PROJECT REVIEWS: TROPODEGRADABLE BROMOCARBON EXTINGUISHANTS - 11 

AND PLUOROALKYL PHOSPHORUS COMPOUNDS 

J. Douglas Mather 

Center for Global Environmental Tcchnologics 

The University ofNew Mexico 

Robert E. Tapscott 

GlobeTech, Inc. 

INTRODUCTION 

In two projects sponsored by the Department of Defense Next-Generation Fire Suppression Technology 

Program (NGP), research efforts at The University of New Mexico are evaluating chemical agents as 

substihites for Halon 1301 [I]. The first of these, a project titled “Tropodegradahle Bromocarbon Extinguishants-11,” is approximately half way through its planned effort. The second project is entitled 

“Fluoroalkyl Phosphorus Compounds.” This project targcts the acquisition and testing of promising 

fluoroalkyl phosphorus compounds and has just received funding. This report summarizes the efforts 

undertaken or to be undertaken in each of these projects and the progress and achievements to date. 

‘TROPODEGRADABLE BKOMOCARBON EXTlNGUlSHANTS - 11 

This effort is a continuation of an earlier successful NGP project, which resulted in the acquisition of 

several tropodegradable compounds with very promising cup-burner flame extinguishments properties. 

Several of these brotnofluoroalkenes were evaluated in acute inhalation toxicity tests [I, 21, hies mutagenicity studies,* and In Vilvo Chromosome Aherration Tests using human peripheral blood lymphocytes.* Cardiac sensitization testing is planned for the most promising compound, Z-bromo-3,3,3-trifluoropropene. Testing results to date are very favorable, and there is strong indication that as a group 

the tropodegradable bromocarbons may well yield acceptable replacements for Halon 1301. 

Based on an analysis of atmospheric reactivity, various chemical families are recognized as having the 

potential to he tropodegradable or capable of essentially complete decomposition within the troposphere 

and therefore not posing a threat to stratospheric ozone. The tropodegradahle chemical families, initially 

of interest for development of tropodegradable bromocarbon extinguishants, are listed below. 

Brominated Alkenes Brominated Ethers 

Brominated Alkyl amines Brominated Alcohols 

Hroininated Aromatics Brominated Carboxylatcs 

Of these chemical familics the brominated alkenes, ethers, and amines were judged the most likely to 

meet desired boiling point restrictions, environmental, and toxicity goals; of these families the bromofluoroalkenes were judged the most favorable based on atmospheric lifetime. Toxicity requirements are 

generally viewed as presenting the most difficult hurdle in the development of halon replacements. 

Early research work on new total-flood agents established the potential of tropodegradahle hromocarbons 

as fire suppressants; however, flame extinguishment experiments were insufficient to relate performance 

(and, for some compounds) flammability to structure [2-61. NMERl’s recent NGP project was conceived 

in part to address the need for more laboratory-scale fire extinuishment information on tropodegradable 

compounds. The first project on tropodegradahle compounds funded under the NGP program identified 

several broinofluoroalkenes and bromofluoroamines with good flame extinguishments performance. No 

bromofluoroethers were acquired or synthesized during this first effort due to funding and time constraints as well as synthesis and sourcing difficulties. 

This report summarizes the current acquisition and extinguishment studies on tropodegradable bromocarbon extinguishants. These studies are adding to the number of characterized compounds and identify- 

* Reports availohlc from the Advanced Agent Working Group. 

llalon Opttons ‘Technical Working Conference 24-26 April 2001 ] 97 
ing compounds with significantly lower boiling point. In addition, new screening techniques have been 

developed for performing IS0 as well as NMERI cup-burner testing of small quantities of compound. 

EARLY DEVELOPMENT EFFORTS 

Commercialized halon replacements such as perfluorocarbons (PFC, FC), hydrochlorofluorocarbons 

(HCFC), hydrofluorocarbons (HFC), hydrofluoropolyethers (HFPE), and iodofluorocarbons (CFJ) do 

not contain bromine and therefore are not as effective in flame extinuishment tests or actual large-scale 

fire suppression tests due for the most part to the absence ofbromine in the stmctures of these chemicals. 

Low atmospheric lifetime compounds provide an opporhmity to retain bromine in the extinguishant 

molecule. Alkenes, for instance, which readily react with atmospheric *OH and 0, can act as a carrier 

(Table 1). The resulting brominated compound will still rapidly degrade in the troposphere and never 

reach the stratosphere or the earth’s ozone layer. 

