NMERI 2003/1/34051 

FLUOROALKYL PHOSPHORUS COMPOUNDS 

Jean’ne M. Shreeve, Rajendra P. Singh, Robert E. Tapscott, and J. Douglas Mather 

Center for Global Environmental Technologies 

NEW MEXICO ENGINEERING RESEARCH INSTITUTE 

The University of New Mexico 

901 University Boulevard SE 

Albuquerque, New Mexico 87106-4339 

Final Report, April 2001 – June 2002 

July 2003 

Sponsored by: 

U. S. Department of Defense 

Strategic Environmental Research and Development Program 

The views and conclusions contained in this document are those of the authors and should not be 

interpreted as representing the official policies, either expressed or implied of the Strategic 

Environmental Research and Development Program or any other part of the U. S. Government. 
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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 

 7/22/2003

3. REPORT TYPE AND DATES COVERED 

Final Report, April 2001 – June 2002

4. TITLE AND SUBTITLE 

Fluoroalkyl Phosphorus Compounds 

5. FUNDING NUMBERS 

 DASW01-01-P-0676 

6. AUTHOR(S) 

Jean’ne M. Shreeve, Rajendra P. Singh, Robert E. 

Tapscott, and J. Douglas Mather 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

New Mexico Engineering Research Institute 

The University of New Mexico 

Albuquerque, New Mexico 87106-4339

8. PERFORMING ORGANIZATION 

REPORT NUMBER 

 NMERI 2003/1/34051

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 

The Department Of Defense 

Strategic Environmental Research and Development 

Program

10. SPONSORING/MONITORING 

AGENCY REPORT NUMBER 

11 SUPPLEMENTARY NOTES 

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE 

13. ABSTRACT (Maximum 200 words)

Under the Montreal Protocol, an international treaty, the production of the fire and explosion protection 

agent Halon 1301 (bromotrifluoromethane, CBrF3) was phased out in the United States at the end of 1993. No 

environmentally acceptable halon substitute that is equivalent to Halon 1301 in toxicity, effectiveness, and 

dimensionality has been identified. The objective of the overall effort is to assess fluoroalkyl-phosphorus 

compounds flame suppression performance. Prior studies have demonstrated that phosphorus based 

suppressants can have very effective flame suppression properties. The current study focused on overcoming 

two of the impediments (high boiling points and flammability) of the earlier studied compounds. The approach 

taken to both reduce boiling point and decrease flammability involves substitution of fluorine for hydrogen 

atoms. Additionally, this project sought to expand on this approach by exploring the fire suppression and 

physical properties of a broad range of phosphorus compound oxidation states and families (phosphonates, 

phosphites, phosphines). 

14. SUBJECT TERMS 

phosphorus, fluoroalkyl, fire, extinguishment, halon, replacement, 

15. NUMBER OF PAGES 

cup-burner, phosphonate, phosphite, phosphine 

16. PRICE CODE 

17. SECURITY CLASSIFICATION OF 

REPORT

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18. SECURITY CLASSIFICATION OF 

THIS PAGE

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ABSTRACT

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Prescribed by ANSI Std 239-18 

i 
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 UNCLASSIFIED 

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ii 
PREFACE 

This report was prepared by the Center for Global Environmental Technologies (CGET) 

Division, New Mexico Engineering Research Institute (NMERI), The University of New 

Mexico, Albuquerque, New Mexico, for the Department of Defense, Strategic Environmental 

Research and Development Program (SERDP), under Defense Supply Service-Washington 

(DSS-W) Contract DASW01-01-P-0676, NMERI Number 8-34051. This Project is element 

4D/14/1 under the Next-Generation Fire Suppression Technology Program (NGP). 

The Start Date was 11 April 2001, and the End Date was 30 June 2002. The Technical 

Program Manager is Dr. Richard G. Gann, National Institute of Standards and Technology; the 

Contracting Officer’s Technical Representative (COTR) is Dr. Ronald S. Sheinson, Naval 

Research Laboratory, and the NMERI Principal Investigator is Dr. J. Douglas Mather. Dr. 

Robert E. Tapscott served as the Deputy PI. 

NMERI 2003/1/34051 

iii 

(The reverse of this page is blank.) 
SUMMARY 

A. TASK OBJECTIVE 

The objective of this project was to expand on earlier promising evaluations of the 

potential of fluorinated alkyl phosphorus compounds to serve as fire extinguishants and 

replacements for halon 1301. Earlier halon replacement studies included a survey of “Main 

Group” compounds for their potential to serve as halon replacements. This study, among others, 

indicated promising fire suppression properties for alkylated phosphorus compounds. Two 

drawbacks, identified in these early studies, to implementation of alkyl-phosphorus compounds 

as fire suppressants were high boiling points (low vapor pressure) and the inherent flammability 

of the alkyl groups attached to the phosphorus. 

This project was conceived in order to overcome both the boiling point and the 

flammability shortcomings through the incorporation of fluorinated alkyl groups as well as 

attempt to advance the study of the flame suppression properties of a wide range of fluorinated 

alkyl-phosphorus compounds. Sufficient fluorination of alkyl-phosphorus compounds was 

expected to result in reduced boiling points and reduction in inherent flammability of alkyl 

groups bonded to the phosphorus. 

