Isocyanates general structure

In sulfamation, also termed IV-sulfonation, compounds of the general structure I NSC H are formed as well as their corresponding salts, acid halides, and esters. The reagents are sulfamic acid (amido—sulfuric acid), SO3—pyridine complex, S03—tertiary amine complexes, aliphatic amine—S03 adducts, and chlorine isocyanate—S03 complexes (3). 

Isocyanates of the general structure shown in Figme 2.2 react vigorously with amines, alcohols, and carboxylic acids. Examples will be discussed later in this chapter. Table 2.1 presents the relative reaction rates of some of the molecules we will use to design our own polymers. 

Isocyanate (Section 30.6C) A compound having the general structure RN=C=0. 

Presently, the isocyanates most commonly used in the formulation of wood adhesives are based on MDI, particularly polymeric MDI (PMDI), which has a low vapor pressure and is therefore preferred because it is less of a hazard. Commercial PMDI is a mixture of oligomers with the generalized structure (24) the value of n typically varies from zero to eight. ... 

Oiganic isocyanates were first synthesized in 1849. Isocyanates (Table 22.1) are highly reactive heterocu-mulene chemicals. The general structure of isocyanates is R—N=C=0, which is distinct from that of cyanate (N=C—O—H). The reactivity of organic isocyanates is due to the strain in the cumulative double bonds (—N=C=0) of isocyanates (Varadarajan et al., 1985). 

Heating phenyl isocyanate or its derivatives in the presence of Lewis acids reportedly gives diazocinediones 42 however, the assignment of structure 2 to the product from phenyl isocyanate is questionable as the melting point (mp 279-280 C)42 differs markedly from the generally agreed literature value (mp 334 C)43 (see also Section 1.5.1.2.3.). 

Bonded phases have been prepared by other general methods besides those indicated so far [64-66]. Reaction of silica with an alcohol or isocyanate resulted in the formation of silicate esters (estersils), but these phases were too hydrolytically unstable to be generally useful. Bonded phases with an Sl-R or Sl-NHR structure are more hydrolytically stable than the estersils but... 

Polyether-based foams account for more than 90% of all flexible polyurethane foams. The properties of foams are controlled by the molecular structure of the precursors and the reaction conditions. In general, density decreases as the amount of water increases, which increases the evolution of carbon dioxide. However, the level of water that can be used is limited by the highly exothermic nature of its reaction with isocyanate, which carries with it the risk of self-ignition of the foamed product. If very low density foams are desired, additional blowing agents, such as butane, are incorporated within the mixing head. 

For this library, we chose to use three types of isocyanates (neutral, electron rich, and electron deficient) to demonstrate the broad utility of the urea-formation reactions. Employing the above strategy and using the split-and-pool approach, we synthesized a 27-membered urea library with purities ranging from 95 to 99%. All the compounds prepared were characterized by 1FI NMR and mass spectroscopy. Acetonitrile can also be used as a substitute for DCM, but lower yields and product purities are generally observed. Attempts to use other protic solvents, such as isopropyl and ethyl alcohol, were unsuccessful. The best results were achieved when a chlorinated solvent (DCM) was used. The structure identity of all products was confirmed by 1FI NMR and MS spectroscopy. Expected molecular ions (M + Na+) were observed for all the products, and in all cases as the base peak. The compounds and yields are listed in Appendix 3.1. 

Due to the necessity for aromatic structure in the commodity isocyanates, and the intensive chemical conversions required to derive the isocyanate reactant, no high-carbon frameworks derived principally from plant sources have been developed into isocyanates. The majority of the derivation of raw materials from high carbon conjugates has been focused on the development of polyols, for which the structural demands are a better fit for available renewable feedstocks. Although there are some notable exceptions [1], as a general rule modification of the... 

The insertion of various isocyanates into chromium(lll) alkoxide M—O bonds has been reported.737 The complexes are prepared by refluxing the isocyanates with a suspension of the alkoxide in benzene. No structural data were given for the products. Unusual bimetallic alkoxides have recently been prepared738 by the reaction of Cr[Al(OPr )4]3 with alcohols and acetylacetone (166). A wide range of spectroscopic methods were used to study them. In general, the results were in accord with a monomeric formulation similar to (166) below Cr[Al(OMe)4]3 was grossly insoluble the small size of the methyl groups may permit extensive polymerization. 

Isocyanates are compounds with the general formula R-N=C=0. They have numerous uses in chemical synthesis, particularly in the manufacture of polymers with carefully tuned specialty properties. Methyl isocyanate is a raw material in the manufacture of carbaryl insecticide. Methyl isocyanate (like other isocyanates) can be synthesized by the reaction of a primary amine with phosgene in a moderately complex process, represented by reaction 15.8.1. Structures of three significant isocyanates are given in Figure 15.7. 

---