Formation of 1-phenylvinyl-1-phosphonic acid

A process for forming 1-phenylvinyl-1-phosphonic acid utilizes reacting a mixture of phosphorus trihalide, such as phosphorus trichloride, and acetophenone with water, under conditions in which the water is gradually added to the mixture with cooling to form a reaction mixture, which can be sparged of excess acetophenone with aqueous acid while under vacuum, comprising the 1-phenylvinyl-1-phosphonic acid. This product can be recovered from the reaction mixture by recrystallization from aqueous mineral acid, such as hydrochloric acid.

BACKGROUND OF THE INVENTION 
The present invention is an improved process for the synthesis of 
1-phenylvinyl-1-phosphonic acid (PVPA), which can be polymerized to higher 
molecular weight species or processed with further polymerizable compounds 
in the manufacture of copolymers. Some representative references which 
describe how this well-known compound can be formed include the following: 
Conant et al. J. Amer. Chem. Soc. 44, 2530-2536 (1922), which shows the 
use of acetophenone, phosphorus trichloride, and glacial acetic acid as 
reagents; and U.S. Pat. No. 4,529,559, which shows the reaction of 
acetophenone, phosphorus trichloride, and water in Example 5 under heating 
conditions of up to 150.degree. C. The temperature conditions used in the 
previously mentioned patent were used to remove residual acetophenone from 
the reaction mixture but they can lead to a lessened product yield due to 
the formation of dimeric and oligomeric by-products. 
SUMMARY OF THE INVENTION 
The present invention is a process for forming 1-phenylvinyl-1-phosphonic 
acid (PVPA) and comprises reacting a mixture of phosphorus trihalide, such 
as phosphorus trichloride, and acetophenone with water, under conditions 
in which the water is gradually added to the mixture with cooling to form 
a reaction mixture, which is sparged of excess acetophenone while under 
vacuum, comprising the 1-phenylvinyl-1-phosphonic acid. This product can 
be recovered from the reaction mixture which results from the sparging 
operation by recrystallization from a dehydrating acid, such as 
hydrochloric acid. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
The present invention is advantageously practiced by first combining 
phosphorus trichloride and a molar excess of acetophenone which serves 
both as a solvent and reagent for the instant process. Approximately a one 
to two molar excess of the acetophenone is adequate. After these reagents 
have been allowed to become thoroughly mixed, preferably at ambient or 
room temperature, water is then gradually added, preferably dropwise, with 
sufficient cooling to preferably maintain the temperature in the range of 
from about 5.degree. C. to about 60.degree. C. The resulting reaction 
mixture will contain the desired PVPA product along with undesired excess, 
non-reacted acetophenone which must be removed. 
The removal of the excess acetophenone is accomplished in accordance with 
the present invention by sparging the reaction mixture, while under 
vacuum, with an acid, such as aqueous HCl, which catalyzes the dehydration 
of the intermediate product initially formed, hydrolyzes any cyclic and/or 
oligomeric compositions which may contain P--O--P bonds and/or 
pyrophosphate linkages, and effectively entrains excess acetophenone at an 
attractively low temperature of below 100.degree. C. minimizing 
temperature-generated by-product formation, to yield a subsequent reaction 
mixture containing the desired PVPA product in higher yield. 
The desired product can be effectively recovered from the reaction mixture 
resulting from the sparging with the dehydrating acid by recrystallization 
from HCl. The use of HCl as a recrystallization agent has several 
advantages. For example, the acid component of filtrate resulting from 
such a recrystallization step can be treated with sodium hydroxide, 
forming salt and water as environmentally acceptable byproducts. The HCl 
is itself easily stripped from the desired product PVPA thereby further 
simplifying the ultimate the recovery of PVPA.

