Organic compounds -- part of the class 532-570 series – Organic compounds – Phosphorus acids or salts thereof
Patent
1993-02-03
1995-02-21
Dees, Jose G.
Organic compounds -- part of the class 532-570 series
Organic compounds
Phosphorus acids or salts thereof
C07F 938
Patent
active
053918150
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
Various methods are known for the preparation of pure vinylphosphonic acid. Thus, for example, vinylphosphonyl dichloride can be hydrolyzed. However, the synthesis of pure vinylphosphonyl chloride is technically laborious. A number of other methods for the preparation of pure vinylphosphonic acid have therefore already been described in the literature.
Thus, a bottom mixture which comprises in total up to 85% of diverse vinylphosphonic acid derivatives is obtained on thermal decomposition of dialkyl acetoxyethanephosphonates in accordance with German Offenlegungsschrift 3 001 894, alkyl acetates and dialkyl ethers being split off. An up to 82% strength vinylphosphonic acid is obtained on hydrolysis of this mixture, for example in accordance with German Offenlegungsschrift 3 110 975. However, this degree of purity is not sufficient for many applications of vinylphosphonic acid since, in general, degrees of purity of about 90-95% are desired and the phosphoric acid content should be less than 5% by weight.
According to the method described in German Offenlegungsschrift 3 120 437 for the preparation of pure vinylphosphonic acid, the bottom mixture obtained in accordance with the abovementioned German Offenlegungsschrift is subjected to thermal decomposition using orthocarboxylic acid esters, with the preparation of dialkyl vinylphosphonates, which, after distillation to give the pure product and hydrolysis, then give more highly concentrated vinylphosphonic acid. Trialkyl phosphate, which is virtually impossible to separate from the relevant dialkyl vinylphosphonate by distillation, is also always formed as a by-product of the vinylphosphonic acid preparation by this method. As a consequence, the vinylphosphonic acid obtained by hydrolysis of the relevant esters still contains at least 7% by weight of phosphoric acid. It is true that separation of the phosphoric acid in the form of magnesium ammonium hydrogen phosphate, which is sparingly soluble in water, is described in the literature, but this signifies a further additional step and gives rise to residual traces of magnesium ammonium salt in the vinylphosphonic acid, which traces interfere in some applications. Furthermore, the use of orthocarboxylic acid esters is economically expensive.
Pure vinylphosphonic acid can be obtained in accordance with German Offenlegungsschrift 3 707 149 by hydrolysis of a vinylphosphonic acid ester which has been obtained by vacuum cleavage of dialkyl acetoxyethanephosphonates. With this method also about 20% of a bottom material are obtained which still comprises diverse vinylphosphonic acid derivatives, which can be converted by thermal after-treatment and subsequent hydrolysis into a 50 to 70% strength vinylphosphonic acid, which must be regarded as lost if the vinylphosphonic acid contained in the mixture cannot be separated off.
The present invention now relates to a method for separating vinylphosphonic acid from crude mixtures, wherein the separation is effected by extraction with alcohols and/or ketones, which, in each case comprise at least 5 carbon atoms, preferably 5 to 15 carbon atoms and in particular 5 to 10 carbon atoms.
The alcohols used as extraction agent according to the invention are generally monohydric or dihydric, preferably monohydric; their hydrocarbon radical is preferably a branched or straight-chain aliphatic radical or a cycloaliphatic radical, which optionally can be substituted by (C.sub.1 -C.sub.4)-alkyl groups, the number of which is generally 1 to 3. These radicals can optionally also comprise hetero atoms, such as oxygen atoms, or have groups which contain hetero atoms and are inert with respect to the crude mixture. Examples of such alcohols which may be mentioned here are: 2-ethylhexanol, cyclohexanol, the diverse heptanols, nonyl alcohol and the like. 2-ethylhexanol is in this case the preferred extraction agent.
The ketones which are similarly employed according to the invention as extraction agents have either two hydrocarbon radicals, preferably branched or straight-chain
REFERENCES:
patent: 3896163 (1975-07-01), Jacques
patent: 4585636 (1986-04-01), Iosef et al.
patent: 4739092 (1988-04-01), Nozaki et al.
Conrad Joseph M.
Dees Jos,e G.
Hoechst Aktiengesellschaft
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