N,N'-Dicyclohexylcarbodiimide
"N","N"′-Dicyclohexylcarbodiimide (DCC or DCCD) is an organic compound with the chemical formula (CHN)C. It is a waxy white solid with a sweet odor. Its primary use is to couple amino acids during artificial peptide synthesis. The low melting point of this material allows it to be melted for easy handling. It is highly soluble in dichloromethane, tetrahydrofuran, acetonitrile and dimethylformamide, but insoluble in water. Structure and spectroscopy. The C−N=C=N−C core of carbodiimides (N=C=N) is linear, being related to the structure of allene. The molecule has idealized C symmetry. The N =C=N moiety gives characteristic IR spectroscopic signature at 2117 cm. The N NMR spectrum shows a characteristic shift of 275 ppm upfield of nitric acid and the C NMR spectrum features a peak at about 139 ppm downfield from TMS. Preparation. DCC is produced by the decarboxylation of cyclohexylisocyanate using phosphine oxides as a catalyst: Alternative catalysts for this conversion include the highly nucleophilic OP(MeNCHCH)N. Other methods. Of academic interest, palladium acetate, iodine, and oxygen can be used to couple cyclohexyl amine and cyclohexyl isocyanide. Yields of up to 67% have been achieved using this route: DCC  has also been prepared from dicyclohexylurea using a phase transfer catalyst. The disubstituted urea, arenesulfonyl chloride, and potassium carbonate react in toluene in the presence of benzyl triethylammonium chloride to give DCC in 50% yield. Reactions. Amide, peptide, and ester formation. DCC is a dehydrating agent for the preparation of amides, ketones, and nitriles. In these reactions, DCC hydrates to form dicyclohexylurea (DCU), a compound that is nearly insoluble in most organic solvents and insoluble in water. The majority of the DCU is thus readily removed by filtration, although the last traces can be difficult to eliminate from non-polar  products. DCC can also be used to invert secondary alcohols. In the Steglich esterification, alcohols, including even some tertiary alcohols, can be esterified using a carboxylic acid in the presence of DCC and a catalytic amount of DMAP. In protein synthesis (such as Fmoc solid-state synthesizers), the N-terminus is often used as the attachment site on which the amino acid monomers are added. To enhance the electrophilicity of carboxylate group, the negatively charged oxygen must first be "activated" into a better leaving group. DCC is used for this purpose. The negatively charged oxygen will act as a nucleophile , attacking the central carbon in DCC. DCC is temporarily attached to the former carboxylate group forming a highly electrophilic intermediate, making nucleophilic attack by the terminal amino group on the growing peptide more efficient. Moffatt oxidation. In combination with dimethyl sulfoxide (DMSO), DCC effects the Pfitzner-Moffatt oxidation. This procedure is used for the oxidation of alcohols to aldehydes and ketones. Unlike metal-mediated oxidations, such as the Jones oxidation, the reaction conditions are sufficiently mild to avoid over-oxidation of aldehydes to carboxylic acids. Generally, three equivalents of DCC and 0.5 equivalents of proton source in DMSO are allowed  to react overnight at room temperature. The reaction is quenched with acid. Biological action. DCC is a classical inhibitor of ATP synthase. DCC inhibits ATP synthase by binding to one of the "c" subunits and causing steric hindrance of the rotation of the F subunit. Safety. DCC is a potent allergen and a sensitizer, often causing skin rashes.