DABCO explained

DABCO (1,4-diazabicyclo[2.2.2]octane), also known as triethylenediamine or TEDA, is a bicyclic organic compound with the formula N₂(C₂H₄)₃. This colorless solid is a highly nucleophilic tertiary amine base, which is used as a catalyst and reagent in polymerization and organic synthesis.^[1]

It is similar in structure to quinuclidine, but the latter has one of the nitrogen atoms replaced by a carbon atom. Regarding their structures, both DABCO and quinuclidine are unusual in that the methylene hydrogen atoms are eclipsed within each of the three ethylene linkages. Furthermore, the diazacyclohexane rings, of which there are three, adopt the boat conformations, not the usual chair conformations.

Reactions

The pK_a of [HDABCO]⁺ (the protonated derivative) is 8.8, which is almost the same as ordinary alkylamines. The nucleophilicity of the amine is high because the amine centers are unhindered. It is sufficiently basic to promote a variety of coupling reactions.

Catalyst

DABCO is used as a nucleophilic catalyst for:

• formation of polyurethane from alcohol and isocyanate functionalized monomers and pre-polymers.^[2]
• Baylis–Hillman reactions of aldehydes and unsaturated ketones and aldehydes.^[3]

Lewis base

thumb|left|Selectfluor|110pxThe reagent Selectfluor is derived by alkylation of DABCO with dichloromethane following by treatment with fluorine. A colourless salt that tolerates air, Selectfluor has been commercialized for use for electrophilic fluorination.^[4]

As an unhindered amine, it is a strong ligand and Lewis base. It forms a crystalline 2:1 adduct with hydrogen peroxide^[5] and sulfur dioxide.^[6]

Quencher of singlet oxygen

DABCO and related amines are quenchers of singlet oxygen and effective antioxidants,^[7] and can be used to improve the lifetime of dyes. This makes DABCO useful in dye lasers and in mounting samples for fluorescence microscopy (when used with glycerol and PBS).^[8] DABCO can also be used to demethylate quaternary ammonium salts by heating in dimethylformamide (DMF).^[9]

Production

It is produced by thermal reactions of compounds of the type H₂NCH₂CH₂X (X = OH, NH₂, or NHR) in the presence of zeolitic catalysts. An idealized conversion is shown for the conversion from ethanolamine:^[10]

3 H₂NCH₂CH₂OH → N(CH₂CH₂)₃N + NH₃ + 3 H₂O

Uses

In chemical and biological defense, activated carbon is impregnated with DABCO for use in filters for masks, collective protection systems, and the like.^[11]

Further reading

• Cecchi, L. . DeSarlo, F. . Machetti, F. . 1,4-Diazabicyclo[2.2.2]octane (DABCO) as an Efficient Reagent for the Synthesis of Isoxazole Derivatives from Primary Nitro Compounds and Dipolarophiles: The Role of the Base . European Journal of Organic Chemistry . 2006 . 21 . 4852–4860 . 2006 . 10.1002/ejoc.200600475. .

Notes and References

1. Uppuluri V. Mallavadhani, Nicolas Fleury-Bregeot. "1,4-Diazabicyclo [2.2.2]octane". In Encyclopedia of Reagents for Organic Synthesis, 2010, John Wiley & Sons, Ltd.
2. Web site: Polyurethane additives guide . https://web.archive.org/web/20160306222927/http://www.airproducts.com/~/media/Files/PDF/industries/en-pua-guide-americas.pdf . dead . 2016-03-06 . Air Products & Chemicals.
3. Baylis, A. B.; Hillman, M. E. D. German Patent 2155113, 1972.
4. Book: 10.1002/047084289X.rc116.pub2. 1-(Chloromethyl)-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane Bis(tetrafluoroborate). Encyclopedia of Reagents for Organic Synthesis. 2007. Banks. R. Eric. Murtagh. Vincent. An. Ilhwan. Maleczka. Robert E.. 978-0471936237.
5. P. Dembech, A. Ricci, G. Seconi, and M. Taddei "Bis(trimethylsilyl) Peroxide" Org. Synth. 1997, volume 74, pp. 84.
6. Ludovic Martial and Laurent Bischoff "Preparation of DABSO from Karl-Fischer Reagent" Org. Synth. 2013, volume 90, pp. 301.
7. Ouannes, C. . Wilson, T. . Quenching of singlet oxygen by tertiary aliphatic amines. Effect of DABCO (1,4-diazabicyclo[2.2.2]octane) . . 1968 . 90 . 23 . 6527–6528 . 10.1021/ja01025a059.
8. Valnes, K. . Brandtzaeg, P. . Retardation of immunofluorescence fading during microscopy . Journal of Histochemistry and Cytochemistry . 33 . 8 . 755–761 . 1985 . 3926864 . 10.1177/33.8.3926864 . free .
9. Ho, T. L. . Dealkylation of Quaternary Ammonium Salts with 1,4-Diazabicyclo[2.2.2]octane . . 1972 . 1972 . 12 . 702 . 10.1055/s-1972-21977.
10. Karsten Eller, Erhard Henkes, Roland Rossbacher, Hartmut Höke "Amines, Aliphatic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.
11. Mahle, J. . etal . Role of TEDA as an Activated Carbon Impregnant for the Removal of Cyanogen Chloride from Air Streams: Synergistic Effect with Cu(II) . Journal of Physical Chemistry C . 114 . 47 . 20083–20090 . 2010 . 10.1021/jp106730j . 2022-03-17.