Aromatic phosphinic acids containing sulfone linkage

Phosphinic acids of the formula ##STR1## wherein (A) R is ##STR2## (1) X is 3-phenylene or 4-phenylene, and (2) Y is a direct bond, ##STR3## (B) R' is R, lower alkyl of from 1 to 3 carbon atoms, 4-biphenylyl, or phenyl. These acids are neutralized with an equivalent amount of alkali metal carbonates to form alkali metal salts which react with ZnCl.sub.2 to form polymers having high thermal stability.

BACKGROUND OF THE INVENTION 
This invention generally relates to phosphinic acids and more particularly 
to aromatic sulfonyl substitute phosphinic acids. 
Polymeric metal dialkyl, diaryl and arylalkyl-phosphinates have been 
discussed in the literature. For instance, see "polymeric Metal 
Phosphinates", B. P. Block, Inorg. Macromol. Rev. 1 (1970) 115-125. Of 
particular interest are the polymers containing tetrahedral zinc (II) 
centers and symmtrical bridging O,O'-phosphinate groups in polymeric 
structures, such as 
##STR4## 
wherein R and R' may be alkyl or aryl groups. 
The zinc (II) and phosphinates groups are strong electrostatic centers. 
Strong electrostatic attraction between centers on adjacent polymer chains 
gives the dialkyl-, diaryl- and arylalkyl- zinc phosphinate polymers the 
properties of three dimensional polymers having crosslinkage between 
chains. As a result, the polymer chains do not easily slide over each 
other, causing the polymers to form brittle rather than flexible coatings. 
For instance, the diphenyl- and dimethyl- zinc phosphinate polymers form 
very brittle coatings. If the aryl and alkyl side groups are large enough 
to insulate the electrostatic centers on adjacent chains from each other, 
the polymer coatings will be flexible. For example, zinc phosphinate 
polymers in which the side groups are alkyl of 8 carbon atoms have a 
flexibility comparable to polyethylene. Unfortunately, polymers having 
these large aryl or alkyl side chains have poor thermal stability. The 
problem is therefore to develop polymers which are both flexible and 
thermally stable. 
In addition to being flexible and thermally stable, the zinc (II) 
bis(phosphinate) polymers should be melt and/or solution processable. The 
symmetric diaryl or dialkyl zinc (II) bis(phosphinate) polymers, such as 
the diphenyl- or dimethyl-, have high energies of crystalization. As a 
result, these symetric polymers have very high melting points at which 
they usually decompose rather than melt; they also are insoluble in common 
solvents. 
SUMMARY OF THE INVENTION 
Accordingly, one object of this invention is to provide new phosphinic 
acids and alkali metal salts of these acids. 
Yet another object of this invention is to provide new chemical compounds 
which react with ZnCl.sub.2 to produce polymer coatings having high 
thermal stability. 
A further object of this invention is to provide new chemical compounds 
which react with ZnCl.sub.2 to produce polymer coating which resist 
oxidation at high temperatures. 
A still further object of this invention is to provide new chemical 
compounds which react with ZnCl.sub.2 to produce flexible polymer 
coatings. 
Yet another object of this invention is to provide polymers which are melt 
or solution processable. 
These and other objectives of this invention are accomplished by providing 
phosphinic acids of the formula 
##STR5## 
wherein (A) R is 
##STR6## 
(1) X is selected from the group consisting of 3-phenylene and 4-phenylene, 
and 
(2) Y is selected from the group consisting of a direct bond, 
##STR7## 
(B) R' is selected from the group consisting of R, lower alkyl of from 1 
to 3 carbon atoms, 4-biphenylyl, and phenyl, wherein R is as defined 
above. 
