No abstract

The reaction of o-hydroxybenzyl alcohol with phenyl isocyanate has been investigated in different polar solvents with in situ FT-IR. The rate constants for the reactions of the phenolic hydroxyl group and the aliphatic hydroxyl group were calculated as k 1 and k 2 , respectively. It is found that the phenolic hydroxyl group reacts more easily than the aliphatic hydroxyl group. It is also found that k 1 increases with increasing solvent polarity, while the trend of k 2 is the opposite. Moreover, the reaction kinetics is second-order with respect to toluene, butyl acetate, cyclohexanone and pyridine, but is first-order with respect to NMP and DMF without distinction for the two kinds of hydroxyl groups.

Using tolylene-2,4-diisocyanate as standard compound, the relationship between ANCO absorbance and concentration was studied with in situ FTIR. The linear relationship appeared correct only for concentrations lower than 0.4 mol L À1 . Then, the urethane reaction kinetics of phenol with tolylene-2,4-diisocyanate were investigated in different solvents, such as dimethyl sulfoxide, cyclohexanone, n-butyl acetate, 1,4-dioxane, and xylene. It showed that solvents largely affected reaction rates. The reaction was largely accelerated in polar solvents, following the order of dimethyl sulfoxide > cyclohexanone > n-butyl acetate > 1,4-dioxane > xylene. It was in contrast to the alcohol-diisocyanate reaction. Finally, an appropriate reaction mechanism was proposed. The HAO bond in phenol was polarized under the influence of solvents, which made the combination of hydrogen to nitrogen and alkoxyl group to carbenium easier. After that the solvent was dissociated and the carbamate generated. The kinetic equation could be derived as

In this study, the urethane reaction of several phenols with isocyanate was monitored with in-situ FT-IR. Reaction rate constants were calculated out to investigate the effect of substituents in phenols, as well as the polarity of different solvents. It showed that the polarity of solvents largely affected the reaction rate even without catalyst. The reactivity increased in the following order: Xylene < 1,4-Dioxane < Cyclohexanone. Furthermore, an electron-withdrawing substituent in phenols increased the reactivity of hydroxyl with isocyanate. The reason may be that the H-O bond in phenols could be easily polarized under the influence of electron-withdrawing substituent, where the hydrogen atom was more likely to attack the nitrogen atom of -NCO, thus the nucleophilic addition happened easier.

A series of theoretical calculations were performed on thienyl-functionalized polysilanes in order to understand their geometries, excited state spectra, energy band structures, and adsorption stability onto Au (111) surfaces. The thienyl functionalization causes a significant red-shift of the electronic spectra of the oligosilanes, which is due to the maximum absorption energy resulting from r ? p* transition in oligo(methylthienylsilane) much lower than that from r ? r* transition, and a great decrease of the r ? r* transition energy in thienyl endfunctionalized oligo(dimethylsilane). The thienyl substitution exerts a small effect on the band gap of the polysilane, and yet disturbs slightly the r electronic delocalization. There exists a stable adsorption between thienyl-functionalized polysilanes and Au (111) surfaces through nonbonding interaction of thiophenes with Au.