FLUOROALKYL PHOSPHORUS COMPOUNDS 

NGP ELEMENT: 4D/14/1 

J. Douglas Mather, Ph. D. 

Chemical Development Studies, Inc. 

7636 William Moyers Ave. NE 

Albuquerque, NM 87122 

505-797-9706 

dougmather@speakeasy.net

Robert E. Tapscott, Ph.D. 

GlobeTech Inc. 

8200 Montgomery Blvd. NE 

Albuquerque, NM 87109 

505-883-9399 

GlobeTech@speakeasy.net

Professor Jean’ne M. Shreeve 

Chemistry Department 

University of Idaho 

Moscow, Idaho 83844 

208-885-6215 

jshreeve@uidaho.edu

Dr. Rajendra P. Singh 

Advance Research Chemicals, Inc. 

5005 N. Skiatook Road 

Catoosa, OK 74014 

918 266-6789 

rsingh@fluoridearc.com

ABSTRACT 

In work sponsored by the Next-Generation Fire Suppression Technology Program, 

research efforts at the New Mexico Engineering Research Institute extended earlier 

promising studies on alkyl phosphorus compound flame extinguishment performance to 

the study of several new partially and fully fluorinated alkyl phosphorus compounds from 

the phosphine and phosphonate families[1]. 

Researchers have demonstrated that phosphorus compounds appear to provide a chemical 

fire extinguishment mechanism, and in fact some appear to be highly effective flame 

extinguishants. Much reported work has been performed on dimethyl methyl 

phosphonate (DMMP) and related compounds [2,3]. Though DMMP shows very 

promising flame suppression characteristics, this compound and most of the related 

compounds studied to date have serious practical drawbacks. Specifically, most of the 

standard phosphorus compounds studied to date are flammable and have low vapor 

pressures. 

For phosphorus based compounds to be employed as fire extinguishant compounds 

effective nonflammable and lower boiling structures needed to be identified. 

The introduction of one or more polyfluoroalkyl or polyfluoroalkoxy moieties, e.g., 

[O=P(OCH3)2-n(OCF3)n CH3] (n = 1, 2) or [O=P(OCH3)2CF3] offers an opportunity to 

minimize or possibly eliminate both of these unfavorable properties. Of particular initial 

interest for testing is the totally fluorinated trimethoxy phosphonate O=P(OCF3)3, which 

has a boiling point of 32 oC [4]. 

This project involved the initial selection of eight promising fluoroalkyl- and 

hydrofluoroalkyl-substituted phosphorus compounds followed by their synthesis in the 

laboratory of Dr. Jean’ne Shreeve at the University of Idaho. Seven of the eight 

fluoroalkyl and hydrofluoroalkyl phosphorus compounds targeted for synthesis were 

ultimately prepared for flame extinguishment characterization using the NMERI Cupburner. 
INTRODUCTION 

A number of compounds of silicon, phosphorus, and other materials based on chemical 

elements other than carbon have been examined as fire extinguishants and possible 

replacements for Halon 1301[5]. Of particular interest have been compounds of 

phosphorus [1]. Phosphorus compounds appear to provide a chemical fire 

extinguishment mechanism, and some appear to be highly effective [6]. 

Phosphorus compounds show extraordinary effectiveness as flame extinguishants, and 

there is evidence for a chemical mechanism. Most work to date, however, has 

emphasized alkyl phosphonates and other nonhalogenated phosphorus-containing esters 

or phosphonitriles. The former compounds are often flammable and both types of 

compounds have low volatilities. Incorporation of fluorine in the alkyl structures 

appeared to be a viable approach to reducing compound boiling point and decreasing

flammability. The effect of fluorine on toxicities of the phosphorus compounds, 

however, is unknown. 

