Chemistry of inorganic compounds – Nitrogen or compound thereof – Oxygen containing
Reexamination Certificate
1999-04-02
2001-06-26
McKane, Joseph K. (Department: 1613)
Chemistry of inorganic compounds
Nitrogen or compound thereof
Oxygen containing
C548S473000, C548S456000
Reexamination Certificate
active
06251354
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for recovering sodium nitrite, potassium nitrite, lithium nitrite, or nitrite mixtures containing at least one of the foregoing from the reaction mixture resulting from the synthesis of a polyimide such as, for example, an aromatic bis(ether phthalimide).
2. Brief Description of the Related Art
Sodium nitrite may be produced as a reaction by-product in aromatic displacement reactions such as the synthesis of aromatic bis(ether phthalimide) compounds. Synthesis of these compounds has been described in U.S. Pat. No. 5,068,353 to Dellacoletta. Of particular interest is the product of sodium nitrite as the reaction by-product of the synthesis of bisimide having the formula (I).
Several techniques have been used to recover bisimide from a reaction mixture including solid-liquid separation techniques such as filtering at a temperature at which the bisimide is substantially completely soluble while alkali metal salt impurities are substantially insoluble. (See U.S. Pat. No. 5,068,353.)
Bisimide has also been recovered by extractive purification employing a conventional caustic wash as the extractant. In this process, bisimide in the toluene reaction solvent is extracted with a sodium hydroxide wash to remove the sodium nitrite, unreacted starting materials, catalyst and other reaction by-products. A disadvantage to this method is that the sodium hydroxide also hydrolyzes some of the bisimide product, converting it to aqueous, soluble amide-acid sodium salts. (See U.S. Pat. No. 5,068,353.)
The sodium hydroxide wash, containing the bulk of the sodium nitrite present in the reaction mixture, is typically disposed of by concentrating and burning in an incinerator or is disposed of through biotreatment. The organic materials in the wastewater (i.e., the sodium hydroxide wash) are destroyed and the sodium nitrite is converted to nitrogen and sodium carbonate in the burning process. A disadvantage to this process is the violent, uncontrollable nature of the reaction due to the high amounts of organic impurities present in the sodium hydroxide wash. As the sodium nitrite by-product can itself be marketed, it would be advantageous to recover the sodium nitrite from the reaction mixture in sufficient purity to be marketable.
What is needed in the art is a method for recovering useable sodium nitrite from the reaction mixture formed from the synthesis of aromatic bis(ether phthalimides).
SUMMARY OF THE INVENTION
The process of the present invention comprises forming a reaction mixture comprising one or more products including a recoverable amount of a metal nitrite, preferably at least one of sodium nitrite, lithium nitrite, and potassium nitrite, in a non-polar solvent; treating the reaction mixture with a polar solvent in an amount effective to produce two phases comprising an aqueous solution phase of the metal nitrite and an organic non-polar phase; and separating the aqueous solution phase from the organic non-polar phase.
Various features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a process for recovering lithium nitrite, potassium nitrite, sodium nitrite, or mixtures containing at least of the foregoing from a reaction mixture formed from the synthesis of a polyimide. For ease of discussion, the present application will discuss the process of the present invention as it applies to the recovery of sodium nitrite from a reaction mixture formed from the synthesis of bisimide, wherein the reaction mixture comprises a recoverable amount of sodium nitrite, bisimide, unreacted material, and by-products and impurities, dissolved in a non-polar organic solvent. The reaction mixture is thus referred to as non-polar.
For example, bisimide is synthesized by reacting 4-nitro-N-methylphthalimide of the formula (II):
with bisphenol A disodium salt of the formula (III)
in a non-polar solvent, such as refluxing toluene, in the presence of a phase transfer catalyst.
Suitable non-polar organic solvents useful in the present invention include solvents in which the major reaction product, bis(ether phthalimide), is soluble and sodium nitrite is insoluble. Some possible solvents include, but are not limited to, toluene, xylene, trimethylbenzene, dichlorobenzene, chlorobenzene, anisole, and higher hydrocarbon solvents including dodecane.
Meanwhile, preferred phase transfer catalysts include quaternary ammonium salts and phosphonium salts including bis(tri-n-butyl)-1,6-hexylene diammonium dibromide, tetrapropylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium fluoride, tetrabutylammonium acetate, tetrabutylphosphonium bromide, tetraphenylphosphonium bromide and hexaethylguanidinium chloride, among others, with hexaethylguanidinium chloride catalyst of the formula (IV):
particularly preferred.
The resulting reaction mixture comprises, for example, the major reaction product, bisimide, along with sodium nitrite, the minor reaction product monoimide of the formula (V):
unreacted starting material, catalyst, such as hexaethylguanidinium chloride, and by-products having the formulas (VI):
and H
2
NEt
2
(diethylamine), wherein “Et” is an ethyl group, along with unidentified organic impurities.
In order to separate the sodium nitrite from the reaction mixture, a polar solvent, typically water, is added to the reaction mixture in an amount effective to dissolve the sodium nitrite, resulting in two immisible phases: for example, an aqueous phase comprising an aqueous solution of sodium nitrite and a small amount of organic materials, typically less than about 3 percent by weight (“wt %”) organic materials based upon a combined weight of organic materials, catalyst, and sodium nitrite; and an organic non-polar phase comprising bisimide, catalyst, reaction by-products and impurities, which are not appreciably soluble in water, dissolved in a non-polar solvent. The amount of water added is tailored to produce the desired percent solution of sodium nitrite according to customer requirements or the subsequent purification technique to be used. Typically, up to about 45 wt % sodium nitrite solution based on the total weight of aqueous solution, is desirable for most purification techniques, with about 10 wt % to about 42 wt % sodium nitrite preferred, and about 37 wt % to about 42 wt % especially preferred. The pH of the water utilized is general about neutral with deionized water often preferred.
Dissolution of the sodium nitrite in water can optionally be facilitated via the addition of heat. A dissolution temperature can readily be selected empirically by one of skill in the art based on the choice of solvent, with such temperature typically between about 25° C. and about 110° C. For example, for reactions in which the non-polar organic solvent is toluene, a temperature of about 70° C. to about 85° C. is preferred.
Once the two phases have reached equilibrium, the aqueous solution of sodium nitrite is readily separated from the non-polar reaction mixture, typically by drawing out the sodium nitrite solution through the bottom of the reaction vessel. The separated aqueous sodium nitrite solution is herein referred to as the “water wash” to distinguish from the conventional caustic wash. At this point, the sodium nitrite is sufficiently free of organic material such that it may be marketed as is or subjected to further purification techniques.
The determination of whether further purification techniques will be employed is based upon the desired purity of the sodium nitrite, and the yield of the reaction mixture employed. High yield reaction mixtures are required to achieve a clean separation between the organic non-polar phase and the aqueous phase. If the reaction yield is not sufficiently high, bisphenol A disodium salt will be present in the aq
Greenwell Robert E.
Guggenheim Thomas Link
Johnson Norman Enoch
Odle Roy Ray
Webb Jimmy Lynn
General Electric Co.
McKane Joseph K.
Murray Joseph
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