Preparation of dialkyl tellurium and dialkyl selenium

Details Preparation of dialkyl tellurium and dialkyl selenium Preparation of dialkyl tellurium and dialkyl selenium

1994-06-13

1995-08-15

Shaver, Paul F.

Organic compounds -- part of the class 532-570 series

Organic compounds

Selenium or tellurium containing

C07F 1100, C07C39500, C07C39100

Patent

active

054421128

DESCRIPTION:

BRIEF SUMMARY
This application is a 35USC371 of PCT/GR92/01782, filed Sep. 29, 1992.
This invention relates to a method for the preparation of dialkyls of the group VI metals tellurium and selenium.
The metals tellurium and selenium are of importance in semiconductor technology, for example, in the preparation of the infrared detector material cadmium mercury telluride (CMT) and in light sensing switches respectively.
Frequently, these metals or, in particular, their compounds such as CMT are deposited on substrates by the process of Metal-Organic Vapour Phase Epitaxy (MOVPE) which involves vapour phase co-decomposition of volatile compounds of the component metals, in the case of tellurium this is most usually a dialkyl. Dialkyls have the advantages that as well as being volatile they can be easily purified by formation of adducts which can be easily decomposed to form the pure dialkyl as described for example in GB-A-850955 and PCT/GB88/01062. Dialkyl ditellurides, in addition to being useful as precursors in MOVPE, may also be used to prepare unsymmetrical dialkyls (for example in GB 8913799.6).
Unsymmetrical dialkyls are thought to be advantageous for MOVPE because they have the potential for combining high volatility with low temperatures for deposition of the desired material.
The literature preparation of Me.sub.2 Te.sub.2 involves the use of large quantities of liquid ammonia and sodium metal (M. T. Chen and J. W. George J. Organometallic Chemistry, 1968, 12, p40), 1973). Apart from the dangerous nature of this reaction, the yields are extremely variable (from 15-60%).
Other methods using more convenient aqueous routes (D. V. Shenai-Khatkhate, E. D. Orrell, J. B. Mullin, D. C. Cupertino and D. J. Cole-Hamilton, J. Crystal Growth 77 (1986), 27 and K. J. Irgolic, Methods of Organic Chemistry (Houben-Weyl) vol E 12b Ed D Klamann Verlag Stuttgart 1990 and references therein) involving reaction of Na.sub.2 Te.sub.2 or Na.sub.2 Te with methyliodide resulted in low yields, typically 5-15% for Me.sub.2 Te.sub.2 and about 30% for Me.sub.2 Te.
There is therefore a need for an improved method of preparation of dialkyl tellurium, dialkyl selenium, dialkyl ditelluride and dialkyl diselenide, both as direct precursors for MOVPE, and particularly as precursors for unsymmetrical dialkyls in the case of dialkyl ditellurides and dialkyl diselenides.
According to the present invention there is provided a method of preparation of dialkyl tellurium, dialkyl selenium, dialkyl ditelluride and dialkyl diselenide characterised by the reaction of a sodium chalcogenide with an alkyl halide in a two-phase system of solvents, the said two-phase system comprising water and an organic solvent immiscible with water, and by the addition of a phase-transfer catalyst. The phase-transfer catalyst is preferably a quarternary ammonium salt; cetyltrimethylammonium bromide (CTAB) has been found to be most satisfactory.
The sodium chalcogenide may be Na.sub.2 Te, Na.sub.2 Te.sub.2, Na.sub.2 Se or Na.sub.2 Se.sub.2.
The alkyl may be a primary or secondary alkyl containing 1-20 carbon atoms, preferably 1-4 carbon atoms.
The alkyl is most preferably methyl.
The two-phase system may comprise water and an organic solvent immiscible with water, for example diethyl ether, benzene, toluene and the like.
Preferably, the organic solvent is diethyl ether.


BRIEF DESCRIPTION OF DRAWING

The invention will be further apparent from the following description with reference to the single FIGURE, which shows, by way of example only, one form of the method embodying same.
The numbers in bold refer to the FIGURE.


EXAMPLE 1



Preparation of Dimethylditelluride (Me.sub.2 Te.sub.2)

40.3 g (0.32 mol) of Te powder, 58.4 g (0.38 mol) sodium formaldehyde sulphoxylate (Rongalite C) and 50.0 g (1.25 mol) NaOH was dissolved in 300 cm.sup.3 of deaereated, distilled water in a flask 11 and the flask 11 heated to 110.degree. C. in an oil bath for one hour and then cooled rapidly forming the aqueous layer 12. 0.75 g (2.0 mmol) CTAB in 500 cm.sup.3 of solvent ether was added follo

REFERENCES:
patent: 5043476 (1991-08-01), Higa et al.
patent: 5075500 (1991-12-01), Higa et al.
patent: 5091570 (1992-02-01), Mullin et al.
patent: 5166428 (1992-11-01), Cole-Hamilton et al.
patent: 5312983 (1994-05-01), Brown et al.

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