Neutralization of these acids with an equivalence of alkali metal carbonate 
produces the alkali metal salt of the acid. These alkali metal salts react 
with zinc (II) chloride to form polymer coatings having high oxidative and 
thermal stability. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
The symmetric phosphinic acids (R' = R) of this invention can be prepared 
by reacting two moles of RLi with one mole of diethyl 
dichlorophosphoramide, 
##STR8## 
to form a phosphoramide of the formula 
##STR9## 
which can then be hydrolyzed to form the phosphinic acid of the formula 
##STR10## 
Example 1 illustrates the reaction conditions for this synthesis. Note 
that the lithium compound, RLi, is formed in solution by the interaction 
of RBr and butyl lithium. The symmetric phosphinic acid may also be 
synthesized by reacting two moles of RMgBr with one mole of the diethyl 
dichlorophosphoramide under standard grignard conditions and then 
hydrolysing the the resulting phosphoramide to form the acid. A third 
method of synthesizing these symetric phosphinic acids is to react two 
moles of diazonium salt, RN.tbd.N.sup.+ BF.sub.4.sup.-, with one mole of 
the diethyl dichlorophosphoramide, followed by hydrolysis to give the 
acid. In order to force the addition of two moles of R--N.tbd.N.sup.+ 
BF.sub.4.sup.-, the reaction conditions will be more rigorous (e.g. higher 
reaction temperature) than the conditions used in Examples 12, 13, 14, and 
15. 
The unsymmetric phosphinic acid in which R' is lower alkyl or from 1 to 3 
carbon atoms, 4-biphenylyl, or phenyl are synthesized by reacting one mole 
of the RLi with one mole of one of the following: 
diethyl chloromethylphosphoramide, 
diethyl chloroethylphosphoramide, 
diethyl chloro-n-propylphosphoramide, 
diethyl chloroisopropylphosphoramide, 
diethyl chloro(4-biphenylyl) phosphoramide, 
or diethyl chlorophenylphosphoramide 
to form a phosphoramide of the formula 
##STR11## 
which is then hydrolyzed to form the unsymmetric phosphinic acid of the 
formula 
##STR12## 
Examples 4 illustrates the reaction conditions for this synthesis. 
Alternatively, one mole of RMgBr can be used under normal grignard 
reaction conditions in place of RLi. A third method of synthesizing the 
unsymmetric phosphinic acids is to react one mole of diazonium salt, 
RN.tbd.N.sup.+ BF.sub.4.sup.-, with one mole of the chlorophosphoramide to 
produce the phosphoramide which is hydrolyzed to give the acid. 
Examples 12, 13, 14, and 15 illustrate yet another method of synthesizing 
the unsymmtric phosphinic acids. One mole of diazonium, salt, 
RN.tbd.N.sup.+ BF.sub.4.sup.-, is reacted with one of the following: 
dichloromethyl phosphine, 
dichloroethyl phosphine, 
dichloro-n-propyl phosphine, 
dichloroisopropyl phosphine, 
dichloro(4-biphenylyl) phosphine, or 
dichlorophenyl phosphine to form a phosphine of the formula 
##STR13## 
which decomposes when water is added to give the phosphinic acid of the 
formula 
##STR14## 
The RLi and RN.tbd.N.sup.+ BF.sub.4.sup.- are easily synthesized from 
commercially available materials using conventional reaction steps. For 
instance, the synthesis of 3-aminophenyl phenyl sulfone and 4-aminophenyl 
phenyl sulfone are disclosed by M. E. Heppenstall and S. Smiles, J. Chem. 
Soc. 899 (1938). These amines are converted according to the procedures os 
Examples 13 and 14 into diazonium salts of the formulas 
##STR15## 
and 
##STR16## 
These Diazonium salts can be converted by CuBr in a conventional Sandmeyer 
reaction to give 
##STR17## 
and 
##STR18## 
which are converted by butyl lithium to 
##STR19## 
and 
##STR20## 
The decomposition of diazonium salts in water is a conventional method of 
producing pure phenols. Thus, by decomposing the above diazonium salts in 
water, 
##STR21## 
and 
##STR22## 
can be produced. These phenols react with dibromobenzene in the presence 
of copper and base (see example 2) to produce 
##STR23## 
and 
##STR24## 
Treatment with butyl lithium replaces the bromine with lithium on these 
compounds. The sodium salts of the above phenols can be reacted with 
4-chloronitrobenzene under the conditions of example 8 to produce nitro 
compounds. Reduction of the nitro compounds to amines followed by 
treatment with tetrafluoroboric acid would give 
##STR25## 
and 
##STR26## 
Examples 5 through 11 illustrate the steps for converting 
##STR27## 
into 
##STR28## 
starting with 
##STR29## 
the same procedure can be used to produce 
##STR30## 
These diazonium salts can be converted by Sandmeyer reaction (CuBr) to the 
corresponding bromides which will react with butyl lithium to give 
##STR31## 
and 
##STR32## 
The phosphinic acids of the present invention react with zinc (II) chloride 
to produce zinc (II) bis(phosphinate) polymers having sulfonyl side 
groups. Example 16 illustrates and discusses the necessary reaction 
conditions. Although other zinc (II) salts might be used (e.g. 
