Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Utility Patent
1998-02-24
2001-01-02
Kumar, Shailendra (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S463000, C556S412000, C556S463000, C556S466000
Utility Patent
active
06169203
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the preparation of alkali-metal amides and, particularly, to the preparation of lithium, sodium, potassium and cesium amides.
BACKGROUND OF THE INVENTION
Alkali metal alkylamides have been prepared directly from alkali metals under a number of synthetic routes. For example, lithium diisopropylamide (LDA) has been produced directly from lithium metal using an “electron carrier” or “hydrogen acceptor” such as styrene in THF as follows:
See U.S. Pat. No. 4,595,779. Suitable electron carriers are generally conjugated, unsaturated hydrocarbons. These electron carriers are noted to readily accept electrons from an alkali metal to form free radicals or carbanions.
Likewise, lithium alkylamides of the general formula (R
3
M)
x
NLi(R
1
)
y
(LB)
z
, (wherein R and R
1
are C
1
-C
8
alkyl, cycloalkyl or alkylene groups, LB is a Lewis base, x and y are integers having the sum of 2, and z is greater than 1) have been formed from reacting bulk lithium metal with an alkylamine in the presence of a solvent and certain electron carriers. See U.S. Pat. No. 5,493,038. The use of electron carriers in such reactions, however, often results in formation of undesirable byproducts which are very difficult to separate from the desired product.
International Patent Application No. PCT/US96/10923 discloses a process for preparing organometallic amides via a number of reaction schemes in the presence and absence of an electron carrier. However, each of those reactions requires the presence of a solvent. In such reactions, solvents takes up valuable reactor volume and often necessitate difficult separation procedures to arrive at a usable product.
A one-step synthesis of alkali-metal hexamethyldisilazanes without the use of an electron carrier has been developed by Chiu et al. See U.S. Pat. No. 5,420,322. Under this method, lithium, sodium or potassium is reacted with a 1,1,1,3,3,3-hexamethyldisilazane at a reaction temperature above the melting point of the alkali metal. Although, very pure product is obtained under the method of Chiu et al. without difficult separation procedures, relatively high temperatures and pressures are required (especially in the case of the synthesis of lithium hexamethyldisilazanes).
It is thus very desirable to develop alternative synthetic schemes for the production of alkali-metal alkylamides.
SUMMARY OF THE INVENTION
Generally, the present invention provides a method for synthesizing an alkali-metal amide composition comprising the following step:
charging a reactor vessel with a reaction mixture comprising an alkali metal selected from the group of lithium, sodium, potassium or cesium, an electron carrier, and a disubstituted amine. The reaction to form the alkali-metal amide product occurs without the use of a solvent.
The disubstituted amine has the formula R
1
R
2
NH, wherein R
1
and R
2
are preferably independently, the same or different, an alkyl group or —SiR
3
, wherein R
3
is an alkyl group, an aryl group, or an aryl group substituted with an alkyl group. The reactants can be added in stoichiometric quantities without the addition of any solvent(s). Potentially difficult separations and potentially undesirable byproducts resulting from the presence of solvent(s) are thereby avoided. Furthermore, valuable reactor space is conserved.
The alkali-metal amide compositions of the present invention have the following general formula: MNR
1
R
2
, wherein M is an alkali metal selected from the group of lithium, sodium, potassium or cesium. Preferably, R
1
and R
2
are the same to form an alkali-metal amide composition of the general formula: MN(R
1
)
2
.
As used herein, the term “alkyl group” refers generally to normal, branched and cyclic alkyl groups. Preferably such alkyl groups are C
1
-C
12
alkyl groups. More preferably, such alkyl groups are C
1
-C
6
alkyl groups.
As used herein, the term “aryl group” refers generally to a phenyl group. Such phenyl groups may be substituted, for example, with one or more alkyl groups. Preferably, such alkyl groups substituents are C
1
-C
6
alkyl groups. Preferred alkyl substituent groups include a methyl group, an ethyl group, an isopropyl group, an n-propyl, a t-butyl group and an n-butyl group.
Preferably, the reaction to form the alkali-metal amide product occurs at a temperature above the melting point of the alkali-metal amide product. In that regard, it is preferable to maintain the alkali-amide product in a liquid state to facilitate heat and mass transfer and to thereby facilitate a complete reaction. Maintenance of the alkali-amide product in a liquid state is not necessary, however. The reaction will proceed, for example, when the reaction mixture is a slurry. Indeed, many of the reactions of the present invention will proceed at temperatures as low as, for example, room temperature (that is, approximately 20° C.).
The reaction to form the alkali-metal amide will proceed regardless of the order of addition of the reagents. However, it is preferable to add the electron carrier last in the reaction to minimize initial pressure within the reactor as well as to minimize the potential for undesirable polymerization of the electron carrier. For example, in one reaction scheme, the reactor vessel is charged with the alkali metal and the disubstituted amine. The reaction vessel is preferably heated to a temperature above the melting point of the alkali-metal amide product either before or after addition of the alkali metal and the disubstituted amine. After charging the reactor vessel with the alkali metal and the alkylamine, the electron carrier is added to the reactor vessel. Alternatively, the reactor vessel can first be charged with the alkali metal, and a mixture of the disubstituted amine and the electron carrier can be added thereto.
Preferably, electron carriers that are converted to a byproduct having a boiling point below the decomposition temperature of the alkali-metal amide product are used in the present invention. Likewise, the electron carrier itself preferably has a boiling point below the decomposition temperature of the alkali-metal amide product. Such electron carriers and their corresponding byproducts are generally easily separable from the product via distillation. Preferably, the electron carriers and their corresponding byproducts have boiling points at least approximately 10° C. below the decomposition temperature of the alkali-metal amide product.
The electron carrier is preferably a conjugated hydrocarbon. More preferably, the electron carrier is a conjugated, aliphatic hydrocarbon. Most preferably, the electron carrier is isoprene. Although it is generally believed in the art that isoprene and other conjugated hydrocarbon electron carriers will polymerize at temperatures above 60° C. in the presence of an alkali metal (see, for example, Allcock, H. R. and Lanyse, F. W.,
Contemporary Polymer Chemistry,
second edition, Prentice-Hall, Inc., p. 320 (1990)) and that a solvent is thus necessary to limit or prevent polymerization, it has been discovered that no polymerization of the electron carrier occurred under the reaction conditions of the present invention.
The reactions of the present invention can be carried out at relatively low pressures and temperatures. Moreover, the absence of a solvent greatly simplifies separation/purification of the alkali-metal amide to achieve a relatively high purity (for example, >99%) as compared to previous reaction schemes requiring the use of an electron carrier and an ethereal or hydrocarbon solvent. Increased reactor loading is also possible with the reactions of the present invention as compared to current reaction schemes for the production of alkali-metal amides in which solvent systems are required. Indeed, approximately 50 to 75% of reactor loading arising from the use of such solvent systems can be eliminated. Further, many of the reactions of the present invention provide substantially quantitative yields with relatively short reactions times (typically, less than one hour).
DETAILED DESCRIP
Bartony, Jr., Esq. H. E.
Kumar Shailendra
Mine Safety Appliances Company
Uber, Esq. J. G.
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