| PATENT ASSIGNEE'S COUNTRY | Germany |
| UPDATE | 10.99 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 26.10.99 |
| PATENT TITLE |
Process for preparing dialkylphosphinate salts |
| PATENT ABSTRACT |
The invention relates to a process for preparing dialkylphosphinate salts, which comprises a) reacting elemental yellow phosphorus with alkyl halides in the presence of alkali metal hydroxide or alkaline earth metal hydroxide to form a mixture which comprises as main constituents the salts of alkylphosphonous, phosphorous and hypophosphorous acids, b) adjusting the mixture to a pH below 7 and then reacting the mixture with olefins in the presence of a free-radical initiator and c) reacting the dialkylphosphinic acids obtained according to b) and/or alkali metal salts thereof with metal compounds of Mg, Ca, Al, Sb, Sn, Ge, Ti, Zn, Fe, Zr, Ce, Bi, Sr, Mn, Li, Na and/or K to give the metal dialkylphosphinate salts. The invention likewise relates to the use of the metal dialkylphosphinate salts prepared by the process according to the invention to prepare flame retardants. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 24.11.98 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT REFERENCES CITED | This data is not available for free |
| PATENT CLAIMS |
We claim: 1. A process for preparing dialkylphosphinate salts, which comprises a) reacting elemental yellow phosphorus with alkyl halides in the presence of alkali metal hydroxide or alkaline earth metal hydroxide to form a mixture which comprises as main constituents the salts of alkylphosphonous, phosphorous and hypophosphorous acids, b) adjusting the mixture to a pH below 7 and then reacting the mixture with olefins in the presence of a free-radical initiator and c) reacting the dialkylphosphinic acids obtained according to b) and/or alkali metal salts thereof with metal compounds of Mg, Ca, Al, Sb, Sn, Ge, Ti, Zn, Fe, Zr, Ce, Bi, Sr, Mn, Li, Na and/or K to give the metal dialkylphosphinate salts. 2. The process as claimed in claim 1, wherein, in step a), the elemental yellow phosphorus is reacted with the alkyl halides in the presence of mixtures of aqueous alkali metal hydroxide and alkaline earth metal hydroxide. 3. The process as claimed in claim 1, wherein, as alkyl halides, use is made of methyl chloride or methyl bromide. 4. The process as claimed in claim 1, wherein, in step a), an organic solvent or a solvent mixture is present. 5. The process as claimed in claim 1, wherein, in step a), the reaction is carried out in a 2-phase system in the presence of a phase-transfer catalyst. 6. The process as claimed in claim 5, wherein the phase-transfer catalyst is tetraalkylphosphonium halides, triphenylalkylphosphonium halides or tetraorganylammonium halides. 7. The process as claimed in claim 1, wherein, in step b), the mixture is adjusted to a pH below 7 using mineral acids or carboxylic acids. 8. The process as claimed in claim 1, wherein, as free-radical initiator, use is made of azo compounds. 9. The process as claimed in claim 8, wherein the azo compounds are cationic and/or non-cationic azo compounds. 10. The process as claimed in claim 8, wherein, as cationic azo compounds, use is made of 2,2'-A azobis(2-amidinopropane) dihydrochloride or 2,2'-azobis(N,N'-dimethyleneisobutyramidine) dihydrochloride. 11. The process as claimed in claim 8, wherein, as non-cationic azo compounds, use is made of azobis(isobutyronitrile), 4,4'-azobis(4-cyanopentanoic acid) or 2,2'-azobis(2-methylbutyronitrile). 12. The process as claimed in claim 1, wherein, as free-radical initiator, use is made of inorganic peroxide and/or organic peroxide free-radical initiators. 13. The process as claimed in claim 12, wherein, as inorganic peroxide free-radical initiators, use is made of hydrogen peroxide, ammonium peroxodisulfate and/or potassium peroxodisulfate. 14. The process as claimed in claim 12, wherein, as organic peroxide free-radical initiators, use is made of dibenzoyl peroxide, di-tert-butyl peroxide and/or peracetic acid. 15. The process as claimed in claim 1, wherein, as olefins, use is made of unbranched or branched .alpha.-olefins. 