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OCR for page 203
APPENDIX
D
Agent Neutralization by Hydrolysis
Five of the seven technology packages
include the
destruction of chemical agents by purely chemical re-
actions that reduce the agents to less toxic or nontoxic
products. Four of the five propose neutralization via
hydrolysis with an aqueous alkali solution. Hydrolysis
is a reaction of a target compound with water, an acid,
or a base in which some chemical bond is broken in the
target and OH- or H+ is inserted into the bond cleavage.
The destruction of chemical agent via hydrolysis is of-
ten referred to as chemical neutralization. The military
definition of neutralize is to render something unus-
able or nonfunctional. Technically, neutralization is a
chemical reaction between an acid and a base to form a
salt and water. Chemical agents are neither acids nor
bases, however, and the use of the term neutralization
for two very different processes is somewhat confus-
ing. Nevertheless, in the literature on chemical demili-
tarization, the terms neutralization and hydrolysis have
been used interchangeably. Therefore, unless otherwise
specified, neutralization refers to the destruction of
chemical agent via hydrolysis.
BACKG ROU N D
Agent detoxification has been an essential require-
ment since the introduction of mustard in World War I.
Detoxification is used for decontaminating dispersed
chemical agents on the battlefield, as well as in labora-
tories, production plants, and elsewhere. Many types
of reactions can detoxify chemical agents, but only two
are widely used: nucleophilic substitution (e.g., hydrol-
ysis) and oxidation. The literature is very extensive on
the neutralization of mustard but much less extensive
203
on the neutralization of nerve agents (ERDEC, 1996,
1997~. In general, work on agent decontamination has
identified several problems and the need for more re-
search in the following areas:
· Chemical agents are nonpolar compounds, but
most decontaminating reagents are polar, which
leads to solubility problems. HD (mustard) is very
insoluble in water; VX is somewhat soluble in
water at low pH but not at high pH; GB is reason-
ably soluble in water. Thus, the reaction takes
place only at the phase interfaces, and vigorous
stirring to achieve the desired reaction rates.
Thickeners have been used in some mustard for-
mulations, and some agents have thickened into
gels by some unknown decomposition or polymer-
ization process while in storage. (Gelling occurs
most often for mustard HD and, to a lesser extent,
for GB.)
Investigations to develop decontamination meth-
ods were generally limited to room-temperature
reactions because decontamination is usually per-
formed at ambient temperatures. Higher tempera-
tures, which are feasible for the destruction of bulk
agent, were not investigated.
· Decontamination is generally carried out by flood-
ing the surface or the liquid with a large excess of
decontamination liquid (e.g., 100 to 1~; for the de-
struction of bulk agent, this amount of liquid
would create an unnecessarily large hazardous-
waste disposal problem.
Major studies on chemical-neutralization (NRC, 1993;
Yang, 1995) are summarized in Table D-1. Because
OCR for page 204
204
ALTERNATIVE TECHNOLOGIES FOR DEMILITARIZATION OF ASSEMBLED CHEMICAL WEAPONS
TABLE D-1 Examples of Large-Scale Neutralizations
Country AgentQuantity (tons) Reactant Temperature Disposal Period/Rate
United States Sarin (GB)4,000 Aq NaOH Ambient RCRAa hazardous 1973-1976
landfill
Russia Sarin, Soman,3,000 HoCH2CH2NH2 100°C Incineration 1980-1990
mustard 600 Lreactorb @ 20t/a
V-typeC30 H3PO4 and EGO 140°C Incineration 1980-1990
600 L reactors @ 20t/a
Canada Mustard700 Ca(OH)2 8t batch 95°C Incineration 1974-1976
VX, Tabun,e0.3 20% KOH inMeOH Ambient Incineration 4 months
Soman intermittent
United Kingdom Sarin20 20% NaOH 250 kg Ambient Discharged at depth 1967-1968
per batch into coastal sea
Iraq Sarin, GFe70 Aq NaOH Ambient Discharged to 1992-1993
lined pit @ 1 ton/day
aResource Conservation and Recovery Act.
bA mobile reactor known as the KUASI system.
