Triethylaluminium

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Triethylaluminium
Skeletal formula of triethylaluminium dimer
Ball-and-stick model of the triethylaluminium dimer molecule
Names
IUPAC name
Triethylalumane
Identifiers
3D model (
JSmol
)
Abbreviations TEA,[1] TEAl,[2] TEAL[3]
ChemSpider
ECHA InfoCard
 100.002.382 Edit this at Wikidata
EC Number
  • 202-619-3
UNII
UN number 3051
  • InChI=1S/3C2H5.Al/c3*1-2;/h3*1H2,2H3; checkY
    Key: VOITXYVAKOUIBA-UHFFFAOYSA-N checkY
  • InChI=1/3C2H5.Al/c3*1-2;/h3*1H2,2H3;/rC6H15Al/c1-4-7(5-2)6-3/h4-6H2,1-3H3
    Key: VOITXYVAKOUIBA-DVVALISXAR
  • CC[Al](CC)CC
  • dimer
    : CC[Al-](CC)([CH2+]1C)[CH2+](C)[Al-]1(CC)CC
Properties
C12H30Al2
Molar mass 228.335 g·mol−1
Appearance Colorless liquid
Density 0.8324 g/mL at 25 °C
Melting point −46 °C (−51 °F; 227 K)
Boiling point 128 to 130 °C (262 to 266 °F; 401 to 403 K) at 50 mmHg
Reacts
Solubility Ether, hydrocarbons, THF
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 pyrophoric
GHS labelling:
GHS02: FlammableGHS05: Corrosive
Danger
H250, H260, H314
P210, P222, P223, P231+P232, P260, P264, P280, P301+P330+P331, P302+P334, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P335+P334, P363, P370+P378, P402+P404, P405, P422, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneInstability 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
3
4
3
W
Flash point −18 °C (0 °F; 255 K)
Related compounds
Related compounds
 Trimethylaluminium
Triisobutylaluminium
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Triethylaluminium is one of the simplest examples of an

pyrophoric. It is an industrially important compound, closely related to trimethylaluminium.[4][5]


Structure and bonding

The structure and bonding in Al2R6 and diborane are analogous (R = alkyl). Referring to Al2Me6, the Al-C(terminal) and Al-C(bridging) distances are 1.97 and 2.14 Å, respectively. The Al center is tetrahedral.[6] The carbon atoms of the bridging ethyl groups are each surrounded by five neighbors: carbon, two hydrogen atoms and two aluminium atoms. The ethyl groups interchange readily intramolecularly. At higher temperatures, the dimer cracks into monomeric AlEt3.[7][8]

Synthesis and reactions

Triethylaluminium can be formed via several routes. The discovery of an efficient route was a significant technological achievement. The multistep process uses aluminium,

hydrogen gas, and ethylene, summarized as follows:[4]

2 Al + 3 H2 + 6 C2H4 → Al2Et6

Because of this efficient synthesis, triethylaluminium is one of the most available organoaluminium compounds.

Triethylaluminium can also be generated from ethylaluminium sesquichloride (Al2Cl3Et3), which arises by treating aluminium powder with chloroethane. Reduction of ethylaluminium sesquichloride with an alkali metal such as sodium gives triethylaluminium:[9]

6 Al2Cl3Et3 + 18 Na → 3 Al2Et6 + 6 Al + 18 NaCl

Reactivity

The Al–C bonds of triethylaluminium are

polarized to such an extent that the carbon is easily protonated, releasing ethane:[10]

Al2Et6 + 6 HX → 2 AlX3 + 6 EtH

For this reaction, even weak acids can be employed such as terminal acetylenes and alcohols.

The linkage between the pair of aluminium centres is relatively weak and can be cleaved by

Lewis bases (L) to give adducts
with the formula AlEt3L:

Al2Et6 + 2 L → 2 LAlEt3

Applications

Precursors to fatty alcohols

Triethylaluminium is used industrially as an intermediate in the production of

octyl groups):[4]

Al2(C2H5)6 + 18 C2H4 → Al2(C8H17)6

Subsequently, these trialkyl compounds are oxidized to aluminium alkoxides, which are then hydrolysed:

Al2(C8H17)6 + 3 O2 → Al2(OC8H17)6
Al2(OC8H17)6 + 6 H2O → 6 C8H17OH + 2 Al(OH)3

Co-catalysts in olefin polymerization

A large amount of TEAL and related aluminium alkyls are used in

Ziegler-Natta catalysis. They serve to activate the transition metal catalyst both as a reducing agent and an alkylating agent. TEAL also functions to scavenge water and oxygen.[11]

Reagent in organic and organometallic chemistry

Triethylaluminium has niche uses as a precursor to other organoaluminium compounds, such as diethylaluminium cyanide:[12]

Pyrophoric agent

Triethylaluminium ignites on contact with air and will ignite and/or decompose on contact with water, and with any other oxidizer

enthalpy of combustion, ΔcH°, is –5105.70 ± 2.90 kJ/mol[14] (–22.36 kJ/g). Its easy ignition makes it particularly desirable as a rocket engine ignitor. The SpaceX Falcon 9 rocket uses a triethylaluminium-triethylborane mixture as a first-stage ignitor.[1]

Triethylaluminium

n-hexane, can be used with increased safety by rendering the compound non-pyrophoric until the diluent evaporates, at which point a combined fireball results from both the triethylaluminium and the hexane vapors.[16]
The M202 was withdrawn from service in the mid-1980s owing to safety, transport, and storage issues. Some saw limited use in the Afghanistan War against caves and fortified compounds.

See also

References

  1. ^ a b Mission Status Center, June 2, 2010, 1905 GMT, SpaceflightNow, accessed 2010-06-02, Quotation: "The flanges will link the rocket with ground storage tanks containing liquid oxygen, kerosene fuel, helium, gaserous nitrogen and the first stage ignitor source called triethylaluminum-triethylborane, better known as TEA-TEB."
  2. ^ "Gulbrandsen Chemicals, Metal Alkyls: Triethylaluminum (TEAl)". Gulbrandsen. Archived from the original on December 13, 2017. Retrieved December 12, 2017. Triethylaluminum (TEAl) is a pyrophoric liquid...
  3. ^ Malpass, Dennis B.; Band, Elliot (2012). Introduction to Industrial Polypropylene: Properties, Catalysts Processes. John Wiley & Sons.
    ISBN 9781118463208
    .
  4. ^
    ISBN 978-3527306732
    .
  5. ISBN 978-3-527-29390-2
    .
  6. ISBN 0-12-352651-5
    .
  7. doi:10.1021/om010994h
    .
  8. ISSN 0022-3654
    .
  9. ^ Krause, M. J; Orlandi, F; Saurage, A T.; Zietz, J R, "Organic Aluminum Compounds" Wiley-Science 2002.
  10. ISBN 978-3-527-29390-2
  11. ISBN 9780470504437
    .
  12. ^ Wataru Nagata and Yoshioka Mitsuru (1988). "Diethylaluminum Cyanides". Organic Syntheses; Collected Volumes, vol. 6, p. 436.
  13. ^ TEA Material Safety Data Sheet Archived 2006-11-14 at the Wayback Machine, accessed March 27, 2007
  14. ^ "Triethylaluminum (CAS 97-93-8) - Chemical & Physical Properties by Cheméo".
  15. ^ M202A1 Flame Assault Shoulder Weapon (Flash), inetres.com
  16. ^ Encyclopedia of Explosives and Related Items, Vol.8, US Army
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