Carbonyldiimidazole

Crystalline colorless to yellowish solid

Fixed

116-120 ° C

Decomposition with water

Risk

1071 mg · kg -1 ( LD50, rat, oral)

Template: Infobox chemical / molecular formula search available

1,1 '-carbonyldiimidazole ( also abbreviated as CDI) is a colorless crystalline organic compound. It is used inter alia as a reagent in peptide chemistry, and organic synthesis.

Production

CDI is produced directly by the reaction of phosgene with four equivalents of imidazole under anhydrous conditions. After removal of the by-product, imidazole hydrochloride, and the CDI solvent is obtained in a yield of about 90%.

In this reaction imidazole acts both as a nucleophile as well as the base. In the hydrolysis of CDI arises again with elimination of carbon dioxide, the imidazole. Here, by determining the amount of carbon dioxide developed, the content of CDI can be determined.

For use in organic synthesis

CDI is mainly used in the reaction of alcohols and amines to form the corresponding urea, carbamate, or ester derivatives. CDI is a safe Syntheseequivalent phosgene as its toxicity is much lower.

Carboxylic acid derivatives

CDI can be used to activate carboxylic acids. This first forms a mixed anhydride, which then merges with the elimination of carbon dioxide in a acylimidazole. These activated species react in subsequent reactions as the corresponding carbonyl halides include, but are easier to handle and thus have a considerably wider range of applications.

The mechanism of this transformation is not yet fully elucidated. After the formation of the mixed anhydride two ways are discussed: (A) Intermolecular nucleophilic attack of a cleaved imidazole, followed by the elimination of carbon dioxide and imidazole or (B) Intramolecular nucleophilic attack of the " anhydride - imidazole " group, followed by ring opening and carbon dioxide elimination.

In peptide synthesis as the activated carboxylic acid is added to an appropriate amino acid or peptide, and there is obtained the corresponding amino acid to the peptide extended with elimination of carbon dioxide and imidazole. The Racemesierungsneigung of amino acids is low here due to the mild conditions.

CDI can also be used for esterification. Because behave similar to the CDI carbonyl halides adducts of carboxylic acids, is the product of the reaction with strong nucleophiles such as alkoxides Selbiger the corresponding ester. But the reaction with thiols and selenols are known and lead to the corresponding sulfur and selenium analogues of an ester. Is used as the nucleophile as an acetal to give the corresponding glycoside.

Instead of the alcohol may also be a carboxylic acid be used as the nucleophile, the product is the corresponding anhydride. The carboxylic acid used in the double surplus, since then accumulates the insoluble and easily separable salt of imidazole as a by- product - It is best - when the carboxylic acid is inexpensive. Is formic acid used as the nucleophile, the result is a potent formylation reagent.

Other reactions

Upon reaction with a phosphonium ylide salt is formed. These can in a further step, after deprotonation, are reacted in a Wittig reaction to an α, β -unsaturated carbonyl compound.

Reduction with lithium aluminum hydride yields the aldehyde and on the other hand only a little alcohol or amine. In the reaction with the Grignard reagent is obtained in a manner analogous to the ketone.

With acetyl acetate anions substituted 1,3-diketone is obtained by formation of a new carbon-carbon bond.

CDI can occur as a carbonyl equivalent in the synthesis of tetronic acids or Pulvinonen. For example, acetol ( Hydroxaceton ) reacts with CDI under basic conditions to tetronic acid.