16. The process as claimed in claim 1, wherein, as olefins, use is made of ethylene, n-, i-propylene, n-, i-butene, n-, i-pentene, n-, i-hexene, n-, i-octene, 1-decene, 1,5-cyclooctadiene, 1,3-cyclopentadiene, dicyclopentadiene and/or 2,4,4-trimethylpentene isomeric mixture. 17. The process as claimed in claim 1, wherein, as olefins, use is made of those having an internal double bond, cyclic olefins and cyclic or open-chain dienes and/or polyenes having from 4 to 20 carbon atoms. 18. The process as claimed in claim 1, wherein the olefins bear a functional group. 19. The process as claimed in claim 1, wherein the metal compounds are metal oxides, metal hydroxides, metal hydroxide oxides, metal sulfates, metal acetates, metal nitrates, metal chlorides and/or metal alkoxides. 20. The process as claimed in claim 1, wherein the metal compounds are aluminum oxide or aluminum sulfates. 21. The process as claimed in claim 1, wherein the dialkylphosphinic acids are reacted with the metal compounds at a temperature of from 20 to 150.degree. C. 22. The process as claimed in claim 1, wherein the dialkylphosphinic acids are reacted with the metal compounds in an acetic acid and/or aqueous medium. |
| PATENT DESCRIPTION |
The invention relates to a process for preparing dialkylphosphinate salts and their use. Aluminum and calcium salts of dialkylphosphinic acids are known as flame retardants (EP 0 699 708 A1). They can be prepared by various processes. DE 24 47 727 A1 describes low-flammability polyamide molding compositions which comprise a salt of a phosphinic acid or of a diphosphinic acid. The abovementioned EP-A-0 699 708 A1 describes flame-retardant polyester molding compositions, the polyester molding compositions being flameproofed by adding calcium salts or aluminum salts of phosphinic or diphosphinic acids. These salts are obtained by reacting the corresponding dialkylphosphinic acids with calcium hydroxide or aluminum hydroxide. The abovementioned processes have the disadvantage, in particular, that they start from starting compounds which cannot be prepared industrially, or only with great expense, therefore they are very highly uneconomic. This applies in particular to the particularly preferred dialkylphosphinic acids having short alkyl chains. Thus, for example, for preparing diethylphosphinic acid, no process which has been carried out or can be carried out industrially has to date been demonstrated. Only DE 21 00 779 A1 describes a process for preparing alkyl dialkylphosphinates by the addition of olefins having from 2 to 22 carbon atoms to alkylphosphonous esters. The object underlying the invention is to provide a process for preparing metal dialkylphosphinate salts which avoids the abovementioned disadvantages and starts from elemental phosphorus as feedstock. Furthermore, the synthesis is to succeed without complex purification steps and lead in a simple manner to the metal salts of dialkylphosphinic acids. This object is achieved by a process of the type mentioned at the outset, which comprises a) reacting elemental yellow phosphorus with alkyl halides in the presence of alkali metal hydroxide or alkaline earth metal hydroxide to form a mixture which comprises as main constituents the salts of alkylphosphonous, phosphorous and hypophosphorous acids, b) adjusting the mixture to a pH below 7 and then reacting the mixture with olefins in the presence of a free-radical initiator and c) reacting the dialkylphosphinic acids obtained according to b) and/or alkali metal salts thereof with metal compounds of Mg, Ca, Al, Sb, Sn, Ge, Ti, Zn, Fe, Zr, Ce, Bi, Sr, Mn, Li, Na and/or K to give the metal dialkylphosphinate salts. Preferably, in step a), the elemental yellow phosphorus is reacted with the alkyl halides in the presence of mixtures of aqueous alkali metal hydroxide and alkaline earth metal hydroxide. Such a procedure has the advantage that it is easy to separate off phosphite formed in the reaction, for example as Ca(HPO.sub.3) Preferably, as alkyl halides, use is made of methyl chloride or methyl bromide. Preferably, in step a), an organic solvent or a solvent mixture is present. Preferably, in step a), the reaction is carried out in a 2-phase system in the presence of a phase-transfer catalyst. The