B. GENERAL METHODOLOGY 

This project required the synthesis and cup-burner flame extinguishment evaluation of 

liquid or gaseous compounds from a wide variety of fluorinated alkyl-phosphines, alkylphosphonates, and alkyl-phosphites. A wide range of compounds was chosen for study to give a 

wide range of compound stabilities, toxicities, boiling points and flame suppressant performance. 

Based on the chemistry of phosphorus and the effects of heavily fluorinated alkyl substituents, 

such a broad study could identify potentially useful trends allowing further focusing of attention 

on specific compound types and structures having the desired chemical stability, flame 

suppression efficiency, and low boiling point. This report, which includes the objectives, 

methodology, results, important findings and conclusions, and implications for further research, 

is the final project deliverable. Of particular importance in this effort is an assessment of the 

iv 
potential of fluoroalkyl-phosphorus chemical sub-families and their derivatives to provide 

compounds as Halon 1301 substitutes and the development of a list of potential compounds. 

C. TECHNICAL RESULTS 

With essentially no exception, fluoroalkyl-phosphorus compounds are expected to be 

liquids at room temperature. While this is not a desirable property, the potential of fluoroalkylphosphorus compounds to be effective fire suppressants is well established. Indeed this limited 

study has identified compound(s) evidencing significantly enhanced flame suppression 

performance though it is not known whether the compound or its air breakdown product was 

responsible. 

D. IMPORTANT FINDINGS AND CONCLUSIONS 

Few halon replacement materials with potentially acceptable fire suppression 

performance, dimensionality, and physical (primarily, volatility) and toxicological properties 

have been identified. The lowest molecular weight main group families of compounds (i.e., the 

materials with the highest volatilities) often have hydrogen or halogen atoms directly attached to 

non-carbon atoms. The former (those containing hydrogen) are often flammable, and the latter 

(those containing halogens) are usually toxic (owing to hydrolysis). Both often have low 

stabilities. Moreover, few elements provide catalytic fire suppression capabilities, and 

compounds of most of those do not meet the requirements of this study. A major exception is 

fluoroalkyl phosphorus compounds, which hold significant promise despite their relatively low 

volatility. 

E. SIGNIFICANT HARDWARE DEVELOPMENTS 

The only hardware development made in this project involved incorporation of a heated 

nebulizer for sample dispersion as well as a method for preheating the air flow employed to 

disperse and fully evaporate the nebulized agent mist. These two modifications in conjunction 

with the use of a syringe pump for controlled introduction of the compound under test enabled 

the study of a broad range of compound boiling points, eliminated agent condensation concerns, 

v 
enabled a very accurate characterization of agent/air concentrations, and yielded stable nonfluctuating agent/air mixtures for cup-burner evaluation study. 

F. SPECIAL COMMENTS 

None. 

G. IMPLICATIONS FOR FURTHER RESEARCH 

Fluoroalkylphosphorus compounds studied here have demonstrated a wide range of 

flame extinguishment performance, boiling point and air stability. Further select compounds 

(the trifluoromethyl phosphorus III derivatives) seem to evidence enhanced flame suppression 

properties. It can not be determined at this point whether the compound itself is responsible for 

the markedly effective flame suppression or whether the air break down products (alkylphosphorus oxides) are responsible for the improvement. What is apparent is that the actual air 

concentration of the active species is likely much lower than that listed for the test. It is possible 

that the effective species is present at a mere fraction of the stated 1.8% extinguishment 

concentration observed in flame suppression tests. 

vi 
TABLE OF CONTENTS 

Page

SECTION I. INTRODUCTION ......................................................................................................1 

A. Objective...............................................................................................................1 

B. Scope.....................................................................................................................1 

C. Approach...............................................................................................................1 

D. Background...........................................................................................................1 

SECTION II. FLUOROALKYL PHOSPHORUS COMPOUNDS: SELECTION ACQUISITION 

AND TESTING ...............................................................................................................................3 

A. Phosphorus compound extinguishment studies....................................................3 

1. Suppression effectiveness............................................................................3 

B. Fluoroalkyl phosphorus compounds - acquisition and characterization...............7 

1. Compound selection.....................................................................................8 

2. Synthetic methods and results......................................................................9 

3. Cup-Burner flame extinguishment testing.................................................13 

C. Observations and Conclusions............................................................................17 

D. Recommended studies ........................................................................................19 

E. low temperature limit estimates..........................................................................20 

SECTION III. RESULTS AND CONCLUSIONS........................................................................24 

A. Results.................................................................................................................24 

B. Important Findings and Conclusions..................................................................24 

REFERENCES ..............................................................................................................................26 

vii 
LIST OF FIGURES 

Figure Page

1 Sample nebulizer and air pre-heater. .....................................................................14 

2 Cup-burner equipped with sample nebulizer and evaporation column. ................15 

3 Estimated Maximum Boiling Points That Can Achieve Given 

Concentrations as Function of Ambient Temperature (Simplified), 

Calculated for tc = 88 J/K-mol...............................................................................21 

viii 
LIST OF TABLES 

Table Page

1 Compounds selected for synthesis...........................................................................9 

2 Synthetic results.....................................................................................................12 

3 Summary of cup-burner extinguishments..............................................................16 

4 Air reactivity observations.....................................................................................17 

5 Compounds for future study ..................................................................................20 

6 Maximum Boiling point v.s. ambient temperature and cup-burner 

concentration .........................................................................................................22 

