Isocyanate moiety

As they are considered to be toxic compounds, their use in the manufacture of plastic materials and articles that are intended to come into contact with foods is regulated by Directive 2002/72/EC. Their residual levels in the finished plastics must not exceed 1.0 mg per kg, expressed as isocyanate moiety (NCO). 

The functionalization of silica with PPM and the subsequent immobilization of [Rh(COD)2]BF4 has been achieved by Pugin and Blaser [49]. The PPM ligand was immobilized by grafting the linker, 3-trimethoxysilylpropyl isocyanate, to the silica surface (the silicas used include Grace 332, Merck 100, Merck 60, Merck 40). The isocyanate moiety then reacts with the amine functionality of the PPM ligand to afford an amide linkage (35, Figure 5.17). Introduction of a solution of [Rh(COD)2]... 

Below are a number of resonance forms for the isocyanate moiety. Because it is surrounded on both sides by atoms, N and O, which have greater electronegativities than the carbon atom, the carbon is electron-poor and is the site for attack by amines (polyureas) and alcohols (PUs) ... 

Thus, 3,5-bis[(benzoxycarbonyl)imino]benzylalcohol (26 R = H) was heated in refluxing THF to give the bisisocyanate benzylalcohol and two equivalents of phenol (Scheme 6.8a). Self-addition of the isocyanate moieties with the alkyl alcohol group subsequently gave the hyperbranched carbamate 27 (Scheme 6.8b). 

When stericaUy demanding peptide fragments are coupled in the presence of HOSu, a side reaction that leads to a P-alanine derivative becomes donninant (Scheme In this side reaction, HOSu is activated by DCC and attacked by a second equivalent of HOSu. The nitrene is probably not a real intermediate as it is rearranged conconoitantly to its formation to an isocyanate moiety, which is trapped by a third equivalent of HOSu.t By replacing the HOSu additive with A-hydroxy-5-norbornene-2,3-dicarboximide (18)t or other dinucleo-phUes, this side reaction is efficiently bypassed. 

Divinylcyclopropanes in which one of the vinyl groups has been replaced with an isocyanate moiety also undergo a facile Cope rearrangement. ... 

Butyl-2,3-dihydro[l,2,4]thiadiazolo[4,5-a]benzimidazol-3-one (111 R = Bu") undergoes exchange of the isocyanate moiety (see Section 8.05.10). With DMAD 2,3-dimethoxycarbonyl-thiazolo[3,2-a]benzimidazole (137) is obtained. The reaction with 4-(l-cyclohexen-l-yl)morpholine gives 10a-hydroxy-6a,7,8,9,10,10a-hexahydrobenzimidazo[2,l-ft][l,3]benzothiazole (138) (Scheme... 

Isothiocyanates react with 2-cyclohexyl 2,3-dihydro-imidazo[l,2-with exchange of the isocyanate moiety to give 2,3-dihydro-imidazo[l, 2-d][, 2,4]thiadiazole-3-thione derivative (75) or the isomer 3-imino-3//-imidazo[2,l-c][l,2,4]dithiazole (76), depending on the nature of the group R (see Section 8.05.4.3) (Scheme 37) <88JPC338>. 

The isocyanate moiety of 2-substituted 2,3-dihydro-[l,2,4]thiadiazolo[4,5-a]benzimidazol-3-ones (393) is exchangeable with Other isocyanates or a carbodiimide giving rise to a formal exchange of the 2-substituent as in (394) (Equation (134)). With isothiocyanates 2-substituted 2,3-dihydro[l,2,-4]thiadiazolo[4,5-fl]benzimidazole-3-thiones (395) and/or 3-imino-3//-[l,2,4]dithiazolo[4,3- I]ben-zimidazoles (396) are formed (see Section 8.05.4.3). The reaction with carbon disulfide results in the formation of 3//-[l,3,4]-dithiazolo[4,5-u]benzimidazole-3-thione (397). All these exchange products react with isocyanates and are reconverted into compounds (393). 

