Applications of Carbodiimides

The generation of catalytic amounts of carbodiimides from diisocyanates is also applied in the manufacturing of polyamides from MDI and dicarboxylic acids and/or dicar-boxylic acid terminated prepolymers. These thermoplastic polyamides are produced continuously by reaction polymerization using a vented extruder to remove the carbon dioxide byproduct. Thermoplastic polyamides are manufactured today by the Dow Chemical Co., which purchased the Chemical Division of Upjohn in 1980. 

Oligomeric carbodiimides derived from sterically hindered aromatic diisocyanates are used as stabilizers for polyester based polymers because the carbodiimide groups in the oligomers, or in sterically hindered diisocyanates, mop up HCl, which catalyzes the depolymerization of polyesters. The carbodiimide stabilizers are commercially available under the tradename Stabaxol from Rhein Chemie, a subsidiary of Bayer. 

The most widely used carbodiimides are N,N -dicyclohexylcarbodiimide (DCC) and the water soluble N-ethyl-NL(3-dimethylamino)propylcarbodiimide (EDC) and its hydrochloride salt (EDCCl). Also, analogs of DCC, such as the fluorescent N-cyclohexyl-N -(l-pyrenyl)carbodiimide (PCD) and the paramagnetic N-cyclohexyl-N -(2,2,6, 

Chemistry and Technology of Carbodiimides Henri Ulrich 2007 John Wiley Sons, Ltd. ISBN 978-0-470-06510-5 

6-tetramethylpiperidineoxy)carbodiimide are used in protein applications to mark the reactive sites in the macromolecules. 

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The remaining chapters are carbodiimides with unsaturated substituents, halogenated carbodiimides, acyl-, thioacyl- and imidoylcarbodiimides, silicon substituted carbodiimides, nitrogen substituted carbodiimides, phosphorous substituted carbodiimides, sulfur substituted carbodiimides, metal substituted carbodiimides, cyclic carbodiimides, polymeric carbodiimides and application of carbodiimides. 

The last chapter includes the numerous biochemical applications of carbodiimides, and the chapters on silicon substituted carbodiimides and metal substituted carbodiimides include their role as precursors for ceramic materials. 

Since the pressure build up is primarily due to the evolution of CO as MDI is being decomposed to carbodiimide, the thermodynamic relationship PV = nRT may be applied to convert the pressure profiles to plots of moles of CO2 generated vs. time. This is shown for the 225 °C isotherm in Figure 3. The theoretical curve obtained through the application of zero-order kinetics is also shown in this plot and the data seem to be well accommodated by this rate law throughout the majority of the run. 

Smith, M., Moffatt, J.G., Khorana, H.G. (1958) Carbodumides. VIII. Observations on the Reactions of Carbodiimides with Acids and Some New Applications in the Synthesis of Phosphoric Acid Esters. Journal of the American Chemical Society, 80, 6204-6212. 

Preparation of carbodiimides by dehydration of the corresponding ureas is of general applicability and is well adapted to the laboratory preparation of substantial quantities. The intermediates for this particular preparation are commercially available at moderate cost. 

Title Macrocyclic Carbodiimides (MC-CDI) and Their Derivatives, Syntheses, and Applications of the Same... 

Since depsipeptides, in contrast to classical peptides, contain units constructed from amino and hydroxy acid residues, the various methods for their preparation are generally pathways involving the formation of ester bonds. The novel achievements in this area discussed (vide infra) are associated with further developments in the mixed anhydride technique, the application of effective catalysts in the carbodiimide procedure, and adaptation of the known Mitsunobu reaction to the depsipeptide case. A number of significant and efficient esterification procedures utilized for the preparation of depsipeptides are considered. 

The carbodiimide method has been employed in several syntheses of depsipeptides. However, direct application of DCC for the formation of the ester bond between the amino acid and hydroxy acid components under the usual conditions of amide coupling affords the desired depsipeptides in acceptable yields only in the case of unhindered co-hydroxy units [54] or an active hydroxy group, such as in TV-benzoyl-u-hydroxyglycine benzyl ester. For example, Ravdel et al.[55 have performed the esterification of various benzyloxycarbonyl- and phthalylamino acids with /V-benzoyl-a-hydroxyglycine benzyl ester with DCC in 50-65% yield. On the other hand, Shemyakin et all21 failed to obtain the expected depsipeptide products on condensation of bulky benzyloxycarbonyl- or phthalylvaline with a-hydroxy-isovaleric acid benzyl ester. The main product was acylurea in the first case and phthalylvaline anhydride in the second. Thus, the classical carbodiimide procedure could not be applied in practical depsipeptide preparation. 

Since the most common group of 1,3-diazocines is related to cyclic urea 104 (called, for example, perhydro-l,3-diazocine-2-one or N,N -pentamethyleneurea), a separate section is devoted to the synthesis, chemistry, and applications of 104, substituted 104, and related molecules such as thiourea 105, guanidines 106, and carbodiimide 107. 

It may be mentioned that bis(imino)thiazetidines (68), which are prepared by the reaction of carbodiimides with isothiocyanates, react with hydrazoic acid to give an aminothiatriazole. Although this reaction may be of interest from other points of view, it has no general synthetic application (equation 41) (81BSB63). 

An interesting application of the isocyanate addition is a reaction which initially yielded carbodiimide that reacted with a simple enamine to give an intermediate leading in a hetero-Diels-Alder reaction to a phenanthridine derivative13 (equation 9). 

Often reactions of carbodiimides are performed in an aqneons system requiring the use of water soluble carbodiimides. The workhorse in this application is N-ethyl-N -(3-dimethylaminopropyl)carbodiimide (EDC) and its hydrochloride salt (EDCl). However, many other water solnble carbodiimides are also used. Nobel laureat Sheehan used water soluble carbodiimides in the synthesis of penicillins. 

The reactions of carbodiimides outlined in Section 2.4 demonstrate the use of carbodiimides in organic synthesis. In the current chapter only some of the more important applications... 

Twenty years after the appearance of Klebe and Murray s patent, the applicability of PSCs as precnrsors for Si-C-N ceramics was discovered. Riedel et al. ° fonnd that analogons to aUcoxysilanes, pyridine-catalyzed reactions of chlorosilanes and bis(trimethylsilyl)carbodiimide possess typical sol-gel characteristics (Fignre 18.4). ° ... 

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