One way to address both problems of flammability and low volatility is to work with 

phosphorus compounds containing fluoroalkyl or hydrofluoroalkyl groups. These groups 

have the potentially of lower boiling points and reduction in the presence of hydrogen 

atoms contributes to a reduction in flammability. For example, tris(2,2,2-

trifluoroethyl)phosphite (P(OCH2CF3)3 ,TFEP) had a cup burner extinguishment 

concentration of 1.78 vol.% for n-heptane fuel [7]. This can be compared with the 

concentration of approximately 3 vol% for Halon 1301. TFEP has a normal boiling point 

of approximately 131° C compared to 181° C for DMMP and is non flammable. 

There is still, however, a major problem with TFEP. Though the volatility is improved, it 

is still not nearly what one would like for application as a fire suppressant. For that 

reason, one needs to examine fluoroalkyl phosphorus compounds with lower molecular 

weights. The compound O=P(OCF3)3, tris(trifluoromethyl)phosphate, has been reported 

to have a normal boiling point of 32 C. The hypothetical compound P(OCF3)3, 

tris(trifluoromethyl)phosphite should also have significant volatility as its reported 

boiling point is 32o C. 

Several phosphorus compounds representing alkyl phosphonates and phosphines (+5 and 

+3 oxidation states, respectively) containing fluoroalkyl and hydrofluoroalkyl groups, 

were identified for acquisition based on predictions of the success of available synthetic 

methods. Expectations of nonflammablity due to replacement of alkyl hydrogen's with 

fluorine in these new compounds were balanced by a recognition that increased 

fluorination could well result increased instability to air. 

COMPOUND SELECTION

Compound selection guidelines were identified to rule out compounds likely to be 

flammable, susceptible to hydrolysis, or toxic. Compounds such as PH3 or P(CH3)3 were 

ruled out as being flammable while compounds involving P-F bonds were ruled out due 

to expected hydrolysis and unacceptable toxicity. 

Fluoroalkyl and hydrofluoroalkyl phosphorus compounds containing substituent groups -

CF3, -CF2H, -CH2CF3, -CF2CH2F, -CF2CF3, and/or related structural isomers were 

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identified as unlikely to suffer the problems of flammability, hydrolysis and toxicity 

while possibly achieving the lower boiling points desired. These expectations were not 

fully realized as will be described further on in this report. The compounds selected for 

synthesis are listed in Table 1. 

Table 1. Selected Target Compounds 

# Compound Formula

1 Tris(trifluoromethyl) Phosphonate O=P(CF3)3

2 Bis(trifluoromethyl)methoxy Phosphine P(OCH3)(CF3)2

3 Tris(2,2,2-trifluoroethoxy) Phosphine P(OCH2CF3)3

4 Bis(trifluoromethyl) trifluoromethoxy

Phosphonate 

O=P(OCH3)(CF3)2

5 Bis(2,2,2-trifluoroethoxy) trifluoromethyl 

Phosphine 

P(OCH2CF3)2CF3

6 Bis(trifluoromethyl) 2,2,2-trifluoroethoxy

Phosphine 

P(OCH2CF3)(CF3)2

7 Bis(trifluoromethyl) 2,2,2-trifluoroethoxy

Phosphonate 

O=P(OCH2CF3)(CF3)2

8 Tris(trifluoromethoxy) Phosphonate O=P(OCF3)3

The compounds listed represent a range of related structures and include both phosphine 

and phosphonate compounds. Including in the study both P(III) and P(V) phosphorus 

oxidation states as well as incorporating, where possible, similar fluorinated substituents 

increases the probability of identifying promising chemical families. Promising 

compounds would serve as guides to future research and compound synthetic efforts. 

SYNTHETIC APPROACH 

The compounds were synthesized utilizing bench top and vacuum line procedures. Each 

of the products was purified and then characterized, as needed for structure verification, 

by 19F, 31P and 13C NMR, infrared and mass spectral measurements and by elemental 

analysis. The syntheses performed as well as relevant literature references are briefly 

described below. 

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Synthesis 1: 

This two step synthesis involved reaction of red phosphorus with CF3I forming the 

flammable intermediate (CF3)3P followed by an oxidation insertion reaction with nitrous 

oxide and nitrogen dioxide to form the phosphonate, (CF3)3P=O[8]. 