- 

TABLE 1. TROPODEGRADABLE 

- 

CARRIERS AND BROMINATED DERIVATIVES 

Tropodegradable Base Structure Tropodegradable Bromocarbon Derivative 

CH,=CHCF, CH2=CBrCF3, CHBr=CHCF3 

CHz=CFCF, CHBr=CFCF, 

CH2=CFCF2H CH2=CHCF2Br, CHBr=CFCF2H 

CHF=CHCF, CFBFCHCF,, CHF=CBrCF, - 

When bromine is contained within the molecular structure of a short atmospheric lifetime compound, the 

resulting chemical is referred to a tropodegradable bromocarbon. All the carrier compounds would only 

be partially fluorinated. Other incorporated chemical features reactive with atmospheric *OH or 03 are 

found in partially fluorinated amines, ethers, and alcohols. Iodinated compounds such as CF,I are short 

atmospheric lifetime tropodegradable compounds due to the rapid photolysis of the C-I bond, which 

results from exposure to sunlight. 

Although tropodegradable compound atmospheric lifetimes have been measured, they are generally 

estimated based on data generated for functional groups such as sites of unsaturation, numbers of C-H 

bonds, and substitution patterns. For alkenes, atmospheric lifetimes as low as a few days have now been 

experimentally determined.* Amines are estimated to have atmospheric lifetimes on the order of one or 

more months. Ethers are estimated to have atmospheric lifetimes of days to months. The brominated 

ether CH,OCF,CHFBr (commonly known as Rofluorane) has been reported to have an atmospheric 

lifetime of 14 days [7]. 

The reactions that cause atmospheric decomposition of a molecule differ for alkenes, ethers, and amines. 

For alkenes, reactions with hydroxyl free radicals or with tropospheric or ground level ozone are expected to target the double bond while ethers and amines would be subject to hydrogen abstraction reactions 

by the *OH radical. As stated above, photolysis of the C-I bond is the predomninant reaction pathway 

for iodinated fluoroalkanes such as CFJ. 

The problem is one of selecting appropriate toxicity end points and developing a ranking of their relative 

importance. This information became part of the basis for the preliminary screening prior to actual 

acquisition and or synthesis efforts. An example of the selection criteria developed early in the Halon 

1301 replacement program is presented in Table 2. 

* Vladimir Orkin, NIST, personal communication, April 2000. 

198 Halon Options Technical Working Conference 24-26 April 2001 
TABLE 2. HALON 1301 REPLACEMENT CANDIDATE CRITERIA. ______ 

Criteria Value 

Boiling point <-5O"C 

LC,," (4-hour) 

Cup-burner performance < 5.0% 

ODP <0.02 

GWP < 5,000 

Atmospheric lifetime Days to months 

Cardiac sensitization (CSNOAEL) 

> 50,000 ppm (5.0%) 

> 2 times cup-hurner performance 

'Lowest concentration causing death in 50% of an animal test population. 

The initial selection criteria listed in Table 1 do not do justice to the challenges facing halon replacement 

research. Some of the major hurdles, yet to be addressed, are listed below. Prominent ainong these are 

manufacturahility and end-user cost. To have the greatest likelihood of success, the program must identify as many functionally and environmentally acceptable compounds as is practical. This is one reason 

why continued compound acquisition efforts are essential. 

Other toxicity and exposure criteria Manufacturahility (production cost) 

Chemical Stability Materials Compatibility 

Functional upper limits for the boiling points of compounds for total-flood agent applications are presented in Table 3. Estimates of theoretical ambient vapor pressure as a function of boiling point and ambient 

temperature (based on Trouton's constant) are shown, hut of course they say nothing about the time 

required to establish the targeted air concentration. In the case of total-flood agents, vapor pressure under 

the conditions of usage are seen as a primary factor in the fire or explosion performance of an agent. 

This table has been presented elsewhere and is shown here in a modified form to illustrate the problems 

associated with developing agents for low temperature applications and the significance of identifying 

compounds with lower boiling points and cup-burner values. The shaded area of the chart reflects the 

lowest boiling points of the compounds acquired and tested in our previous project. From the chart it can 

be seen that to achieve an additional - 1 0 OC lower application temperature the upper limit on agent hoiling point must be reduced by 13 "C. Similarly, dropping the cup-burner based required extinguishant air 

concentration by 1% is equivalent to allowing compounds with 6-8 OC higher boiling points to he considered. If both a IO "C lower boiling point and a 1% lower cup-burner effect are combined, the "Ambient 

Temperature" application limit is decreased approximately 15 "C. 

