Hydrogen phosphonates and polymers containing them as flame retardants

The present invention relates to cyclic phosphorus compounds and processes for the preparation thereof. The present invention relates to a process for the preparation of certain derivatives of cyclic hydrogenphosphonates. Azomethine, sulfonyl isocyanate, isocyanate, and isothiocyanate derivatives are a part of the present invention. The cyclic phosphorus compounds are useful as flame retardants with organic polymers, such as polyurethanes, polyesters, and polyamides.

BACKGROUND OF THE INVENTION 
The present invention relates to cyclic phosphorus compounds, such as 
certain cyclic hydrogen phosphonate derivative, processes for the 
preparation of such compounds and their derivatives and to flame retardant 
compositions containing the said cyclic phosphorus compounds. 
Certain phosphonates have been employed as flame retardant additives, but 
have suffered from the defect of causing undesirable crosslinking of 
polymeric materials in which the phosphonates were employed. For example, 
the addition of such phosphonates to a molten polymer such as polyethylene 
terephthalate or a nylon, preliminary to the extrusion or spinning step 
has shown that the crosslinking prevents the formation of acceptable 
fibers. As a result of the crosslinking, the fibers contain lumps and 
irregular sections so that the extrusion through spinnerettes is hampered 
and the stretching, washing and other physical treatments of the fiber 
become impossible. 
It has now however been found that certain cyclic phosphorus compounds 
including cyclic phosphonates are particularly useful as flame retardants 
for organic polymeric materials. The invention includes combinations of 
the present cyclic phosphorus compounds together with organic polymers 
such as polyurethanes, polyesters, e.g. polyethylene terephthalate, and 
polyamides e.g., the nylons. 
SUMMARY OF THE INVENTION 
The general formula for the cyclic phosphorus derivatives of the invention 
is: 
##STR1## 
where Y is selected from the group consisting of 
##STR2## 
and where X is selected from the group consisting of 
______________________________________ 
##STR3## where R.sub.a is an alkyl radical of 1 to 4 carbon atoms, 
R.sub.b is a phenyl radical of 6 to 10 carbon atoms. 
##STR4## where R.sub.c is phenyl with 0 to 2 halo- gens or phenyl with 
0 to 2 nitro groups or phenyl with 0 to 2 methyl groups. 
##STR5## where R.sub.d is phenyl with 0 to 2 halo- gen atoms, or phenyl 
with 0 to 2 methyl groups, or an alkyl or alkenyl radical of 1 
to 3 carbon atoms. 
##STR6## where R.sub.e is phenyl with 0 to 2 halo- gens, or alkyl or 
alkenyl of 1 to 3 carbon atoms. 
______________________________________ 
The above compounds are derivatives of cyclic hydrogenphosphonates. They 
are obtained by the reaction of a crude or purified hydrogen phosphonate 
with azomethines, sulfonyl isocyanates, isocyanates and isothiocyanates 
respectively. 
Representative examples of azomethines are N-(p-chlorobenzylidene) 
ethylamine, and N,N'-terephthalylidene-di-p-toluidine, and benzylidene 
ethylamine, and p-chlorobenzylidenemethylamine, and methyl 
benzylidenemethylamine. 
The general reaction for the preparation of the azomethine derivatives is: 
##STR7## 
Examples of isocyanates that can be used are: p-toluenesulfonylisocyanate, 
methyl sulfonylisocyanate, ethyl sulfonylisocyanate, 
phenylsulfonylisocyanate, chlorophenylsulfonylisocyanate, 
p-nitrophenylsulfonylisocyanate, p-nitrophenyl isocyanate, allyl 
isocyanate, p-chlorophenylisocyanate, 2-fluorophenylisocyanate, 
.alpha.,.alpha.,.alpha.-trifluoro-m-tolyl isocyanate, methyl isocyanate, 
3-bromophenyl isocyanate, tolylene-2,4-diisocyanate, and 
1,6-diisocyanatehexane. Examples of isothiocyanates that can be used are: 
allylisothiocyanate, ethyl isothiocyanate, 4-fluorophenyl isothiocyanate, 
2-naphthyl isothiocyanate, methyl isothiocyanate, and 4-chloro-2-naphthyl 
isothiocyanate. 
