From isocyanate reacted with

Four-membered heterocycles are easily formed via [2-I-2] cycloaddition reac tions [65] These cycloaddmon reactions normally represent multistep processes with dipolar or biradical intermediates The fact that heterocumulenes, like isocyanates, react with electron-deficient C=X systems is well-known [116] Via this route, (1 lactones are formed on addition of ketene derivatives to hexafluoroacetone [117, 118] The presence of a trifluoromethyl group adjacent to the C=N bond in quinoxalines, 1,4-benzoxazin-2-ones, l,2,4-triazm-5-ones, and l,2,4-tnazin-3,5-diones accelerates [2-I-2] photocycloaddition processes with ketenes and allenes [106] to yield the corresponding azetidine derivatives Starting from olefins, fluonnaied oxetanes are formed thermally and photochemically [119, 120] The reaction of 5//-l,2-azaphospholes with fluonnated ketones leads to [2-i-2j cycloadducts [121] (equation 27)... 

Isocyanates react with carboxylic acids to form amides, ureas, anhydrides, and carbon dioxide, depending on reaction conditions and the structure of the starting materials (Scheme 4.13). Aliphatic isocyanates more readily give amides. Aromatic isocyanates tend to react with carboxylic acids to first generate anhydrides and ureas, which at elevated temperatures (ca. 160°C) may further react to give amides. In practice, the isocyanate reaction with carboxylic acid is rarely utilized deliberately but can be an unwanted side reaction resulting from residual C02H functionality in polyester polyols. 

In all cases, the initial addition to generate 520 was diastereospecific, that is, the isocyanate always adds to 519 from the face opposite to the 4-ethyl substituent of the oxazoline. In the cases wherein 521 was isolated (Entries 17-20 from Table 8.33), the stereochemistry of the two additional chiral centers from the secondary [2 + 2] cycloaddition was controlled by the chiral center formed during the initial reaction, that is, the isocyanate reacts with 520 from the opposite face of the neighboring Ri group. For Ri = H, R2 = Me, 519 reacted with an arylisocyanate (R3 = Ar) to give tricyclic adducts 521a and 521b as a 1.7 1 mixture of diaster-eomers (Entries 18-20). For Rj = Ph, R2 = Me, 519 reacted with phenylisocyanate... 

The nature of a hydrophilic prepolymer permits the addition of large amounts of water. The isocyanate reacts with the water to abstract COt. The amine that also results from the reaction then reacts with an isocyanate group to produce a urea linkage. The reaction continues until the water or the isocyanates are consumed. If provisions are made to trap the CO2 in the mass, a foam is produced. If such provisions are not made, the CO, will bubble away, leaving behind a low gel-strength hydrogel. Careful examination of the resultant molecule might cause one to rename it a polyurethane/polyurea. 

A similar reaction can be effected by the treatment of amides with lead tetraacetate.2 4 In this case the initial isocyanate and the amine formed from it react with the acetic acid liberated from the lead tetraacetate to give, respectively, ureas and amides. If the reaction is carried out in the presence of an alcohol, carbamates are formed (6-8). 

Urethane adhesives take their name from the product of the most common step-growth polymerization reaction used to generate the adhesive polymers. Isocyanates react with hydroxyl groups to create urethane (or carbamate) linkages ... 

Polyols from EPOP react with isocyanates at a slower rate than do polyols based on petrochemicals. The resulting foams, however, have regular cell structures and exhibit good hydrophobicity. With suitable formulations these properties could be fully exploited to give rise to interesting products (124). 

Phenyl isocyanate reacts with 2-ethoxycarbonyl-3-methylcyclopropanone dimethyl acetal (7) at 85 °C to yield a mixture of the [ 2 -l- 2J cycloadduct 8 and two diastereomeric consecutive products arising from addition of the C-H-acidic p-oxo ester 8 to a second molecule of phenyl isocyanate. ... 

Carbodimides 92, obtained from aza-Wittig reactions of iminophosphorane and aromatic isocyanates, reacted with primary amines to give isolable intermediate guanidines 93. Cyclization afforded selectively regjoisomer 94 with sodium ethoxide, whereas in its absence another regioisomer 95 was obtained <05CL1022>. 

