Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-05-30
2002-09-03
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
Reexamination Certificate
active
06444862
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to metal alkoxides and to the preparation and isolation of metal alkoxides, and especially, to metal alkoxides that are liquid when pure and/or exhibit increased solubility in a wide variety of solvents, and to methods of preparation of such metal alkoxides.
BACKGROUND OF THE INVENTION
Metal alkoxides, and particularly alkali metal alkoxides, are widely used in industry as catalysts and as stoichiometric reagents. These reagents are used in diverse reaction chemistries such as alkylation, isomerization, rearrangements, condensations, transesterifications and eliminations. See, for example, D. E. Pearson, C. A. Buehler Chemistry Reviews 74, 45 (1974).
As pure solid compounds, these materials are ionic in character as a result of the strongly electropositive nature of the metals. See, for example, D. C. Bradley, R. C. Mehrotra, D. P. Gaur,
Metal Alkoxides
, Academic Press, London (1978). For derivatives of the same element, the covalent character of the metal-oxygen bond increases with the greater inductive effect of the alkyl group. For example, a tertiary butoxide has a higher covalent character than the corresponding primary n-butoxide. The trend in covalent character relative to the counter ion in the case of alkali metals, for example, is that lithium alkoxides are more covalent than sodium or potassium alkoxides. This phenomenon, coupled with steric factors, leads to a slightly greater inherent stability of the isolated solid tertiary alkoxides. Unfortunately, these caustic solids readily react with atmospheric water and carbon dioxide. Furthermore, these solid metal alkoxides are rather dusty, which can be problematic when handled on a large scale. Some of the primary alkoxides are also prone to spontaneous combustion in air. See Y. El-Kattan, J. McAtee, “Sodium Methoxide”
Encyclopedia of Reagents for Organic Synthesis
, 4593, Ed. L. A. Paquette, John Wiley and Sons, NY (1995).
To provide a safer material, metal alkoxides are often dissolved in a solvent. In general, liquids are, for example, easier to transfer from drums or cylinders into reactors (reducing the exposure of human handlers to dangerous materials), more easily kept under an inert atmosphere, and provide more options for modes of addition to the substrate. Unfortunately, alkali metal alkoxides and other metal alkoxides exhibit only rather low solubility in the alcohols from which the alkoxides are made, usually in the range of 2-25 wt %. For example, sodium isopropoxide is only soluble up to about 2 wt % in isopropanol. The low solubilities of many alkoxides have been attributed to the ionic character and the extent of oligomerization or polymerization in solution. Another factor affecting solubility in an alcohol solvent is the propensity of alkoxides to form insoluble alcoholate complexes with the alcohol. Metal alkoxides are somewhat more soluble in polar ethereal solvents such as tetrahydrofuran and the polyethers (glymes). However, even in ethers, the solubility is generally less than 50%, especially at or below room temperature (that is, at or below 25° C.). Moreover, the range of polar solvents is somewhat limited as a result of the reactivity of the alkoxide. Furthermore, in some cases the solvent of choice for the desired reaction involving a metal alkoxide is not compatible with the alkoxide or the metal alkoxide is insoluble therein.
It is very desirable to develop metal alkoxide reagents that facilitate the diverse reactions in which those reagents are use.
SUMMARY OF THE INVENTION
The present invention provides generally a method to produce relatively highly concentrated solutions of metal alkoxides in a wide variety of solvents. Solvents suitable for use in the present invention include aliphatic and aromatic hydrocarbons, and polar aprotic solvents such as dimethylformamide (DMF) and ethers. Preferably, the solubility of the metal alkoxide in the solvent is at least approximately 25 wt %. More preferably, the solubility of the metal alkoxide in the solvent is at least approximately 50 wt %. Most preferably, the solubility of the metal alkoxide in the solvent is at least approximately 75 wt %. These solubilities are achievable at relatively low temperature. Preferably, for example, these solubilities are exhibited in a temperature range of approximately −40° C. to approximately 50° C. More preferably, these solubilities are exhibited in a temperature range of approximately −25° C. to approximately 25° C. Most preferably, these solubilities are exhibited in a temperature range of approximately 0° C. to approximately 25° C. Surprisingly, the relatively high solubilities of the present invention are achievable even in aliphatic hydrocarbons and aromatic hydrocarbons.
The present invention also provides for isolation and characterization of the first pure liquid alkali metal alkoxide reagent and other liquid metal alkoxide reagents. As used herein, the terms “pure” or “neat” refer to a liquid having a purity of at least approximately 97 wt % (that is, the liquid is at least 97% metal alkoxide by weight). The purity is more preferably at least approximately 98 wt %. Most preferably, the purity is at least approximately 99 wt %. Unlike current metal alkoxide reagent compositions, the neat, liquid alkoxide reagents of the present invention are highly miscibile in all proportions with a wide variety of solvents, including, for example, aliphatic hydrocarbon solvents such as hexane and heptane or aromatic hydrocarbon solvents. Other suitable solvents include ethers and polar aprotic solvents. Furthermore, the compositions of the present invention are relatively easy to handle or transport. Moreover, the highly concentrated and/or neat liquid metal alkoxide reagents of the present invention allow higher reactor loading than is possible with current compositions, thereby maximizing productivity.
In one aspect, the present invention provides a method for synthesizing highly soluble metal alkoxides comprising the step of: reacting a tertiary alcohol with at least a stoichiometric amount of a metal reagent. Preferably, the reaction proceeds for a period of time sufficient for the reaction to go to completion. The metal reagent is preferably a group I metal, a group II metal, zinc, a metal alloy of a group I metal, a metal alloy of a group II metal, a metal alloy of zinc (suitable metal alloys, include, for example, NaK, NaHg or KHg), a compound of a group I metal, a compound of a group II metal or a compound of zinc (suitable, metal compounds include, for example, LiH, NaH, KH, Et
2
Zn or Bu
2
Mg) Preferred metals for use in the present invention include K, Li, Na, Cs, Mg, Ca or Zn. Likewise, metal alloys and metal compounds for use in the present invention preferably include K, Li, Na, Cs, Mg, Ca or Zn. In the case that a metal is used, the reaction preferably takes place above the melting point of the metal. Preferably, formation of a metalalcoholate complex is avoided. To avoid forming a metalalcoholate complex, an excess of metal reagent (for example, metal, metal alloy and/or metal compound) is preferably used.
Tertiary alcohols suitable for use in the present invention preferably have the general formula:
(or HOCR
1
R
2
R
3
) wherein R
1
, R
2
, and R
3
are, independently, the same of different, an alkyl group, an alkenyl group, an alkynyl group or an aryl group, and at least one of R
1
, R
2
, and R
3
is a group of at least 3 carbon atoms. Preferably, at least on of R
1
, R
2
, and R
3
is a branched group of at least 3 carbon atoms. More preferably, at least one of R
1
, R
2
, and R
3
is a branched group of at least 6 carbon atoms. As used herein, the term “alkyl group” includes generally branched and unbranched alkyl group of the formula —C
n
H
2n+1
(wherein n is an integer) and cyclic alkyl groups of the formula —C
m
H
2m
wherein m is an integer equal to or greater than 3. Alkyl groups preferably have 1 to 20 carbons. The term “alkenyl” refers generally to a straight or branched chain hydrocarbon group with at least one
Burkhardt Elizabeth R.
Corella, II Joseph A.
Ellenberger David H.
Sutton Christopher P.
Bartony, Jr. H. E.
Barts Samuel
Mine Safety Appliances Company
Price Elvis O.
Uber J. G.
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