N,N'-Dicyclohexylcarbodiimide

• Dicyclohexylcarbodiimide
• DCC
• Carbodiimidyldicylohexan

Colorless solid

Fixed

0.95 g · cm -3 ( 40 ° C)

35-36 ° C

154-156 ° C (at 15 hPa)

Insoluble in water

Risk

1110 mg · kg -1 ( LD50, rat, oral)

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N, N'- dicyclohexylcarbodiimide ( abbreviated as DCC, and N, N'- Dicyclohexylmethandiimin ) is a reactive organic compound is selected from the group of the carbodiimides, which is frequently used in synthetic chemistry. In standard conditions DCC is a colorless solid with a faint characteristic odor.

Representation and extraction

A view seen from the dicyclohexylthiourea, wherein the target compound is produced by the reaction with mercury ( II) oxide with a sulfur-oxygen exchange intermediate the corresponding urea derivative, and, after subsequent dehydration.

In a similar synthetic route dicyclohexylurea is dehydrated in the presence of p-toluenesulfonyl chloride and triphenylphosphine and potassium carbonate as a base or triethylamine as base.

Properties

Dicyclohexylcarbodiimide is a low melting solid with a melting point of 34-35 ° C. In colder ambient temperatures, the fabric may also be present as liquid supercooled melt. Since the compound tends to polymerize at high temperatures and decomposition, a distillation can be carried out only under a reduced pressure. The boiling point is at a pressure of 15 mbar at 148 to 152 ° C. The flash point is 113 ° C is relatively high.

Use

DCC is used mainly in the synthesis of organic esters and amides using. Especially with bulky reactants leading to important increases in yield. Furthermore, it allows - in contrast to the Fischer esterification - esterification and amidation reactions under very mild conditions, which is acid labile reactants such as tert -butyl alcohol of interest. Therefore, DCC also plays an important role in the in vitro peptide synthesis and in the introduction of protecting groups.

Esterification and amidation reactions with DCC

Carboxy quickly add to a C = N double bond of the DCC, and the corresponding O- acylisourea is formed. This ester is very reactive (comparable to an acid anhydride ), so that it is easily converted to the amide of amines. For the reaction with alcohols in addition an acyl - transfer agents such as DMAP is required and it is called a Steglich esterification. In sum, the acid resulting from the condensation of the alcohol / amine hydrogen is absorbed by the DCC and this implemented by the N, N' -dicyclohexylurea.

Esterification occurs at a competing reaction is often the 1,3- rearrangement, into which the O - acylisourea reacts irreversibly to the N- acyl urea. Both acyl - carrier and acid catalysis can suppress this reaction, but both are still the subject of current research. Other problems of these reactions result in particular in the cleaning product from the resultant N, N'- dicyclohexylurea formed, or by also acid anhydrides.

DCC -activated esterification reactions are generally carried out at 0 to 25 ° C and in dry (DCC is sensitive to water ) dichloromethane performed because hereby in the past, the best yields were obtained. Also the forming urea derivative is insoluble in dichloromethane and falls from the reaction solution.

As an alternative to the DCC other carbodiimides, and the standard protective group of di-tert -butyl dicarbonate ( Boc2O ) have been proposed.

Safety

DCC may already be toxic in contact with skin, but also cause severe irritation of the respiratory tract or eye damage. DCC has a sensitizing effect.