Note: Descriptions are shown in the official language in which they were submitted.
s~
-- 2 --
HOE ~1/~ 125
It is known that pure vinylphosF~honic acid can be
obtained from vinylphosphonic acid dichloride. However,
the synthesis o~ ?ure vinylphosphonic acid dichloride is
technically elaborate. A simpler process to prepare
vinylphosphonic acid is therefore desirable.
It has now been founc` that vinylphosphonic acid
ean be prepared in a simple and economical manner by
heating dialkyl 2-acetoxyethanephocphonates of the formula
C~l3CCH2CH2~(OR)2
in which ~ denotes allcyl grou?s having 1 to 4. preferably
1 to 2, carbon atoms, at 150 to 270C, preferably 170 to
230C, in the presence of acid or basic catalysts, react-
ing the resulting reaction product with orthoesters of the
general formula
R'C(OR)3
in which R' denotes hydrogen, C1-C~-alkyl or C1-C4-allcoxy
ancl R denotes alkyl groups having 1 to ~, preferably 1 to
2, carbon atoms, at 30 to 200C and hydrolyzing the
resultinp, vinylphosphonic acid diester with t~ater at tem-
peratures between 130 and 230C, preferably between 140and 175C, while simultareously distillirg off the alco-
hols formed.
It is surprisine that in this process the ortho-
35;~6~
-- 3 --
esters are not added onto the vinylphosphonic acid group.
For it is known that orthoesters can be added onto un-
saturated compounds, such as, for example, vinyl ethers
or vinyl esters, in the presence of acid catalysts
tHouben-~eyl, ~ethoden der Organischen Chemie [Methods of
Organic Cher~istryl, Volume VI/3, pages 247-248, Georg
Thieme Verlag Stuttgart, 1965).
Examples of possible starting materials are the
dimethyl, diethyl, diisopropyl and di-n~butyl ester of 2-
acetoxyethanephosphonic acid. Dimethyl 2-acetoxyethane-
phosphonate is particularly preferable. Examples of
orthoesters which are particularly suitable are trimethyl
orthoformate, triethyl orthoformate, trimethyl ortho-
acetate, triethyl orthoacetate, triethyl orthopropionate
and tetramet;-yl orthocarbonate.
Numerous compounds are possible as acid or basic
catalysts. Acid catalysts us d can be:
- A) sulfuric acid or phosphoric acid
B) halo~en-containing carboxylic acids having a PKa
value ~ 2.5, such as dichloroacetiC acid, trichloroacetic
acid or trifluoroacetic acid
C) aromatic sulfonic acids having a P value c 2.5,
such as benz~rlesulfonic acid or p-toluenesulfonic aci~
D) preferably phospninic acids having 2 to l& carbon
atoms, such~s ~ir,lethylpho~phin_c acid, rnethylethylphos-
phinic acid, dioctylphosphinic acid, methylphenylphosphinic
acid or diph~nylphosphinic acid
E) particularly preferably phosphon,c acids having 1 to
1~ carbon atoms and their half-esiers havin~ 1 to 4 carbon
5262
-- 4 --
atoms ln the alcohol radical, such as methanephosphonic
.acid~ propanephosphonic acid, propanephosphonic acid mono-
methyl ester, octadecanephosphonic acid, 2-acetoxyethane-
phosphonic acid, 2-acetoxyethanephosphonic acid monomethyl
ester, vinylphosphonic acid, vinylphosphonic acid mono-
methyl ester, vinylphosphonic acid monoethyl ester or
benzenephosphonic acid
F) likewise p~rticularly preferably pyrophosphonic aeids
or their half-esters, such as methanepyrophosphonic aeid,
benzenepyrophosphonic acid, vinylpyrophosphonic acid or
vinylpyrophosphonic acid monomethyl ester
G) acid reaction mixtures which are produced in the pro-
cess according to the invention are also highly suitable.