CA VX analog: MeP(O)(OCH2CHMe2)(S(CH2)NEt2).
dEthylene glycol, (EG).
eTabun is (Me2N)P(O)(OC2Hs)CN; OF is MeP(O)(OR)F where R = cyclohexyl.
Source: Adapted from NRC, 1993; Yang, 1995.
the hydrolysis technologies proposed for the As-
sembled Chemical Weapons Assessment (ACWA) all
start with either NaOH-solution (three proposals) or
KOH-solution (one proposal) for nerve agents and wa-
ter for mustard (four proposals), the discussion below
is limited to agent detoxification with these materials.
Aqueous systems have some obvious advantages:
reduced fire and other chemical hazards; a more sub-
stantial research basis than for other reagents; and a
smaller volume of organic material to dispose of.
HYDROLYSIS OF GB
Basic aqueous solutions react readily with GB by
the following reaction:
o
11
(CH3)2CHO P F + 2NaOH
1
CH3
sarin (GB)
o
11
(CH3)2CHO P O~ + 2 Na + H2O + F (1)
1
CH3
isopropyl-methylphosphonic acid
Yang (1995) states that, "The reaction is a bimo-
lecular displacement (SN 2 (P)) of F- by OH- to produce
the phosphonate anion." The rate can be high; the sec-
ond-order rate constant at 25°C (77°F) is 25 (molarity-
sec)~1 (Gustafson and Martell, 1962~:
d [GB] = -25~0H] [GB]
dt
where the brackets represent concentration. Assuming
caustic is maintained at 0.1 molar, the concentration of
GB should be reduced one million-fold in 5.5 seconds.
Sarin is soluble in water, although the exact solubil-
ity limit does not appear to have been reported. It has
been reported, however, that a 1: 1 volume mix of sarin
and water was immediately miscible (Reeves and
Macy, 1947~. Alcohol (methanol or ethanol) is some-
times added to keep the GB in solution.
Excess NaOH or KOH is required to maintain the
high pH. A typical impurity in GB is a diester:
o
1l/O (isopropyl)
H3C P.\
O (isopropyl)
If the pH of the final solution falls below 7, this diester
can react with fluoride ion to reform GB (Beaudry et
al., 1993~. The reaction is very slow, however.
OCR for page 205
APPENDIX D
TABLE D-2 Effect of pH on Equilibrium of
Remaining GB
GB
pH
Moles/L
ng/L
3
0
9
8
lo-l
10-4
10-5
lo-6
10-~9
10-13
10-11
10-9
1.4 x 10-8
0.014
.4
40
Excess NaOH is also required to ensure the "com-
plete" conversion of GB. The estimated equilibrium
constant, Ke, for the hydrolysis reaction is (Harris et
al., 1982~:
K = [IMP][F ~ = 1Oi9
[GB] [OH ~
where tIMP] is the concentration of the isopropyl
methylphosphonate (IMP) ion; EF-] is the concentra-
tion of fluoride ion; [OH-] is the concentration of hy-
droxyl ion; and KGB] is the concentration of GB re-
maining. All concentrations are in gram-moles per liter.
This equilibrium constant was calculated from elemen-
tal reaction rates (see Harris et al., 1982~.
The effect of pH on the amount of GB remaining in
solution has been calculated based on this equilibrium
constant (see Table D-2. For this calculation it was
assumed that the IMP and F- concentrations were
0.1 molar each. The calculation suggests that the pH
must be maintained at 9 or more for the GB to be re-
duced to below the detection level. (Note: The equilib-
rium quoted above has been questioned [Ward, 1998a],
but it is certain that GB can reform at low pH at about
the levels suggested in Table D-2. An alternative ex-
planation for the reformation of GB at low pH is the
reaction of the diester impurity.) Isopropyl methyl-
phosphonic acid, the major product of the hydrolysis
of GB, is a Schedule 2 compounds and must be irre-
versibly destroyed to meet the requirements of the
Chemical Weapons Convention (CWC).
