DABCO

DABCO

Names
IUPAC name 1,4-Diazabicyclo[2.2.2]octane
Other names Triethylenediamine, TEDA
Identifiers
CAS Number	280-57-9
ChemSpider	8882
IUPHAR/BPS	2577
Jmol interactive 3D	Image Image
PubChem	9237
InChI InChI=1S/C6H12N2/c1-2-8-5-3-7(1)4-6-8/h1-6H2 Key: IMNIMPAHZVJRPE-UHFFFAOYSA-N InChI=1S/C6H12N2/c1-2-8-5-3-7(1)4-6-8/h1-6H2 Key: IMNIMPAHZVJRPE-UHFFFAOYSA-N InChI=1/C6H12N2/c1-2-8-5-3-7(1)4-6-8/h1-6H2 Key: IMNIMPAHZVJRPE-UHFFFAOYAP
SMILES C1CN2CCN1CC2 N12CCN(CC1)CC2
Properties
Chemical formula	C6H12N2
Molar mass	112.18 g·mol^−1
Appearance	White crystalline powder
Melting point	156 to 160 °C (313 to 320 °F; 429 to 433 K)
Boiling point	174 °C (345 °F; 447 K)
Solubility in water	Soluble, hygroscopic
Acidity (pKa)	3.0, 8.8 (in water)[1]
Hazards
Main hazards	Harmful
GHS hazard statements	H228, H302, H315, H319, H335, H412
GHS precautionary statements	P210, P261, P273, P305 + P351 + P338
R-phrases	R11, R22, R36/37/38, R52/53
S-phrases	S26, S60
NFPA 704	[2] 2 2 1
Flash point	62 °C (144 °F; 335 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

DABCO (1,4-diazabicyclo[2.2.2]octane) is an organic compound with the formula N₂(C₂H₄)₃. This colorless solid is a highly basic amine, which is used as a catalyst and reagent in polymerization and organic synthesis.^[3]

Quinuclidine has a similar structure, with one of the nitrogen atoms replaced by a carbon atom.

Reactions and applications

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 C-C coupling of terminal acetylenes, for example, phenylacetylene couples with electron-deficient iodoarenes.

Catalyst

DABCO is used as a base-catalyst for:

• formation of polyurethane from amines and isocyanates.^[4]
• Baylis-Hillman and Morita-Baylis-Hilman reactions of aldehydes and unsaturated ketones and aldehydes.^[5]

Lewis base

As an unhindered amine, it is a strong ligand and Lewis base. It forms a crystalline 2:1 adduct with hydrogen peroxide^[6] and sulfur dioxide.^[7]

Quencher of singlet oxygen

DABCO and related amines are quenchers of singlet oxygen and effective antioxidants,^[8] 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).^[9] DABCO can also be used to demethylate quaternary ammonium salts by heating in dimethylformamide (DMF).^[10]

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:^[11]

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

References

1. D. H. Ripin, D. A. Evans (2002). "pKa's of Nitrogen Acids" (PDF).
2. "Safety data for 1,4-diazabicyclo[2.2.2]octane (see MSDS)". Sigma-Aldrich.
3. 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. doi:10.1002/047084289X.rd010m.pub2
4. "Polyurethane additives guide" (PDF). Air Products & Chemicals.
5. Baylis, A. B.; Hillman, M. E. D. German Patent 2155113, 1972.
6. P. Dembech, A. Ricci, G. Seconi, and M. Taddei "Bis(trimethylsilyl) Peroxide" Org. Synth. 1997, volume 74, pp. 84. doi:10.15227/orgsyn.074.0084
7. Ludovic Martial and Laurent Bischoff "Preparation of DABSO from Karl-Fischer Reagent" Org. Synth. 2013, volume 90, pp. 301. doi:10.15227/orgsyn.090.0301
8. Ouannes, C.;, Wilson, T. (1968). "Quenching of singlet oxygen by tertiary aliphatic amines. Effect of DABCO (1,4-diazabicyclo[2.2.2]octane)". Journal of the American Chemical Society 90 (23): 6527–6528. doi:10.1021/ja01025a059.
9. Valnes, K.; Brandtzaeg, P. (1985). "Retardation of immunofluorescence fading during microscopy" (pdf). Journal of Histochemistry and Cytochemistry 33 (8): 755–761. PMID 3926864.
10. Ho, T. L. (1972). "Dealkylation of Quaternary Ammonium Salts with 1,4-Diazabicyclo[2.2.2]octane". Synthesis 1972 (12): 702. doi:10.1055/s-1972-21977.
11. Karsten Eller, Erhard Henkes, Roland Rossbacher, Hartmut Höke "Amines, Aliphatic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. doi:10.1002/14356007.a02_001

Further reading

• Cecchi, L.; DeSarlo, F.; Machetti, F. (2006). "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. doi:10.1002/ejoc.200600475..