Basic catalysts used can be:
A) Tertiary a i~h~tic and aromatic amines and phosphines
having 3 to 1& carbon atoms, such as trimethylamine, tri-
propylamine, tributylamine, triphenylamine, trimethylphos-
phine, triethylphosphine, tripropylphosphine, tributyl-
phosphine, triphenylphosphine and tris-(p-diethylamino-
phenyl)-phosphine and the corresponding mi~ced amines,
.phosphines, pho$pholanes and phospholenes, such as
dimethylethylamine, diethylbutylamine, N-dimethylaniline,
4-methyl-N-dirr.ethylalliline, N-diethylaniline, N,l~-tetra-
rnethylphenylcliamine or N-methylpyrrolidine; methyldiethyl-
phospiline, dim~thylpropylphosphine, diethylben~ylphosphine,1-methylphosphol-3-ene and 1-ethyl-3-methylphosphol-3-ene.
B) Quaternary ammonium salts and phosphonium salts having
3 to 18 carbon atoms, su~h as tet-amethylammonium chloride,
tetramethylammonium brornide or tetraethylphosphoniu~n
~l852~
-- 5 --
chloride, trimethylbenzylam~nonium chloride, triethylbenzyl-
~nMcnium chloride, triethylben ylammonium bromide, tri-
methylbenzylphosphonium chloride or triphenylethylphos-
phonium 2,4-diaminoben~enesulfonate.
C) Heterocyclic com?ounds having aromatic character, such
as pyridine, quinoline, their various alkyl and dialkyl,
preferably methyl or dimethyl derivatives, imidaæole, N-
vinylimidazole, benzothiazole, 2-amino-~-ethoxybenzo-
thiazole, and also phosphabenæenes.
D) Acid amides, such as dimethylfor,.,amide, N-dimethyl-
acetamide, N-diethylpropionamide, N-dimethylbenzamide, N-
methylpyrrolidone or N,N'-tetr2methylterephthalic acid
diamide or ure~s, such as tetramethylurea or trimethyl-
phenylurea.
15 E) Other nitroge-~ compGunds or phosphorus compounds
having a higher valency of one N atom or P atom than 3,
such as pyridine-N-oxi~e, trimethylphosphine oxide, tri-
butylphosphine oxide, trihexylphosphine oxide, triphenyl-
phosphine oxide,.dimethylphenylphosphine oxide, dimethyl-
phenylphosphine sulfide, dirnethylchloromethylphosphineoxide, dimethyleicosylphosphine oxide, dimethyldod~cyl-
phosphine oxide, dimethylphosphine oxide, dimethylpyrrolid--.
inyl-1-methylphosphine oxide, tri?henylphosphinc dichlor-
ide, dimcthyldod~cylphosphine sulfide, triphcnylphosphine-
25 imine, dimet~ylchloromethylphosphine dic)-loride, N-2-
dimethylphos?hinylethylmethylacetamide or N-2-climethyl-
phosphinylethylnethylamine, or phospholene oxide, such as
1-met)~ylphosphcl-1-ene oxide or 1-ethyl-3-methylphosphol--
1-ene oxide.
2~
-- 6 --
F) Amides of phosphinous and phosphonous acids and of
phosphinic and phosphonic acids and also their thio
analogs, such as ethanephosphonic acid bis-diethylamide,
methanebutanephosphinous acid dimethylamide or diethyl-
phosphinous acid isobutylamide. Also triamides of phos-
phoric and olf thiophosphoric acid, such as hexamethylphos-
phoric acid triamide~
The catalysts are used in amounts of 0.01 to 10,
preferably 0.1 to 5, /0 by weight. When vinylphosphonic
acid, monoalkyl esters thereof or acid reaction mixtures
already obtained are used,even larger amounts of 10 to 50%
by weight call be used.
The process is in general carried out by mixing
the starting material with the catalyst and raising the
mixture to the required reaction temperatu.e OI 150 to
270C, preferably 170 to 230C.