ZnSO.sub.4), ZnCl.sub.2 is preferred because the HCl byproduct it produces 
is volatile. 
R groups in which X is 4-phenylene are preferred because the para-linkage 
permit freer rotation of the sulfonyl chain and thus provides greater 
thermal stability. Similarly, R groups containing only two benzene rings 
(i.e. Y represents a direct bond) are preferred because they have greater 
thermal stability than R groups containing 3 benzene rings. Thus, 
4-(phenylsulfonyl)phenyl is the most preferred R group. 
The unsymmtic phosphinic acids of this invention (i.e., R' is lower alkyl 
of from 1 to 3 carbon atoms, 4-biphenylyl or phenyl) are preferred because 
they produce polymers which are easier to melt and/or solution process 
than do the symetric phosphinic acids (i.e., R' = R). R' is limited to 
alkyl of up to 3 carbon atoms because polymers containing larger alkyl 
groups do not have sufficient thermal stability. Methyl is the preferred 
alkyl group because it is more thermally stable than the ethyl and propyl 
groups. Similarly, phosphinic acids in which R' is phenyl produce polymers 
with greater thermal stability than do phosphinic acids in which R' is 
4-(biphenylyl). 
Dimethyl formamide appears to be the best solvent for applying the polymer 
coatings; it dissolves sulfonyl containing compounds or polymers better 
than most solvents and it is acceptable for use in paints. Although 
chloroform will dissolve many of these polymers, it is unsuitable for 
coatings such as paints because it is volatile and poisonous. 
Even if a polymer is not solution or melt processable, a suitable coating 
can frequently be obtained by dissolving the phosphinic acid and 
ZnCl.sub.2 together and then spraying the solution onto the surface to be 
coated. The solvent is allowed to evaporate and the resulting polymer 
coating is cured. 
The general nature of the invention having been set forth, the following 
examples are presented as specific illustrations thereof. It will be 
understood that the invention is not limited to these specific examples 
but is susceptible to various modifications that will be recognized by one 
of ordinary skill in the art.

EXAMPLE I 
bis [4-(phenylsulfonyl)phenyl] phosphinic acid 
##STR33## 
A solution of 30 grams (0.1 mole) of 4-bromophenyl phenyl sulfone in 500 
ml. of tetrahydrofuran was cooled to -100.degree. C. in a liquid 
nitrogen-toluene slush, and 42 ml. (0.1 mole) of 2.38 M n-butyl lithium in 
hexane was added, forming 4-phenylsulfonyl-phenyl lithium. After about 10 
minutes, 9.5 grams (0.05 mole) of diethyl dichlorophosphoramide was added, 
and the reaction mixture was allowed to warm slowly to room temperature, 
and then to stand a room temperature for 18 hours, forming diethyl bis 
[4-(phenylsulfonyl)phenyl] phosphoramide. Next, 125 ml. of 6 M HCl was 
added, and the reaction mixture was heated under reflux for 4 hours to 
hydrolyze the phosphoramide group. The tetrahydrofuran was removed by 
distillation, and 7.5 grams of almost white solid, M.P. 
115.degree.-130.degree. C., was collected by filtration. This solid was 
recrystallized from tetrahydrofuran to give 7 grams (28% yield) of the 
bis[4-(phenylsulfonyl)phenyl] phosphinic acid product, m.p. 
155.degree.-165.degree. C. 
Analysis. Calculated for C.sub.24 H.sub.19 O.sub.6 PS.sub.2 (weight 
percent): 
C, 57.8; H, 3.84; P, 6.21; S, 12.86. 
