3D model (Jmol)
|Molar mass||206.33 g·mol−1|
|Appearance||white crystalline powder|
|Density||1.325 g/cm3, solid|
|Melting point||34 °C (93 °F; 307 K)|
|Boiling point||122 °C (252 °F; 395 K) (at 6 mmHg)|
|R-phrases||R22 R24 R41 R43|
|S-phrases||S24 S26 S37/39 S45|
|Flash point||113 °C (235 °F; 386 K)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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N,N'-Dicyclohexylcarbodiimide is an organic compound with the chemical formula C13H22N2 whose primary use is to couple amino acids during artificial peptide synthesis. Under standard conditions, it exists in the form of white crystals with a heavy, sweet odor. 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. The compound is often abbreviated as DCC or DCCD.
Structure and spectroscopy
The C-N=C=N-C core of carbodiimides (N=C=N) is linear, being related to the structure of allene. Three principal resonance structures describe carbodiimides:
- RN=C=NR ↔ RN+≡C-N−R ↔ RN−-C≡N+R
The N=C=N moiety gives characteristic IR spectroscopic signature at 2117 cm−1. The 15N NMR spectrum shows a characteristic shift of 275.0 ppm upfield of nitric acid and the 13C NMR spectrum features a peak at about 139 ppm downfield from TMS.
Of the several syntheses of DCC, Pri-Bara et al. use palladium acetate, iodine, and oxygen to couple cyclohexyl amine and cyclohexyl isocyanide. Yields of up to 67% have been achieved using this route:
- C6H11NC + C6H11NH2 + O2 → (C6H11N)2C + H2O
DCC has also been prepared from dicyclohexylurea using a phase transfer catalyst by Jaszay et al. The disubstituted urea, arenesulfonyl chloride, and potassium carbonate react in toluene in the presence of benzyl tetraethylammonium chloride to give DCC in 50% yield.
DCC is a dehydrating agent for the preparation of amides, ketones, 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.
Reaction of an acid with hydrogen peroxide in presence of DCC leads to formation of peroxide linkage.
A solution of DCC and dimethyl sulfoxide (DMSO) effects the so-called Pfitzner-Moffatt oxidation. This procedure is used for the oxidation of alcohols to aldehydes and ketones. Unlike metal-mediated oxidations, the reaction conditions are sufficiently mild to avoid over-oxidation of aldehydes to carboxylic acids. Generally, three equivalents of DCC and 0.5 equivalent of proton source in DMSO are allowed to react overnight at room temperature. The reaction is quenched with acid.
Alcohols can also be dehydrated using DCC. This reaction proceeds by first giving the O-acylurea intermediate which is then hydrogenolyzed to produce the corresponding alkene:
- RCHOHCH2R' + (C6H11N)2C → RCH=CHR' + (C6H11NH)2CO
Inversion of secondary alcohols
Secondary alcohols can be stereochemically inverted by formation of a formyl ester followed by saponification. The secondary alcohol is mixed directly with DCC, formic acid, and a strong base such as sodium methoxide.
DCC-promoted peptide coupling
During 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.
DCC is a potent allergen and a sensitizer, often causing skin rashes.
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- Neises, B.; Steglich, W. (1985). "Esterification of Carboxylic Acids with Dicyclohexylcarbodiimide/4-Dimethylaminopyridine: Tert-Butyl Ethyl Fumarate". Org. Synth. 63: 183. ; Coll. Vol., 7, p. 93
- An excellent illustration of this mechanism can be found here: .