Higher temperatures are possible, but they do not
yield any benefit. The danger o~ an increased formation
of by-products, ~.d also of polymerization, then arises.
This reaction eliminates an alkyl acetate and
essentially produces a vinylphosphonic acid half-ester.
The alkyl acetate is distilled off together ~Jith small
amounts of an alkanol and of a dialkyl ether. The dis-
tillation is carried out under atmospheric pressure, if
appropriate ~/ith the aid of an inert gas, such as, for
example, nitrogen. However, in particular cases it may
be advantageous to distil off in vacuo. The elimina-
tion of the alkyl acetate is cornplete after 2 to about 20
hours. It can be advantageous to continue stirring
262
-- 7 --
thereafter for another 1 to 4 hours at the reaction tem-
perature. Theprocesscan alsobecarriedoutirlacontinuous
manner. To prevenipolymeri~ation,it is advantageous to
add correspondinginhibitors, such as, forexample,hydro-
5 quinone,hydro~uino~le monomethyl etherorphenothia~ine.
If 2-acetoxyethanephosphonic acid diesters which
are contaminated from their preparation with small amounts
of the corresponding monoester are used as a starting
material,a further addition of a catalyst is not necessarily
10 required. It is here advantageous to start the reaction
at about 250C. When the acid reaction product which
actually also acts as a catalyst for the elimination has
been formed to a sufficient extent7the process can be con-
tinued at lower tem?eratures, for example at 180 to 220C.
The crud~ vi~ylph~sph~n_c aci~alf-esterproducedin
the first stage is reacted with the orthoesters at 30 to
200C, and carboxylates or carbon dioxide and the corres-
ponding alcohols are formed at the same time. In the
reaction to give the carboxylates and alcohols, it is
20 advantageous to operate within a temperature range which
is such that the carboxylates and alcohols distil off
after they have been formed. As a rule at least one mole,
preferably 1.5 to 2 moles, of orthoester are used peI` mole
Or vinylphosphonic acid half-ester. Excesses which are
25 grcater yie~d no cssential benefit. A particularly advan-
tageous method of carrying out the reaction is to mix the
half-ester with a?proximately the same amount of fully
formed vinylphos?honic acid diester, iT) the state in which
it is obtained as reaction product, and to leave the mix-
:1~85Z6~ `
-- 8 --
t~re for about 1 hour at an elevated temperature, foreY~ampl~'at lbOC, and thereafter to react this reaction
mixture with the orthoester. In this procedure, the àmount
of dialkyl ether which is other~ise necessarily obtained
is small, and the exploitation of the alkylating potential
of the orthoester is very high. It is also possible to
mix the crude vinylphosphonic acid half-ester with the
orthoester, that is initially to introduce the orthoester
and to meter in the vinylphosphonic acid hal~-ester, or
vice versa, and to allow the resuiting mixture to react
to completion at the particular reaction temperature
required. When using orthocarbonates, this reaction tem-
perature is at about 30 to 90C, while in the case of
orthoformate and the higher ort~.ocarboxylates a tempera-
ture of about 30 to i6GC is required. Tne process canalso be carried out in a continuous manner.
The vinylphosphonic acid diesters obtained in the
presentprocess are puri~ied, if desired, by distillation. As a n~e,
they contain relati~ely sr~l a~ounts of trialkyl phosphates which,
if it is desired, can be separated off by suitable methods,
for example by distillation methods.
The dialkyl vinylphosphonates prepared in this
process step and any trialkyl phosphates present are then
reacted with water at the reactioll temperature required
2~ and the resulting alcollcl is advantageously distilled off
via a column. Srnall amounts of a dialkyl ether and ole-
fins can be formed in this reaction. Th~ reaction with
water is complete when no mcre alcohol is split orf. Here
it can be advantageous to add relatively large amGunts of
~ ~52~;~
g
water toward the er.d of the reaction and to distil of~
some of the unreacted water together ~Yith the alcohol.
