Dicyclohexyl urea

DCC is a waxy solid that is often difficult to remove from a bottle. Its vapors are extremely hazardous to inhalation and to the eyes. It should always be handled in a fume hood. The isourea by-product of a DCC-initiated reaction, dicyclohexyl urea (DCU) (Figure 3.5), is also water-insoluble and must be removed by organic solvent washing. For synthesis of peptides or affinity supports on insoluble matrices this is not a problem, because washing of the support material can be done without disturbing the conjugate coupled to the support. For solution phase chemistry, however, reaction products must be removed by solvent washings, precipitations, or recrystallizations. 

Remove the insoluble dicyclohexyl urea (DCU) by-product by filtration using a glass fiber filter pad and vacuum. 

QH5CO—O—O—OCQH, + CftHji-NHCNHQHii Dibenzoyl peroxide Dicyclohexyl urea... 

Dicyclohexyl carbodimide [538-75-0] M 206.3, m 34-35°, b 95-97°/0.2mm, 120-I2l°/0.6mm, 155°/llmm. It is sampled as a liquid after melting in warm HzO. It is sensitive to air and it is a potent skin irritant. It can be distd in a vacuum and stored in a tightly stoppered flask in a freezer. It is very soluble in CH2CI2 and pyridine where the reaction product with H20, after condensation, is dicyclohexyl urea which is insoluble and can be removed by filtration. Alternatively dissolve in CH2C12 add powdered anhyd MgS04 shake 4h, filter, evaporate and distil at 0.6 mm press and oil bath temperature 145°. [Biochem Prep 10, 122 1963 A 571 83 1951, A 612 11 1958]. 

Urea A is the starting material for preparing the carbodiimide C, which activates carboxylic acids according to the same mechanism and for the same reason as DCC, with which you are already familiar (Figures 6.15 and 6.26). If the carbodiimide C from Figure 7.5 were not so much more expensive than DCC, everybody would use the former instead of the latter for carboxylic acid activation. There is a practical reason for this. When a heteroatom nucleophile is acylated with the DCC adduct of a carboxylic acid, besides the desired carboxylic acid derivative one obtains dicyclohexyl urea (formula B in Figure 7.5). This (stoichiometric) by-product must be separated from the acylation product, which is relatively laborious when realized by chromatography or by crystallization. When a carboxylic add has been activated with the carbodiimide C and the subsequent acylation of a heteroatom nucleophile has been effected, one also obtains a urea as a stoichiometric by-product. It has the structure D and is therefore... 

Use of DCC as a Peptide Coupling Agent The final reaction needed for the Merrifield procedure is the peptide bond-forming condensation. When a mixture of an amine and an acid is treated with 7V,iV -dicyclohcxylcarbodiimidc (abbreviated DCC), the amine and the acid couple to form an amide. The molecule of water lost in this condensation converts DCC to N,N -dicyclohexyl urea (DCU). 

Figure 15 Experimental (left) and calculated (right) 170 MAS spectra of [170]-N,N-dicyclohexyl-urea at various sample spinning rates. Reproduced with permission from Ref. 33.

Diisooctyl phthalate (plasticiser) Diisooctyl phthalate (plasticiser) Diisooctyl phthalate (plasticiser) Dicyclohexyl urea (DCU)... 

A carboxylic acid and an amine readily react to form an amide in the presence of an additional reagent, dicyclohexylcarbodiimide (DCC), which is converted to the by-product dicyclohexyl-urea in the course of the reaction. 

Fig. 6.31). The isolated yields of dicyclohexyl urea and dibenzyl urea were 85% and 83%. These results suggested that the activation of CO2 over polymer-supported nanogold catalysts could be universal. 

---