Found: C, 58.5; H, 4.55; P, 6.02; S, 13.06. 
This reaction was repeated using a greater ratio of the bromide to diethyl 
dichlorophosphoramide without significant increase in yield. 
EXAMPLE 2 
4-bromophenyl 4-(phenylsulfonyl)phenyl ether 
##STR34## 
To a mixture of 22.4 grams of powdered potassium hydroxide and 94 grams of 
4-(phenylsulfonyl)phenol in 100 ml. of dimethylformamide were added while 
stirring under nitrogen, 400 grams of 4-dibromobenzene and 2 grams of 
precipitated copper. The reaction mixture was heated at 
190.degree..+-.5.degree. C. for 16 hours, and excess dibromobenzene was 
then removed by distillation. The pot residue was dissolved in 500 ml. of 
benzene and washed with 10% aqueous potassium hydroxide and water. The 
benzene was removed under reduced pressure, and the residue was dissolved 
in 4 liters of ether. A small amount of insoluble material was removed by 
filtration, and 68 grams of 4-bromophenyl 4-(phenylsulfonyl)phenyl ether, 
m.p. 114.degree.-117.degree. C. was precipitated by adding methanol while 
the ether was boiled off. 
Analysis. Calculated for C.sub.18 H.sub.13 BrO.sub.3 S (weight percent): C, 
55.53; H, 3.37; Br, 20.54; Found: C, 55.72; H, 3.50; Br, 20.63. 
EXAMPLE 3 
bis{4-[4-(phenylsulfonyl)phenoxy]phenyl} phosphinic acid 
##STR35## 
The procedure given in example 1 was used to convert 30 grams of 
4-bromophenyl 4-(phenylsulfonyl)phenyl ether (produced in example 2) to 14 
grams of bis{4-[4-(phenylsulfonyl)phenoxy]phenyl} phosphinic acid, m.p. 
225.degree.-230.degree. C. 
Analysis. Calculated for C.sub.36 H.sub.27 O.sub.8 PS.sub.2 (weight 
percent): C, 63.33; H, 4.00; P, 4.53. Found: C, 61.40; H, 4.05; P, 4.92. 
EXAMPLE 4 
methyl[4-(phenylsulfonyl)phenyl]phosphinic acid 
##STR36## 
The procedure given in example 1 was used to convert 29.7 grams of 
4-bromophenyl phenyl sulfone and 18.7 grams of diethyl 
chloromethylphosphoramide to 3 grams of 
methyl[4-(phenylsulfonyl)phenyl]phosphinic acid, m.p. 
73.degree.-76.degree. C. 
Analysis. Calculated for C.sub.13 H.sub.13 O.sub.4 PS (weight percent): C, 
52.71; H, 4.43; P, 10.43. Found. C, 50.50; H, 4.82; P, 10.59. 
EXAMPLE 5 
4-(Dimethylthiocarbamoyloxy)phenyl phenyl sulfone 
##STR37## 
To a slurry of 190 grams (0.81 mole) of 4-(phenylsulfonyl)-phenol in a 
solution of 32 grams (0.81 mole) of sodium hydroxide in 2 liters of water 
was added slowly with stirring a solution of 112 grams (0.9 mole) of 
dimethylthiocarbamoyl chloride in 800 ml. of ether while the temperature 
of the reaction was maintained in the 0.degree.-10.degree. C range with 
external cooling. After the addition was complete, the basicity of the 
solution was adjusted to pH 8 by addition of dilute sodium hydroxide. The 
reaction mixture was stirred at room temperature for 2 hours, and 187.5 
grams (72% yield) of crude product, m.p. 91.degree.-110.degree. C was then 
collected. After the analytical sample was recrystallized from ethanol, it 
melted at 134.degree.-135.5.degree. C. 
Analysis. Calculated for C.sub.15 H.sub.15 NO.sub.3 S.sub.2 (weight 
percent): C, 56.1; H, 4.70. Found: C, 56.0; H, 5.02. 
EXAMPLE 6 
4-(Dimethylcarbamoylthio)phenyl phenyl sulfone 
##STR38## 
Heating of the crude solid product of example 5 for 3 hours at 160.degree. 
