Process for preparing metal salts of arylalkylphosphinic acids

Details Process for preparing metal salts of arylalkylphosphinic acids Process for preparing metal salts of arylalkylphosphinic acids

1998-11-24

2001-05-15

Vollano, Jean F. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Phosphorus acids or salts thereof

Reexamination Certificate

active

06232493

ABSTRACT:

The invention relates to a process for preparing metal salts of arylalkylphosphinic acids and to the use of the compounds prepared by this process.
Aluminum 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 compounds which comprise a salt of a phosphinic acid or of a diphosphinic acid.
EP-A-0 699 708 describes flame-retardant polyester molding compounds, the polyesters being given a flame-retardant finish by adding calcium salts or aluminum salts of phosphinic acid or diphosphinic acid. The abovementioned 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 can only be prepared with great expenditure.
However, no process which can be carried out industrially is known to date by which metal salts of arylalkylphosphinic acids can be prepared.
The object underlying the invention is to provide a process for preparing metal salts of arylalkylphosphinic acids which leads to the desired end products in a simple manner.
This object is achieved by a process of the type described at the outset, which comprises
a) reacting olefins with arylphosphonous acids and/or alkali metal salts thereof in the presence of a cationic free-radical initiator, and
b) reacting the arylalkylphosphinic acids and/or alkali metal salts thereof obtained by a) 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 arylalkylphosphinate salts.
Preferably, the olefins are unbranched or branched &agr;-olefins.
Preferably, the olefins are ethylene, n-propylene, isopropylene, n-butene, isobutene, n-pentene, isopentene, n-hexene, isohexene, n-octene, isooctene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, n-eicosene and/or 2,4,4-trimethylpentene isomer mixture.
Preferably, as olefins, use is made of those having an internal double bond, 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
where R
1
-R
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.
Suitable compounds are likewise cycloolefins of the formula
in particular cyclopentene, cyclohexene, cyclooctene and cyclodecene.
Use can also be made of open-chain dienes of the formula
where R
5
-R
10
are identical or different and are hydrogen or a C
1
to C
6
alkyl group and R
11
is (CH
2
)
n
where n=0 to 6. Preference is given in this case to butadiene, isoprene and 1,5-hexadiene.
Preferred cyclodienes are 1,3-cyclopentadiene, dicyclopentadiene and 1,5-cyclooctadiene and norbornadiene.
Preferably, the arylphosphonous acid and/or alkali metal salts thereof are phenylphosphonous acid and/or alkali metal salts thereof.
Preferably, the aryl radical of the arylalkylphosphinic acids and arylphosphonous acids is an aromatic having from 6 to 12 carbon atoms, which can be monosubstituted or polysubstituted by halogens, hydroxyl, aryl, alkyl, ether, ester, keto, carboxyl, sulfonyl and/or chloroalkyl groups.
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.
Compounds which are also suitable according to the invention are non-cationic azo compounds such as azobis(isobutyronitrile), 4,4′-azobis(4-cyanopentanoic acid) and 2,2′-azobis(2-methylbutyronitrile).
Compounds which are likewise suitable according to the invention as free-radical initiators are inorganic peroxide free-radical initiators (hydrogen peroxide, ammonium peroxodisulfate, potassium peroxodisulfate etc.) and/or organic peroxide free-radical initiators (dibenzoyl peroxide, di-tert-butyl peroxide, peracetic acid, etc.).
A broad selection of suitable free-radical initiators may be found, for example, in Houben-Weyl, Supplementary Volume 20 in the chapter “Polymerisation durch radikalische Initiierung” [Polymerization by free-radical initiation] on pages 15-74.
Preferably, the metal compounds are metal oxides, metal hydroxides, metal hydroxideoxides, metal sulfates, metal acetates, metal nitrates, metal chlorides and/or metal alkoxides.
Particularly preferably, the metal compounds are aluminum hydroxide or aluminum sulfates.
Preferably, the reaction is carried out in the presence of carboxylic acids.
Particularly preferably, the carboxylic acid is acetic acid.
Preferably, the reaction is carried out at a temperature of from 40 to 130° C.
Particularly preferably, the reaction is carried out at a temperature of from 60 to 100° C.
In particular, the process is preferably carried out at a temperature of from 80 to 95° C.
Preferably, the reaction is carried out in a pressure reactor. This applies in particular if the boiling point of the olefins is below the reaction temperature.
The reaction in step b) here is carried out after adjusting to a pH range for the salt precipitation which is optimum for the respective arylalkylphosphinic acid/metal compound system.
The invention also relates to the use of the arylalkylphosphinic acids and/or alkali metal salts thereof obtained by the process described above for preparing flame retardants.
The invention likewise relates to the use of the arylalkylphosphinic acids and/or alkali metal salts thereof obtained by the process described above for preparing flame retardants for thermoplastic polymers such as poly(ethylene terephthalate), poly(butylene terephthalate), polystyrene or polyamide, and for thermosetting plastics.
The arylalkylphosphinic acids and/or metal salts thereof obtained by the process described above are also used as additives in polymeric compounds, as extraction media and surfactants.


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