The general reactions for the preparation of the sulfonyl isocyanate 
derivatives, isocyanate derivatives and isothiocyanates are shown below: 
##STR8## 
Where R is an alkylene, or haloalkylene (halo is chlorine or bromine), 
group of a 1,2-glycol having from 2 to 8 carbon atoms, or of a 1,3 glycol 
having from 3 to 8 carbon atoms. 
The present cyclic phosphorus compounds of the invention including hydrogen 
phosphonates, are useful per se as flame retardant materials which provide 
phosphorus as a component to reduce flammability. Improvement in flame 
retardant properties result when the present derivatives are used with 
organic polymers. Such resultant products do not burn readily, and instead 
inhibit flammability of an organic polymer, for instance a polyurethane 
which is useful in the production of an elastomer or a rigid or flexible 
foam. An example of an elastomeric polyurethane is the product obtained by 
heating together poly(tetramethylene ether)glycol and methylene 
bis(p-phenylisocyanate). 
The cyclic phosphorus compounds including the cyclic hydrogen phosphonates 
of the present invention are useful as flame retardant modifiers for 
organic polymers. The cyclic phosphorus compounds have less tendency to 
cause cross linking. These compounds can be added directly to the molten 
polymer or the components of a foam composition before polymerization, 
e.g. before spinning fibers or forming films or other shaped objects 
including foamed plastics. Typical polymers are polyesters, polyamides, 
polyurethanes, polyolefins, nitrile polymers such as polyacrylonitrile, 
vinyl polymers such as vinyl chloride, styrene polymers and copolymers 
such as acrylonitrile-butadienestyrene compositions. 
The general reaction of the process for the production of hydrogen 
phosphonates is based upon the use of formic acid with a 
phosphorohalidite, such as a phosphorochloridite, represented in the 
process below by the structure, 
##STR9## 
where R is an alkylene, or haloalkylene group of a 1,2-glycol having from 
2 to 8 carbon atoms, or of a 1,3 glycol having from 3 to 8 carbon atoms, 
and Z is Cl or Br. An example is: 
##STR10## 
Examples of specific useful phosphorochloridites are the 
bis(phosphorochloridites), such as 
3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro 5.5!undecane, 
##STR11## 
corresponding bromo derivative; 
2-chloro-5,5-bis(bromomethyl)-1,3,2-dioxaphosphorinane, 
##STR12## 
and the related phosphorochloridites, 
2-chloro-5,5-dimethyl-1,3,2-dioxaphosphorinane, and 
2-chloro-5-ethyl-5-methyl-1,3,2-dioxaphosphorinane, and 
2-bromo-5,5-bis(chloromethyl)-1,3,2-dioxaphosphorinane, and 
2-chloro-5-phenyl-1,3,2-dioxaphosphorinane, and 
2-chloro-5-(4-fluoro-3-bromophenyl)-1,3,2-dioxaphosphorinane. 
The process of converting cyclic phosphorochloridites to cyclic hydrogen 
phosphonates can also be applied to five-membered ring 
phosphorochloridites, e.g., 4,5-dimethyl-2-chloro-1,3,2-dioxaphospholane, 
2-chloro-1,3,2-dioxaphospholane, 2 butyl-1,3,2-dioxaphospholane, 
4-chloromethyl-1,3,2-dioxaphospholane, and 
4-methyl-1,3,2-dioxaphospholane. 
The method of treating cyclic phosphorochloridites with formic acid 
provides an improved process for producing cyclic hydrogenphosphonates, 
sometimes called cyclic phosphites. Some earlier workers in this area of 
phosphorus chemistry have also called these compounds cyclic hydrogen 
phosphites, but preferable general terminology is to call these compounds 
cyclic hydrogenphosphonates because it better describes the predominant 
pentavalent state of the phosphorus. A number of methods are known for 
preparing cyclic hydrogenphosphonates, such as the use of triethylamine as 
an acid-binding agent in the hydrolysis of cyclic chlorophosphites (cyclic 
phosphorochloridites). In this procedure, an amine hydrochloride is 
produced as a by-product, and this must then be separated from the desired 
cyclic hydrogenphosphonate. 