TABLE 3. ESTIMATES OF MAXIMUM USABLE BOILING POINTS. 

Air Con- Ambient Temperature, OC 

centration 

5 0 13 26 77 90 103 

10 -14 -1 I1 89 72 84 

15 -22 -10 2 49 61 73 

Example. To achieve a 4 vol YO concentration at -20 "C, the maximum allowable boiling point is 87 OC 

I ~ 

Halon Options lechnical Working Conference 24-26 April 2001 I99 
CURRENT PROJECT EFFORTS 

The list of bromofluoroalkenes acquired prior to the start of the current project are listed in Table 4. The 

data all indicate that regardless of compound structure, straight chain or branched, and propene, butene, 

or pentene derivative, the flame extinguishment is generally below 4% with most of the tested compounds 

TABLE 4. BROMINATED TROPODEGRADABLE HALOCARBON CUP-BURNER VALUES. 

Compound Formula Boiling Pt, OC Cup Burner,% 

1 -Bromo-3,3,3-trifluoropropene CF,CH=CHBr 40 3.5* 

3-Bromo-3,3-difluoropropene 

2-Bromo-3,3,3-trifluoropropene 

4-Bromo-3,3,4,4-tetrafluorobutene 

2-Bromo-3,3,4,4,4-pentafluorobutene 

2-Bromo-3,3,4,4,5,5,5- 

heptafluoropentene 

2-Bromo-3-trifluoromethyl-3,4,4,4- 

tetrafluorobutene 

2-Bromo-3-trifluoromethoxy-3,4,4,4- 

tetrafluorobutene 

1 -Bromo-2-trifluoromethyl-3,3,3- 

trifluoropropene 

1 -Bromo-4,4,4,3,3-pentafluorobutene 

CBrF,CH=CH, 

CF,CBr=CH, 

CF,BrCF,CH=CH, 

CF,CF,CBFCH, 

CF,CF,CF,CBFCH, 

CF,CF( CF,)CBr=CH, 

CF,CF(OCF,)CBr=CH, 

(CF,),C=CHBr 

CF,CF,CH=CHBr 

42 

34 

54 

56 

78 

78 

75 

63 

58 

4.5 

2.6 

3.5 

3.8* 

3.7% 

3.3% 

3.8* 

2.6* 

3.1* 

* Testing performed using premixed agenuair mixtures 

yielding NMERI cup-burner values comparable to Halon 1301. Only when the degree of fluorination 

falls to less than 50% of available positions (total of number of Hs, fluorines, and bromines) does the 

cup-burner value rise significantly above 4%. 

The current project seeks to identify and acquire highly effective flame extinguishments compounds with 

boiling points significantly below 34 OC. Those compounds acquired thus far are listed in Table 5. Data 

for those whose extinguishments have been tested in the NMERI cup-burner are indicated. Boiling points 

for several of the acquired compounds are as much as 9 "C lower than observed earlier. Additional compounds are now being selected for acquisition. 

TABLE 5. SUMMARY OF NEW COMPOUNDS ACQUIRED. 

Compound Formula Boiling Pt, "C Cup Burner,% 

1 -Bromopentafluoropropene CFBFCFCF, 27 - 28 ____ 2-Bromopentafluoropropene CF,=CBrCF, 25 - 26 (3.5) 

2-Bromo- 1,3,3,3-tetrafluoro-l -propene CFH=CBrCF, 29 - 32 (3.7) 

3-Bromo-I, 1,3,3-tetrafluoro-l-propene CF,=CHCF,Br 33 (3.3) 

I-Bromo-l,3,3,3-tetrafluoro-I-propene CFBFCHCF, -_-- -___ 

Bromoethyl trifluoromethyl ether CBrH,CH,-0-CF, _____ -___ 

Bromomethyl trifluoromethyl ether CH,Br-0-CF, 39-41 3.2 

Bromomethyl difluoromethyl ether CH,Br-0-CF,H 70 -___ 

* Testing performed using premixed agenuair mixtures (VN); ( ) indicates preliminary data. 

