Lithium tertiary alkoxides

Details Lithium tertiary alkoxides Lithium tertiary alkoxides

1996-12-09

2001-02-27

Shippen, Michael L. (Department: 1621)

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

Organic compounds

Oxygen containing

Reexamination Certificate

active

06194617

ABSTRACT:

This application is a continuation-in-part of application Ser. No. 08/129,818 filed Sep. 30, 1993, now abandoned.
This invention concerns a process for preparing lithium tertiary alkoxides by reacting lithium metal in gross or bulk form with a tertiary alcohol.
Alkali metal alkoxides and especially alkali metal tertiary alkoxides such as lithium tertiary butoxide are used in the preparation of pharmaceutical intermediates and in the synthesis of polymers and in general organic synthesis. In co-pending application U.S. Ser. No. 08/973,116 filed Nov. 6, 1992 now U.S. Pat. No. 5,276,219, there is a described a process for preparing clear, suspensoid-free solutions of lithium tert-butoxide in tetrahydrofuran at reflux by reaction of lithium metal in finely divided dispersed particle form with an excess of tert-butyl alcohol.
Although lithium metal in a finely divided dispersed state reacts rapidly with tert-butyl alcohol in THF medium, it is costly to produce, requiring the steps of (a) heating of bulk lithium metal and mineral oil to about 190-200° C. in the presence of a dispersion aid, such as oleic acid, (b) stirring the resultant molten mixture at high speeds in a special dispersion unit to produce the required smali particle sizes (generally less than 100 microns), then (c) cooling the product (preferably without stirring), and then finally (d) removing the mineral oil from the solidified lithium metal particles by washing several times with a volatile hydrocarbon solvent, such as hexane or pentane. The volatile hydrocarbon solvent can optionally be removed by purging with an inert gas such as argon, or more preferably, be washed one or more times with tetrahydrofuran before reaction with the tert-butyl alcohol.
Besides being costly to produce, lithium dispersion also may add undesirable impurities to the subsequent lithium tert-butoxide product in THF such as, e.g., mineral oil and oleic acid breakdown products, and volatile hydrocarbons.
Because of the extremely small sizes of the lithium metal particles, a high proportion of solid impurities, small in size, are generally present after reaction with the alcohol is complete. Impurities on the lithium surface slow down the initial reaction. These impurities arise from side reactions with traces of oxygen in the inert atmosphere, of traces of water in the solvent and alcohol, and with the solvent itself. These small solid impurities (including any unreacted lithium metal particles) cause filtration problems, although the use of an excess of the alcohol generally takes care of any unreacted lithium metal.
The present invention provides a process for quickly preparing easily separable solutions of lithium tert-alkoxides in an economically feasible time period (1 to 10 hours), comprising the steps of: reacting lithium metal in bulk solid form, containing less than 0.1% by weight of sodium, with a tertiary alcohol in mole ratios of lithium metal to alcohol ranging from 1 to 1 to 10 to 1 in an ethereal or hydrocarbon medium under an inert atmosphere at elevated temperature between 25 and 100° C., cooling the product and separating the product solution from the unreacted lithium metal in the reactor; the process is conveniently continued when higher mole ratios of lithium to alcohol (>2) are employed by adding additional solvent, sufficient lithium metal and alcohol to the unreacted metal in the reactor to maintain the mole ratio of lithium metal to alcohol, and continuing the reaction, thereby to form further lithium tert-alkoxide, and repeating said steps a number of times. Optionally the reaction may be catalyzed with small amounts of a C
1
to C
3
alcohol. “Bulk” form is defined herein as lithium metal obtained as castings, or pieces thereof, from manufacture in an electrolytic cell,or from an extrusion process, including subsequent cutting into smaller, more manageable pieces or even by directly slicing the cell “ingot” into smaller pieces but generally not smaller than 0.5 grams. These pieces of bulk lithium have volumes of at least one cubic centimeter. It should be noted that the bulk metal is maintained in solid form throughout the reaction although the pieces diminishes somewhat in size. The metal is never reacted in a liquified form (as per Lenz in U.S. Pat. No. 3,971,833). It is known that in liquified form, the metal (sodium) is reduced to a particulate form by the reactant alcohol and is not reacted in bulk form (as per Alkali Metal Dispersions, by I. Fatt & M. Tashima, D. van Nostrand, Inc., Princeton, N.J., 1961 page 80, ref. 108). In addition, the high reaction temperature required to dissociate the alcohol of complexation with sodium alkoxides is not required when the alkali metal is lithium and could be detrimental because of the ease of sublimation of lithium tert-butoxide at 200° C. and potential pyrolysis of the product.
Unexpectedly, the process of the present invention overcomes problems experienced with the use of lithium metal in a finely divided (dispersed) state without experiencing an overly great increase in reaction time by the use of a sufficient excess of lithium metal in bulk form (over and above the alcohol used) in the essential absence of any hydrocarbon or other (solid) impurities. Impurities on the lithium surface slow down the initial reaction. Surprisingly, the amount of lithium metal in bulk form needed to preserve a comparable overall reaction time when compared to lithium in dispersed form is only in the order of about three times. For example, the surface area of one gram equivalent of lithium metal particles 20 microns in diameter is about 13,000 square centimeters, while the surface area of an equivalent amount of lithium metal cubes with dimensions of one centimeter by one centimeter by one centimeter is only 79 square centimeters, a one hundred sixty-six times greater surface area for the dispersed lithium. One would therefore expect the relative amount of lithium in bulk form needed to give a overall reaction rate comparable to the dispersed lithium to be in the order of one hundred sixty-six times greater. Instead, only three equivalents of lithium metal in the form of cubes was found to react with one equivalent of the alcohol in a comparable overall time (180 minutes) as did one equivalent of lithium metal dispersed to 20 micron diameter particles (135 minute overall reaction time). Although the sizes of the solid bulk lithium metal pieces are reduced somewhat in size during reaction, the amount of excess lithium metal employed is such as to cause this size reduction to be minimal. Resupply of the equivalent(s) of metal lost in each reaction maintains this state for a great number of runs. See Table I. Lithium tertiary butoxide in the tables I-V is abbreviated as LTB and elsewhere as lithium tert-butoxide and lithium t-butoxide.
After the reaction of one of the three equivalents of the bulk lithium metal is completed, the slightly hazy product solution can be easily decanted from the unreacted (floating) lithium metal and filtered quickly. Another reaction can be started in the same reactor, adding only another equivalent each of lithium metal and alcohol and the required amount of solvent. When the process is to be repeated one or more times in the same reactor it is advantageous to immediately add additional solvent after the product of the preceding reaction is recovered. Surprisingly, the overall reaction time decreases still further in the second run (130 minutes) and then stays constant for the next two consecutive runs (120 minutes). This decrease in time is thought to be due to preconditioning of the lithium metal. (Removal of surface impurities).
The use of only one equivalent or slightly greater than one equivalents of bulk lithium metal especially if the lithium contains an appreciable amount of sodium (0.1%) slows the reaction rate inordinately and makes the recovery of high yields of lithium tert-alkoxide impractically low (see, e.g. Lockman and see the comparative example Table 3).
The ease of separation of the product solution from unreacted lithium metal is m

Affiliated with

Also associated with

Rating

Lithium tertiary alkoxides does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Lithium tertiary alkoxides, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lithium tertiary alkoxides will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2586807