Organic compounds -- part of the class 532-570 series – Organic compounds – Phosphorus esters
Reexamination Certificate
2000-03-30
2001-09-18
Geist, Gary (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Phosphorus esters
C558S037000, C544S337000
Reexamination Certificate
active
06291700
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the preparation of phosphoramidates, and more particularly to their preparation from nitrogen bases and diaryl chlorophosphates.
The use of sterically hindered phosphoramidates such as N,N′-bis[di-(2,6-xylyl)phosphoryl]piperazine (hereinafter sometimes “XPP”) as flame retardant additives for synthetic resins, especially thermoplastic resins such as polycarbonates, ABS resins and blends thereof, has been discovered to have particular advantages including improved high temperature stability of the resulting blends. Reference is made, for example, to U.S. Pat. No. 5,973,041 and to copending, commonly owned applications Ser. Nos. 09/235,679 and 09/364,915.
XPP and analogous compounds may be conveniently prepared by the reaction of a diaryl chlorophosphate, such as di-(2,6-xylyl) chlorophosphate, with a heterocyclic compound containing at least two basic N-H groups, such as piperazine. According to the prior art as illustrated by Talley,
J. Chem. Eng. Data
, 33, 221-222 (1983), this reaction may be conducted in chloroform as solvent, in the presence of triethylamine as an acid acceptor. The triethylamine is employed in stoichiometric amount or in excess, and reacts with the by-product hydrogen chloride to drive the reaction to completion.
The Talley paper describes the preparation of a number of analogous compounds including those derived from such nitrogen compounds as benzylamine, cyclohexylamine, aniline, ethylenediamine and p-phenylenediamine as well as piperazine. Reported yields were as high as 90% for the reaction with aniline, and as low as 61% for the reaction with p-phenylenediamine. Piperazine afforded XPP in a yield of only 68%, one of the lowest reported.
If the use of XPP as a flame retardant additive is to be commercially feasible, it is necessary to improve its yield by a significant amount. Also, it is desirable to minimize use of the relatively toxic solvent chloroform on a commercial scale.
It is of interest, therefore, to develop high-yield methods employing relatively harmless materials for the preparation of XPP and analogous compounds.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that solvents other than chloroform, in particular methylene chloride and aromatic hydrocarbons, may be employed for the preparation of sterically hindered phosphoramidates in high yield from sterically hindered diaryl chlorophosphates and nitrogen bases. In the case of aromatic hydrocarbons, yields are significantly improved if a catalyst is present.
Accordingly, in one embodiment the invention is a method for preparing a sterically hindered phosphoramidate which comprises contacting a sterically hindered diaryl chlorophosphate with a basic nitrogen compound containing at least two basic N—H groups in the presence of at least one acid acceptor and at least one solvent selected from the group consisting of methylene chloride and aromatic hydrocarbons, with the proviso that if the solvent is at least one aromatic hydrocarbon there is also present a reaction rate increasing proportion of at least one dipolar aprotic nitrogen compound.
In another embodiment the invention is a method for preparing a sterically hindered phosphoramidate which comprises contacting a sterically hindered diaryl chlorophosphate with a basic nitrogen compound containing at least two basic N—H groups in the presence of at least one acid acceptor and at least one solvent selected from the group consisting of methylene chloride and aromatic hydrocarbons, with the proviso that if the solvent is at least one aromatic hydrocarbon there is also present a reaction rate increasing proportion of at least one dipolar aprotic nitrogen compound, said phosphoramidate having a glass transition temperature of at least about 0° C., preferably of at least about 10° C., and most preferably of at least about 20° C.