7 Temperature limits for extinguishing concentration .............................................23 

ix 
LIST OF ABBREVIATIONS 

CGET Center for Global Environmental Technologies 

COTR Contracting Officer’s Technical Representative 

DEMP diethyl methylphosphonate 

DIMP diisopropyl methylphosphonate 

DMMP dimethyl methylphosphonate 

IMP isopropyl methylphosphonate 

ISO International Standards Organization 

MPA methylphosphonic acid 

NGP Next-Generation Fire Suppression Technology Program

NIST National Institute of Standards and Technology 

NMERI New Mexico Engineering Research Institute 

SERDP Strategic Environmental Research and Development Program

TFEP tris(2,2,2-trifluoroethyl)phosphite 

TMP trimethylphosphate 

USAF United States Air Force 

x 
LIST OF UNITS AND SYMBOLS 

C concentration 

K Kelvin 

Pb external pressure at boiling point 

p vapor pressure 

R ideal gas constant 

T temperature 

Tb boiling point temperature 

Tc Trouton’s constant 

Vol % percent by gas volume 

°C degrees Celsius 

xi 
SECTION I. 

INTRODUCTION 

A. OBJECTIVE 

The objective was to evaluate the potential of compounds other than simple halocarbons 

and transition metal compounds as replacements for halon fire extinguishing agents. Only 

compounds that are not solids at room temperature and are representative of the broad range of 

oxidation states of phosphorus are targeted. 

B. SCOPE 

This project requires the assessment of liquid compounds of the fluoroalkyl-phosphorus 

chemical family as halon replacements. Of particular importance is an assessment of the relative 

ability of phosphorus III and V compounds as represented by a range of phosphonates and 

phosphite compounds to provide flame extinguishment and ultimately serve as Halon 1301 

substitutes. The compounds studied were intended to serve as a survey of the performance of 

this general family of compounds with expectation that a refined set of fluoroalkyl-phosphorus 

compounds identified later in this report would subsequently be acquired and tested. 

C. APPROACH 

Much of the information acquired in earlier studies of the flame suppressing properties of 

organophosphorus compounds was employed is the selection of an initial list of fluoroalkylphosphorus compounds for synthesis and cup-burner testing. The compounds selected for 

synthesis were prepared under subcontract to the University of Idaho and were tested for their 

cup-burner flame extinguishment at the New Mexico Engineering Research Institute located at 

the University of New Mexico . 

D. BACKGROUND 

Past work under the United States Air Force (USAF) and the Advanced Agent Working 

Group (AAWG) performed an brief assessment of the fire suppressant potential of compounds in 

1
a number of elemental families [1]. As a result of this initiative, it was recommended that 

tropodegradable bromocarbons [2], silicon compounds [3], phosphorus compounds [4], and 

metal compounds [5] receive particular attention. The study of phosphorus based suppressants 

was extended further in NGP sponsored research which demonstrated the effectiveness of certain 

phosphorus based compounds to act as flame extinguishants. Moreover, significant past work 

under the Next-Generation Fire Suppression Technology Program (NGP) has been performed on 

phosphorus compounds as well as amines, ethers, and silicon compounds [6, 7]. 

This project represents a much needed examination of a broad range of fluorophosphorus compounds with emphasis on heavily fluorinated phosphonates and phosphite 

chemical structures. 

Some results from this present project have been reported at the recent HOTWC 20003 

conference [8]. 

2
SECTION II. 

FLUOROALKYL PHOSPHORUS COMPOUNDS: SELECTION ACQUISITION AND 

TESTING 

A. PHOSPHORUS COMPOUND EXTINGUISHMENT STUDIES 

1. Suppression effectiveness 

A review of the proposed extinguishment mechanisms and testing of phosphorus 

compounds has been presented [7]. In addition, several reports addressing the combustion or 

oxidative chemistry and flame extinguishment performance of alkyl phosphorus compounds 

have appeared. 

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[9]. 

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 [15,10]. 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[11-14]. 

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 

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

point of 52 oC [11]. 

A kinetic model has been developed for the combustion chemistry of dimethyl 

methylphosphonate (DMMP, CCOD ID 1375, O=P(CH3)(OCH3)2) [12]. The opposed-jet burner 

has been shown to be effective for studying this low-volatility compound [13], and studies with 

this apparatus have shown that DMMP is a better suppressant when introduced in the oxidizer 

stream [14] and that DMMP and trimethylphosphate (TMP, CCOD ID 1225, O=P(CH3)3) are 

approximately forty times more effective than nitrogen on a per-mole basis in suppressing flames 

and two to four times more effective than Halon 1301 [15]. Like Halon 1301, the effectiveness 

is greater when DMMP is introduced on the oxidizer side, rather than the fuel side, of nonpremixed flames even when the amounts actually reaching the flame are taken into account [16]. 

This behavior is not observed with argon, which has no chemical contribution to flame 

suppression. 

