted) 1,3-XDI come as given by Equations (1)- 3:…”

“…In this work, the following tasks were performed: (i) The effect of the length of the alkyl chain of primary alcohols on the reaction rate coefficient. (ii) The reactivity of 1,3-XDI towards alcohols and polyols, especially concerning those of MDI and TDI (To obtain comparable kinetic data, the same reaction conditions were used in this study as those applied for other diisocyanate-alcohol reactions [17,18]). (iii) Prediction of the product distribution in the 1,3-XDI-polyol reactions using the kinetic data obtained in the reaction of 1,3-XDI with alcohol mimicking the chain-end of the given polyol.…”