Step 1. 

 232° C, 60hr 

Red Phosphorus + CF3I ————————h P(CF3)3 (52% yield) 

Step 2. 

 NO2 

P(CF3)3 —————h (CF3)3P=O (100 % yield) 

Synthesis 2: 

The (CF3)2PI formed as one of the products in 25% yield from the reaction of CF3I and 

red phosphorus was reacted at 25  ̊C with AgCl to form (CF3)2PCl in ~100% yield. The 

chloride was subsequently reacted with methanol in the presence of triethyl amine [9]. 

 CH3OH 

(CF3)2PCl —————h (CF3)2POCH3 (85% yield) 

 (CF3CH2)3N 

Synthesis 3: 

The synthesis of P(OCH2CF3)3 was carried out by adding trifluoroethanol dropwise into a 

vigorously stirring solution of phosphorus trichloride (slight excess) at 0 ̊C. After five 

hours, fractional distillation gave the desired product. 

PCl3 + CF3CH2OH —————h P(OCH2CF3)3 (100% yield) 

Synthesis 4: 

The (CF3)2POCH3 was oxidized with a slight molar deficiency of nitrogen dioxide as in 

Synthesis l. The NO was removed under vacuum. 

 NO2 

(CF3)2POCH3 —————h (CF3)2P(O)OCH3 (100% yield) 

Synthesis 5: 

This synthesis is very similar to Synthesis 2 above. 

 2eq CF3CH2OH 

(CF3)PCl2 ———————h (CF3)P(OCH2CF3)2 

 2eq (CF3CH2)3N 

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Synthesis 6: 

This synthesis is very similar to Synthesis 2 above. 

 CF3CH2OH 

(CF3)2PCl ———————h (CF3)2POCH2CF3

 (CF3CH2)3N 

Synthesis 7: 

This synthesis is very similar to Synthesis 4 above. 

 NO2

(CF3)2POCH2CF3 ———————h (CF3)2P(O)OCH2CF3

Synthesis 8: 

This synthesis attempt was unsuccessful but very similar to Synthesis 1 in execution. 

 O2

(CF3)3P ———————h (CF3O)3P=O (reaction failed to yield isolable product) 

The synthetic products of the above reaction are summarized in Table 2. Final product 

weights and boiling points are listed. 

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Table 2. Compound Synthesis Status and Boiling Points 

# Compound - Formula Boiling Point oC Synthetic 

product 

weight (g) 

1 Tris(trifluoromethyl) Phosphonate 

O=P(CF3)3

32o C 7.3 

2 Bis(trifluoromethyl)methoxy Phosphine,

P(OCH3)(CF3)2

55o C 5.3 

3 Tris(2,2,2-trifluoroethoxy) Phosphine, 

P(OCH2CF3)3

130o C @ 743 mm 50.0 

4 Bis(trifluoromethyl) trifluoromethoxy

Phosphonate, O=P(OCH3)(CF3)2

42o C @ 745 mm 5.5g 

5 Bis(2,2,2-trifluoroethoxy) trifluoromethyl 

Phosphine, P(OCH2CF3)2CF3

111o C 7.2 

6 Bis(trifluoromethyl) 2,2,2-trifluoroethoxy

Phosphine, P(OCH2CF3)(CF3)2

25o C @ 50mm 6.5 

7 Bis(trifluoromethyl) 2,2,2-trifluoroethoxy

Phosphonate, O=P(OCH2CF3)(CF3)2

130o C (estimate) 7.0 

8 Tris(trifluoromethoxy) Phosphonate,

O=P(OCF3)3

32o C Not 

synthesized 

CUP-BURNER FLAME EXTINGUISHMENT TESTING

Cup burner evaluation and air stability observations were performed at the University of 

New Mexico. The University currently operates two different cup burners, the NMERI 

Standard Cup Burner and the larger ISO Cup Burner. The smaller NMERI Standard Cup 

Burner was employed for this project due to the reduced requirement for agent for 

testing. Due to the limited amount of compound to be prepared (5 to 10 grams) the cupburner methodology employed provides an upper bound extinguishment concentration 

which is expected to be slightly higher than the actual minimum extinguishment 

concentration. 