Because of their carcinogenicity, amines have to be monitored. For example, primary aromatic amines (PAAs) are substances that can be transferred from food packaging materials into foodstuffs. In the production of multilayer plastic materials it is common to use reactive adhesive mixtures containing aromatic isocyanate monomers. In cases of incomplete curing, residues of the aromatic isocyanates react with water to produce PAAs. Some of these amines, including... 

The [4+2] cycloaddition of acylisocyanates to isocyanates to give 2,4-dioxo-2,4-2/-l,3 5-oxadiazines is well established <1981BSF28, 1970ZNB1180>. Thus, the water-sensitive 1,3,5-oxadiazine 61, formed from acylisocyanate 284 and phenyl isocyanate, reacts with 0,0-diethyl dithiophosphate to afford the oxadiazine 92 (Scheme 59) <1996SC783>. However, these oxadiazines are difficult to isolate as they undergo rapid decomposition. 

Desmodur N3200 [34], an oligomeric form of hexamethylene di-isocyanate (HDI). Heating causes reaction of the isocyanates with surface amines as shown in Scheme 15.2B. The length of the polyurea cross-links depends on both the di-isocyanate concentration in the soak solution and the amount of residual water from the hydrolysis left in the gels. This is because isocyanate reacts with water to generate an amine that can react with other isocyanates to cause chain extension. 

One-part urethane adhesives have been used for many years as high performance sealants. In this capacity they provide a useful combination of strength, flexibility, and elastic recovery. As adhesives, these systems have limited use im-less formulated to overcome their inherent disadvantages. One-part polyurethane adhesives are typically moisture-cured and rely on a multistep reaction sequence as follows isocyanate reacts with water to form carbamic acid, the unstable car-bamic acid loses carbon dioxide and generates an amine, the amine reacts with additional isocyanate to form a urea, and the urea reacts with additional isocyanate to form a biuret, which includes a cross-link. Unless it diffuses out of the system, the CO2 can cause foaming. Formulators learn to minimize the isocyanate content (%NCO) of a system in order to balance cure speed with foam control. Cure speeds—and foaming rates—of these systems decrease from the outside in and vary with the amount of atmospheric moisture in the air, which changes hourly and seasonally. 

Fig. 25.6 Proposed reactions during the isocyanate treatment of GO where organic isocyanates react with the hydroxyl left oval) and carboxyl groups right oval) of graphene oxide sheets to form carbamate and amide functionalities, respectively (Reprinted with permission from Stankovich et al. 2006a, Copyright 2006 Elsevier)...

The intermediate formed in the reaction of phenyl isocyanate with the carbene generated from diazomethane reacts with another eqivalent of diazomethane to give the )3-lactam... 

Aromatic isocyanates react with regular olefins only in the presence of metal catalysts. For example, reaction of ethylene with phenyl isocyanate in the presence of liganded nickel (o) catalysts under argon in THF at -20 °C affords a five-membered ring metalla-cycle, which on hydrolysis gives a Af-substituted carboxylic acid amide. Heating of the metallacycle causes jS-elimination with formation of Af-substituted acrylic acid amides Diolefines and allenes also undergo this reaction with phenyl isocyanate. From 1,1-bis-p-dimethylaminophenylethylene and p-nitrophenyl isocyanate a linear 1 1 adduct is obtained... 

In the reaction of ynamines with phenyl isocyanate, 2- and 4-quinolones are formed. In these reactions the double bond of the benzene ring of phenyl isocyanate participates as an A=B substrate. For example, the ynamine 183, derived from butadiyne, reacts with phenyl isocyanate to give the [2+2+2] cycloadduct 184. ... 

Also, Os3(H)2(CO)9(PMe2Ph) reacts with p-tolyl isocyanate to give a bridged carbamate complex . When Os3(H)2(CO)io is used, formamide complexes and other products resulting from fragmentation reactions are obtained. For example, p-tolyl isocyanate reacts with the osmium hydride complex and ruthenium complexes to form formamido, ureylene... 

Alkyl and aryl isocyanates react with aluminum azide, generated in situ from sodium azide, to give 1-substituted 5-hydroxy-l//-tetrazoles 442" ". Better yields are obtained... 

Phenylthiocarbonyl isocyanate reacts with carbodiimides to give the [4+2] cycloadducts 65. From Af-phenyl-Af -cyclohexylcarbodiimide and phenylthiocarbonyl isocyanate two isomeric [4+2] cycloadducts are obtained. Aliphatic thiocarbonyl isocyanates react similarly to give [4+2] cycloadducts... 

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