C with subsequent crystallization from ethanol gave 18 grams of crude 
product, m.p. 107.degree.-111.degree. C. An analytical sample, which was 
recrystallized from ethanol, melted at 121.degree.-125.degree. C. 
Analysis. Calculated for C.sub.15 H.sub.15 NO.sub.3 S.sub.2 (weight 
percent): C, 56.1; H, 4.70. Found: C, 55.9; H, 4.79. 
Confirmation of the rearrangment was obtained from the appearance of an 
amide CO band at 1640 cm.sup.-1 in the ir. 
EXAMPLE 7 
4-(phenylsulfonyl)thiophenol 
##STR39## 
The 4-(dimethylcarbamoylthio)phenyl phenyl sulfone formed in Example 6 was 
hydrolyzed by refluxing it in dilute KOH in water for about 1 to 2 hours. 
The concentration of the KOH was not critical. The product formed was 
4-(phenylsulfonyl)thiophenol. 
EXAMPLE 8 
4-nitrophenyl 4-(phenylsulfonyl)phenyl sulfide 
##STR40## 
Sodium metal was added to ethanol to form sodium ethoxide, CH.sub.3 
CH.sub.2 ONa. Next the 4-(phenylsulfonyl)thiophenol formed in Example 8 
was added to the sodium ethoxide, forming the sodium salt of the 
thiophenol, 
##STR41## 
Finally, the 4-chloronitrobenzene was added and the mixture was refluxed 
for 3 hours, forming the 4-nitrophenyl 4-(phenylsulfonyl) phenyl sulfide. 
EXAMPLE 9 
4-(4-nitrophenylsulfonyl)phenyl phenyl sulfone 
##STR42## 
A solution of 8.1 grams (0.05 mole) of potassium permanganate in 150 ml of 
water was added slowly to a solution of 14 grams (0.038 mole) of the 
4-nitrophenyl4-(phenylsulfonyl)phenyl sulfide produced in example 9 in 250 
ml. of acetic acid. The resulting mixture was stirred for 1.5 hours, 
warmed on a steam bath for another 1.5 hours, and then the excess 
manganese dioxide was decomposed with sodium bisulfite. The reaction 
mixture was then cooled with an equal volume of ice, and 14.2 grams (88% 
yield) of product, m.p. 289.degree.-298.degree. C, was collected by 
filtration. 
Analysis. Calculated for C.sub.18 H.sub.13 NO.sub.6 S.sub.2 (weight 
percent): C, 53.6; H, 3.25; N, 3.47. Found: C, 53.4; H, 3.35; N, 3.68. 
EXAMPLE 10 
4-(4-aminophenylsulfonyl)phenyl phenyl sulfone 
##STR43## 
A warm slurry of 13.5 grams (0.034 mole) of the 
4-(4-nitrophenylsufonyl)phenyl phenyl sulfone of example 9 in 450 ml. of 
dimethylformamide was hydrogenated at an initial hydrogen pressure of 60 
psi and in the present of 10 ml. of slurry of Raney nickel in ethanol. The 
theoretical amount of hydrogen was consumed in 6 hours. The catalyst was 
removed by filtration, and the filtrate was concentrated to dryness. The 
residue was crystallized in 50 ml. of ethanol to give 10 grams (79% yield) 
of product, m.p. 231.degree.-5.degree. C. An analytical sample was 
recrystallized from ethanol to give material melting at 
234.5.degree.-237.degree. C. 
Analysis. Calculated for C.sub.18 H.sub.15 NO.sub.4 S.sub.2 (weight 
percent); C, 57.9; H, 4.06; N, 3.75. Found: C, 57.8; H, 4.29, N, 3.82. 
EXAMPLE 11 
4-[4-(phenylsulfonyl)phenylsulfonyl]benzenediazonium tetrafluoroborate 
##STR44## 
To a slurry of 10 grams (0.027 mole) of finely ground 
4-(4-aminophenylsulfonyl)phenyl phenyl sulfone (prepared in example 9) in 
200 ml. of tetrafluoroboric acid solution was added slowly 5 grams (0.073 
mole) of sodium nitrite in 10 ml. of water, with cooling to 
0.degree.-10.degree. C. The resulting solid was collected by filtration, 
washed with 10 ml. of cold aqueous tetrafluoroboric acid, then 10 ml of 
ethanol, and finely 50 ml of ether, and dried. Yield of 
4-[4-(phenylsulfonyl)phenylsulfonyl]benzenediazonium tetrafluoroborate 11 
grams (95%). m.p. 120.degree.-130.degree. C. 
