Titanium ethoxide

Titanium ethoxide is a chemical compound with the formula Ti4(OCH2CH3)16. It is a commercially available colorless liquid that is soluble in organic solvents but hydrolyzes readily. Its structure is more complex than suggested by its empirical formula. Like other alkoxides of titanium(IV) and zirconium(IV), it finds used in organic synthesis and materials science.[1]

Titanium ethoxide

Abbreviated structure of titanium(IV) ethoxide tetramer. The ethoxide ligands are represented by O's. The terminal ethoxide ligands are designated by Oa, the doubly bridging ligands by Ob, and the triply bridging ligands by Oc.
Names
IUPAC name
ethanolate; titanium(4+)
Systematic IUPAC name
titanium(4+) tetraethanolate
Other names
Ethyl titanate, tetraethyl titanate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.019.464
EC Number
  • 221-410-8
UNII
  • InChI=1S/4C2H5O.Ti/c4*1-2-3;/h4*2H2,1H3;/q4*-1;+4
    Key: JMXKSZRRTHPKDL-UHFFFAOYSA-N
  • CC[O-].CC[O-].CC[O-].CC[O-].[Ti+4]
Properties
C32H80O16Ti4
Molar mass 228.109 g/mol
Appearance colorless liquid
Density 1.088
Melting point 54 °C (129 °F; 327 K)
Boiling point 150–152 °C (302–306 °F; 423–425 K) (@10 mmHg)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Syntheses

Titanium ethoxide is prepared by treating titanium tetrachloride with ethanol in the presence of an amine:[2]

TiCl4 + 4 EtOH + 4 Et3N → Ti(OEt)4 + 4 Et3NHCl

The purity of titanium ethoxide is commonly assayed by proton NMR spectroscopy. Ti(OEt)4 1H NMR (90 MHz, chloroform-d, ppm): 4.36 (quartet, 8H, CH2), 1.27 (triplet, 12H, CH3).[3]

Structure

Both Ti(OEt)4 exist mainly as tetramers with an octahedral coordination environment around the metal centers. There are two types of titanium centers, depending on the number of terminal vs bridging alkoxide ligands. Zr(OEt)4 is structurally similar.[2][4] The virtual symmetry of the M4O16 core structure for the tetramer structures of these compounds is C2h.[5]

Titanium methoxide

Like the ethoxide, titanium methoxide Ti(OMe)4 exists as a tetramer with each of the TiIV metal centers having an octahedral coordination environment.[6]

Titanium isopropoxide
Main article: Titanium isopropoxide

With bulky alkyl groups, Ti(OiPr)4 in contrast exist as a monomer with a tetrahedral environment around the Ti center. This lower degree of coordination to the metal center is attributed to the steric bulk of the iPr groups versus the n-alkyl groups, this serves to prevent bridging interactions between the metal centers.[7]

Zirconium ethoxide

Zirconium ethoxide can be prepared in a manner similar but not identical to the titanium compound:[8]

ZrCl4 + 5 NaOEt + EtOH → NaH[Zr(OEt)6] + 4 NaCl
NaH[Zr(OEt)6] + HCl → Zr(OEt)4 + NaCl + 2 EtOH

A more common synthesis for zirconium ethoxide is to treat zirconium tetrachloride with the desired alcohol and ammonia:[8]

ZrCl4 + 4 ROH + 4 NH3 → Zr(OR)4 + 4 NH4Cl

Zirconium ethoxide can also be prepared with zirconocene dichloride:[9]

Cp2ZrCl2 + 4 EtOH + 2 Et3N → 2 CpH + 2 Et3NHCl + Zr(OEt)4

Zirconium propoxide

Zr(OnPr)4 also adopts the titanium ethoxide structure.[4][5]

Reactions

Hydrolysis of Ti alkoxides can be used to deposit TiO2:[10]

