Diglyme, or bis(2-methoxyethyl) ether, is an organic compound with the chemical formula (CH3OCH2CH2)2O. It is a colorless liquid with a slight ether-like odor. It is a solvent with a high boiling point. It is the dimethyl ether of diethylene glycol. The name diglyme is a portmanteau of diglycol methyl ether. It is miscible with water as well as organic solvents.
It is prepared by a reaction of dimethyl ether and ethylene oxide over an acid catalyst.
Solvent
Because of its resistance to strong bases, diglyme is favored as a solvent for reactions of alkali metal reagents even at high temperatures. Rate enhancements in reactions involving organometallic reagents, such as Grignard reactions or metal hydride reductions, have been observed when using diglyme as a solvent.23
Diglyme is also used as a solvent in hydroboration reactions with diborane.45
It serves as a chelate for alkali metal cations, leaving anions more active.
Safety
The European Chemicals Agency lists diglyme as a substance of very high concern (SVHC) as a reproductive toxin.6
At higher temperatures and in the presence of active metals diglyme is known to decompose, which can produce large amounts of gas and heat.7 This decomposition led to the T2 Laboratories reactor explosion in 2007.8
References
Siegfried Rebsdat; Dieter Mayer. "Ethylene Glycol". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a10_101. ISBN 978-3-527-30673-2. 978-3-527-30673-2 ↩
J. E. Ellis; A. Davison; G. W. Parshall; E. R. Wonchoba (1976). "Tris[Bis(2‐Methoxyethyl)Ether]Potassium and Tetraphenylarsonium Hexacarbonylmetallates(1–) of Niobium and Tantalum". In Fred Basolo (ed.). Inorganic Syntheses. Vol. 16. pp. 68–73. doi:10.1002/9780470132470.ch21. ISBN 978-0-470-13247-0. 978-0-470-13247-0 ↩
J. E. Siggins; A. A. Larsen; J. H. Ackerman; C. D. Carabateas (1973). "3,5-Dinitrobenzaldehyde". Organic Syntheses. 53: 52. doi:10.15227/orgsyn.053.0052. /wiki/Doi_(identifier) ↩
Michael W. Rathke; Alan A. Millard (1978). "Boranes in Functionalization of Olefins to Amines: 3-Pinanamine". Organic Syntheses. 58: 32. doi:10.15227/orgsyn.058.0032. /wiki/Doi_(identifier) ↩
Ei-ichi Negishi; Herbert C. Brown (1983). "Perhydro-9b-Boraphenalene and Perhydro-9b-Phenalenol". Organic Syntheses. 61: 103. doi:10.15227/orgsyn.061.0103. /wiki/Doi_(identifier) ↩
"Inclusion of Substances of Very High Concern in the Candidate List (Decision of the European Chemicals Agency)". 19 Dec 2011. https://www.echa.europa.eu/documents/10162/ee023359-daa8-43a2-8c82-242f0a7588f7 ↩
Pitt, Martin J. (July 12, 2010). "Chemical Safety: Dangers Of Diglyme". cen.acs.org. Archived from the original on 2012-05-11. Retrieved 2021-09-01. https://cen.acs.org/articles/88/i28/Chemical-Safety-Dangers-Diglyme.html ↩
Willey, Ronald J.; Fogler, H. Scott; Cutlip, Michael B. (March 2011). "The integration of process safety into a chemical reaction engineering course: Kinetic modeling of the T2 incident". Process Safety Progress. 30 (1): 39–44. doi:10.1002/prs.10431. hdl:2027.42/83180. S2CID 109207593. https://onlinelibrary.wiley.com/doi/10.1002/prs.10431 ↩