The reactions of diisocyanates with alcohols

The most reactive group should be the 4-position isocyanate group, which is activated by the 2-position isocyanate group. The 2-position group has 

In diisocyanates where the two isocyanate groups are on different aromatic rings or where they are separated by aliphatic chains the effect of one isocyanate or urethane group on a second isocyanate group is less pronounced. The effect becomes still less as the aromatic rings are separated further and further from each other, for example, by progressively longer aliphatic chains. 

The reactions of several diisocyanates with a large excess of 2-ethyl-hexanol have been reported by Bailey et al. [122]. Reactions were run in benzene with the extent of reaction being followed by loss of infrared absorption at 4.4 pm, characteristic for the isocyanate group. A sharp decrease in the rate of reaction of 2,4-tolylene diisocyanate and the 80 20 isomer ratio of tolylene diisocyanate at approximately 50% reaction was found. In contrast, 2,6-tolylene diisocyanate, 4,4 -diphenyImethane diisocyanate, p-phenylene diisocyanate and m-phenylene diisocyanate showed only a slight decrease in rate as the reaction proceeded. 

While nearly all previous rate data were obtained by following the rate of disappearance of isocyanate, Kogon [129] followed the rate of formation of urethane, using infrared absorption at 6750 cm The second-order plot of the uncatalysed reaction of 2,4-tolylene diisocyanate was linear to about 60% reaction, and that of 2,6-tolylene diisocyanate to 30% reaction. 

To throw additional light on the relative reactivity of diisocyanates at higher temperatures Cunningham and Mastin [130] measured rates of reactions with alcohols at 115°C. To provide both primary and secondary hydroxyl groups, 1- and 2-octanol were used (Table 9). At 115°C the 

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