In the above process, using formic acid instead of water, the by-products 
are anhydrous hydrogen chloride and carbon monoxide, gaseous products 
which are easily removed, leaving easily isolated cyclic 
hydrogenphosphonate. For example, when attempts were made to prepare 
3,9-H-3,9-dioxo-2,4,8,10-tetraoxa-3,9-diphosphaspiro 5.5!undecane(I), 
##STR13## 
by treatment of 
3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphospiro 5.5!undecane with water 
by the prior art procedures, none of the desired product could be isolated 
from the mixture of side reaction products. However, when formic acid is 
used according to the present invention, essentially pure and easily 
isolated compound I is obtained. 
Catalysts are unnecessary in the above process for preparing hydrogen 
phosphonates. A solvent is generally unnecessary when formic acid is used 
for conversion of cyclic phosphorochloridites to cyclic 
hydrogenphosphonates. Inert solvents or suspending liquids, e.g. 
acetonitrile, benzene and 1,2-dichloroethane, can however be used to aid 
mixing and temperature control. 
The reaction is usually carried out by the addition of formic acid to the 
stirred phosphorochloridite at 10.degree. to 100.degree. C, preferably 
30.degree. to 70.degree. C, while allowing the by-products hydrogen 
chloride (or hydrogen bromide) and carbon monoxide to be expelled through 
a condenser and then trapped or absorbed by suitable and safe methods such 
as neutralization. In one case, this mixture of gases is passed into a 
stirred suspension of aluminum trichloride and toluene to produce 
p-tolualdehyde by the Gatterman-Koch Reaction, thus confirming the 
composition of the effluent gases and demonstrating a practical by-product 
recovery application. 
The process for the preparation of the said derivatives or adducts, e.g., 
the azomethine, sulfonyl isocyanate, isocyanate or isothiocyanate 
derivatives, is carried out at 0.degree. to 100.degree. C. No solvent is 
necessary, although inert solvents such as benzene, toluene and 
chlorobenzene may be used. 
For the process, a basic catalyst is desirable. Examples of presently 
useful basic catalysts are, e.g. the heterocyclic nitrogen bases such as 
N-methylmorpholine, pyridine, quinoline, N-ethylpiperidine, picoline, 
quinaldine, 4-methylpyrinidine, or N-phenylpyrazole; the tertiary amines 
such as triethylamine, trimethylamine, tri-tert-butylamine, 
N,N-dimethylaniline, N-benzyl-N-methylaniline, and alkylene polyamines 
such as triethylenediamine; quaternary ammonium compounds such as 
benzyltrimethylammonium methoxide or tetrabutylammonium butoxide; alkali 
metal alkoxides such as sodium or potassium methoxide or propoxide, etc. 
The quantity of catalyst to be used will depend upon the nature of the 
azomethine isocyanate, and cyclic hydrogenphosphonate, obviously the more 
reactive reactants will require less catalyst than will the somewhat more 
sluggish reaction components. Whether or not a diluent is used will 
likewise regulate catalyst quantity. Also variable is the temperature at 
which reaction is effected; for, here again must be taken into 
consideration the nature of the reactants, catalyst quantity, and whether 
or not a diluent is used. The reaction is generally exothermic; hence the 
present addition reactions can be conducted at ordinary room temperature 
or even at decreased temperatures, but heating of the reaction mixture may 
be needed to complete the reaction. All of these variables, i.e. catalyst 
quantity, use of diluent and temperature conditions can readily be arrived 
at by easy experimentation. 
The cyclic hydrogenphosphonates and azomethines react according to the 
following equation to produce products of the present invention. 
##STR14## 
An example of the reaction of sulfonylisocyanates with cyclic 
hydrogenphosphonates is illustrated by the following equation. 
##STR15## 
Isothiocyanates and cyclic hydrogenphosphonates react similarly as 
represented in the following equation. 
