Tetraethyl orthosilicate

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Structural formula
Structural formula of tetraethylorthosilicate
General
Surname Tetraethyl orthosilicate
other names
  • Tetraethyl orthosilicate
  • Tetraethyl silicate
  • Tetraethoxysilane
  • Tetraethyl silicate
  • Ethyl silicate
  • TEOS
Molecular formula C 8 H 20 O 4 Si
Brief description

colorless liquid with a pungent odor

External identifiers / databases
CAS number 78-10-4
EC number 201-083-8
ECHA InfoCard 100,000,986
PubChem 6517
Wikidata Q421458
properties
Molar mass 208.32 g mol −1
Physical state

liquid

density

0.94 g cm −3

Melting point

−82.15 ° C

boiling point

168 ° C

Vapor pressure

9.21 hPa (20 ° C)

solubility

almost insoluble in water

Refractive index

1.3928 (20 ° C)

safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
02 - Highly / extremely flammable 07 - Warning

Caution

H and P phrases H: 226-332-319-335
P: 210-261-280-303 + 361 + 353-304 + 340 + 312-370 + 378-403 + 235
MAK

DFG / Switzerland: 10 ml m −3 or 85 mg m −3

Toxicological data

6270 mg kg −1 ( LD 50ratoral )

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Tetraethylorthosilicate , and tetraethoxysilane , silicic or ethyl silicate , in short TEOS called, is a ethyl ester of orthosilicic acid .

Manufacturing

TEOS is produced on an industrial scale by alcoholysis of silicon tetrachloride with ethanol.

properties

Tetraethoxysilane is a colorless liquid that boils at 168 ° C under normal pressure . According to Antoine, the vapor pressure function results from log 10 (P) = A− (B / (T + C)) (P in bar, T in K) with A = 4.17312, B = 1561.277 and C = −67.572 in the temperature range from 289 to 441.7 K. The enthalpy of vaporization is 49.5 kJ · mol −1. As a solid, the compound can exist in two polymorphic crystal forms. Crystal form II is present below −85.45 ° C. At this temperature, this transforms in a solid phase transition with a conversion enthalpy of 13.2 kJ mol −1 into the crystal form I, which then melts at −82.15 ° C with a melting enthalpy of 11.14 kJ mol −1 .

Tetraethoxysilane forms flammable vapor-air mixtures above the flash point. The compound has a flash point of 37 ° C. The explosion range is between 0.77% by volume (67 g / m 3 ) as the lower explosion limit (LEL) and 23% by volume as the upper explosion limit (UEL). The ignition temperature is 230 ° C. The substance therefore falls into temperature class T3.

use

It is used in sol-gel processes as silica - precursor for the preparation of colloidal sol-gel used systems. The compound is largely insoluble in water. A mixture of ethanol and water is therefore usually used as the reaction medium. In the neutral state , TEOS hydrolyzes very slowly (several hours) in water to form orthosilicic acid and ethanol:

where the orthosilicic acid formed further breaks down into silicon dioxide through the formation of Si – O – Si bonds and the release of water:

The hydrolysis in acidic or alkaline conditions takes place considerably faster , since both catalyze the reaction considerably . In ammonia , monodisperse silicon dioxide particles can be obtained from a TEOS / ethanol mixture which contains some water . In the so-called Stöber synthesis , the particle size can be set in the range of approx. 20–500 nm by selecting the concentrations, temperatures and the amount of ammonia  . The process is used, for example, for the production of photonic crystals and artificial opals .

In dental technology, tetraethylsilicate is used in the setting process of silicate-bonded investment materials .

See also

literature

  • K. Nozawa, et al .: Smart control of monodisperse Stöber silica particles: effect of reactant addition rate on growth process. In: Langmuir . No. 21, 2005, pp. 1516-1523, doi : 10.1021 / la048569r .
  • T. Suratwala, ML Hanna, P. Whitman: Effect of humidity during the coating of Stöber silica sols. In: Journal of Non-Crystalline Solids. No. 349, 2004, pp. 368-376, doi : 10.1016 / j.jnoncrysol.2004.08.214 .

Individual evidence

  1. a b c d e f g h Entry on tetraethyl orthosilicate in the GESTIS substance database of the IFA , accessed on January 9, 2019(JavaScript required) .
  2. a b c d Datasheet Tetraethylorthosilicate (PDF) from Merck , accessed on March 14, 2010.
  3. a b c d Van der Vis, MGM; Cordfunke, EHP; Konings, RJM; Van Den Berg, GJK; Van Miltenburg, JC: Tetraethoxysilane, Si (OC 2 H 5 ) 4 : heat capacity and thermodynamic properties at temperatures from 0 to 440 K in J. Chem. Thermodyn. 24 (1992) 1103-1108, doi : 10.1016 / S0021-9614 (05) 80022-9 .
  4. David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-254.
  5. Entry on tetraethyl orthosilicate in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
  6. Schweizerische Unfallversicherungsanstalt (Suva): Limit values ​​- current MAK and BAT values (search for 78-10-4 or tetraethylorthosilicate ), accessed on November 2, 2015.
  7. Entry on tetraethyl orthosilicate in the ChemIDplus database of the United States National Library of Medicine (NLM) .
  8. Georg Brauer , with the collaboration of Marianne Baudler a . a. (Ed.): Handbook of Preparative Inorganic Chemistry . 3rd, revised edition. tape I . Ferdinand Enke, Stuttgart 1975, ISBN 3-432-02328-6 , pp. 702 .
  9. a b Stull, DR: Vapor Pressure of Pure Substances Organic Compounds in Ind. Eng. Chem. 39 (1947) 517-540, doi : 10.1021 / ie50448a022 .
  10. ^ A b E. Brandes, W. Möller: Safety-related parameters - Volume 1: Flammable liquids and gases , Wirtschaftsverlag NW - Verlag für neue Wissenschaft GmbH, Bremerhaven 2003.
  11. Werner Stöber, Arthur Fink, Ernst Bohn: Controlled growth of monodisperse silica spheres in the micron size range. In: J. Colloid Interface Sci. , No. 26, 1968, pp. 62-69; doi : 10.1016 / 0021-9797 (68) 90272-5 .
  12. Jian Li, Weihuan Huang, Zhe Wang, Yanchun Han: A reversibly tunable colloidal photonic crystal via the infiltrated solvent liquid-solid phase transition. In: Colloids and Surfaces A: Physicochemical and Engineering Aspects , No. 293, 2007, pp. 130-134; doi : 10.1016 / j.colsurfa.2006.07.017 .
  13. Martyn E. Pemble, Maria Bardosova, Ian M. Povey, Richard H. Tredgold, Debra Whitehead: Novel photonic crystal thin films using the Langmuir – Blodgett approach , in Physica B: Condensed Matter , 394/2007, pp. 233-237 ; doi : 10.1016 / j.physb.2006.12.017 .
  14. L. Pallavidino, et al .: Synthesis, characterization and modeling of silicon based opals. In: Journal of Non-Crystalline Solids , No. 352, 2006, pp. 1425-1429; doi : 10.1016 / j.jnoncrysol.2005.10.047 .