The press~:re to be used in this process is not critical,
but the process is preferably carried out under approxi-
mately a-tmospheric pressure. In this process stage also
it is ad~antageous to admix an amount of final pro-
duct, namely vinylphosphor.ic acid, to the dimethyl vinyl-
phosphor.ate before the hydrolysis.
The reaction temperatures in ~his process step are
betweer. 130 and 230C. The reaction is preferably carried
out within a temperature range of 140 to 175C. The reac-
tion with water can also be carried out in a continuous
manner. lhe resu~ting vinylphosphonic acid can be freed
from relat-vely small amounts of dissolved water in vacuo
at an elevated temperature. Tne acid contains phosphoric
acid as a secondar" constituent if the trialkyl
phosphate was not separated from the vinylphosphonic acid
diester before the hydrolysis. It is possible to
separate the phosphoric acid from the vinylphosphcnic acid
via the salts.
Vinylphosphor,ic acid is suitable for use as a
corrosion inhibitor in aqueous systems and, in particular,
also as intermediate in the preparation of f]ame-retardants.
Vinylpllosphonic ?~cids can also be converted into poly-
vinylphosphonic acid for whic~ there are many inductrialuses.
ExamDle 1
__ _
lO0 g of dimethyl 2-acetoxyethanephosphollate were
heated with stirring at 220 to 230C. A mixture c~f 200 g
~5;~ Ei2
-- 10 --
of dimethyl 2-acetoxyethanephosphonate and 3 g of 4--
(dimethylamino)-pyridine were added dropwise in the course
of 6 hours and 112 g of methyl acetate distilled off over
the same time period. 6 g of dimethyl ether were collec-
ted in a cold trap do~rnstream o~ the apparatus. 171 g ofcrude monomethyl vinylphosphonate remained. This quan-
. . .
ti~y was rrixed with 200 g of methyl orthoacetate, and -the
resultin~ mix-ture was gradually heated in the course of
4.5 hours with stirring to an internal temperature o-f
l~ 150C while a mixture of methanol and methyl acetate dis-
tillecl off. A further 70 g of trimethyl orthoacetate
werethenadded at room temperature (molar ratio of mono-
m~thyl vinylphosphonate to orthoester was about 1 : 1.6)
and the mixture was again gradually heated to 150C while
methyl acetate ænd methællol distilled off. A total of
192 g of a mixture of methanol and methyl acetate were
obtained. The residue was distilled off under 0.5 mm ~g.
172 g of dimethyl vinylphosphonate were obtained which,
according to a 31P-NMR spectrum, contained 7% of trimethyl
phosphate. These 172 g o~ dimethyl vinylphosphonate
were mixed with 17 g of vinylphosphonic acid, and the
mixture was heated with stirring at 160 to 175C. Water
was metered in at the same time, while rr.ethanol dis-tillecl
off via a cclumn with a silver-coated jacket. 12 g of
dimethy] ether were collected in a cold trap downstream
of the apparatus. After about 7 hours, the water con-
tainecl in the reaction mix-ture~lasdistilled cf~ a-t 90C
and under C.5 mm ~Ig. 153 g of vin~lphosphonic acid
rernained which hacl a content of 7% Gf phosphcric acid and
5;~iEiZ
- 2% of the compound
- O O
CH2=CH-?-OcH2cH2P(OH)2
0
as measured from the 31P~NMR spectrum~
Example 2
-
350 g cf dimethyl vinylphosphonate, as prepared in
Example 1, and 35 g of vinylphosphor.ic acid were mixed,
and the mixture was heated with stirring to 145C. Water
was then metered in for 14 hours while methanol distilled
off via a columr with a silver-coated jacket. 3 g of
dimethyl ether were eollected in a eold trap downstream
of the apparatus. The water ccntaining the reaction mix-
ture was then distilled off at gOC and under 0.5 mm Y.g.
310 g of vinylphosphonic acid remain~d.
