Reactivity phenol with phenyl isocyanate

Relatively little basic information has been published regarding the kinetics of phenol-formaldehyde intermediates, especially of phenols, methylol phenols, benzyl alcohol and benzylic ethers with isocyanates. Due to the fact that a typical resole contains both phenolic and benzylic hydroxyl groups, it was of interest to determine their reactivity toward isocyanates in the presence of various catalysts, as well as the effect of substitution on their reactivity. This investigation describes the kinetics of model phenols and model benzyl alcohols with phenyl isocyanate catalyzed with either a tertiary amine (dimethylcyclo-hexylamine, DMCHA) or an organotin catalyst, dibutyltin dilaurate (DBTDL) in either dioxane or dimethylformamide solution. 

The reactivity of the model phenols and benzyl alcohols with phenyl isocyanate was determined in the presence of a tertiary amine (DMCHA) and a tin catalyst (DBTDL) by measurement of the reaction kinetics. The experimental results based on initial equal concentrations of phenyl isocyanate and protic reactants showed that the catalyzed reactions followed second order reaction with respect to the disappearance of isocyanate groups (see Figure 1). It was also found that a linear relationship exists between the experimental rate constant kexp, and the initial concentration of the amine catalyst (see Figure 2). In the case of the tin catalyst, the reaction with respect to catalyst concentration was found to be one-half order (see Figures 3-4). A similar relationship for the tin catalyzed urethane reaction was found by Borkent... 

EFFECT OF SUBSTITUTION ON REACTIVITY OF MODEL PHENOLS WITH PHENYL ISOCYANATE IN DIOXANE AT 25°C... 

The effect of type of catalyst on the reactivity of phenol and benzyl alcohol with phenyl isocyanate can be seen in Table III. In the case of tertiary amine (DMCHA), there is a relatively small difference in the reactivity of both the phenol and benzyl alcohol with phenyl isocyanate. Using DBTDL as catalyst, benzyl alcohol was found to be 26 times more reactive than phenol in the reaction with phenyl isocyanate. 

It is also of interest to point out that DBTDL is about three times more effective a catalyst than DMCHA in the reaction of phenol with phenyl isocyanate. Baker and Gaunt [21] found that ethyl alcohol was 30 times more reactive than phenol in the uncatalyzed reaction with phenyl isocyanate. However, in the presence of a tertiary amine (triethylamine), the reactivity of phenol increased significantly and was found to be similar to that of ethyl alcohol (see Table IV). 

EFFECT OF SOLVENTS ON REACTIVITY OF PHENOL WITH PHENYL ISOCYANATE AT 25°C... 

EFFECT OF CATALYSTS ON THE REACTIVITY OF PHENOL BENZYL ALCOHOL AND ETHYL ALCOHOL WITH PHENYL ISOCYANATE... 

Isocyanates form addition products reversibly with compounds which contain moderately reactive hydrogen, such as phenol, oximes, lactams and malonates. Fig. 14 is an example of a typical blocking-unblocking reaction. These addition compounds, called blocked isocyanates, are stable to water. They have been used in place of free isocyanate. The phenol-blocked isocyanates are the most common. In 1957 the DuPont Co. developed an aqueous dip based on blocked isocyanate. This process, called D-417, used phenol-blocked methylene bis(4-phenyl isocyanate) and a water soluble epoxide, the reaction product of glycerine and epichlorohydrin. RFL is used as the topcoat or second step dip ... 

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