##STR16## 
The compounds of the present invention are useful in flame-retardant 
materials. The method of testing flame-retardant properties is A.S.T.M. 
Designation D 2863-70, entitled "Standard Method of Test for Flammability 
of Plastics Using the Oxygen Index Method." 
In the oxygen index (OI) testing procedure the relative flammability of a 
plastic material such as nylon, or polyethylene terephthalate is 
determined by measuring the minimum concentration of oxygen in a slowly 
rising mixture of oxygen and nitrogen that will just support combustion. 
Consequently the oxygen index expresses such minimum concentration of 
oxygen, expressed as volume percent, in a mixture of oxygen and nitrogen 
that will just support combustion. 
The test is conducted by burning the material in a test column which is a 
heat resistant glass tube of 75 mm minimum inside diameter and 450 mm 
minimum height. At the bottom of the tube is a bed of glass beads about 
100 mm deep to mix and distribute the gas mixture. Within the glass tube 
used as the test column there is a specimen holder to support the treated 
plastic material while the apparatus is supplied with oxygen and nitrogen 
flow and control devices. The apparatus is also provided with an igniter 
which is a separate tube through which a combustible gas such as natural 
gas is used to ignite the test specimen. In the present testing program 
glass scrim supported molded sheets of nylon or polyethylene terephthalate 
ca. 0.2 mm thick and about 25 mm by 100 mm in size are used as the test 
specimens which are prepared from nylon or polyethylene terephthalate 
powder and 1% to 20.degree. by weight of the fire retardant additive; the 
data in the present work correspond to about 10% by weight of additive. As 
a result of the molding of the organic polymer, e.g, nylon or polyethylene 
terephthalate, and the additive, an intimate admixture or melt of the 
molecules of the components is obtained. 
In conducting the test, the specimen is clamped in the holder in the test 
column after which the desired initial concentration of oxygen is 
introduced to the ignited specimen. A number of tests are conducted to 
determine the minimum concentration of oxygen that will just support 
combustion. 
The present condensation products are useful in combination with organic 
polymers generally to reduce combustibility. The normally flammable 
organic polymers which are rendered fire retardant in accordance with the 
invention may be natural or synthetic but are preferably a solid synthetic 
polymer, more preferably a nylon or ester type polymer. Examples of the 
polymer are cotton, wool, silk, paper, natural rubber, and paint, and also 
the high molecular weight homopolymers and copolymers of amides, e.g., 
(nylon 6,6 and nylon 6). Other polymers include esters such as 
polyethylene terephthalate, and polymers of other unsaturated aliphatic 
and aromatic hydrocarbons, e.g. ethylene, propylene, butylene, styrene, 
etc., and also acrylic polymers, e.g., polyacrylonitrile, polymethyl 
methacrylate, alkyd resins, as well as cellulose derivatives, e.g., 
cellulose acetate, methyl cellulose, etc. Still other polymers include 
epoxy resins, furan resins, isocyanate resins such as polyurethanes, 
melamine resins, vinyl resins such as polyvinyl acetate and polyvinyl 
chloride, resorcinol resins, synthetic rubbers such as polyisoprene, 
polybutadiene-acrylonitrile copolymers, butadiene-styrene polymers, butyl 
rubber, neoprene rubber, ABS resins and mixtures thereof. Since the 
compositions of the invention are unusually effective flame retardants 
they are normally combined in flame retarding proportions with the organic 
polymer at relatively low concentrations, e.g., about 1-20 wt. %, 
preferably about 3-15% based on additive plus the polymeric substrate, 
such as by milling, or impregnation, e.g., from a water or alcohol 
dispersion or solution or by dissolving or dispersing in the molten 
polymer before extrusion such as in the form of fibers or sheets. It 
should be noted that it is within the scope of the invention to 
incorporate such ingredients as dyes, pigments, stabilizers, antioxidants, 
antistatic agents and the like into the novel compositions.

