Alcohol-isocyanate reaction

In actual practice, catalysts are usually employed to catalyze the isocyanate/ alcohol reaction at room temperature. Typical catalysts for this reaction are the tin(IV) salts, e.g., dibutytin dilaurate, or tertiary amines, such as triethylene diamine [2]. 

One way of obtaining the more useful cross-linked polyurethanes is by using a trifunctional reagent. Thus either the TDI can react with a triol or the propylene oxide can be polymerized in the presence of a triol. Then the isocyanate-alcohol reaction would of course give a cross-linked urethane. 

For the catalysis of isocyanate-alcohol reactions in apolar solvents, several mechanisms have been proposed. However, the results of the kinetic measurements in DMF could not be explained with these mechanisms. So we concluded that, in the polar solvent DMF, the mechanism of the catalyzed urethane formation differs from the published mechanisms in apolar solvents. The behavior in DMF can be explained from a mechanism in which dibutyltin dilaurate dissociates into a catalytic active species. 

Reactions of alkoxylated lignin with diisocyanates produce thermoset materials because the lignin polyol is always polyfunctional with a functionality greater than 2. The isocyanate-alcohol reaction produces a urethane linkage that when repeated creates a crosslinked, nonreformable polyurethane. This is shown in Fig. 6. A broad spectrum of lignin-based urethanes have been made and tested. The data show that these materials match if not exceed the properties of synthetic polyurethanes made without lignin [60]. 

Multivalent metals may serve as Lewis acids in some cases, and metal oxides may function as Lewis bases. At least in some reactions, such as the isocyanate/alcohol reactions, the metal atom may act as an acid, and also hold both reactants in essentially ideal proximity for reaction, viz. 

Baker et al. [18—20] published the first detailed kinetic treatment of the isocyanate/alcohol reaction. They proposed the existence of both a catalysed reaction... 

Many other investigators have studied the isocyanate/alcohol reaction and have extended the findings of Baker et al. Some have found systems with somewhat different balances of the kinetic parameters, so that their results differed somewhat from those cited above. Farkas and Strohm [121] have reviewed briefly most of the variations which have been found in the amine catalysed reaction. In general, however, the early studies of Baker et al. have provided a sound basis for understanding the kinetics of these reactions. 

While activation energies have been published for many isocyanate/ alcohol reactions, relatively few reports have been made of the heat of reaction. Bayer [136] reported a heat of reaction of 52 kcal mole , or 26 kcal equiv", for the hexamethylene diisocyanate/1,4-butanediol reaction. Lovering and Laidler [137] measured heats of reactions for the butyl alcohol isomers with several aromatic isocyanates. Values ranged from 18.5 to 25 kcal equiv . ... 

The kinetics of the isocyanate/water reaction appear to be similar to those of the isocyanate/amine and isocyanate/alcohol reactions. Morton et al. [186, 187] showed that the rate depended on the water concentration, as indicated in Table 19. From these data it was shown that a plot of (HaO)// versus (HjO) gave a straight line, in agreement with the mechanism ... 

The kinetic studies of Isocyanate-alcohol reactions catalyzed by DBTDL showed that the dependence of the rate constants on the concentration of DBTDL was not linear (14, 18, 20). In order to explain this behavior various mechanisms were proposed based on series of consecutive complexing equilibrium (14), dissociation of a catalyst (18, 19) or dissociation of OH bond in the alcohol-DBTDL complex (20). 

A survey of the literature indicates that the catalysis of isocyanate-alcohol reactions has produced a variety of mechanistic explanations. The proposed reaction pathways in the literature are often based on limited information and are unable to explain many of the experimental observations well known to scientists and technologists active in the field (1, 2, 3, 4) ... 

Rate Constant of Phenyl Isocyanate-Alcohol Reactions Catalyzed by Organometallic Compounds (15,)... 

Tertiary amines and tin carboxylates are important catalysts in the production of polyurethane foams from polyisocyanates and and polyhydroxy compounds. Many articles have been written on the mechanism of the catalysis of the isocyanate-alcohol reactions by such compounds. Farkas and Mills (1), Entelis and Nesterov (2), Frisch and Rumao (3)and Petrus (4) have written excellent reviews on this subject. Wolf (5) has shown that these catalysts are synergistic to each other. 

If the mechanism of the catalysis of isocyanate-alcohol reaction by tin carboxylates does indeed proceed via the alkoxide as proposed by Bloodworth and Davies (11), then the synergism of the amine to tin can readily be explained from the above equilibrium. The amine will assist in the alcoholysis step and speed up the decomposition of the tin-carbamate complex by the alcohol to the urethane and tin alkoxide. 

Isocyanate-alcohol reaction n. Reaction involving a very reactive chemical group, -N=C=0 with an alcohol to form a highly cross-linked polymer, importance in polyurethane formation. Odian GC (2004) Principles of polymerization. John Wiley and Sons Inc., New York. 

The reaction of isocyanates with alcohols and with water can be catalyzed by amines and by organometallic compounds. Tertiary amines, such as l,4-diazo-[2.2.2]-bicyclooctane (DABCO) or triethylamine, are particularly effective in promoting the isocyanate-water reaction, while organometallic complexes, such as dibutyltin dilaurate or stannous octoate, are very useful for catalyzing isocyanate-alcohol reactions. Numerous articles have been written on various aspects of the catalysis of isocyanate reactions and representative examples are cited in refs. 8-10. 

Rapid growth of urethane technology can be attributed to the development of catalysts. Catalysts for the isocyanate-alcohol reaction can be nucleophilic (e.g., bases such as tertiary amines, salts and weak acids) or electrophilic (e.g., organometallic compounds). In the traditional applications of polyurethanes (cast elastomers, block foams, etc.) the usual catalysts are trialkylamines, peralkylated aliphatic amines, triethylenediamine or diazobiscyclooctane (known as DABCO), N-alkyl morpholin, tindioctoate, dibutyl-tindioctoate, dibutyltindilaurate etc. 

The mechanisms of the reactions between isocyanates and various active hydrogen compounds are probably broadly similar, but most experimental investigations in this field have involved the isocyanate-alcohol reaction. In the absence of an added catalyst, this reaction is believed to proceed by the following mechanism, in which the alcohol itself acts catalytically [1] ... 

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