The solution of tetrafluoroboric acid used in these examples was prepared 
by dissolving 184 grams of boric acid in 454 grams of 48% hydrofluoric 
acid. 
EXAMPLE 12 
Phenyl{4-[4-(phenylsulfonyl)phenylsulfonyl]phenyl}phosphinic acid 
##STR45## 
A slurry of 11 grams (0.026 mole) of the 
4-[4-(phenylsulfonyl)phenylsulfonyl]benzenediazonium tetrafluoroborate 
prepared in Example 11, 0.01 grams of copper (I) bromide, and 5 ml. (0.06 
mole) of dichlorophenylphosphine in 100 ml. of ethyl acetate was warmed at 
40.degree.-50.degree. for 30 minutes. The resulting solution was cooled, 
and 200 ml. of water was added. Ethyl acetate and volatile by-products 
were removed by steam distillation, and the crude product was collected by 
filtration. This solid was partially dissolved in 500 ml. of 5% potassium 
carbonate and reprecipitated with hydrochloric acid to give 3.1 grams of 
solid, m.p. 125.degree.-150.degree.. Recrystallation from 200 ml. of 
ethanol gave 2 grams (15% yield) of the 
phenyl{4-[4-(phenylsulfonyl)phenylsulfonyl]phenyl}-phosphinic acid, m.p. 
227-230. 
Analysis. Calculated for C.sub.24 H.sub.19 O.sub.6 PS.sub.2 (weight 
percent): C, 57.8; H, 3-84; P, 6.21; S, 12.86. Found: C, 57.6: H, 4.04; P, 
6.17; S, 12.80. 
EXAMPLE 13 
phenyl[4-(phenylsulfonyl)phenyl]phosphinic acid 
##STR46## 
4-(phenylsulfonyl)benzene diazonium tetrafluoroborate was prepared from 
4-aminophenyl phenyl sulfone according to the method of example 11. A 
slurry of 44 grams of the 4-(phenylsulfonyl)benzenediazonium 
tetrafluoroborate, 22.8 ml of dichlorophenylphosphine, and 0.5 grams of 
copper (I) chloride in 400 ml. of ethyl acetate was heated at 30.degree. C 
for 1.5 hours, cooled, and decomposed by adding 125 ml. of water. The 
ethyl acetate was removed by steam distillation, and the solid was 
collected by filtration of the aqueous residue. This solid was extracted 
with 2 liter of 10% sodium hydroxide, and the extract was acidified with 
hydrochloric acid to give crude acid. Crystallization from 80% ethanol 
gave 20 grams (45% yield) of phenyl[4-(phenylsulfonyl)phenyl]phosphinic 
acid, m.p. 225.degree.-228.degree. C. 
Analysis. Calculated for C.sub.18 H.sub.15 O.sub.4 PS (weight percent): C, 
60.3; H, 4.23; P, 8.64; S, 8.95. Found: C, 60.2; H, 4.49; P, 8.77; S, 
9.49. 
EXAMPLE 14 
phenyl[3-(phenylsulfonyl)phenyl]phosphinic acid 
##STR47## 
3-(phenylsulfonyl)benzene diazonium tetrafluoroborate was prepare from 
3-aminophenyl phenyl sulfonate according to the method of example 11. 14.3 
grams of the 3-(phenylsulfonyl)benzene diazonium tetrafluoroborate was 
reacted with 20 grams of dichlorophenyl phosphine according to the 
procedure of example 13 and gave 6.1 grams (39.5% yield) of phenyl 
[3-(phenylsulfonyl)phenyl]phosphinic acid, m.p. 175.degree.-177.degree. C. 
Analysis. Calculated for C.sub.18 H.sub.15 O.sub.4 PS (weight percent): C, 
60.3; H, 4.23; P, 8.64. Found: C, 60.3; H, 4.52; P, 8.47. 