Exchange of the isocyanate moiety of 2-substituted 2,3-dihydro[l,2,4]thiadiazolo[l,2-with cyanates and trichloroacetonitrile to yield the corresponding 3-substituted [l,2,4]thiadiazolo[l,2-J]benzimidazoles (400) and (399) (see Section 8.05.6.4.2) (Equation (135)) <85JCS(P1)1007>... 

In the reaction of benzoyl isocyanate with phosphorus pentachloride reaction occurs exclusively on the C=0 group attached to the isocyanate moiety, and the chloroimidoyl-N-carbonyl chloride XXV is obtained in good yield ( ). 

The isocyanate moiety is highly reactive towards poly(ol)s. This reaction is utilized in the preparation of poly(urethane)s (PU)s. With catalysts such as amines, the reaction occurs rapidly at room temperature. Consequently, urethane polymers are mostly prepared from two components, one containing the isocyanate component, and the other containing the polyol component. The components are nuxed prior to curing. 

Zhang et demonstrated that polyamide 6 (PA6) can be grafted onto PS by a grafting from approach. The strategy involves the use of a copolymer of styrene (S) and 3-isopropenyl-a,a-dimethylbenzene isocyanate (TMI), P(S-co-TMI), to activate the polymerization of s-caprolactam (CL) in the presence of sodium e-caprolactam (NaCL) as an anionic catalyst. The authors showed that the isocyanate moieties had all participated in the activation of the polymerization, implying that each isocyanate moiety yielded a PA6 graft. However, the final product is a mixture of the expected PS-g-PA6 graft copolymer, homo-PA6, and unreacted CL. 

Conventional (single-component) polyurethane spray foams are cured by a reaction of prepolymers containing isocyanate moieties and monomeric isocyanates with moisture to generate a urea unit and CO2 [7]. The latter serves as propellant or — more often — as co-propellant besides being a physical blowing agent. 

A different strategy used the isocyanate moiety in 7.7037 as an amine surrogate. Reaction with HCl gave 2-amino-4-cyclohexene-l-carboxylic acid, 7.71.38... 

Hawker and coworkers studied SCNP formation using viscometric measurements (Figure A.S)." In this experiment, they studied two parent polymers (100 kDa and 150 kDa) with pendant isocyanate moieties that were collapsed by an external diamine cross-linker. They found that the intrinsic viscosity of a particle is inversely proportional to the degree of crosslinking. The SCNPs, despite a 50% increase in molecular mass compared to their parents, both decreased in intrinsic viscosity compared to their parent polymers and the viscosities of the two nanoparticles were similar to one another. These data are consistent with Einstein s prediction that the intrinsic viscosity of a constant density sphere is independent of its molecular weight. 

The high reactivity of the isocyanate moiety has been exploited to yield polyurethane/urea hydrogels. A polyisocyanate prepolymer obtained by fiinctiontdizing a moderate molecular weight polyether diol or triol with a diisocyanate will crosslink on exposure to an aqueous environment due to partial hydrolysis and urea formation (55). A similar hydrogel results by reacting a polyisocyanate... 

Rovis and coworkers reported the first enantioselective rhodium-catalyzed [4-I-2-I-2] cycloaddition of terminal alkynes 131 with ( i-dienyl isocyanates 132 to construct the bicyclo[6.3.0]azocines [48]. Heating a toluene solution (110 °C) of 131 and 132 in the presence of a catalytic amount of [Rh(C2H4)2Cl]2 and chiral phosphoramidite afforded the [4-I-2-I-2] cycloadducts 133 in good yields with excellent enantiomeric excesses [49], Initial oxidative cyclization between the diene and the isocyanate moiety of 132 afforded rhodacycle 134. Coordination and insertion of alkyne 131 to 134 followed by reductive elimination of the resulting rhodacycle 135 provided the [4-I-2-I-2] adduct 133 (Scheme 4.27). 

More specifically, the hydroxyl terminated polymer is polystyrene (PS-OH). This latter can be prepared relatively easily following classical anionic polymerization procedures. The isocyanate moiety involved in the polymer chains is 3-isopropenyl-a, a -dimethylbenzyl isocyanate (TMI), which is randomly distributed along the chain. If the polymer backbone bearing TMI is identical or miscible with PS-OH, the reactive system is homogeneous. 

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