- For a discussion of copiers using the diazo process, see Whiteprint.
Diazo refers to a type of organic compound that has two linked nitrogen (azo) compounds. The general formula is R2C=N2. The simplest example of a diazo compound is diazomethane. The electronic structure of diazo compounds involves a positive charge on the central nitrogen and negative charge distributed between the terminal nitrogen and the carbon. Some of the most stable diazo compounds are α-diazoketones and α-diazoesters since the negative charge is delocalized into the carbonyl. In contrast, most alkyldiazo compounds are explosive.
Diazo compounds are used as precursors to carbenes, which are generated by thermolysis or photolysis, for example in the Wolff rearrangement. They are also used in transition metal-catalyzed cyclopropanation reactions for example in a synthesis of tranylcypromine   in scheme 1  in which the sodium salt of benzaldehyde tosyl hydrazone is converted to a rhodium metal carbene through the diazo intermediate.
An unusual biomolecule sporting a diazo group was synthesized in 2006 with in its final stage the reaction of a carbonyl group with the hydrazine 1,2-bis(tert-butyldimethylsilyl)hydrazine to the hydrazone followed by reaction with the periodinane difluoroiodobenzene to the diazo compound  
Another commercially relevant diazocompound is Ethyl diazoacetate N2CH2COOEt.
- Catalytic Cyclopropanation of Alkenes Using Diazo Compounds Generated in Situ. A Novel Route to 2-Arylcyclopropylamines Varinder K. Aggarwal, Javier de Vicente, and Roger V. Bonnert Org. Lett.; 2001; 3(17) pp 2785 - 2788; (Letter) Abstract
- Notes: benzaldehyde reacts with p-toluenesulfonyl hydrazide to the hydrazone.Its sodium salt reacts with N-Vinylphthalimide and rhodium acetate, a phase transfer catalyst and PTC to the cyclopropane. The phthalimide group is removed by hydrazine. The product is the cis isomer but by switching to ClFeTPP the amount of trans isomer increases to 33%
- Total Synthesis of the Diazobenzofluorene Antibiotic (-)-Kinamycin C1 Xiaoguang Lei and John A. Porco, Jr. J. Am. Chem. Soc.; 2006; ASAP Web Release Date: 26-Oct-2006; (Communication) doi: 10.1021/ja066621v
- Elusive Natural Product Is Synthesized Stu Borman Chemical & Engineering News October 31, 2006 Link.