Gas-phase studies in nitrogen show that diethyl methylphosphonate (DEMP, 

O=P(CH3)(OCH2CH3)2) pyrolyzes to form ethene (CH2=CH2), ethanol (CH3CH2OH), and ethyl 

methylphosphonate (O=P(OH)(CH3)(OCH2CH3)) [17]. Formation of ethene may result from

formation of a six-membered ring transition state or by scission of a PO-CH2CH3 bond with 

subsequent loss of a hydrogen atom from the ethyl radical (•CH2CH3). Similar results have been 

found in pyrolysis studies of diisopropyl methylphosphonate (DIMP), which gives propene 

(CH2=CHCH3), 2-propanol (CH3CH(OH)CH3), isopropyl methylphosphonate (IMP, 

O=P(OH)(CH3)(OCH(CH3)2)), and methylphosphonic acid (MPA, O=P(OH)2(CH3)) [18]. A 

six-membered ring transition state is proposed for formation of 2-propene. Derivatization 

followed by gas chromatography/mass spectrometry has identified DMMP, methyl 

methylphosphonate (O=P(OH)(CH3)(OCH3)), dimethyl phosphate (O=P(OH)(OCH3)2), 

monomethyl phosphate (O=P(OH)2(OCH3)), MPA, orthophosphoric acid (O=P(OH)3), 

phosphorous acid (P(OCH3)3), and phosphonic acid (O=PH(OH)2) as combustion products in a 

CH4/O2/N2 flame doped with DMMP [19]. 

Based on opposed-flame burner results, there has been significant interest in 

DMMP as a potential fire extinguishing material. No cup burner values have, however, been 

determined for DMMP and it would be difficult to obtain such values because of its very high 

4
boiling point (181 °C, [20]) and low vapor pressure (1.2 Torr at 25 °C, [21]). Attempts to 

determine a cup burner extinguishment concentration for a higher volatility non-fluorinated 

compound, trimethyl phosphite (P(OCH3)3), has also been unsuccessful, due, in this case, to its 

flammability. All of the phosphorus compounds discussed above in this section are, in fact, 

flammable.

There are two ways around the flammability problem. One is to blend the 

material with a nonflammable carrier; the other is to work with fluorinated alkyl derivatives of 

phosphorus. Cup burner testing using both of these approaches has been carried out and the 

results are presented in this report. 

Prior work has shown that the compound tris(2,2,2-trifluoroethyl)phosphite (1), 

TFEP (boiling point of 130 to 131 °C at 743 Torr [22]) exhibits a particularly low cup-burner 

extinguishment concentration [7]. More recent studies yielded an extinguishing concentration of 

1.69 vol% for n-heptane fuel. Based on these results the lower molecular weight 

tris(trifluoromethyl)phosphite (2) or tris(trifluoromethyl)phosphate (3), were seen as promising 

materials for future study. Both of these compounds are expected to be lower in boiling point 

than tris(2,2,2-trifluoroethyl)phosphite (1). The effects of fluorination are generally expected to 

reduce the flammability of the alkyl substituents, however, phosphorus +3 phosphite and 

phosphine compounds can be air sensitive to a degree and so fluorination can lead to increased 

air reactivity. The phosphonates (P=O) structures are not affected in this manner as the 

phosphorus oxidation state is already +5. 

OCH2CF3

OCH2CF C 3 F3CH2O

P

(1) 

5
OCF3

OCF3

CF3O

P

(2) 

OCF3

OCF3

CF3O

P

O

(3) 

Tris(trifluoromethyl)phosphite (P(OCF3)3) has not been reported; however, 

tris(trifluoromethyl)phosphate (O=P(OCF3)3) has been prepared by oxidation of 

tris(trifluoromethyl)phosphine (P(CF3)3 [23]. The phosphate has a boiling point of 52 °C at 

760 Torr pressure and a melting point of -86 °C. The vapor pressure p in Torr can be fit to the 

equation log10p = -1445/T + 7.33, where T is in units of K, corresponding to a Trouton’s 

Constant of 85.22 J/mol-K. This equation gives a calculated vapor pressure of 304 Torr at 

25 °C. 

This project was conceived to further investigate the potential of phosphorus 

based compounds to perform as fire suppressants and to advance the understanding of the effects 

of the diverse structural chemistry on the flame suppression process. Following the 

identification of eight promising fluoroalkyl- and hydrofluoroalkyl-substituted phosphorus 

compounds and their synthesis in the laboratory of Dr. Jean’ne Shreeve at the University of 

6
Idaho, seven of the eight fluoroalkyl and hydrofluoroalkyl phosphorus compounds were 

ultimately evaluated for their flame extinguishment performance using the NMERI Cup-burner. 

This work is presented in full below. 

B. FLUOROALKYL PHOSPHORUS COMPOUNDS - ACQUISITION AND 

CHARACTERIZATION 

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[24]. Of particular interest have been compounds of phosphorus 

[9]. Phosphorus compounds appear to provide a chemical fire extinguishment mechanism, and 

some appear to be highly effective [7]. 

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. Incorporating 

fluorinated alkyl groups potentially decreases boiling points and simultaneously reduces 

compound flammability. For example, tris(2,2,2-trifluoroethyl)phosphite (P(OCH2CF3)3 ,TFEP) 

has 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)phosphonate, has been reported to have a 

7
normal boiling point of 52 C. The hypothetical compound P(OCF3)3, 

tris(trifluoromethyl)phosphite may also have a low boiling point. 

Several 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 non-flammability 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. 

1. 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 

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. 

8
TABLE 1. COMPOUNDS SELECTED FOR SYNTHESIS 

# 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) phosphite 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. 

2. Synthetic methods and results 

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. 

Compound 1, synthesis of tris(trifluoromethyl)phosphonate, O=P(CF3)3. 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 [7]. These steps are described in Reactions 1 and 2 

below. 

9
Reaction 1. Step 1: Synthesis P(CF3)3 intermediate 

 232° C, 60hr 

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

Reaction 2. Step 2:Oxidative conversion to O=P(CF3) 

 NO2 

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

Compound 2, synthesis of bis(trifluoromethyl)methoxyphosphine, (CF3)2POCH3. 

