Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
1998-12-17
2001-05-22
Kumar, Shailendra (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S230000, C564S237000, C564S240000, C548S473000, C548S485000
Reexamination Certificate
active
06235934
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to phase transfer catalysis. More particularly, it relates to the preparation of aqueous solutions of hexasubstituted guanidinium salts useful as phase transfer catalysts, and to the use of such solutions in the preparation of polyetherimides and intermediates therefor.
The use of hexaalkylguanidinium salts as phase transfer catalysts in various reactions is known. Many of these reactions are characterized by the necessity of conducting them under anhydrous conditions. This makes it very difficult to introduce measured amounts of the hexasubstituted guanidinium salt into the reaction mixture, since such salts are solids and are only sparingly soluble in the organic solvents employed.
Hexasubstituted guanidinium salts may be prepared by a series of three reactions: the phosgenation of a secondary amine to produce a tetrasubstituted urea; further phosgenation of the tetrasubstituted urea to form a chloroformamidinium chloride, also known as a “Vilsmeier salt” and sometimes designated as such hereinafter; and finally, the reaction of the Vilsmeier salt with further secondary amine to produce the hexasubstituted guanidinium chloride. The third of these reactions must be conducted under anhydrous conditions, and the second is preferably anhydrous also.
It is frequently found that preparation of the Vilsmeier salt in good yield cannot be achieved unless expensive solvents such as acetonitrile are employed or a substantial excess of phosgene is used. This is true, for example, of the method described in Kantlehner et al.,
Liebigs Ann. Chem.
1984, 108-126, which afforded the hexasubstituted guanidinium salt in 94% yield but employed acetonitrile as the solvent. A method employing phosphorus oxychloride in toluene is described in Example 1 of U.S. Pat. No. 5,132,423; it afforded the product in 87% yield. A method employing phosgene and toluene, described in Barton et al.,
J. Chem. Soc., Perkin Trans.,
1982, 2085-2090, resulted in a relatively low yield (85%) even with the use of a substantial excess of phosgene (molar ratio 1.95:1). The use of a large excess of phosgene, in any event, is undesirable since phosgene is toxic and is difficult to contain during the reaction. Moreover, disposal of a large excess of phosgene generally requires a sparging operation including passage through a caustic scrubber, presenting a potential hazardous waste problem upon disposal.
The product of the above-described series of reactions is invariably the hexasubstituted guanidinium chloride. It has further been found that the chlorides are hygroscopic, making their use under anhydrous conditions complicated. Therefore, they are often converted to other salts such as the bromides. This necessitates an additional reaction step, which is also expensive and therefore undesirable.
The use of hexasubstituted guanidinium salts as phase transfer catalysts in the reaction of bisphenol salts with halo- or nitro-substituted phthalimides to form bisimides, which are conventional intermediates for polyetherimide production, is described in Example 4 of U.S. Pat. No. 5,081,298. Its use in the direct preparation of polyetherimides by the reaction of bisphenol salts with similarly substituted bis(phthalimido) compounds is disclosed in U.S. Pat. No. 5,229,482. In each case, the guanidinium salts were added in solid form, which, as previously mentioned, presents numerous problems in commercial operations. Anhydrous conditions are mandatory in these reactions, since the presence of even traces of water can drastically decrease yields.
Methods of preparing hexasubstituted guanidinium salts in high yield and using them in a convenient manner as phase transfer catalysts in commercial operations, therefore, continue to be desirable subjects of investigation.
SUMMARY OF THE INVENTION
The present invention has numerous aspects relating to the preparation of hexasubstituted guanidinium salts and intermediates therefor, compositions comprising such salts and the use of such compositions as phase transfer catalysts in the preparation of polyetherimides and intermediates therefor. Each aspect is summarized immediately below.
First aspect: a method for preparing an aqueous solution of a hexasubstituted guanidinium salt which comprises the steps of:
(A) passing phosgene into a mixture comprising an aliphatic or alicyclic secondary amine, water and an organic solvent of low polarity at a reaction temperature in the range of about 40-80° C. and a pH in the range of about 10-13 maintained by the addition of an alkali metal base; the proportion of water being effective to produce a solution of by-product alkali metal chloride having a concentration of at least about 95% by weight of the saturation concentration under the prevailing reaction conditions, the ratio of equivalents of phosgene to said amine being in the range of 1.0-1.15:1, the volume ratio of organic solvent to water being in the range of about 0.8-5.0:1 and the proportion of amine being calculated to afford about a 25-90% by weight solution of product in said organic solvent assuming complete conversion, to produce a first product mixture comprising tetrasubstituted urea;
(B) removing water, amine and alkali metal chloride from said first product mixture to produce a first product mixture;
(C) adjusting said first product mixture to a tetrasubstituted urea concentration in the range of about 40-80% by weight by the addition or removal of organic solvent if necessary;
(D) introducing phosgene at a temperature in the range of about 60-80° C., the proportion of phosgene added being effective to react with any water present plus a ratio of equivalents of phosgene to said tetrasubstituted urea in the range of 1.05-1.15:1, to produce an anhydrous mixture comprising tetrasubstituted chloroformamidinium chloride;
(E) removing any unreacted phosgene from said anhydrous mixture;
(F) adding secondary amine to said anhydrous mixture in an amount effective to convert said tetrasubstituted chloroformamidinium chloride to hexasubstituted guanidinium salt; and
(G) diluting said hexasubstituted guanidinium salt with water in a basic medium to produce aqueous and organic phases, removing said organic phase comprising unreacted secondary amine, and acidifying said aqueous phase containing said hexasubstituted guanidinium salt as necessary to adjust its pH to a value in the range of 2-12.
Second and third aspects: methods for preparing a tetrasubstituted urea which comprises step A, and for preparing a tetrasubstituted chloroformamidinium chloride which comprises steps D and E, all as defined above.
Fourth aspect: a method for preparing an aqueous solution of a hexasubstituted guanidinium salt having one or more chains containing at least 3 carbon atoms attached to each nitrogen atom which comprises the steps of:
(H) passing phosgene into a mixture comprising an aliphatic or alicyclic secondary amine, water and an organic solvent of low polarity at a reaction temperature in the range of about 40-80° C. and a pH in the range of about 10-13 maintained by the addition of an alkali metal base, to produce a first product mixture comprising tetrasubstituted urea;
(J) removing water, amine and alkali metal chloride from said first product mixture to produce a first product mixture;
(K) introducing phosgene at a temperature in the range of about 60-80° C. to produce an anhydrous mixture comprising tetrasubstituted chloroformamidinium chloride;
(L) removing any unreacted phosgene from said anhydrous mixture;
(M) adding secondary amine to said anhydrous mixture in an amount effective to convert said tetrasubstituted chloroformamidinium chloride to hexasubstituted guanidinium salt in a second product mixture;
(N) diluting said second product mixture with an amount of water in a basic medium, said amount of water being effective to cause the formation of three liquid phases, isolating the middle phase comprising said hexasubstituted guanidinium salt and acidifying said middle phase as necessary to adjust its pH to a value in the range of 2-12.
Fifth a
Brunelle Daniel Joseph
Caringi Joseph John
Faler Gary Ray
Flowers Larry Ivis
Guggenheim Thomas Link
Brown S. Bruce
General Electric Company
Johnson Noreen C.
Kumar Shailendra
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