To determine the cup-burner flame extinguishments, NMERl developed a reliable method for preparing 

aidagent mixtures that requires as little as 2 g oftest compound (Figure I). This enables the study of 

compounds that can be acquired only from sources of custom synthesis at a cost that in general would 

prohibit the acquisition of the large amounts of test material typically required (50-200 g). The method 

200 Halon Opiions Technical Working Conference 24-26 April 200 I 
Metering Valve 

(Regulated to 26 IMn' 1 

Figure I. NMERI cup-burner agenvair sample flow diagram 

TABLE 6. COMPARISON OF IS0 AND NMERI CUP-BURNERS. 

~ 

.... ~~~ ~~ ~~~~ .... ~ ....,.. ~~ n-Heptane ~~ ~~ ....... Flame ~~~ ~ Extinguishment ..... ~~ ~~~ ~ ...... ~ ... . .. Air Concentration, 

% (VN) SSO Burner: (20Limin) (30Limin) NMERI Burner: (IOLjmln) 

3.6 Yes Yes Yes 

3.2 Yes Yes Yes 

3.1 Yes No Yes 

3.0 Yes No Yes 

2.8 No .._ No a__r m_ 

as first developed employed the 1OL TedlarrM air sampling bag typically used in environmental or Industrial hygiene monitoring. The TedlarTM bag itself is contained within a rigid walled airtight outer container. Air, at the flow rate being employed in the cup-burner test, is directed into the region betweeii the 

rigid container and TedlarTM bag resulting in discharge of the airlagent mixture from the TedlarTM sample 

bag into the base of the cup burner. The method allows for serial dilution of the air agent mixture and 

sequential extinguishment tests at ever decreasing agentlair concentrations. The method has now been 

extended to 1 OOL TedlarTM sample bags. This has allowed the side-by-side comparison of NMERI and 

IS0 cup burners using the same aidagent sample. Flame extinguishment data from this comparison 

(Table 6) demonstrate the relative similarity ofNMERI and IS0 cup-burner data for gaseous agents. 

This study is being extended to liquid agents such as those being acquired in this project. 

CONCLUSION 

As presented in this review, tropodegradable broinofluoroalkenes have been demonstrated to be effective 

fire extinguishants in both streaming and total flood applications. Cup-burner data indicate that for compounds where the degree of fluorination is equal to or greater than 50% the extinguishment concentrations are as low as 2.6%. Boiling points for many of the compounds acquired now range from a low of 

25 to 74 "C. Actual testing of the performance of these compounds in fire and explosion suppression 

tests at sub-ambient temperature conditions is needed to assess performance and evaluate the significance 

of dispersion and droplet size effects on extinguishment. Toxicity testing results for the broniofluoroalkenes continue to be very promising, and further testing is planned in the near future. 

~~ 

Halon Options Technical Working Conference 24-26 April 2001 201 
Overall, the compound search has had very positive results. Bromofluoroalkenes as a class have exhibited considerable promise as potential halon replacements. Further acquisition of compounds related to 

2-bromo-3,3,3-trifluoropropene and 4-bromo-3,3,4,4-tetrafluorobutene will likely lead to the identification of additional low boiling candidates. Continued acquisition and testing programs will also include 

studies of bromofluoroethers and, to a lesser extent, bromofluoroamines as these two classes of compounds have shown promise in the limited testing performed. 

Develop new lists of bromofluoroalkenes and bromofluoroethers for acquisition and testing with 

the continued focus being on low boiling compounds. 

Perform additional flame extinguishments studies comparing the performance of IS0 and 

NMERl cup burners. 

0 

FLUOROALKYL PHOSPHORUS COMPOUNDS 

On 1 1 April, the project Fluoroalkylphosphorus Compounds was awarded under the Next-Generation 

Fire Suppression Technology Program (Project 4D/14/1). The primary objective of the project, which is 

scheduled to run from 11 April 2001 through IO April 2002, is the synthesis and extinguishant testing of 

low molecular weight fluoroalkylphosphorus compounds. 

OVERVIEW 

Phosphorus compounds show extraordinary effectiveness as flame extinguishants, and there is evidence 

for a chemical mechanism [SI. 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. A well-studied example is dimethyl 

methyl phosphonate [(O)P(OCH,),CH,], which exhibits good fire suppression, but which is flammable 

and has a very low volatility [9,10]. Phosphorus compounds containing fluoroalkyl and hydrofluoroalkyl 

groups are often nonflammable and have higher volatilities than the non-fluorinated analogs. At the 

Halon Options Technical Working Conference (HOTWC ZOOO), the Defense Evaluation and Research 

Agency reported extinguishing concentrations for a number of partially fluorinated phosphates [ 1 11. 

