Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Patent
1999-03-26
2000-08-01
Ambrose, Michael G.
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
562 8, C07F 930
Patent
active
060969148
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for preparing aluminum salts of dialkylphosphinic acids.
The aluminum salts of dialkylphosphinic acids (also referred to as aluminum phosphinates below) have increasing industrial importance as flame retardants for plastics and plastic molding compositions. In particular, they are an alternative for the halogen-containing flame retardants used hitherto, which, because of their halogen content, have corrosive effect and also have ecological disadvantages.
Processes for preparing aluminum phosphinates have already been described. For example, N. M. Karayannis et al. in Transition Met. Chem., 6, 79-82 (1981) discloses a process for preparing the aluminum salt of methylphenylphosphinic acid, in which methyl methylphenylphosphinate is reacted with anhydrous aluminum chloride. However, a large excess of methyl ester is required here, and stoichiometric amounts of the ecologically questionable methyl chloride are produced. A further disadvantage is that the chloride ions have a corrosive action on the steel equipment which is usual in industry. In addition, some of the chloride ions can remain in the aluminum phosphinate which is produced, and this can give problems when it is used, because the chloride ions have corrosive action.
French Patent 1,558,606 describes a process for preparing aluminum alkylhydroxyphenylalkylphosphinate from the corresponding alkali metal salt, the reaction likewise using aluminum chloride.
It is also known that aluminum phosphinates can be prepared (EP-A-0 699 708) by neutralization of the corresponding phosphinic acids with a suspension of aluminum hydroxide in water.
However, this process requires a very long reaction time and is therefore complicated and expensive for preparation on an industrial scale; this greatly reduces the possibilities for use of the products as flame retardants for plastics. For example, the reaction time necessary for aluminum ethylmethylphosphinate, which is of particular interest as a flame retardant, is 65 hours at from 80 to 85.degree. C. The phosphinic acids which are to be used as starting material are obtained by acid hydrolysis of phosphinic esters (DE-A-2 441 878, DE-A-2 441 783), and, for the preparation of ethylmethylphosphinic acid, this requires reaction temperatures of more than 180.degree. C. over a period of more than 30 hours.
There has therefore been a need for a process for preparing aluminum dialkylphosphinates which allows the desired products to be obtained simply and in a short time, while avoiding ecologically questionable, chloride-containing starting materials and by-products.
According to the invention, it has now been found that aluminum phosphinates of the formula (I) ##STR1## where R.sup.1 and R.sup.2 are identical or different and are linear or branched, C.sub.1 -C.sub.8 -alkyl, preferably C.sub.1 -C.sub.6 -alkyl, e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, tert-butyl, n-pentyl or an isomer thereof, or n-hexyl or an isomer thereof, or phenyl, can be prepared in a simple and economical manner by reacting the corresponding alkali metal phosphinate of the formula (III) ##STR2## with aluminum sulfate.
In formula (III), R.sup.1 and R.sup.2 are as defined above and M is a metal of group I of the periodic table, M=sodium being particularly preferred.
FIG. 1 shows the process according to EP-A-0 699 708.
FIG. 2 shows the novel process (step 3) and the preparation of the precursors (steps 1 and 2).
The aluminum phosphinate of the formula (I) is formed by dropwise addition of the aluminum sulfate at a temperature of preferably from 20 to 27.degree. C. (room temperature). Surprisingly, the product to be formed precipitates immediately during this procedure, so that the time of from about 10 minutes to 4 hours during which the dropwise addition continues corresponds to the reaction time. Continued stirring is unnecessary.
The aluminum phosphinates may be isolated by simple filtration and washing a number of times with water in order to remove any sulfate which may still be adheri
REFERENCES:
patent: 3563948 (1971-02-01), Spivack et al.
patent: 4272448 (1981-06-01), Bernard et al.
patent: 4972011 (1990-11-01), Richardson et al.
Ambrose Michael G.
Ticona GmbH
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