EXAMPLE 15 
4-(biphenylyl) [4-(phenylsulfonyl)phenyl]phosphinic acid hydrate 
##STR48## 
The reaction of 18.9 grams of 4-(phenylsulfonyl)benzene diazonium 
tetrafluroborate with 15.7 grams of 4-biphenylyldichlorophosphine 
according to the procedure of example 13 gave 9 grams of 4-(biphenylyl) 
[4-(phenylsulfonyl)phenyl]-phosphinic acid hydrate, m.p. 
179.degree.-230.degree. C. 
Analysis. Calculated for C.sub.24 H.sub.19 O.sub.4 PS.1.2H.sub.2 O weight 
percent: C, 63.21; H, 4.74; S, 7.03. Found: C, 63.04; H, 4.52; S, 6.73. 
EXAMPLE 16 
Synthesis of Zinc Phosphinates 
All of the zinc bis(phosphinates) were synthesized by the same general 
procedure. The phosphinic acid (or acids for the copolymer) was first 
neutralized with K.sub.2 CO.sub.3 in a tetrahydrofuran/water mixture by 
treating it with the stoichiometric amount of K.sub.2 CO.sub.3 (0.5 mole 
per mole of acid). An excess of K.sub.2 CO.sub.3 was avoided, so that zinc 
hydroxy phosphinates would not be formed in the next step. The potassium 
phosphinate solution was then added slowly with stirring to an aqueous 
solution of zinc sulfate (0.5 mole of zinc sulfate per mole of potassium 
phosphinate). After the addition was completed, the solution was heated to 
and held at boiling until all the tetrahydrofuran was removed. The 
precipitate that formed was filtered off, washed with water, and dried in 
a vacuum desiccator. Yields were 85% or better. Table I gives analytical 
and softening point data for five of the zinc bis(phosphinates) prepared 
and molecular weights for the two polymers that are soluble in chloroform. 
The thermal stabilities of the various zinc phosphinates were measured in 
both nitrogen and air, and the results are given in Table II. 
Table I 
__________________________________________________________________________ 
Summary of Analytical Data for Zinc Phosphinate Polymers and Copolymers 
Molecular 
Analysis (%) a 
Softening 
weight b 
C H Zn Point (.degree. 
in CHCl.sub.3 
__________________________________________________________________________ 
1 
##STR49## 54.0 (54.4 
3.42 3.42 
6.16 6.08) 
&gt;400 c 
##STR50## 55.0 (55.4 
4.00 3.62 
7.98 8.38) 
180 c 
##STR51## 54.1 4.06 3.42 
5.72 6.16) 
400 c 
##STR52## 55.7 (55.4 
4.03 3.62 
8.40 8.38) 
140 20,000 (8,000) 
##STR53## 55.4 (55.4 
3.94 3.62 
7.93 8.38) 
155 28,000 (15,000) 
__________________________________________________________________________ 
a Calculated values in parentheses. 
b Values in parenthesis are for unpurified CHCl.sub.3 (0.75% C.sub.2 
H.sub.5 OH). Values are .+-.5%. 
c Insoluble in chloroform. 
Table II 
______________________________________ 
Thermogravimetric Analyses 
of Zinc Phosphinate Polymers and Copolymers 
Temp. (.degree. C) for Indicated Wt. Loss.sup.b 
Polymer Atmos..sup.a 
Initial 2% 5% 10% 
______________________________________ 
1. N 440 450 485 495 
A 440 450 480 500 
2. N 440 450 465 475 
A 450 460 495 500 
3. N 385 400 440 460 
A 350 400 450 470 
4. N 410 415 440 455 
A 355 400 440 455 
5. A 365 400 450 460 
______________________________________ 
.sup.a The atmosphere during the run was nitrogen (N) or air (A). 
.sup.b Heating rate 5.degree./min. 
With the exception of polymer number 3, these zinc (II) bis(phosphinate) 
polymers are soluble in organic solvents such as dimethylformamide 
tetrahydrofuran and/or chloroform. 
Obviously, numerous modification and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims the invention may 
be practiced otherwise than as specifically described herein.