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

and red phosphorus were reacted at 25  ̊C with AgCl to form (CF3)2PCl in an approximate 100% 

yield. The chloride was subsequently reacted with methanol in the presence of triethyl amine [7] 

substituting the methoxide for the chlorine. These reactions are summarized in Reaction 3 

below. 

Reaction 3. Methanol replacement of Cl 

 CH3OH 

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

 (CF3CH2)3N 

Compound 3, synthesis of tris(2,2,2-trifluoroethoxy)phosphite, P(OCH2CF3)3. 

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

vigorously stirred solution of phosphorus trichloride (slight excess) at 0 ̊C. After five hours, 

fractional distillation gave the desired product. These reactions are summarized in Reaction 4 

below. 

Reaction 4. Conversion of the chlorophosphine to trifluoroethoxide 

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

Compound 4, synthesis of bis(trifluoromethyl) trifluoromethoxyphosphonate 

O=P(OCH3)(CF3)2. The (CF3)2POCF3 intermediate was oxidized with a slight molar deficiency 

10
of nitrogen dioxide as in Synthesis l. The NO was removed under vacuum. This reaction is 

summarized in Reaction 5 below. 

Reaction 5. Oxidation to Phosphonate 

 NO2 

 (CF3)2POCF3 —————h (CF3)2P(O)OCH3 (100% 

yield) 

Compound 5, synthesis of bis(2,2,2-trifluoroethoxy) trifluoromethylphosphine, 

(CF3)P(OCH2CF3)2. This synthesis is very similar to the synthesis of Compound 2 above. This 

reaction is summarized in Reaction 6 below. 

Reaction 6. Conversion to fluoroalkoxide 

 2eq CF3CH2OH 

 (CF3)PCl2 ———————h (CF3)P(OCH2CF3)2 

 2eq (CF3CH2)3N 

Compound 6, synthesis of bis(trifluoromethyl) 2,2,2-trifluoroethoxyphosphine, 

(CF3)2POCH2CF3: This synthesis is very similar to Synthesis 2 above. This reaction is 

summarized in Reaction 7 below. 

Reaction 7. Conversion to fluoroalkoxide 

 CF3CH2OH 

 (CF3)2PCl ———————h (CF3)2POCH2CF3

 (CF3CH2)3N 

Compound 7, synthesis of bis(trifluoromethyl) 2,2,2-trifluoroethoxyphosphonate, 

(CF3)2P(O)OCH2CF3. This synthesis is very similar to Synthesis 4 above. This reaction is 

summarized in Reaction 8 below. 

Reaction 8. Conversion to fluoroalkoxide 

 NO2

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

11
Compound 8, attempted synthesis of tris(trifluoromethoxy)phosphonate, 

(CF3O)3P=O. This synthesis attempt was unsuccessful but employed a strategy similar to that 

used in the successful preparation of Compound 1. The Reaction attempted is outlined in 

Reaction 9 below [23]. 

Reaction 9, Attempted oxidation of (CF3)3P. 

 O2

 (CF3)3P ———————h (CF3O)3P=O (no isolable product) 

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

product weights and boiling points are listed. 

TABLE 2. SYNTHETIC RESULTS 

# Compound - Formula Boiling Point oC Synthetic 

product 

weight (g) 

1 Tris(trifluoromethyl) phosphonate 

O=P(CF3)3

32 oC 7.3 

2 Bis(trifluoromethyl)methoxy phosphine,

P(OCH3)(CF3)2

55 oC 5.3 

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

P(OCH2CF3)3

130 oC @ 743 mm 50.0 

4 Bis(trifluoromethyl) trifluoromethoxy

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

42 oC @ 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

25 oC @ 50mm 6.5 

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

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

130 oC (estimate) 7.0 

8 Tris(trifluoromethoxy) phosphonate,

O=P(OCF3)3

52o C Not 

synthesized 

12
3. 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 prepared (5 to 10 grams), the cup-burner 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 cupburner was required. These issues were addressed using a preheater for the inlet air stream as 

depicted in Figures 1 and 2. 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 cupburner chimney prior to a test run and as a result no condensation of agent 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. 

13
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 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 3 hp compressor. 

Air flows were set and monitored using a mass flow meter. 

14
Figure 2. Cup-burner equipped with sample nebulizer and evaporation column. 

15
TABLE 3. SUMMARY OF CUP-BURNER EXTINGUISHMENTS 

# Compound, Formula Cup-burner Testing 

1 Tris(trifluoromethyl) Phosphonate, O=P(CF3)3 No flame lift-off or 

extinguishment @ 5% 

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

on exposure to air * 

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

Lift-off but 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. 

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. Air reactivity observations 

are summarized in Table 4. 

16
TABLE 4. AIR REACTIVITY OBSERVATIONS 

# Compound - Formula Observations on 

exposure of test agent 

to air 

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) phosphite,

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 

C. 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. 

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 decomposition and efficient fire suppression there are limited chemical options and therefore 

17
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). Phosphines 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. Phosphorus +3 fluoroalkyls

(Compounds 2 (bis(trifluoromethyl)methoxyphosphine, P(OCH3)(CF3)2), 3 (tris(2,2,2-

trifluoroethoxy) phosphite, P(OCH2CF3)3), 5 (bis(2,2,2-trifluoroethoxy) trifluoromethylphosphine, P(OCH2CF3)2CF3), and 6 (bis(trifluoromethyl) 2,2,2-trifluoroethoxyphosphine, 

P(OCH2CF3)(CF3)2)) 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 

n-heptane 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. 

