Diethyl azodicarboxylate

Diethyl azodicarboxylate, often abbreviated DEAD, is the organic compound CH3CH2O2CN=NCO2CH2CH3. As indicated with this formula, the molecule consists of a central azo functional group, RN=NR, flanked by two ethyl ester groups. This red orange liquid is a valuable reagent but also quite dangerous.

Preparation
Although widely available, diethyl azodicarboxylate can be prepared in the laboratory. A two-step synthesis starts from hydrazine, first by alkylation with ethyl chloroformate. followed by treating the resulting ethyl hydrazodicarboxylate with chlorine.
 * 2 CH3CH2O2CCl +    N2H4  → CH3CH2O2CN(H)N(H)CO2CH2CH3  +  2  HCl
 * CH3CH2O2CN(H)N(H)CO2CH2CH3 +  Cl2  →  CH3CH2O2CN=NCO2CH2CH3  +  2 HCl

Red fuming nitric acid can also be used in the second step.

Applications
DEAD is an efficient component in Diels-Alder reactions and in click chemistry, for example the synthesis of Bicyclo[2.1.0]pentane, which originates from Otto Diels.

DEAD is an important reagent in the Mitsunobu reaction where it forms an adduct with phosphines. In one study the compound together with triphenylphosphine and a chalcone formed a pyrazoline:


 * [[Image:HuisgenZwitterion.png|400px|reraction of DEAD / triphenylphosphine with chalcones]]

Safety
DEAD is toxic, shock sensitive, and thermally unstable. It is handled as a solution, rarely as the pure compound.