In view of the wide range of boiling points represented by the compounds synthesized, a 

means for preventing the condensation on to cooler surfaces and countering the 

evaporative cooling effects of the nebulized agent as it is dispersed into the air stream of 

the cup-burner was required. These issues were addressed using a preheater for the inlet 

air stream. Heating the inlet air to between 50 and 55 oC counteracted the evaporative 

cooling effects of the misted agent at the tip of the nebulizer and enhanced droplet 

vaporization. On mixing with the cooler nebulized agent/air stream, the column

temperature drops to between 45 to 50 oC. The preheated air was also employed to warm

the entire cup-burner chimney prior to a test run and as a result no condensation of agent 

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was observed during or following extinguishment testing. Extinguishment testing results 

are summarized in Table 3. 

All compounds tested were shipped and stored in sealed glass vials prior to use and were 

tested immediately on opening. Generally opening the vials and exposing the liquid 

contents to air was not particularly remarkable, Table 4. However, in two cases the 

compounds reacted quite vigorously on air exposure. Extremely vigorous reaction on air 

exposures occurred for compound 2, bis(trifluoromethyl)methoxy phosphine, 

P(OCH3)(CF3)2, and compound 6, bis(trifluoromethyl) 2,2,2-trifluoroethoxy phosphine, 

P(OCH2CF3)(CF3)2, on breaking open their respective glass sealed vials. This reaction 

occurred as air entered and contacted the liquid agent. It seems very likely that both 

compounds would react, at least partially, to form unknown products prior to entering the 

flame zone. For each compound extinguishment testing started at air concentrations of 5 

vol. % and followed by retests at progressively lower air concentrations until either the 

sample of test compound was exhausted or extinguishment failed to occur. 

Figure 1. Sample nebulizer and air pre-heater.

The nebulizer employed in this apparatus is a standard feature in all atomic emission 

inductively coupled spectrometers. These devices readily aspirate samples at rates of 1 to 

3 cc’s per minute at air pressures of ~40psig. They can also be forced to higher levels of 

output by employing a syringe pump or similar device. Two air flows are employed in 

this experimental setup. The first aspirates the sample and the second provides a makeup 

air flow bringing the total air flow to nominally 10 l/min. in the cup-burner. Air 

requirements were met using a regulated air flow from a storage tank supplied in turn by 

an oil-less 3hp compressor. Air flows were set and monitored using a mass flow meter. 

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Figure 2. Cup-burner equipped with sample nebulizer and evaporation column 

Table 3. Summary of Cup-Burner Results 

# Compound, Formula Cup-burner Testing 

1 Tris(trifluoromethyl) Phosphonate, O=P(CF3)3 No extinguishment 5% 

2 Bis(trifluoromethyl)methoxy Phosphine, P(OCH3)(CF3)2 Spontaneously ignites 

w/air * 

3 Tris(2,2,2-trifluoroethoxy) Phosphine, P(OCH2CF3)3 3.1%

4 Bis(trifluoromethyl) trifluoromethoxy Phosphonate, 

O=P(OCH3)(CF3)2

4.6% 

5 Bis(2,2,2-trifluoroethoxy) trifluoromethyl Phosphine, 

P(OCH2CF3)2CF3

3.0% 

6 Bis(trifluoromethyl) 2,2,2-trifluoroethoxy Phosphine, 

P(OCH2CF3)(CF3)2

1.8% 

7 Bis(trifluoromethyl) 2,2,2-trifluoroethoxy Phosphonate, 

O=P(OCH2CF3)(CF3)2

No extinguishment 

 @ 5% 

8 Tris(trifluoromethoxy) Phosphonate, O=P(OCF3)3 Not synthesized

*Note: In view of the low cup-burner test value of compound 6, the structurally similar 

compound 2 was preserved in order to provide a future opportunity to identify the 

product of its reaction with air. 