18
D. RECOMMENDED STUDIES 

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 phosphorusbased suppressants for aircraft applications. A compound that can be easily dispersed as a gas or 

vapor and which subsequently decomposes to form a highly effective flame extinguishant may 

have some applicability to aircraft dry bays and other unoccupied areas. It may be that the 

required extinguishing concentration of such an agent could be in the 1% or lower range. The 

nature and toxicity of Compound 6 air decomposition products needs to be determined. 

The break down products of Compound 2 (bis(trifluoromethyl)methoxyphosphine, P(OCH3)(CF3)2)are likely to be similar to those of Compound 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 acquisition of fluoro-phosphorus compounds 

similar to P(OCH3)(CF3)2 with -OCFH2 instead of -OCH3 is indicated. 

The synthesis of Compound 8 (tris(trifluoromethoxy)phosphonate, O=P(OCF3)3) 

has been reported in the literature [23]. While this projects synthesis attempt of O=P(OCF3)3) 

was unsuccessful, a realistic expectation of Compound 8’s acquisition still exists. The 52o C 

boiling point of Compound 8 as well as its similarity to the structures thought to be the 

breakdown products from Compound 6, that may be contributing to 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

19
which could possibly have prevented breakdown in the flame zone and failure to act as a flame 

extinguishant at the 5% initial test concentration. 

These recommended compounds are summarized below 

TABLE 5. COMPOUNDS FOR FUTURE STUDY 

Phosphorus III compounds Phosphorus V compounds 

P(OCH3)(CFH2)2 O=P(CHF2)3

P(OCH3)(CHF2)2 O=P(CHF2)(CF3)2

P(OCF3)(CF3)2 O=P(CF3)(CHF2)2

P(OCF3)3 O=P(CFH2)(CF3)2

P(CF3)3 O=P(CF3)(CFH2)2

P(CH3)(CF3)2 O=P(OCF3)3

P(OCHF2)(CF3)2

P(OCFH2)(CF3)2

E. LOW TEMPERATURE LIMIT ESTIMATES 

A major criterion for use of any compound is the ability to evaporate and fill a space to 

the desired concentration within the time required for extinguishment. Evaporation properties 

must be taken into account, specifically, evaporation equilibrium and evaporation rate. 

Estimates of the ability of a compound to achieve the required air concentration under 

specific ambient temperature conditions can be made using the previously developed tables and 

figures below. 

Assuming that the Troutons constants for the fluoroalkyl phosphorus compounds studied 

in this project are comparable to the 88 J/K-mol employed in the calculations upon which 

Figure 3 and Table 6 are based, yields the low temperature limit estimates listed in Table 7. 

20
Confounding this assessment is the air reactivity of several of the compounds. Air 

reactivity would likely warm aerosolized droplets thus enhancing evaporation and dispersion of 

the chemical. 

-30

-20

-10

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50

Ambient Temperature, °C

Maximum Boiling Point, °

1%

3%

5%

7%

10%

15%

20%

Figure 3. Estimated Maximum Boiling Points That Can Achieve Given Concentrations as 

Function of Ambient Temperature (Simplified), Calculated for tc = 88 J/K-mol. 

21
Table 6. Maximum Boiling point vs. ambient temperature and cup-burner concentration 

Conc. Ambient Temperature, °C 

% -60 -50 -40 -30 -20 -10 0 10 20 30 40 50

1 33 47 61 76 90 105 119 133 148 162 176 191

2 19 33 46 60 74 87 101 115 128 142 156 169

3 11 24 37 51 64 77 91 104 117 130 144 157

4 5 18 31 44 57 70 83 96 109 122 135 148

5 0 13 26 39 52 65 77 90 103 116 129 142

6 -3 9 22 35 47 60 73 85 98 111 123 136

7 -6 6 19 31 44 56 69 81 94 106 119 131

8 -9 3 16 28 40 53 65 78 90 102 115 127

9 -11 1 13 25 38 50 62 74 87 99 111 124

10 -14 -1 11 23 35 47 59 72 84 96 108 120

11 -16 -3 9 21 33 45 57 69 81 93 105 117

12 -17 -5 7 19 31 43 55 67 79 91 103 115

13 -19 -7 5 17 29 41 53 65 77 88 100 112

14 -20 -9 3 15 27 39 51 63 74 86 98 110

15 -22 -10 2 14 25 37 49 61 73 84 96 108

16 -23 -11 0 12 24 36 47 59 71 83 94 106

17 -24 -13 -1 11 22 34 46 57 69 81 92 104

18 -25 -14 -2 9 21 33 44 56 68 79 91 102

19 -27 -15 -3 8 20 31 43 54 66 78 89 101

20 -28 -16 -5 7 19 30 42 53 65 76 88 99

22
Table 7. Temperature limits for extinguishing concentration 

Compound, Formula Boiling point, 

Cup-burner 

extinguishment %

Estimated lowest 

temperature at which 

extinguishing 

concentration is 

achievable 

Bis(trifluoromethyl)methoxy phosphine, 

P(OCH3)(CF3)2

55 C, NA -38 C* 

Tris(2,2,2-trifluoroethoxy) phosphite, 

P(OCH2CF3)3

130 C, 3.1% 30 C 

Bis(trifluoromethyl) trifluoromethoxy 

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

42C, 4.6% -32 C 

Bis(2,2,2-trifluoroethoxy) 

trifluoromethyl phosphine, 

P(OCH2CF3)2CF3

111C, 3.0% 15 C 

Bis(trifluoromethyl) 2,2,2-

trifluoroethoxy phosphine, 

P(OCH2CF3)(CF3)2

~ 100 C, 1.8% ~ 5 C 

* Assuming an extinguishment concentration equivalent to that of P(OCH2CF3)(CF3)2

