Triethyl aluminum

Structural formula
Monomer (top), dimer (bottom)
General
Surname	Triethyl aluminum
other names	Aluminum triethyl TEA
Molecular formula	C 6 H 15 Al (monomer)
Brief description	colorless self-igniting liquid
External identifiers / databases
CAS number 97-93-8 EC number 202-619-3 ECHA InfoCard 100.002.382 PubChem 16682930 Wikidata Q416298
properties
Molar mass	114.17 g mol −1
Physical state	liquid
density	0.8324 g cm −3 (25 ° C)
Melting point	−52.5 ° C
boiling point	187 ° C
Vapor pressure	4 h Pa (at 20 ° C)
solubility	violent decomposition in water
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 250-260-314 EUH: 014 P: 210-231 + 232-280-302 + 334-303 + 361 + 353-304 + 340 + 310-305 + 351 + 338-370 + 378-422
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Triethylaluminum , also known as TEA or aluminum triethyl (ATE), is an organometallic compound of aluminum . The compound is pyrophoric and can self-ignite on contact with air. TEA reacts extremely violently with water to form aluminum hydroxide and ethane . TEA is a Lewis acid due to the electron gap on the aluminum atom, which has only six valence electrons .

Presentation and extraction

The technical synthesis takes place through the conversion of aluminum , hydrogen and ethene , whereby a starting amount of triethylaluminium is necessary. Aluminum alone does not react directly with hydrogen. In the presence of triethylaluminum, diethylaluminum hydride is formed as an intermediate compound which, with ethene, gives the target compound.

${\displaystyle \mathrm {2\ Al+3\ H_{2}+4\ (C_{2}H_{5})_{3}Al\longrightarrow \ 6\ (C_{2}H_{5})_{2}AlH} }$ and

${\displaystyle \mathrm {(C_{2}H_{5})_{2}AlH+CH_{2}{=}CH_{2}\longrightarrow \ (C_{2}H_{5})_{3}Al} }$

The sum equation then reads

${\displaystyle \mathrm {2\ Al+3\ H_{2}+6\ CH_{2}{=}CH_{2}\longrightarrow \ 2\ (C_{2}H_{5})_{3}Al} }$

The synthesis can be carried out as a continuous two-stage process, with part of the triethylaluminum being recycled.

A second synthesis variant is based on the reaction of aluminum with ethyl chloride , where the ethyl aluminum sesquichloride is obtained first .

${\displaystyle \mathrm {2\ Al+3\ C_{2}H_{5}Cl\longrightarrow \ (C_{2}H_{5})_{3}Al_{2}Cl_{3}} }$

A reduction reaction with sodium then gives the target compound.

${\displaystyle \mathrm {2\ (C_{2}H_{5})_{3}Al_{2}Cl_{3}+3\ Na\longrightarrow \ 3\ (C_{2}H_{5})_{2}AlCl+Al+3\ NaCl} }$ and

${\displaystyle \mathrm {3\ (C_{2}H_{5})_{2}AlCl+3\ Na\longrightarrow \ 2\ (C_{2}H_{5})_{3}Al+Al+3\ NaCl} }$

properties

Physical Properties

Triethylaluminum is a pyrophoric, colorless to yellowish liquid. The compound boils at 187 ° C. under normal pressure. The enthalpy of vaporization here is 73.2 kJ mol ⁻¹ . The vapor pressure function results according to Antoine according to log ₁₀ (P) = A− (B / (T + C)) (P in bar, T in K) with A = 7.41394, B = 3451.295 and C = 2, 14 in the temperature range from 330 K to 399 K. The melting point of the compound is −50.7 ° C. The heat of fusion is 10.6. kJ · mol ⁻¹ The triple point is at −48 ° C. and 0.0017 Pa

Chemical properties

In the solid and liquid state, triethylaluminum is present as a dimer , whereas in the gas phase it is in monomeric form. With alkali halides and cyanides 1: 1 complex of the type M [(C ₂ H ₅ ) ₃ AlX] and 1: 2 complexes of the type M [(C ₂ H ₅ ) ₆ Al ₂ X] (with M - alkali metal ion and X - halide, cyanide). When solid, anhydrous aluminum halides are introduced into triethylaluminum, the corresponding diethylaluminum halides or ethylaluminum dihalides are formed, depending on the stoichiometry.

${\displaystyle \mathrm {AlX_{3}+2\ (C_{2}H_{5})_{3}Al\longrightarrow \ 3\ (C_{2}H_{5})_{2}AlX} }$ and

${\displaystyle \mathrm {2\ AlX_{3}+(C_{2}H_{5})_{3}Al\longrightarrow \ 3\ (C_{2}H_{5})AlX_{2}} }$ with X = Cl, Br, I

A real transalkylation succeeds in the reaction with zinc chloride , whereby the desired diethylzinc can be separated from the by-product diethylaluminum chloride by distillation .

${\displaystyle \mathrm {2\ (C_{2}H_{5})_{3}Al+ZnCl_{2}\longrightarrow \ Zn(C_{2}H_{5})_{2}+2\ (C_{2}H_{5})_{2}AlCl} }$

With oxygen , aluminum triethanolate is formed in a radical chain reaction at the aluminum-carbon bonds . This reaction is very exothermic with a reaction enthalpy of −1017 kJ mol ⁻¹ , so that an appropriate reaction control with regard to the oxygen supply is necessary in order to avoid uncontrolled self-ignition processes.

