Diethyl azodicarboxylate, conventionally abbreviated as DEAD and sometimes as DEADCAT, is an organic compound with the structural formula CH3CH2O2CN=NCO2CH2CH3. Its molecular structure consists of a central azo functional group, RN=NR, flanked by two ethyl ester groups. This orange-red liquid is a valuable reagent but also quite dangerous and explodes upon heating. Therefore, commercial shipment of pure diethyl azodicarboxylate is prohibited in the United States and is carried out either in solution or on polystyrene particles. DEAD is an aza-dienophile and an efficient dehydrogenating agent, converting alcohols to aldehydes, thiols to disulfides and hydrazo groups to azo groups; it is also a good electron acceptor. While DEAD is used in numerous chemical reactions it is mostly known as a key component of the Mitsunobu reaction, a common strategy for the preparation of an amine, azide, ether, thioether, or ester from the corresponding alcohol. It is used in the synthesis of various natural products and pharmaceuticals such as zidovudine, an AIDS drug; FdUMP, a potent antitumor agent; and procarbazine, a chemotherapy drug. Properties DEAD is an orange-red liquid which weakens its color to yellow or colorless upon dilution or chemical reaction. This color change is conventionally used for visual monitoring of the synthesis. DEAD dissolves in most common organic solvents, such as toluene, chloroform, ethanol, tetrahydrofuran and dichloromethane but has low solubility in water or carbon tetrachloride; the solubility in water is higher for the related azo compound dimethyl azodicarboxylate. DEAD is a strong electron acceptor and easily oxidizes a solution of sodium iodide in glacial acetic acid. It also reacts vigorously with hydrazine hydrate producing diethyl hydrazodicarboxylate and evolving nitrogen. Linear combination of atomic orbitals molecular orbital method (LCAO-MO) calculations suggest that the molecule of DEAD is unusual in having a high-lying vacant bonding orbital, and therefore tends to withdraw hydrogen atoms from various hydrogen donors. Photoassisted removal of hydrogen by DEAD was demonstrated for isopropyl alcohol, resulting in pinacol and tetraethyl tetrazanetetracarboxylate, and for acetaldehyde yielding diacetyl and diethyl hydrazodicarboxylate. Similarly, reacting DEAD with ethanol and cyclohexanol abstracts hydrogen producing acetaldehyde and cyclohexanone. Those reactions also proceed without light, although at much lower yields. Thus, in general DEAD is an aza-dienophile and dehydrogenating agent, converting alcohols to aldehydes, thiols to disulfides and hydrazo groups to azo groups. It also undergoes pericyclic reactions with alkenes and dienes via Ene and Diels–Alder mechanisms. Preparation Although available commercially, diethyl azodicarboxylate can be prepared