DETAILED DESCRIPTION; PREFERRED EMBODIMENTS
Within the context of the present invention a sterically hindered phosphoramidate is one in which at least one aryl substituent linked to heteroatom-phosphorus has at least one substituent on the aryl ring ortho to the aryl-heteroatom-phosphorus linkage. The sterically hindered diaryl chlorophosphates include those having the formula I
wherein A is an aromatic group, each R
1
is independently alkyl, aryl or halo, Q
1
is oxygen or sulfur, Q
2
is oxygen, sulfur, or NR
1
, and n has the value of 1 up to the number of free valency sites on the aromatic ring and at least one R
1
substituent on the aryl ring is ortho to the heteroatom-phosphorus linkage. Preferably, A is a phenyl ring and n has the value of 1-5. Preferably, each R
1
is C
1-4
primary or secondary alkyl; most preferably, methyl, and n is 2 with each substituent ortho to the phosphorus linkage.
Preferred sterically hindered diaryl chlorophosphates include those having the formula II:
wherein A is an aromatic radical, each R
1
is independently alkyl, aryl or halo, n is from 1 to the number of free valency sites on the aromatic ring(s) and at least one R
1
moiety is ortho to the O-P linkage. Preferably, A is a phenyl ring and n is 1-5. More preferably, each R
1
is C
1-4
primary or secondary alkyl, most preferably methyl, and n is 2 or 3 with two substituents ortho to the O-P linkage. Particularly preferred chlorophosphates are di-(2,4,6-trimethylphenyl) chlorophosphate and di-(2,6-dimethylphenyl) chlorophosphate, also known as di-(2,6-xylyl) chlorophosphate.
Any compound, acyclic or cyclic, containing at least two basic N—H groups may be employed. Suitable compounds include those of the formula III
R
2
NH—CH
2
CH
2
—NHR
2
, (III)
wherein each R
2
is a C
1-4
primary or secondary alkyl radical or both R
2
radicals taken together are ethylene. Illustrative acyclic compounds are N,N′-dimethylethylenediamine and N,N′-diethylethylenediamine. Heterocyclic compounds are generally preferred; they are illustrated by piperazine and 1,2,3,4-tetrahydroquinoxaline, both unsubstituted and substituted. Piperazine is most preferred.
In a preferred embodiment, the method of the invention may be used to produce a phosphoramidate having a glass transition temperature of at least about 0° C., preferably of at least about 10° C., and most preferably of at least about 20° C. In particular, the method of the invention may be used to produce a phosphoramidate of the formula IV:
wherein each Q
1
is independently oxygen or sulfur; and each of A
1-4
is independently an alkyloxy, alkylthio, aryloxy, or arylthio residue, or an aryloxy or arylthio residue containing at least one alkyl or halogen substitution, or mixture thereof; or an amine residue. In an especially preferred embodiment of the invention, each Q
1
is oxygen, and each A
1-4
moiety is a 2,6-dimethylphenoxy moiety or a 2,4,6-trimethylphenoxy moiety. These phosphoramidates are piperazine-type phosphoramidates. In the above formula wherein each Q
1
is oxygen, and each A
1-4
moiety is a 2,6-dimethylphenoxy moiety, the glass transition temperature of the phosphoramidate is about 62° C. and the melting point is about 192° C.
In another preferred embodiment, the method of the invention may be used to produce a phosphoramidate having a glass transition temperature of at least about 0° C., preferably of at least about 10° C., and most preferably of at least about 20° C., of the formula V:
wherein each Q
1
is independently oxygen or sulfur; and each of A
5-9
is independently an alkyloxy, alkylthio, aryloxy, or arylthio residue, or an aryloxy or arylthio residue containing at least one alkyl or halogen substitution, or mixture thereof; or an amine residue; and n is from 0 to about 5. In a more preferred embodiment, each Q
1
is oxygen, and each A
5-9
moiety is independently phenoxy, 2,6-dimethylphenoxy, or 2,4,6-trimethylphenoxy, and n is from 0 to about 5.
In another embodiment the method of the invention may be used to produce a phosphoramidate having a glass transition temperature of at least about 0° C., preferably of at least about 10° C., and mo
Campbell John Robert
Cella James Anthony
Howson Paul Edward
Brown S. Bruce
Geist Gary
General Electric Company
Johnson Noreen C.
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