phase-transfer catalyst is preferably tetraalkyl-phosphonium halides, triphenylalkylphosphonium halides or tetraorganylammonium halides. Preferably, in step b), the mixture is adjusted to a pH below 7 using mineral acids or carboxylic acids. Preferably, as free-radical initiator, use is made of azo compounds. Preferably, the azo compounds are cationic and/or non-cationic azo compounds. Preferably, as cationic azo compounds, use is made of 2,2'-azobis(2-amidinopropane) dihydrochloride or 2,2'-azobis(N,N'-dimethyleneisobutyramidine) dihydrochloride. Preferably, as non-cationic azo compounds, use is made of azobis(isobutyronitrile), 4,4'-azobis(4-cyano-pentanoic acid) or 2,2'-azobis(2-methylbutyronitrile). Preferably, as free-radical initiator, use is made of inorganic peroxide and/or organic peroxide free-radical initiators. Preferably, as inorganic peroxide free-radical initiators, use is made of hydrogen peroxide, ammonium peroxodisulfate and/or potassium peroxodisulfate. Preferably, as organic peroxide free-radical initiators, use is made of dibenzoyl peroxide, di-tert-butyl peroxide and/or peracetic acid. A broad selection of suitable free-radical initiators can be found, for example, in Houben-Weyl, Supplementary Volume 20, in the chapter "Polymerisation durch radikalische Initierung" [Polymerization by free-radical initiation] on pages 15-74. Preferably, as olefins, use is made of unbranched or branched .alpha.-olefins. Preferably, as olefins, use is made of ethylene, n-, i-propylene, n-, i-butene, n-, i-pentene, n-, i-hexene, n-, i-octene, 1-decene, 1,5-cyclooctadiene, 1,3-cyclopentadiene, dicyclopentadiene and/or 2,4,4-trimethylpentene isomeric mixture. Equally preferably, as olefins, use is made of those having an internal double bond, cyclic olefins and cyclic or open-chain dienes and/or polyenes having from 4 to 20 carbon atoms. Preferably, the olefins bear a functional group. Suitable olefins are compounds of the formula ##STR1## where R.sup.1 -R.sup.4 can be identical or different and are hydrogen, an alkyl group having from 1 to 18 carbon atoms, phenyl, benzyl or alkyl-substituted aromatics. Equally suitable are cycloolefins of the formula ##STR2## in particular cyclopentene, cyclohexene, cyclooctene and cyclodecene. Use can also be made of open-chain dienes of the formula ##STR3## where R.sup.5 -R.sup.10 are identical or different and are hydrogen or a C.sub.1 - to C.sub.6 -alkyl group and R.sup.11 is (CH.sub.2).sub.n where n=0 to 6. Preference is given in this case to butadiene, isoprene and 1,5-hexadiene. As cyclodienes, preference is given to 1,3-cyclopentadiene, dicyclopentadiene and 1,5-cyclooctadiene, and also norbornadiene. Preferably, the metal compounds are metal oxides, metal hydroxides, metal hydroxide oxides, metal sulfates, metal acetates, metal nitrates, metal chlorides and/or metal alkoxides. Particularly preferably, the metal compounds are aluminum hydroxide and aluminum sulfates. Preferably, the dialkylphosphinic acids are reacted with the metal compounds at a temperature of from 20 to 150.degree. C. Preferably, the dialkylphosphinic acids are reacted with the metal compounds in an acetic acid and/or aqueous medium. This takes place, if necessary after adjusting to a pH range for the salt precipitation which is optimum for the respective dialkylphosphinic acid/metal compound system. The invention also relates to the use of the metal dialkylphosphinate salts prepared by the process according to the invention to prepare flame retardants. The invention also relates to the use of the metal dialkylphosphinate salts prepared by the process according to the invention to prepare flame retardants for thermoplastic polymers and thermosetting plastics. The invention finally also relates to the use of the metal dialkylphosphinate salts prepared by the process according to the invention to prepare flame retardants for polystyrene, poly(ethylene terephthalate), poly-(butylene terephthalate) and polyamide. The invention finally also relates to the use of the metal dialkylphosphinate salts prepared by the process according to the invention as additives in polymeric molding compounds. |
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