Owing to their high molecular weights, however, these compounds still had a very low volatility. 

This project targets the identification, synthesis, and laboratory testing of fluoroalkyl- and hydrofluoroalkyl-containing phosphorus compounds as fire extinguishants, with an emphasis on low molecular 

weight compounds. These materials are expected to be more volatile and effective than the corresponding non-fluorinated compounds and more volatile than the higher molecular weight fluorinated compounds studied in the past. The following will be accomplished: (1) lower molecular weight phosphates, 

phosphites, phosphonates, and related compounds containing fluoroalkyl and hydrofluoroalkyl groups 

that have potential to be synthesized and are expected to perform well as fire extinguishants will be 

identified; (2) under a subcontract to The University of New Mexico, Prof. Shreeve (University of Idaho) 

will prepare the compounds identified in Task 1; and (3) cup-burner and physical property determinations 

will be performed. 

COMPOUNDS SELECTED 

Although this project has only very recently been initiated, a preliminary list of compounds to be targeted 

has been developed (Table 7). This list is still subject to modification. 

ACKNOWLEDGMENTS 

The authors wish to gratefully acknowledge the support of the DOD Next-Generation Fire Suppression 

Technology Program, funded by SERDP. 

202 Halon Options Technical Working Conference 24-26 April 2001 
1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

TABLE 7. SELECTED COMPOUNDS. 

- 

Compound Boiling Point 

O=P(CF,) 32 “C 

P(OCFA 

O=P(OCH,)(CF,), 42 “C (745 mm) 

P(OCHZCFA 55 OC 

O=P(OCF,), 51 “C 

O=P(OCH,CF,)(CF,), 

P(OCH,CF,)(CF,), 

P(OCH,CF,), 130-131 “C (743 mtn) 

P(OCH,CF,),CF, 11 0- 1 12 “C 

- ______E 

REFERENCES 

Defense Supply Service-Washington (DSS-W), PO HQ0038-7350-0007, Tropodegradable 

Bromocarbon Extinguishants. 

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

Assessment of Tropodegradable Halocarbons, NMERl911413293 0, for Wright Laboratories 

and Applied Research Associates, Tyndall Air Force Base, FL, 1997. 

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

Preliminary Assessment, Advanced Agent Working Group, November 1996. 

Heinonen, E. W., Lifke, J. L., and Tapscott, R. E., Advanced Streaming Agmt Development, 

Volume IV: Tropodegrudable Halocarbons, Val. 4 of 5, NMERI 9614132540, for Wright 

Laboratories and Applied Research Associates, Tyndall Air Force Base, FL, 1996. 

Tapscott, R. E., Review and Assessment of Tropodegrudable Total Flooding Agents, Final 

Report, NMERI 96120/32730, for Naval Research Laboratory, Washington, DC, 1996. 

Advanced Streaming Agent Development, Defense Supply Service-Washington (DSS-W) PO 

HQ0038-7350-0007 and Applied Research Associates SEAMAS SSG Task I .4.6, Tyndall Air 

Force Base, FL, 1997. 

Chattaway, Adam, Grigg, Julian, and Spring, David, “Investigation of Chemically Active 

Candidate Halon Replacements,” Proceedings, Halon Options Technical Working Conference 

Albuquerque, NM, pp. 33-44,1998. 

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

Phosphorus Compounds, Vol. 3 of 5, NMERI 9615132540, for Wright Laboratories and 

Applied Research Associates, Tyndall Air Force Base, FL, 1996. 

MacDonald, M.A., Jayaweera, T.M., Fisher, E.M., and Gouldin, F.C., “Inhibition of NonPremixed Flames by Dimethyl Methylphosphonate,” Proceedings, Technical Meeting, Central 

States Section of The Combustion Institute, Point Clear, AL, not paginated, 1997. 

MacDonald, M.A., Jayaweera, T. M., Fisher, E.M., and Gouldin, F. C., “Inhibition of NonPremixed Flames by Phosphorus-Containing Compounds,” Combustion and Flame, Vol. 1 16, 

pp. 166-176, 1999. 

Riches, J., Knutsen, L., Morrey, E., and Grant, K.A., “A Flame Ionisation Detector as a Screening Tool for Halon Alternatives,” Proceedings, Halon Alternatives Technical Working 

Conference, Albuquerque, NM, pp. 11 5-125, 2000. 

Halon Options Technical Working Conference 24-26 April 2001 203