Military grade GB is not very pure. Early lots (1 to
241) were manufactured to a specification of 92 per-
cent and were distilled. Later lots (242 to 431) were
manufactured to a specification of 88 percent and were
iSchedule 2 compounds are defined as those that can be readily con-
verted to chemical agent. Any high valence phosphorus compound with
alkyl side chain in the range Cat to C4, iS considered a Schedule 2 compound.
205
not distilled (U.S. Army, 1996~. Stabilizers were added
to all lots to retard degradation. The first stabilizer
used was tributylamine (TBA); later, diisopropyl-
carbodiimide (DICDI) was used. Some of the older GB
has been found to contain crystalline material, believed
to result from the TEA inhibitor. Some GB has been
recovered, redistilled, and restabilized with DICDI.
Thus, considerable variation in GB composition should
be expected during the stockpile disposal program. The
purity of GB at loading of weapons is reported to be
between 73 percent and 93 percent.
Hydrolysis of VX (described in the next section)
produces a two-phase product: a small organic layer,
which is reported to result primarily from the DICDI
inhibitor, remains separate from the main aqueous
phase. This same behavior has recently been reported
from the hydrolysis of GB (Ward, 1998b). The organic
layer amounts to approximately 2 to 5 percent of the
original agent volume. The flash point of this organic
layer has not been reported.
During the large-scale disposal of satin at the Rocky
Mountain Arsenal in 1973-1976 (Item 1 in Table D-1),
GB apparently persisted in the brine at a very low level.
The brine had to be certified to have less than 2 ng/ml
(2 ppb w/v) of GB before going to a dryer, where the
liquid was evaporated and the solid residue was pack-
aged to be buried. Several explanations for the persis-
tence of GB were offered (Harris et al 1982~. The one
most generally accepted at present is a problem in the
analytical procedure, with GB reforming during analy-
sis. The analytical method now proposed by ERDEC
is: extraction in chloroform at high pH (e.g., pH of 11),
followed by gas chromatography (GC) and mass spec-
trometry (MS). The extraction at high pH eliminates
the problem of GB reforming.
The problem was serious at the Rocky Mountain
Arsenal because hydrolysis was the only process being
used. A follow-up process is now required to eliminate
the major Schedule 2 product (isopropl-methyl-
phosphonic acid; see Eqn. 1~. This process could be
used to ensure the complete destruction of low-level
residual GB.
Hydrolysis of GB has also led to a problem with
formation of a solid precipitate believed to be sodium
fluoride (Ward, 1998c), which has only limited solu-
bility in water (i.e., about 4 percent). A ferrous oxide or
hydroxide has also been suggested. GB hydrolysate,
OCR for page 206
206
ALTERNATIVE TECHNOLOGIES FOR DEMILITARIZATION OF ASSEMBLED CHEMICAL WEAPONS
provided by the Chemical Agent and Munitions Dis-
posal Systems (CAMDS) for use by the ACWA tech-
nology providers in their process demonstrations, was
prepared in fairly dilute solution to avoid formation of
the precipitates. The formulation used was 7 gallons of
GB with 93 gallons of 5 percent NaOH solution in
water. (This represents roughly 10 percent excess of
NaOH solution in water and resulted in a pH between
l l and 12.)
The hydrolysate will probably be determined to be
toxic when animal toxicity studies are completed (by
analogy with VX-hydrolysate, below). Thus, it should
be handled with care as a toxic material.
HYDROLYSIS OF VX
The hydrolysis of VX proceeds much more slowly
than that of GB. In dilute solution, at 22°C (72°F):
d[~X] = -5.2 x 10-3 [OH] [VX]
dt
The rate constant shown is 4,800 times smaller than
that of GB. A reduction in concentration by a factor of
one million would require more than 7 hours. The acti-
vation energy for the reaction is given as 15.0 kcal/mol
(at pH = 12~. Thus, increasing reaction temperature
from 22°C to 90°C, for example, would increase the
reaction rate by a factor of 117; the reaction time would
be correspondingly reduced. The temperature chosen
for hydrolysis of VX at Newport is 90°C (194°F).