23
SECTION III. 

RESULTS AND CONCLUSIONS 

A. RESULTS 

The only non-halogen, non-transition metal elements that appear to provide any 

significant catalytic fire suppression capabilities are the alkali metals, tin, lead, phosphorus, and 

the heavier halogens (bromine, iodine, and, to a limited extent, chlorine). 

B. IMPORTANT FINDINGS AND CONCLUSIONS 

With one major exception, the results of the search have been disappointing as the lower 

boiling compound of the series tested did not demonstrate flame extinguishing properties and the 

lowest boiling compounds to evidence extinguishing properties were not any more effective than 

many of the previously studied compounds. The exception to this general conclusion is the 

intriguing extinguishing performance of bis(trifluoromethyl) 2,2,2-trifluoroethoxyphosphine, 

P(OCH2CF3)(CF3)2. While the compound is clearly flammable, it or its oxidation products did 

yield the lowest extinguishment concentration observed for the compounds tested. The 

structurally similar compound, bis(trifluoromethyl)methoxy phosphine, P(OCH3)(CF3)2, may 

also perform well is flame extinguishment once tested. As stated previously, prior work has 

shown that the compound tris(2,2,2-trifluoroethyl)phosphite [25]) also exhibits a particularly low 

cup-burner extinguishment concentration [7] with some recent studies yielded an extinguishing 

concentration of 1.69 vol%. The authors have previously hypothesized that the high heat 

employed to vaporize the tris(2,2,2-trifluoroethyl)phosphite sample may have resulted in partial 

or full decomposition prior to the vapor entering the flame zone. Indeed, this project’s 

reexamination of tris(2,2,2-trifluoroethyl)phosphite using our nebulizer based aerosolization 

equipment as described (see Section II.B.3), which does not subject compounds to possible 

thermally induced degradation yielded a cup-burner flame extinguishment value of 3.1%. These 

results coupled with the failure of tris(trifluoromethyl)phosphonate O=P(CF3)3 to even cause 

flame lift off much less flame extinguishment when tested at an air concentration of 5% seem to 

support a tentative conclusion that for a flame extinguishment of the fluoroalkyl phosphorus 

24
compound to be effective they must decompose readily either in the flame zone or prior to 

entering the flame zone. 

The afore stated, tentative, conclusion may reasonably be seen as a basis to curtail 

interest in the further investigation of this family of compounds as halon replacements. 

However, incorporation of otherwise stable compounds in heat generating solid propellant gas 

generator devises could significantly enhance the gas generators fire suppressing effectiveness. 

Few materials based on main group elements with potentially acceptable physical 

(primarily, volatility) and toxicological properties have been identified. The lowest molecular 

weight materials (i.e., the materials with the highest volatilities) often have hydrogen or halogen 

atoms directly attached to non-carbon atoms. The former (containing hydrogen) are often 

flammable, and the latter (containing halogens) are usually toxic (owing to hydrolysis). Both 

often have low stabilities. Moreover, few elements provide catalytic fire suppression 

capabilities, and compounds of most of those do not meet the requirements of this study. A 

major exception is fluoroalkyl phosphorus compounds, which hold significant promise despite 

their relatively low volatility. 

25
REFERENCES 

1. Tapscott, R. E., Heinonen, E. W., and Brabson, G. D., Advanced Agent Identification and 

Preliminary Assessment, WL-TR-95-XX, NMERI Report No. 1995/15/31883, Wright 

Laboratory (WL/FIVCF), Tyndall Air Force Base, Florida, December 1996. 

2. Heinonen, E. W., Lifke, J. L., and Tapscott, R. E., Advanced Streaming Agent 

Development, Volume IV: Tropodegradable Halocarbons, WL-TR-96-XX, NMERI 

Report No. 96/4/32540, Vol. 4 of 5, Wright Laboratories (WL/FIVCF), Tyndall Air 

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

Florida, May 1996. 

3. Gobeli, G. W., Tapscott, R. E., and Kaizerman, J. A., Advanced Streaming Agent 

Development, Volume I: Silicon Compounds, WL-TR-96-XX, NMERI Report No. 

96/1/32540, Vol. 1 of 5, Wright Laboratory (WL/FIVCF), Tyndall Air Force Base, 

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

1996. 

4. Kaizerman, J. A., and Tapscott, R. E., Advanced Streaming Agent Development, Volume 

III: Phosphorus Compounds, WL-TR-96-XX, NMERI Report No. 96/5/32540, Vol. 3 of 

5, Wright Laboratories (WL/FIVCF), Tyndall Air Force Base, Florida, and Applied 

Research Associates, Inc., Tyndall Air Force Base, Florida, June 1996. 

5. Patterson, R. A., Gobeli, G. W., Brabson, G. D., and Tapscott, R. E., Advanced Streaming 

Agent Development, Volume II: Metal Compounds, WL-TR-96-XX, NMERI Report No. 