The following examples illustrate specific embodiments of the invention but 
are not restrictive of the scope of the invention: 
EXAMPLE 1 
A stirred mixture of 0.1 mole each of the cyclic hydrogenphosphonate, 
5,5-bis(bromomethyl)-2-H-2-oxo-1,3,2-dioxaphosphorinane, having the 
structure, 
##STR17## 
and of phenyl isocyanate in 50 ml. of benzene is treated with 6-8 drops of 
triethylamine. This causes a temperature increase of about 45.degree. C, 
and a solid product separates. The mixture is warmed to 80.degree. C, 
filtered while hot, and the solid product is washed with benzene and 
dried, giving a white solid, m.p. 167.degree.-169.degree. C, .sup.31 P nmr 
10.8 ppm, which is 
5,5-bis(bromomethyl)-2-oxo-2-(phenylcarbamoyl)-1,3,2-dioxaphosphorinane, 
having the structure, 
##STR18## 
Other basic catalysts which accomplish the same result are 
N-ethylpiperidine; N,N-dimethylaniline; triethylenediamine; 
tetrabutylammonium butoxide; and sodium methoxide. 
Analogous cyclic phosphorus compounds are obtained when other isocyanates 
and isothiocyanates are used, specifically p-toluenesulfonylisocyanate, 
methyl sulfonylisocyanate, ethyl sulfonylisocyanate, 
phenylsulfonylisocyanate, chlorophenylsulfonyl isocyanate, 
p-nitrophenylsulfonylisocyanate, p-nitrophenylisocyanate, allyl 
isocyanate, p-chlorophenylisocyanate, 2-fluorophenylisocyanate, 
.alpha.,.alpha.,.alpha.-trifluoro-m-tolyl isocyanate, methyl isocyanate, 
and 3-bromophenylisocyanate. Examples of other isothiocyanates that can be 
used to prepare analogous cyclic phosphorus compounds are: 
allylisothiocyanate, ethyl isothiocyanate, 4-fluorophenyl isothiocyanate, 
naphthyl isothiocyanate, methyl isothiocyanate, and 4-chloro-2-naphthyl 
isothiocyanate. 
EXAMPLE 2 
A mixture of 0.1 mole of 
3,9-H-3,9-dioxa-2,4,8,10-tetraoxa-3,9-diphosphaspiro 5.5!undecane, having 
the formula shown below: 
##STR19## 
and 0.22 mole of phenyl isocyanate in 100 ml. of benzene is stirred as 
triethylamine is added dropwise, and the mixture is warmed to reflux. An 
additional 50 ml. of benzene is added to aid stirring. The temperature is 
kept at 70.degree. to 80.degree. C for 1 hr, and then the reaction mixture 
is filtered while hot. The solid product is washed with benzene, water, 
and acetone, giving a white solid, m.p. 229.degree.-232.degree., .sup.31 P 
nmr 8.9 ppm, which is 
3,9-dioxo-3,9-bis(phenylcarbamoyl)-2,4,8,10-tetraoxa-3,9-diphosphaspiro 5. 
5!undecane, 
##STR20## 
EXAMPLE 3 
A mixture of 0.1 mole of 
5,5-bis(bromomethyl)-2-H-2-oxo-1,3,2-dioxaphosphorinane, having the 
structure, 
##STR21## 
and 0.1 mole of benzylidenemethylamine in 100 g. of benzene is stirred and 
warmed at 45.degree.-50.degree. C for 1 hr. The reaction mixture is then 
cooled and filtered. The solid collected is washed with benzene and then 
dried at 65.degree./0.15 mm., giving a white solid, m.p. 
93.0.degree.-95.5.degree., .sup.31 P nmr -19.0 ppm, that is 
5,5-bis(bromomethyl)-2- .alpha.-(methylamino)benzyl!-2-oxo-1,3,2-dioxaphos 
phorinane, 
##STR22## 
Analysis - Calcd. for C.sub.13 H.sub.18 Br.sub.2 NO.sub.3 P: 36.56C; 4.25H; 
37.42 Br; 3.28N; 7.25P. Found: 36.46C; 4.24H; 37.42 Br; 3.24N; 7.38P. 
EXAMPLE 4 
Similarly, the hydrogen phosphonate of Example 2 reacted with 
benzylidenemethylamine gives a white solid, m.p. 174.degree.-182.degree. 
