Carboxylic acids and isocyanates

Figure 7 Identification of GW 2433. The biased library comprised a biasing fibrate monomer at Rl. R2 and R3, derived from carboxylic acids and isocyanates, were chosen for diversity by means of experimental design techniques.

Carbamic carboxylic anhydrides from carboxylic acids and isocyanates... 

Trimerization to isocyanurates (Scheme 4.14) is commonly used as a method for modifying the physical properties of both raw materials and polymeric products. For example, trimerization of aliphatic isocyanates is used to increase monomer functionality and reduce volatility (Section 4.2.2). This is especially important in raw materials for coatings applications where higher functionality is needed for crosslinking and decreased volatility is essential to reduce VOCs. Another application is rigid isocyanurate foams for insulation and structural support (Section 4.1.1) where trimerization is utilized to increase thermal stability and reduce combustibility and smoke formation. Effective trimer catalysts include potassium salts of carboxylic acids and quaternary ammonium salts for aliphatic isocyanates and Mannich bases for aromatic isocyanates. 

In another report, aspects for automating preparative chemistry are described [130]. A comprehensive description of the Ugi reaction is given in [132] and the vision of a micro multi-component reaction as automated parallel micro-channel synthesis is sketched. An interesting point is to convert aldehydes, chiral primary amines, carboxylic adds and isocyanates into corresponding a-amino acids and peptides (U-4CR). 

The goal for our team of researchers is just that, however to develop an immobilization technique that is economical, scalable to production-size equipment, and accomplishes its task with commonly available raw materials. We already discussed the reaction of isocyanate, a component in all polyurethanes, with alcohols. It is well known, however, that isocyanates also react vigorously with amines, carboxylic acids, and other moieties. 

Zirconium and hafnium tetraalkoxides are highly reactive compounds. They react with water, alcohols, silanols, hydrogen halides, acetyl halides, certain Lewis bases, aryl isocyanates and other metal alkoxides. With chelating hydroxylic compounds HL, such as j8-diketones, carboxylic acids and Schiff bases, they give complexes of the type ML (OR)4 these reactions are discussed in the sections dealing with the chelating ligand. 

Isocyanates are liquids or solids which are highly reactive and undeigo addition reactions across the C=N double bond of the NCO group. Reactions with alcohols, carboxylic acids, and amines have been widely exploited in developing a variety of commercial products. Cydoaddition reactions involving both the C=N and the C=0 double bond of the NCO group have been extensively studied and used for product development (1—9). 

The use of polar solvents, such as N,N-dimethylformamide [68-12-2% is noted to result in extensive trimer formation. However, if the isocyanate is trapped using compounds such as alcohols, carboxylic acids, and amines which contain active hydrogen, high yields are obtained (93). 

Among the procedures which have been developed for /J-lactam syntheses (as reviewed [58] [59]) are the cyclization of /3-haIopropionamides [60] from azetidine-2-carboxylic acids and esters [61] the addition of ketenes to Schiff bases [62] ring-contraction procedures [63] [64] [65] [3+1] cyclizations of a-phenylthioacetamide [66] the cyclization of aminoacids [67], and styrene and N-chlorosulphonyl isocyanate [68]. 

Phosgene-free synthesis of isocyanates directly from carboxylic acids and diphenylphos-phonic azide (PhO)2P(0)N3 in combination with proton sponge 1 followed by Curtius rearrangement has been also described222. 

Ketones Aldehydes Quinones Carboxylic acids and derivatives Thioureas Ureas Oximes Carbonates Imines Isocyanides Cyanides Isothiocyanates Thiocyanates Isocyanates Cyanates Carbodiimides Heteroaromatics Aromatics... 

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