Process for preparing arylalphosphinic acids

Details Process for preparing arylalphosphinic acids Process for preparing arylalphosphinic acids

1998-11-24

2001-06-05

Vollano, Jean F. (Department: 1621)

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

Organic compounds

Phosphorus acids or salts thereof

Reexamination Certificate

active

06242642

ABSTRACT:

The invention relates to a process for preparing arylalkylphosphinic acids and/or alkali metal salts thereof by reacting olefins with arylphosphonous acids and/or alkali metal salts thereof and to the use of the compounds prepared by this process.
The addition of carbon-carbon double bonds to phenylphosphonous acid to give phosphinic acid derivatives having two phosphorus-carbon bonds is known in principle, but leads to unsatisfactory yields (Houben-Weyl, Methoden der organischen Chemie [Methods in organic chemistry], Vol. XII/1, 4th Edition 1963, pp. 228 ff, and Vol. E2, 1982, pp. 123 ff). A mixture of reaction products which must be laboriously worked up is also frequently obtained.
In particular, when use is made of olefins which are not activated by electron-withdrawing substituents, such as alpha-olefins, cycloolefins, dienes or cyclodienes, it is not possible by the abovementioned method to prepare the wanted target compounds in yields which are adequate for industrial syntheses.
The object therefore underlying the invention is to provide a process for preparing arylalkylphosphinic acids or alkali metal salts thereof by reacting olefins with arylphosphonous acids and/or alkali metal salts thereof, which process avoids the abovementioned disadvantages and leads to high yields of arylalkylphosphinic acids in short times.
This object is achieved by a process of the type described at the outset which comprises carrying out the reaction in the presence of a free-radical initiator.
Preferably, the olefins are unbranched or branched &agr;-olefins.
Preferably, the olefins are ethylene, propylene, 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 aromatic systems.
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 system 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 free-radical initiator has an azo group, which is cationic or non-cationic.
As cationic free-radical initiators, use is preferably 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 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 5 a temperature of from 80 to 95° C.
Preferably, the reaction is carried out in a pressure reactor. This applies, in particular, when the boiling point of the olefins is below the reaction temperature.
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 alkali 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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