96/3/32540, Vol. 2 of 5, Wright Laboratories (WL/FIVCF), Tyndall Air Force Base, 

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

1996. 

6. Tapscott, R. E., Heinonen, E. W., and Mather, J. D., Identification and Proof Testing of 

New Total Flooding Agents: Toxicity and Global Environmental Assessment, Interim

Report, NMERI Report No. 97/29/33010, U. S. Department of Defense, Strategic 

Environmental Research and Development Program and Defense Advance Research 

Projects Agency, Arlington, Virginia, February 1998. 

7. Tapscott, R. E., Mather, J. D., Heinonen, E. W., Lifke, J. L., and Moore, T. A., 

Identification and Proof Testing of New Total Flooding Agents: Combustion 

Suppression Chemistry and Cup Burner Testing, Final Report, NMERI Report No. 

97/6/33010, U. S. Department of Defense, Strategic Environmental Research and 

Development Program and Defense Advance Research Projects Agency, Arlington, 

Virginia, May 1998. 

8. Tapscott, R. E., and Mather, J. D., “Fluoroalkyl Phosphorus Compounds,” Proceedings, 

Halon Options Technical Working Conference, Albuquerque, New Mexico, May 12-15, 

2003. 

26
9 Kaizerman, J. A., and Tapscott, R. E., Advanced Streaming Agent Development, Volume 

III: Phosphorus Compounds, WL-TR-96-XX, NMERI Report No. 96/5/32540, Vol. 3 of 

5, Wright Laboratory (WL/FIVCF), Tyndall Air Force Base, Florida and Applied 

Research Associates, Inc., Tyndall Air Force Base, Florida, May 1996. 

10 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. 

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

18, No. 2, pp. 352-354, 1979. 

12. Werner, J. H., and Cool, T. A., “Kinetic Model for the Decomposition of DMMP in a 

Hydrogen/Oxygen Flame,” Combustion and Flame, Vol. 117, pp. 78-98, 1998. 

13. Jayaweera, T. M., MacDonald, M. A., Fisher, E. M., and Gouldin, F. C., “A Novel 

Method for Evaluating the Effectiveness of Low Volatility Flame Inhibitors With an 

Opposed-Jet Burner,” Proceedings, Chemical and Physical Processes in Combustion, 

1997 Fall Technical Meeting, The Eastern States Section of the Combustion Institute, 

Hartford, Connecticut, 27-29 October 1997, pp. 87-90. 

14. MacDonald, M. A., Jayaweera, T. M., Fisher, E. M., and Gouldin, F. C., “Inhibited 

Counterflow Non-Premixed Flames with Variable Stoichiometric Mixture Fractions,” 

Proceedings, Chemical and Physical Processes in Combustion, 1997 Fall Technical 

Meeting, The Eastern States Section of the Combustion Institute, Hartford, Connecticut, 

27-29 October 1997, pp. 91-94. 

15. MacDonald, M. A., Jayaweera, T. M., Fisher, E. M., and Gouldin, F. C., “Inhibition of 

Non-Premixed Flames by Phosphorus-Containing Compounds,” Combustion and Flame, 

Vol. 116, pp. 166-176, 1999. 

16. MacDonald, M. A., Jayaweera, T. M., Fisher, E. M., and Gouldin, F. C., “Variation of 

Chemically Active and Inert Flame-Suppression Effectiveness with Stoichiometric 

Mixture Fraction,” Twenty-Seventh Symposium (International) on Combustion, 

University of Colorado, Boulder, Colorado, 2-7 August 1998. 

17. Zegers, E. J. P., and Fisher, E. M., “Gas-Phase Pyrolysis of Diethyl Methylphosphonate,” 

Combustion Science and Technology, Vol. 116-117, pp. 69-89, 1996. 

18. Zegers, E. J. P., and Fisher, E. M., “Gas-Phase Pyrolysis of Diisopropyl 

Methylphosphonate,” Combustion and Flame, Vol. 115, pp. 230-240, 1998. 

19. Rapp, D. C., Nogueira, M. F. M., Fisher, E. M., and Gouldin, F. C., “Identification of 

Stable Phosphorus-Containing Combustion Byproducts by Gas Chromatography/Mass 

Spectrometry Preceded by Derivatization,” Environmental Engineering Science, Vol. 14, 

No. 2, pp. 133-140, 1997. 

27
20. CRC Handbook of Chemistry and Physics, 78th Edition, Lide, D. R., and Frederikse, H. 

P. R., editors, CRC Press, Inc., Boca Raton, Florida, USA, 1997. 

21. Information Handling Services, Material Safety Data Sheets Service, Microfiche Edition, 

Bimonthly Updates #1060-028, A-04, August/September 1989 

22. Catalog Handbook of Fine Chemicals 1996-1997, Aldrich Chemical Company, Inc., 

Milwaukee, Wisconsin. 

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

18, No. 2, pp. 352-354, 1979. 

24. Tapscott, R. E., Moore, T. A., Kaizerman, J. A., Kibert, C. J., and Tetla, R. A., 

“Advanced Agent Halon Substitutes,” Proceedings, International CFC and Halon 

Alternatives Conference, Washington, D.C., pp. 644-648, 23-25 October 1995. 

25. Catalog Handbook of Fine Chemicals 1996-1997, Aldrich Chemical Company, Inc., 

Milwaukee, Wisconsin. 

28