Organic compounds -- part of the class 532-570 series – Organic compounds – Selenium or tellurium containing
Patent
1990-07-31
1992-02-25
Shaver, Paul F.
Organic compounds -- part of the class 532-570 series
Organic compounds
Selenium or tellurium containing
C07C39500
Patent
active
050915703
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method for the preparation of dialkyl of the Group VI metals tellurium and selenium.
The metals Tellurium and Selenium are of importance in semi-conductor technology, for example in the preparation of the infra red detector material cadmium mercury telluride (CMT) and in light sensing switches respectively.
It is well known that the presence of impurities in semi-conductor materials is extremely undesirable. It is therefore useful to be able to prepare semiconductor materials and chemical precursors used in their manufacture in a high degree of purity. An important series of such chemical precursors is the alkyls of the relevant semiconductor material, which can relatively easily be thermally dissociated to form an epitaxial layer of the material or a layer containing the material. Such alkyls have the additional advantage that they are otherwise relatively stable and may be purified further via the formation of adducts with for example Lewis base adjuvants such as trialkyl or triaryl Group V compounds.
The formation of various addjucts for semiconductor purification is described for example in GB 850955-A, together with a method for preparation of Group II metal alkyls. The preparation of other alkyls can present problems, and in particular the preparation of the Group VI alkyls such as those of tellurium and selenium in a pure state has until now presented great difficulty.
At present methods for preparation of tellurium alkyls are known. Synthetic Communications 12(3), (1982), 163-165 describes a method for preparation of dialkyl ditellurium by reaction of the corresponding lithium alkyl and elemental tellurium in THF with atmospheric oxidation, tellurium dialkyl not being formed. Similarly J. Organometallic Chemistry 255, (1983), 61-70 describes the preparation of mixtures of tellurium dialkyls and ditellurium dialkyls by reaction of the corresponding Grignard reagent RMgCl with tellurium IV chloride. This reaction is believed to result in contamination of the product with RTeCl.
The present invention seeks to overcome or alleviate the problems outlined above by providing a method for the preparation of dialkyls of tellurium and selenium in a substantially more pure state, or at least in a state that facilitates further purification. Other objects and advantages of the present invention will be apparent from the following description.
According to the present invention a method for the preparation of dialkyl tellurium or dialkyl selenium comprises reacting either elemental tellurium or elemental selenium, or a tellurium IV or selenium IV halide with a Group I metal alkyl in a solvent which is or contains at least one C.sub.4 -C.sub.10 aliphatic ether, and optionally also contains a liquid alkane.
The reaction is preferably carried out under conditions which exclude atmospheric oxygen, for example under an inert atmosphere eg nitrogen. Oxidation by the atmosphere can result in impurities.
A preferred temperature is below 20.degree. C., especially -40.degree. C. to 0.degree. C. Above room temperature impurities may be formed, such as neohexyl Group I metal alkyls.
The method is suitable for the preparation of all dialkyls, but is especially suitable for the preparation of di- C.sub.1 -C.sub.4 alkyls of tellurium and selenium, which may be straight chain, branched or tertiary alkyls, for example tellurium and selenium dimethyl, diethyl, dipropyl (n- and iso-) or dibutyl (n-, iso- and tert-), especially tellurium dimethyl and di-tert.-butyl.
The Group I metal is preferably lithium, sodium or potassium, especially lithium. Preferred Group I metal alkyls are therefore MeLi and tert.-BuLi.
Preferably the ether is a di- C.sub.2 -C.sub.5 alkyl ether, especially a di-n-alkyl ether. The alkyl groups of the dialkyl or di-n-alkyl ether may be the same or different and a particularly preferred ether is diethyl ether. Whatever ether is/are used, it/they should preferably have a low boiling point.
If an alkane is present it must be liquid at the reaction temperature, and suitable alkanes in
REFERENCES:
patent: 1578731 (1926-03-01), Hochwalt
patent: 4946994 (1990-08-01), Higa
International Publication WO89/05292, 6/15/89.
Engman et al., "Synthetic Communication", 12(3), pp. 163-165, 1982.
Jones et al., "J. Organomet. Chem.", 255, pp. 61-70, 1983.
Cole-Hamilton David J.
Mullin John B.
Shenai-Khatkhate Deodatta V.
Webb Paul
Secretary of State for Defence in her Britannic Majesty's Gov. o
Shaver Paul F.
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