The present invention will be further understood by the Examples which 
follow. 
EXAMPLE 1 
Acetophenone (327.5 gm, 2.726 moles) and 249.9 gm (1.82 moles) of PCl.sub.3 
were placed into a nitrogen-blanketed 500 cc reaction flask and were 
allowed to stir at room temperature for one hour. The reactor was then 
vigorously stirred with ice/water cooling, and 49 gm (2.726 moles) of 
water were added dropwise starting at 7.degree. C. and completed at 
50.degree. C. The total water addition time was fifty minutes. The 
reaction proceeded with formation of large amounts of HCl that were 
trapped in a caustic scrubber. When the HCl evolution subsided at 
80.degree.-85.degree. C., vacuum was applied, and the reaction mixture was 
sparged with 2% HCl at 100.degree. C. and water aspirator pressure for six 
hours and forty minutes. 
The stripped crude reaction mixture contained 86.6 mol % of 
1-phenylvinyl-1-phosphonic acid (PVPA) (by .sup.31 P NMR) with 1.4% of 
acetophenone remaining (by G.C.) 
The crude reaction mixture was then treated at 95.degree. C. with 151 gm of 
37% HCl (50% of the crude yield). The HCl addition took five minutes 
resulting in a temperature drop to 75.degree. C. This mixture was then 
vigorously stirred and cooled in a water bath to 35.degree. C. when it was 
seeded with a small amount of PVPA. Cooling continued to 25.degree. C. 
(twenty minutes), and the resulting thick slurry was filtered through a 
coarse fritted funnel. The PVPA crystals were washed with 35 gm of 37% 
Hcl. The yield of the air-dried first crop was 58.2% (of theoretical 
yield), M.P. 109.5.degree.-110.degree. C. 
EXAMPLE 2 
Acetophenone (538.7 gm, 4.48 moles), 513 gm (3.74 moles) of Pcl.sub.3, and 
100.9 gm (5.605 moles) of water were reacted as described in Example 1. 
The reaction mixture was sparged with 2% HCl. for nine hours. The crude 
product contained 86.5 mol % of PVPA (by .sup.31 NMR) with 2.9% 
acetophenone remaining. Crystallization from 315 gm of concentrated HCl 
afforded 400 gm of (air-dried) PVPA (first crop), 58% of theory. 
COMATIVE EXAMPLE 3 
This Example was a repetition of the synthesis reaction shown in Example 5 
of U.S. Pat. No. 4,529,559. 
Acetophenone (158.3 gm, 1.3176 moles) and 150.7 gm (1.093 moles) of 
PCl.sub.3 were placed into a nitrogen-blanketed 500 cc reaction flask and 
were allowed to stir at room temperature for two hours. Then, 29.6 gm 
(1.646 moles) of water were added into the vigorously stirred reactor in 
thirty-nine minutes. At this stage, the exotherm reached 43.degree. C. The 
reactor was then heated to 100.degree. C. in ten minutes. The reactor was 
then placed under vacuum of 12 mm Hg, and the excess acetophenone was 
distilled to 150.degree. C. in one hour. The stripped residue was then 
hydrolyzed with 88 gm of water by heating to 100.degree. C. in forty-five 
minutes. The results of .sup.31 P NMR analysis: 82.6 mole % PVPA; 7.6 mole 
% phosphorous acid; 0.6 mole % phosphoric acid; and other dimeric and 
oligomeric by-products. 
The yield of PVPA in this Example in the stripped crude reaction mixture 
was inferior to that in Examples 1 and 2. 
COMATIVE EXAMPLE 4 
This Example was another repetition of the synthesis reaction shown in 
Example 5 of U.S. Pat. No. 4,529,559. 
Acetophenone (217.8 gm, 1.813 moles) and 207.4 gm (1.51 moles) of PCl.sub.3 
were placed into a nitrogen-blanketed 500 cc reaction flask and were 
allowed to stir at room temperature for two hours. Then, 40.77 gm (2.265 
moles) of water were added into the vigorously stirred reactor in 
fifty-three minutes while the temperature ranged from 24.degree. C. to 
75.degree. C. The reactor was then heated to 110.degree. C. in 
twenty-seven minutes. The crude reaction mixture was then placed under 
vacuum of 12 mm Hg, and 105.degree. C.-150.degree. C. for fifty-five 
minutes to remove excess acetophenone. The glassy stripped residue was 
then hydrolyzed with 121 gm of water at 100.degree. C. in forty minutes. 
The hydrolysate was then stripped again at 12 mm Hg and 50.degree. C. for 
one hundred and ten minutes. The results of 31P NMR analysis: 80.1 mole % 
PVPA; 4.4 mole % phosphorous acid; 0.7 mole % phosphoric acid; and other 
dimeric and oligomeric byproducts. 
The yield of PVPA in this Example in the stripped crude reaction mixture 
was inferior to that in Examples 1 and 2. 
The foregoing Examples are presented for illustrative purposes only and, 
for that reason, should not be construed in a limiting sense. The scope of 
protection sought is set forth in the Claims which follow.