Triisopropylamine

Not to be confused with Triisopropanolamine.
Triisopropylamine
Skeletal formula of triisopropylamine
Skeletal formula of triisopropylamine
Names
Preferred IUPAC name
N,N-Di(propan-2-yl)propan-2-amine
Other names
Tri(propan-2-yl)amine
(Triisopropyl)amine
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.020.289 Edit this at Wikidata
EC Number
  • 222-317-5
UNII
  • InChI=1S/C9H21N/c1-7(2)10(8(3)4)9(5)6/h7-9H,1-6H3 ☒N
    Key: RKBCYCFRFCNLTO-UHFFFAOYSA-N ☒N
  • CC(C)N(C(C)C)C(C)C
Properties
C9H21N
Molar mass 143.274 g·mol−1
Appearance Colorless liquid
Odor Ichtyal, ammoniacal
Density 0.752 g/cm3
Boiling point 131.8 °C (269.2 °F; 404.9 K) 47°C at 1.9 kPa
Related compounds
Related amines
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Triisopropylamine is an organic chemical compound consisting of three isopropyl groups bound to a central nitrogen atom.[1][2] As a hindered tertiary amine, it can be used as a non-nucleophilic base and as a stabilizer for polymers; however, its applications are limited by its relatively high cost and difficult synthesis.

Structure

In the early 1990s, theoretical studies and electron diffraction analysis of the 3D structure of the molecule, in the gas phase or in non-polar solvents, indicated that the bonds between the nitrogen atom and the three carbon atoms were nearly coplanar in the ground state, instead of forming a trigonal pyramid as in simpler amines.[3][4] The average C-N-C angle was claimed to be 119.2°,[2] much closer to the 120° of the flat configuration than to the 111.8° of trimethylamine. This peculiarity was attributed to steric hindrance by the bulky isopropyl radicals. However, in 1998 X-ray diffraction analysis of the crystallized solid showed that the C3N core is actually pyramidal, with the N atom lying approximately 0.28 Å off the carbons' plane (whereas in trimethylamine the distance is about 0.45 Å). However the researchers could not rule out the crystal field effect as the cause of the asymmetry.[5]

The C-C-C planes of the isopropyl groups are slightly tilted (about 5°) relative to the threefold symmetry axis of the C3N core.[3][5][6]

Even more hindered amines

Triisopropylamine is notable as being among the most sterically hindered amines currently known. To date, di(tert-alkyl)(sec-alkyl)amines like di-tert-butyl(isopropyl)amine (tBu2iPrN) and diadamantylcyclohexylamine (Ad2CyN) have been prepared in low yield, as have a handful of tri-tert-alkylamines in which two of the tert-alkyl groups are tied together in a five-membered ring. As a result of the extreme steric crowding, these tertiary amines were found to be unusually susceptible to β-elimination to give an alkene and a secondary amine, even at temperatures close to room temperature (as low as 40 °C). As a result of these and other synthetic difficulties, the authors of a 2018 study predict that the even more crowded tri-tert-butylamine (tBu3N, unknown as of 2023) will likely remain a longstanding unsolved synthetic challenge, even though ab initio calculations indicate that it would be of reasonable stability if it could be prepared.[7] Calculations indicate that tri-tert-butylamine should be planar at nitrogen. Though arguably a more hindered molecule, the structurally analogous tri-tert-alkyl carbinol 2,2,4,4-tetramethyl-3-t-butyl-pentane-3-ol (tri-tert-butylcarbinol, tBu3COH), has been known for decades (prepared by Bartlett and coworkers in 1945).

Preparation

Steric effects make triisopropylamine difficult to synthesise and unlike less hindered tertiary amines (such as triethylamine) it cannot be produced by the alkylation of ammonia with alcohol; attempts to do so stall at diisopropylamine. It can be prepared from diisopropylamine on the laboratory scale:[2]

See also

References

  1. ^ G. Graner, E. Hirota, T. Iijima, K. Kuchitsu, D. A. Ramsay, J. Vogt and N. Vogt (2003), C9H21N, Triisopropylamine. In Molecules Containing Five or More Carbon Atoms, volume 25D of the series Landolt-Börnstein - Group II Molecules and Radicals. Springer-Verlag. ISBN 978-3-540-42860-2; DOI 10.1007/10735542_789.
  2. ^ a b c Hans Bock; Ilka Goebel; Zdenek Havlas; Siegfried Liedle; Heinz Oberhammer (1991). "Triisopropylamine: A Sterically Overcrowded Molecule with a Flattened NC3 Pyramid and a "p-Type" Nitrogen Electron Pair". Angew. Chem. Int. Ed. 30 (2): 187–190. doi:10.1002/anie.199101871.
  3. ^ a b Arthur M. Halpern; B. R. Ramachandran (1992). "Photophysics of a sterically crowded tertiary-saturated amine: triisopropylamine". J. Phys. Chem. 96 (24): 9832–9839. doi:10.1021/j100203a047.
  4. ^ Christoph Kölmel, Christian Ochsenfeld & Reinhart Ahlrichs (1992). "An ab initio investigation of structure and inversion barrier of triisopropylamine and related amines and phosphines". Theoretical Chemistry Accounts: Theory, Computation, and Modeling. 82 (3–4).
  5. ^ a b Boese, R.; Bläser, D.; Antipin, M. Y.; Chaplinski, V.; de Meijere, A. (1998). "Non-planar structures of Et3N and Pri3N: a contradiction between the X-ray, and NMR and electron diffraction data for Pri3N". Chem. Commun. (7): 781–782. doi:10.1039/a708399h.
  6. ^ Yang M, Albrecht-Schmitt T, Cammarata V, Livant P, Makhanu DS, Sykora R, Zhu W (2009). "Trialkylamines more planar at nitrogen than triisopropylamine in the solid state". J. Org. Chem. 74 (7): 2671–8. doi:10.1021/jo802086h. PMID 19323571.
  7. ^ Banert, Klaus; Heck, Manuel; Ihle, Andreas; Kronawitt, Julia; Pester, Tom; Shoker, Tharallah (2018-05-04). "Steric Hindrance Underestimated: It is a Long, Long Way to Tri- tert -alkylamines". The Journal of Organic Chemistry. 83 (9): 5138–5148. doi:10.1021/acs.joc.8b00496. ISSN 0022-3263. PMID 29630365.