8
Air sensitivity evidenced by a fuming reaction on exposure to air was observed in most 

but not all cases. These observations were made on opening the sealed glass vials all 

compounds were shipped and stored in. In view of the low cup-burner test value of 

compound 6, the structurally similar compound 2 was preserved in order to provide an 

opportunity to identify the product of its reaction with air. It is likely that compound 6 

undergoes an air oxidation to yield a phosphonate structure O=P(OCH2CF3)(CF3)2 or a

undergoes oxygen insertion reactions of the P-CF3 bonds. Air reactivity observations are 

summarized in Table 4. 

Table 4. Air Stability Observations 

# Compound - Formula Observation

1 Tris(trifluoromethyl) Phosphonate 

O=P(CF3)3

No white fumes, does 

not ignite cloth 

2 Bis(trifluoromethyl)methoxy Phosphine,

P(OCH3)(CF3)2

White fumes, ignites 

spontaneously 

3 Tris(2,2,2-trifluoroethoxy) Phosphine, 

P(OCH2CF3)3

No fumes, no ignition 

4 Bis(trifluoromethyl) trifluoromethoxy

Phosphonate, O=P(OCH3)(CF3)2

Some fumes, no ignition 

5 Bis(2,2,2-trifluoroethoxy) trifluoromethyl 

Phosphine, P(OCH2CF3)2CF3

Some fumes, no ignition 

6 Bis(trifluoromethyl) 2,2,2-trifluoroethoxy

Phosphine, P(OCH2CF3)(CF3)2

Ignites cloth, no 

spontaneous ignition, 

fumes strongly 

7 Bis(trifluoromethyl) 2,2,2-trifluoroethoxy

Phosphonate, O=P(OCH2CF3)(CF3)2

No white fumes, does 

not ignite cloth 

8 Tris(trifluoromethoxy) Phosphonate,

O=P(OCF3)3

Not synthesized 

OBSERVATIONS AND CONCLUSIONS 

Phosphonates P (V), having only -CF3 groups are possibly too stable to react in flame. 

When compound 1, tris(trifluoromethyl) phosphonate O=P(CF3)3 , was tested at 5 vol. % 

no evidence of flame lift-off was observable Compound 4, a phosphonate, showed lift-off 

and flame extinguishment well below 5 vol. %. Compound 7, also a phosphonate, 

showed lift-off but no flame extinguishment at 5 vol. %. Limited data (compounds 1, 4, 

and 7) also suggest that phosphonates may need sufficient hydrogen atoms in their 

structures to enable compound break down in the flame zone in order to become

chemically active as combustion suppressants. 

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Only compound 4 approached the desired boiling point range. In the trade-off between 

higher degrees of fluorination to reduce the boiling point and moderate hydrogenation for 

efficient fire suppression, there may limited further promise in this family of compounds. 

This conclusion must be tempered by the observed low cup-burner test value (1.8%) of 

compound 6 and the tentative conclusion that it is likely that air reaction is converting it 

to a very efficient flame suppressant. It can not, however, be concluded at this point that 

the air oxidation produces a complete conversion to a single compound or that the 

reaction is complete by the time the products enter the flame zone. 

The more volatile phosphine P (III) compounds with -CF3 groups tend to be 

spontaneously flammable while those with fluoroethoxy groups were relatively stable 

(compound 3). Phosphenes in general span a wide range of air (O2) reactivities. Some

are air stable while other are quite air reactive. P(CF3)3 is known to spontaneously ignite 

on air exposure while trimethylphosphine - P(CH3)3 is relatively air stable. Phosphines

(compounds 2, 3, 5, and 6) illustrate this range of air reactivities. While the higher 

boiling compounds clearly are not of practical value by themselves for aircraft 

application, they could be incorporated in solid propellant gas generation devices where 

adequate heat is available to fully vaporize, disperse, and possibly initiate the thermal 

breakdown of the compound. The possibility that some of these compounds decompose 

on air exposure to yield highly effective flame extinguishants is tantalizing and the 

opportunity to implement such compounds with gas generating dispersion aids may well 

be worth investigation. Compounds with higher volatility (higher fluorine content) tend 

toward spontaneous flammability. 