Ti(OEt)4 + 2 H2O → TiO2 + 4 EtOH

The course of the hydrolysis is affected by the presence of base or acid catalysts for the hydrolysis. Generally acid-catalysis yields a sol where the polymer chains are randomly oriented and linear. In the base-mediated case bushy clusters or crosslinked networks are produced, these structures can trap solvent and reaction byproducts and form a gel coating.[11] Intermediates in the hydrolysis have been crystallized. They feature interior oxides in addition to the ethoxide on the exterior of the clusters.[12]

The high reactivity of titanium ethoxide toward water is exploited in its use in condensation reactions.[13]

References
  1. Ram C. Mehrotra; Singh, Anirudh (1997). "Recent Trends in Metal Alkoxide Chemistry". In Kenneth D. Karlin (ed.). Progress in Inorganic Chemistry. Vol. 46. John Wiley & Sons. pp. 239–454. doi:10.1002/9780470166475.ch4. ISBN 9780470167045.
  2. F. Albert Cotton; Geoffrey Wilkinson; Murillo, C.; Bochmann, M. (1999). Advanced Inorganic Chemistry (6th ed.). New York: John Wiley & Sons. ISBN 978-0-471-19957-1.
  3. Integrated Spectral Database System of Organic Compounds, version 2011. AIST: Japan, 2011 (accessed October 3rd, 2011).
  4. James A. Ibers (1963). "Crystal and Molecular Structure of Titanium(IV) Ethoxide". Nature. 197 (4868): 686–687. Bibcode:1963Natur.197..686I. doi:10.1038/197686a0. S2CID 4297907.
  5. Day, Victor W.; Klemperer, Walter G.; Pafford, Margaret M. (2001). "Isolation and Structural Characterization of Tetra-n-propyl Zirconate in Hydrocarbon Solution and the Solid State". Inorg. Chem. 40 (23): 5738–5746. doi:10.1021/ic010776g. PMID 11681880.
  6. Wright, D. A.; Williams, D. A. (1968). "The Crystal and Molecular Structure of Titanium Tetramethoxide". Acta Crystallographica B. 24 (8): 1107–1114. doi:10.1107/S0567740868003766.
  7. Ghosh, Rajshekhar; Nethaji, Munirathinam; Samuelson, Ashoka G. (2005). "Reversible double insertion of aryl isocyanates into the Ti–O bond of titanium(IV) isopropoxide". J. Organomet. Chem. 690 (5): 1282–1293. doi:10.1016/j.jorganchem.2004.11.038.
  8. Bradley, D. C.; Wardlaw, W. (1951). "Zirconium alkoxides". J. Chem. Soc.: 280–285. doi:10.1039/jr9510000280.
  9. Gray, Donald R.; Brubaker, Carl H. (1971). "Preparation and characterization of a series of chloroalkoxobis(cyclopentadienyl)zirconium(IV) and dialkoxobis(cyclopentadienyl)zirconium(IV) compounds". Inorg. Chem. 10 (10): 2143–2146. doi:10.1021/ic50104a010.
  10. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  11. Schubert, U. (2003). "Sol–Gel Processing of Metal Compounds". In McCleverty, J. A.; Meyer, T. J. (eds.). Comprehensive Coordination Chemistry II. Reference Module in Chemistry, Molecular Sciences and Chemical Engineering. Vol. 7. Pergamon. pp. 629–656. doi:10.1016/B0-08-043748-6/06213-7. ISBN 978-0-12-409547-2.
  12. Coppens, Philip; Chen, Yang; Trzop, Elżbieta (2014). "Crystallography and Properties of Polyoxotitanate Nanoclusters". Chemical Reviews. 114 (19): 9645–9661. doi:10.1021/cr400724e. PMID 24820889.
  13. Mackey, Pamela; Cano, Rafael; Foley, Vera M.; McGlacken, Gerard P. (2017). "Preparation of anti-1,3-Amino Alcohol Derivatives Through an Asymmetric Aldol-Tishchenko Reaction of Sulfinimines". Organic Syntheses. 94: 259–279. doi:10.15227/orgsyn.094.0259.
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