Diazo refers to a type of organic compound called diazo compound that has two linked nitrogen atoms (azo) as a terminal functional group. 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-diazo-ß-diketones and α-diazo-ß-diesters since the negative charge is delocalized into the carbonyls. In contrast, most alkyldiazo compounds are explosive. A commercially relevant diazo compound is ethyl diazoacetate (N2CHCOOEt). A group of isomeric compounds with only few similar properties are the diazirines, where the carbon and two nitrogens are linked as a ring.
- 1 History
- 2 Diazo synthesis
- 3 Diazo reactions
- 4 Occurence in nature
- 5 See also
- 6 References
Diazo compounds were first produced by Peter Griess who had discovered a versatile new chemical reaction, as detailed in his "preliminary notice on the influence of nitrous acid on aminonitro- and aminodinitrophenol." 
From diazomethyl compounds
By diazo transfer
From N-alkyl-N-nitroso compounds
Hydrazones are oxidized (dehydrogenation) for example with silver oxide or mercury oxide for example the synthesis of 2-diazopropane from acetone hydrazone. Other oxidizing reagents are lead tetraacetate, manganese dioxide and the Swern reagent. Tosylhydrazones RRC=N-NHTs are reacted with base for example triethylamine in the synthesis of crotyl diazoacetate and in the synthesis of phenyldiazomethane from PhCHNHTs and sodium methoxide.
Reaction of a carbonyl group with the hydrazine 1,2-bis(tert-butyldimethylsilyl)hydrazine to form the hydrazone is followed by reaction with the periodinane difluoroiodobenzene yields the diazo compound:
1,3-disubstituted alkyl aryl triazenes can be fragmentated to form diazo compounds. These triazenes (ArN=NNH-CH2R) result from coupling of aromatic diazonium salts with primary amines but the reaction type is rare.
Diazo compounds react as 1,3-dipoles in diazoalkane 1,3-dipolar cycloadditions.
As carbene precursors
Diazo compounds are used as precursors to carbenes, which are generated by thermolysis or photolysis, for example in the Wolff rearrangement. As such they are used in cyclopropanation for example in the reaction of ethyl diazoacetate with styrene. Certain diazo compounds can couple to form alkenes in a formal carbene dimerization reaction.
In the Doyle-Kirmse reaction certain diazo compounds react with allyl sulfides to the homoallyl sulfide. Intramolecular reactions of diazocarbonyl compounds provide access to cyclopropanes. In the Buchner ring expansion diazo compounds react with aromatic rings with ring-expansion.
The Buchner-Curtius-Schlotterbeck Reaction yields ketones from aldehydes and aliphatic diazo compounds:
The reaction type is nucleophilic addition.
Occurence in nature
Two families of naturally products feature the diazo group: kinamycin and lomaiviticin. These molecules are DNA-intercalators, with diazo functionality as their "warheads". Loss of N2, induced reductively, generates a DNA-cleaving fluorenyl radical.
- F.A. Carey R.J. Sundberg Advanced Organic Chemistry, 2nd Edition
- Trevor I. Williams, ‘Griess, (Johann) Peter (1829–1888)’, Oxford Dictionary of National Biography, Oxford University Press, 2004
- Peter Griess (1858) "Vorläufige Notiz über die Einwirkung von salpetriger Säure auf Amidinitro- und Aminitrophenylsäure," (Preliminary notice of the reaction of nitrous acid with picramic acid and aminonitrophenol], Annalen der Chemie und Pharmacie, 106 : 123-125.
- March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7
- New Syntheses of Diazo Compounds Gerhard Maas Angew. Chem. Int. Ed. 2009, 48, 8186 – 8195 doi:10.1002/anie.200902785
- Example Organic Syntheses, Coll. Vol. 3, p.119 (1955); Vol. 26, p.13 (1946).Link
- M. Regitz, Angew. Chem., 79, 786 (1967); Angew. Chem. Intern. Ed. Engl., 6, 733 (1967).
- Organic Syntheses, Coll. Vol. 5, p.179 (1973); Vol. 48, p.36 (1968). Link
- Organic Syntheses, Coll. Vol. 6, p.414 (1988); Vol. 59, p.66 (1979). Link
- Example: Organic Syntheses, Coll. Vol. 6, p.981 (1988); Vol. 57, p.95 (1977). Link
- Organic Syntheses, Coll. Vol. 6, p.392 (1988); Vol. 50, p.27 (1970). Link
- Organic Syntheses, Coll. Vol. 5, p.258 (1973); Vol. 49, p.22 (1969). Link
- Organic Syntheses, Coll. Vol. 7, p.438 (1990); Vol. 64, p.207 (1986).http://www.orgsyn.org/orgsyn/prep.asp?prep=CV7P0438
- Lei, X.; Porco Ja, J. (2006). "Total synthesis of the diazobenzofluorene antibiotic (-)-kinamycin C1". Journal of the American Chemical Society 128 (46): 14790–14791. doi:10.1021/ja066621v. PMID 17105273.
- Elusive Natural Product Is Synthesized Stu Borman Chemical & Engineering News October 31, 2006 Link.
- A Phosphine-Mediated Conversion of Azides into Diazo Compounds Eddie L. Myers and Ronald T. Raines Angew. Chem. Int. Ed. 2009, 48, 2359 –2363 doi:10.1002/anie.200804689
- Organic Syntheses, Coll. Vol. 6, p.913 (1988); Vol. 50, p.94 (1970).Link