Finally, in earlier work tris(2,2,2-trifluoroethoxy)phosphine (P(OCH2CF3)3 ,TFEP) had 

been reported to have a cup burner extinguishment concentration of 1.78 vol.% for nheptane fuel [7]. This value is much lower than that observed here, and differences in 

manner of sample vaporization could well be responsible. In the earlier studies a hot 

sand bath (>250o C) was employed to volatilize the compound as it was introduced into 

the base of the cup-burner. It is possible this method induced thermal decomposition and 

air reaction of the test compound yielding a more effective flame suppressant. 

RECOMMENDATIONS

Several directions for further work in this area present themselves. While the testing 

reported here exposed real limitations to phosphorus compounds as fire suppressants it 

also provided, as initially hoped, a basis for more focused research of promising 

compound structural areas. 

• Compound 6, though air reactive, yielded on testing, an impressively low cupburner value. It is possible this low cup-burner value was due to a break down 

product whose air concentration is actually significantly lower than 1.8%. 

Identification and study of compound 6 (or compound 2) air reaction products 

may lead to significant advancements in phosphorus base suppressants for 

aircraft applications; 

• The break down products of compounds 2 and 6 are predicted to be oxidation 

products containing P=O and P-O-fluoroalkane groups. Some of these 

compounds might (as indicated by compound 4’s 42o C boiling point) border 

on acceptability for aircraft applications. Additional effort directed to the 

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acquisition of fluoro-phosphorus compounds similar to P(OCH3)(CF3)2 with -

OCFH2 instead of -OCH3 is indicated; 

• The synthesis attempted of compound 8 had been reported in the literature. 

While the recent synthesis effort was unsuccessful, a realistic expectation of 

its acquisition still exists. The 32o C boiling point of compound 8 as well as 

its similarity to the structures thought to be the breakdown products from

compound 6, that are thought to possibly result in its demonstrated higher

effectiveness, make compound 8 a prime target for a further acquisition and 

testing effort; 

• Synthesis and testing of compounds where hydrogen substituted CF2H or 

CFH2 groups replace CF3 may over come the apparent lack of reactivity of

compound 1, O=P(CF3)3 which could possibly have prevented breakdown in 

the flame zone and failure to act as a flame extinguishant at the 5% initial test 

concentration. 

ACKNOWLEDGMENTS 

This research is sponsored by the US Department of Defense’s Next Generation Fire 

Suppression Technology Program funded by the DoD Strategic Environmental Research 

and Development Program 

Project COTR: Dr. Ron Sheinson 

Navy Technology Center for Safety & Survivability 

Naval Research Laboratory, Code 6185 

4555 Overlook Ave., S.W. 

Washington, DC 20375-5342 

REFERENCES 

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Volume III: Phosphorus Compounds, WL-TR-96-XX, NMERI Report No. 

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Base, Florida and Applied Research Associates, Inc., Tyndall Air Force Base, 

Florida, May 1996. 

2 MacDonald, M. A., Jayaweera, T. M., Fisher, E. M., and Gouldin, F. C., 

“Inhibition of Non-Premixed Flames by Dimethyl Methylphosphonate,” 

Technical Meeting, Central States Section of The Combustion Institute, Point 

Clear, Alabama, 27-29 April 1997. 

3 MacDonald, M. A., Jayaweera, T. M., Fisher, E. M., and Gouldin, F. C., 

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Combustion and Flame, Vol. 116, pp. 166-176, 1999. 

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4 Mahler, W., “Oxidation of Tris(trifluoromethyl)phosphine,” Inorganic Chemistry, 

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