Steglich esterification

In the Steglich esterification is a name reaction in organic chemistry. She is an esterification method and was first described in 1978 by Wolfgang Steglich. With this method, the sterically demanding alcohols may be esterified with carboxylic acids.

Overview reaction

Under the influence of dicyclohexyl carbodiimide (DCC) and 4-dimethylaminopyridine ( DMAP), secondary and tertiary alcohols are esterified. Here, R1, R2, R3 and R4 are alkyl or aryl radicals is an alkyl, aryl or hydrogen.

Mechanism

The Steglich esterification is an adaptation of the already longer known to the formation of carboxamides method by means of DCC and 1- hydroxybenzotriazole ( HOBT ) dar. In the presentation of carboxylic acid esters with the DCC method, however, can take place undesirable side reactions. Through a [1,3 ] rearrangement to the O- acylisourea reacts irreversibly to this N- acylisourea. This acyl migration prevent acetyl - transfer agents, such as DMAP. By the so-called Steglich catalyst DMAP DCC activated esterification is accelerated so that the formation of by-products and result absent bulky ester at room temperature in good yields.

For clarity, the following reaction mechanism illustrated with a primary alcohol.

The carboxy group of the carboxylic acid 1 is added to a C = N double bond of the DCC ( N, N'- dicyclohexylcarbodiimide ) ( 2), wherein the O- acylisourea 5 is formed. In this case, the carboxylate anion of the compound 3 and 4 is formed as an intermediate step by protonation of the DCCs. The use of DCC accelerates the reaction, since the reactivity of the O- acylisourea is higher than that of the carboxylic acid.

Is to increase the yield of DMAP (4- dimethylaminopyridine ) (6 ) are used. DMAP is more nucleophilic than alcohol and reacted with the O- acylisourea 5 to a reactive N- Acylpyridiniumion 7

The alcohol then reacts with the reactive intermediate, the N- Acylpyridiniumion 7 in an equilibrium reaction, a proton transfer occurs.

In the last step the deprotonated N, N'- dicyclohexylurea engages the proton of the compound 8 to give the corresponding ester 9 forms and 6 is eliminated. The released water with an esterification takes the DCC to form N, N'-dicyclohexylurea (DCU).

(DCU, "U" stands for the Latin name " Urea " for urea)

747415
de