Organic compounds -- part of the class 532-570 series – Organic compounds – Phosphorus acids or salts thereof
Reexamination Certificate
2001-12-19
2003-06-24
Vollano, Jean F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Phosphorus acids or salts thereof
Reexamination Certificate
active
06583315
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for preparing ethanebis(alkylphosphinic) acids, and also to the use of the products prepared by this process.
Phosphinic acids and salts of these may be prepared by a variety of methods, and have been described widely within the literature.
Organic phosphinic acids, and their salts and esters are known flame retardants. For example, EP 0 699 708 A1 describes flame-retardant polyester molding compositions, these being rendered flame-retardant by adding the calcium or aluminum salts of phosphinic or diphosphinic acids. The abovementioned salts are obtained by reacting the corresponding phosphonic acids with calcium hydroxide or aluminum hydroxide.
Due to their high phosphorus content and especially their bidentate. nature, the diphosphinic acids are described as highly effective reactive flame retardants for polyesters, e.g. for textile applications. This also applies to ethanebis(methylphosphinic) acid, specifically in the form of its glycol ester (DE 22 36 037 A1).
The preparation of these diphosphinic acids is technically complicated and takes place by an Arbuzov reaction of phosphonous diesters with alkyl dihalides [P. Mastalerz, Rocziniki Chem 38 (1964), pp. 61-64], followed by cleavage of the esters. The phosphonous diesters used are prepared from the corresponding phosphonous dihalides by reaction with alcohols.
Another way of preparing ethanediphosphonic acids is proposed in DE 23 02 523 A1 by reacting alkylphosphonous esters with acetylene and then cleaving the diester with HCI, with formation of alkyl chlorides. Here again, the alkylphosphonous esters used are prepared from the corresponding phosphonous dihalides by hydrolysis and reaction with alcohols.
The abovementioned process has the disadvantage of first requiring inconvenient preparation of the appropriate organic phosphorus compounds. This applies particularly to the esters of alkylphosphonous acids, which in turn are prepared from the corresponding phosphonous dihalides, such as methyldichlorophosphine. Methyldichlorophosphine is prepared by complicated syntheses (Houben-Weyl, Vol. 12/1, pp. 306). In addition, there are byproducts formed which, like some of the above mentioned starting materials, are toxic, or ignite spontaneously, and/or are corrosive, i.e. are highly undesirable.
Another disadvantage is that all of the processes described above for preparing ethanebis(alkylphosphinic) acids have the technically difficult cleavage of the corresponding esters as a final step.
SUMMARY OF THE INVENTION
The object on which the invention is based is therefore to provide a process which can prepare ethanebis(alkylphosphinic) acids and avoids the abovementioned disadvantages, and can be carried out in a particularly simple and economic manner, and which gives a high yield of single products. This process should also be clearly superior to the known processes in its effect on the environment. The starting material for the process of the invention is elemental yellow phosphorus, which is easily obtainable, and the process cannot require the complicated cleavage of diphosphinic esters.
This object is achieved by a process for preparing ethanebis(alkylphosphinic) acids by
a) reacting elemental yellow phosphorus with alkyl halides in the presence of alkali metal hydroxide or of alkaline earth metal hydroxide to give a mixture whose main constituents are the alkali metal salts and/or alkaline earth metal salts of alkylphosphonous, phosphorous, and hypophosphordus acid,
b) liberating alkylphosphonous, phosphorous, and hypophosphorous acid by adding mineral acids, and also at the same time precipitating the alkali metal ions and, respectively, alkaline earth metal ions in the form of their salt of the mineral acids, and then
c) esterifying the alkylphosphonous acid from the mixture of the alkylphosphonous, phosphorous, and hypophosphorous acid,
d) isolating the ester of alkylphosphonous acid from the mixture and hydrolyzing the same to give alkylphosphonous acid, and
e) preparing, from the alkylphosphonous acid, the corresponding ethanebis(alkylphosphinic) acid of the general formula (I)
where R
1
and R
2
may be identical or different and are hydrogen, a carboxy group, a carboxylic acid derivative, an unsubstituted or substituted alkyl group having from 1 to 10 carbon atoms, phenyl, benzyl, or alkyl-substituted aromatics, and R
3
and R
4
are identical or different and are an unsubstituted or substituted alkyl group having from 2 to 20 carbon atoms, by free-radical-initiated reaction with alkynes.
Compared with the processes known hitherto, the process of the invention has considerable advantages since it, inter alia, avoids the use of phosphines or phosphonous dihalides as starting materials, produces no halogenated organic byproducts, involves no complicated cleavage of phosphinic esters, and also has a positive balance in relation to product distribution. The process is highly effective and economic to carry out.
DETAILED DESCRIPTION OF THE INVENTION
The alkyl halides used are preferably methyl chloride or methyl bromide.
The reaction in step a) is preferably carried out in a two-phase system of aqueous alkali metal hydroxide or alkaline earth metal hydroxide or a mixture of these, and an organic solvent.
The organic solvents preferably used in step a) are straight-chain or branched alkanes, alkyl-substituted aromatic solvents, or water-immiscible or only partially water-miscible alcohols or ethers, alone or in combination with one another.
An organic solvent whose use is particularly preferred is toluene, alone or combined with alcohols.
The reaction is preferably carried out in the presence of a phase-transfer catalyst.
The phase-transfer catalyst is preferably a tetraalkylphosphonium halide, triphenylalkylphosphonium halide, or tetraorganylammonium halide.
The temperature during the reaction in step a) is preferably from −20 to +60° C.
The temperature is particularly preferably from −10 to +30° C.
The reaction is preferably carried out at a pressure of from 0 to 10 bar.
The method of carrying out step a) of the process of the invention is preferably that the yellow phosphorus is suspended in a solvent or solvent mixture and then reacted with alkyl halide and a compound of the formula MOH or M′(OH)
2
, or a mixture of these, where M is an alkali metal and M′ is an alkaline earth metal.
It is preferable for the yellow phosphorus and the alkyl halide to be reacted with one another in a molar ratio of from 1:1 to 1:3, the molar ratio of yellow phosphorus to the compound of the formula MOH or M′(OH)
2
being from 1:1 to 1:5.
Step b) preferably comprises neutralization by addition of a mineral acid.
Step b) preferably comprises neutralization by addition of hydrochloric acid.
The alkali metal salt of the mineral acid and, respectively, alkaline earth metal salt of the mineral acid is preferably precipitated by exchanging the solvent, water, for the alcohol to be used in reaction step c).
The small amounts of phosphines obtained in step b) are preferably removed by oxidation.
The oxidant used preferably comprises hydrogen peroxide.
In step c) the alkylphosphonous acid is preferably esterified directly with a linear or branched alcohol of the general formula R—OH, where R is a linear or branched alkyl radical having from 1 to 10 carbon atoms.
The alcohol is preferably isobutanol, n-butanol, and/or 2-ethylhexanol.
The alkali metal salt of the mineral acid, or alkaline earth metal salt of the mineral acid, precipitated in step b) is preferably filtered off prior to the esterification process.
One way of esterifying the phosphonous acid to give the corresponding monoester is reaction with higher-boiling alcohols, the water formed being removed by azeotropic distillation.
The alkylphosphonous acid used is preferably methanephosphonous acid.
In step d) the ester of the alkylphosphonous acid is preferably removed by distillation.
In step d) the distilled ester of the alkylphosphonous acid is preferably hydro
Schmitz Hans-Peter
Sicken Martin
Weferling Norbert
Bisulca Anthony A.
Clariant GmbH
Vollano Jean F.
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