C, .sup.31 P nmr -19.6 ppm, which is 
3,9-bis .alpha.-(methylamino)-benzyl!-3,9-dioxo-2,4,8-10-tetraoxa-3,9-diph 
osphaspiro 5.5!undecane, 
##STR23## 
Similar products are obtained when using benzylideneethylamine, 
p-chlorobenzylidenemethylamine, or methylbenzylidenemethylamine. 
EXAMPLE 5 
A mixture of 30.8g. of the hydrogenphosphonate used in Example 1 and 19.7 
g. of p-toluenesulfonylisocyanate in 100g of benzene is stirred under 
nitrogen and warmed at 45.degree.-50.degree. C for 1 hr. The reaction 
mixture is then cooled and filtered. The solid collected is recrystallized 
from benzonitrile, giving a white solid, m.p. 179.degree.-186.degree., 
.sup.31 P nmr 10.3 ppm, which is 
5,5-bis(bromomethyl)-2-(p-toluenesulfonylcarbamoyl)-1,3,2-dioxaphosphorina 
ne, 
##STR24## 
Analogous cyclic phosphorus compounds are obtained when other sulfonyl 
isocyanates are used in the same reaction, e.g. 
p-toluenesulfonylisocyanate, methyl sulfonylisocyanate, ethyl 
sulfonylisocyanate, phenylsulfonylisocyanate, chlorophenylsulfonyl 
isocyanate, and p-nitrophenylsulfonylisocyanate. 
EXAMPLE 6 
A mixture of 0.1 mole of the starting hydrogenphosphonate of Example 2 and 
0.2 mole of allyl isothiocyanate in 200 ml of dimethylformamide and 20g of 
triethylamine is stirred and warmed at 65.degree. C for 1 hr. The reaction 
mixture is then stripped to 80.degree. C at reduced pressure, and the 
residue is recrystallized from benzene-acetonitrile and from 
o-dichlorobenzene, giving yellow solid, m.p. 230.degree. (dec.), .sup.31 P 
nmr 10.2 ppm, which is 
N,N'-diallyl-3,9-dioxo-2,4,8,10-tetraoxa-3,9-diphosphaspiro 5.5!undecane-3 
,9-dithiocarboxamide, 
##STR25## 
Analysis- Calcd. for C.sub.13 H.sub.20 N.sub.2 O.sub.6 P.sub.2 S.sub.2 : C, 
36.62; H, 4.73; N, 6.57; P, 14.53; S, 15.04. Found: C, 36.66 H; 4.73; N, 
6.52; P, 14.62; S, 15.15. 
Examples of other isothiocyanates that can be used to prepare analogous 
cyclic phosphorus compounds are: allylisothiocyanate, ethyl 
isothiocyanate, 4-fluorophenyl isothiocyanate, naphthyl isothiocyanate, 
methyl isothiocyanate, and 4-chloro-2-naphthyl isothiocyanate. 
EXAMPLE 7 
Flame retardancy tests are conducted using typical compounds of the 
invention, specifically the compounds of the above examples. These 
compounds do not burn readily when subjected to heat and a flame, and they 
also improve the flame retardant properties of polyamides, specifically 
nylon-6,6 and of polyethylene terephthalate, at concentrations of 1-20% by 
weight, preferably 3-15% by weight, based upon the total mixture, obtained 
by milling, or impregnation or by dissolving or dispersing in the polymer 
in molten form before extrusion such as in the form of fibers or sheets. 
It should be noted that it is within the scope of the invention to 
incorporate such ingredients as dyes, pigments, stabilizers antioxidants, 
antistatic agents, and the like into the novel compositions. 
Test data of the oxygen index test described above for certain compounds at 
10% in polyethylene terephthalate are set forth below: 
______________________________________ 
Compound of Example O-I Value 
______________________________________ 
1 25.7 
2 24.5 
3 24.5 
4 23.5 
______________________________________ 
The azomethine, sulfonyl isocyanate, isocyanate, and isothiocyanate, 
derivatives of the invention, as a group have flame retardant properties 
for polyethylene terephthalate and also polyamides such as nylon 6,6.