${\displaystyle \mathrm {2\ (C_{2}H_{5})_{3}Al+3\ O_{2}\longrightarrow \ 2\ (C_{2}H_{5}O)_{3}Al} }$

Triethylaluminum reacts readily and violently with protic substances such as mineral acids, water, alcohols, mercaptans, phenols, carboxylic acids, ammonia, amines, acetylenes and monosubstituted acetylenes.

use

As a component of Ziegler-Natta catalysts, triethylaluminum is a cocatalyst used on an industrial scale for polyolefin production ; mainly of polyethylene and polypropylene . In the so-called Alfol process, TEA is used to synthesize higher unbranched primary alcohols (" fatty alcohols ") from ethene .

In MOCVD and MBE systems, triethylaluminum is used as a reaction medium for the deposition of III-V semiconductor layers , for example for LEDs .

In military weapons, such as flame throwers , triethylaluminum as a liquid fire agent or thickeners such as polyisobutylene as yellow edge material is (TPA, engl. Thickened pyrophoric agent ) employed. In principle, such weapons can be regarded as successors to the napalm . With regard to the burning temperature and the incendiary effect, they surpass this. TEA itself cannot be extinguished with water because it reacts explosively with water. If it is fought with other extinguishing agents, self-ignition can set in again at any time through contact with air.

safety instructions

The vapors from triethylaluminum are very irritating and burn the mucous membranes . Pulmonary edema can occur with a delay of up to two days . The so-called foundry fever is also often observed. Effects on the skin can cause very painful and difficult-to-heal wounds.

Individual evidence

1. ↑ ^{a b c d e f} Entry on triethylaluminum in the GESTIS substance database of the IFA , accessed on February 1, 2016(JavaScript required) .
2. ↑ ^{a b c d e} M. J. Krause, F. Orlandi, AT Saurage, JR Zietz Jr .: Organic Aluminum Compounds. In: Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH, Weinheim 2005. doi : 10.1002 / 14356007.a01_543
3. ^ ^{A b} W. B. Heck, RL Johnson: Aluminum alkyls - safe handling. In: Ind. Eng. Chem. 54, 12, 1962, pp. 35-38. doi: 10.1021 / ie50636a007
4. ↑ Not explicitly listed in Regulation (EC) No. 1272/2008 (CLP) , but with the specified labeling it falls under the group entry aluminum alkyls in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016 . marketer can use the harmonized classification and labeling expand .
5. ^ K. Ziegler: Consequences and development of an invention - Nobel lecture on December 12, 1963. In: Angew. Chem. 76, 1964, pp. 545-553. doi: 10.1002 / anie.19640761302
6. ↑ K. Ziegler, H.-G. Gellert, H. Lehmkuhl, W. Pfohl, K. Zosel: Organometallic compounds, XXVI aluminum trialkyls and dialkyl aluminum hydrides from olefins, hydrogen and aluminum. In: Liebigs Ann. Chem. 629, 1960, pp. 1-13. doi: 10.1002 / jlac.19606290102
7. ↑ A. Lobo, DC Coldiron: Patent ZA 635722, 1963 Continental Oil Co. In: Chem. Abstr. 63, 1965, p. 13314h.
8. ↑ ^{a b} A. von Grosse, JM Mavity: Organoaluminium Compounds: Methods of Preparation. In: J. Org. Chem. 5, 1940, pp. 106-121. doi: 10.1021 / jo01208a004
9. ^ PA Fowell, Ph. D. Thesis, University of Manchester, 1961.
10. ^ V. Fic, J. Dvorak: Organo-Aluminum Compounds. 1. Vapor Pressure of Triethyl Aluminum and Diethyl Aluminum Chloride. In: Chem. Prum. 15, 1965, pp. 732-735.
11. ↑ ^{a b} I. B. Rabinovich, VP Nistratov, MS Sheiman, KN Klimov, GP Kamelov, AD Zorin: Specific heat and thermodynamic functions of triethylaluminium. In: Zhur. Fiz. Khim. 63, 1989, pp. 522-525.
12. ↑ MS Sheiman, VP Nistratov, GP Kamelova, IB Rabinovich: Low-temperature heat capacity of organic compounds of aluminum and zinc. In: Probl. Kalorim. Khim. Termodin., Docl. Vses. Conf. 10th, 2, 1984, pp. 457-459.
13. ↑ calculated from the vapor pressure function
14. ↑ Gábor Vass, György Tarczay, Gábor Magyarfalvi, András Bödi, László Szepes: HeI Photoelectron Spectroscopy of Trialkylaluminum and Dialkylaluminum Hydride Compounds and Their Oligomers. In: Organometallics. 21, 2002, pp. 2751-2757. doi: 10.1021 / om010994h
15. ↑ K. Ziegler, R. Köster, H. Lehmkuhl, K. Reinert: Organometallic compounds, XXX New complex compounds of aluminum alkyls. In: Liebigs Ann. Chem. 629, 1960, pp. 33-49. doi: 10.1002 / jlac.19606290106
16. ↑ MB Smith: The heats of formation of aluminum alkyls and related compounds. In: J. Organomet. Chem. 76, 1974, pp. 171-201. doi: 10.1016 / S0022-328X (00) 84630-6
17. ↑ K. Ziegler, F. Krupp, K. Zosel: Organometallic compounds, XL Synthesis of alcohols from organoaluminum compounds. In: Liebigs Ann. Chem. 629, 1960, pp. 241-250. doi: 10.1002 / jlac.19606290118
18. ^ W. Baumann, B. Herberg-Liedtke: Chemicals in metal processing: data and facts on environmental protection. Springer, 1996, ISBN 3-540-60094-9 , pp. 462-463.

Web links

• Triethylaluminum at ChemgaPedia