The rates quoted above are for VX in solution. How-
ever, VX has very limited solubility at high pH. There-
fore, the reaction rate will be limited by the mass-trans-
fer rate between the two phases. As reaction proceeds,
CH-P S CH-CH-N NaOH
OCH2 CH3
VX
the products (see Figure D-1), which are soluble in
water, increase the solubility of the remaining VX. In
development work performed for Newport, vigorous
stirring was used to disperse the two phases.
The major reactions in the neutralization process are
shown in Figure D-1. The overall reaction requires
more than 2 moles of NaOH per mole of VX to neutral-
ize the ethyl methylphosphonic acid (EMPA) and me-
thyl phosphoric acid (MPA), as well as the thiolamine,
and to maintain a high pH. VX exhibits behavior simi-
lar to GB: if the pH of the product solution is allowed
to drop, VX will reform. Approximately 90 percent of
the VX reacts directly (by the top reaction), breaking
the P-S bond to form the sodium salt of EMPA and the
his (isopropyl) amino ethyl thiol ("thiolamine"~. How-
ever, about 10 percent of the VX reacts by a second
channel in which the P-O bond is cleaved to form the
intermediate compound shown as EA2192, which is
itself highly toxic but will react slowly to form MPA
and more thiolamine. EA2192 is hydrolyzed at least
ten times more slowly than VX. About six hours at
90°C (194°F) are required for adequate destruction.
Most of the products are soluble in aqueous NaOH,
but a small residue, arising mainly from a stabilizer
added to the original VX, remains as an insoluble or-
ganic layer less dense than water. The organic layer is
flammable with a flash point of 53°C (127°F) (ERDEC,
1998~. This should be recognized as a hazard in carry-
ing out the reaction at 90°C (194°F).
Military grade VX is 90 to 95 percent pure; a typical
analysis is shown in Tables D-3 and D-4. The agent
analysis was obtained by GC with a thermal conduc-
tivity detector. The other organic components were
'CH(CH3~2
~13% ~ ~NaOH
~ -CH3CH2 OH
~/ CH(CH312
CH3 P O~Na++ Na+ ~S CH2-CH2-N
O CH2CH3
EMPA
slow'| -CH3CH2OH
Thiol
CH(CH3~2
/CH(cH312 0 ,CH(CH3~2
CH3 P-S-CH2 CH2 N ~ CH3 P-ONa++Na+~S-CH2-CH2-N
O~Na+ \CH(CH3~2 O~ Na+ CH(CH3~2
EA 2192 MPA Thiol
FIGURE D- 1 Primary reactions involved in VX hydrolysis. Source: Yang et al., 1992; NRC, 1996.
OCR for page 207
APPENDIX D
TABLE D-3 Results of the VX Ton Container Survey Program (Organics~a
Organic Compounds
Mole %
VX
S. S' bis(2-diisopropylaminoethyl) methylphosphonodithiolate
Dimethyl ketone (acetone)
Diisopropylamine
N. N-diisopropylmethylamine
Diisopropylcarbodiimide (stabilizer)
N. N-diisopropylethylamine
O-ethyl methylethylphosphinate
1, 3-diisopropylurea
Diethyl methylphosphonate
2-(diisopropylamino)ethane thiol
O. O-diethyl methylphosphonothiolate
O. S-diethyl methylphosphonothiolate
2-(Diisopropylamino)ethyl ethyl sulfide
Diethyl dimethylpyrophosphonate (pyro)
O. O-diethyl dimethylpyrophosphonothioate
0-(2-diisopropylaminoethyl) O-ethylmethylphosphonate (QB)
1, 2-bis (ethyl methylphosphonothiolo)ethane
Unknowns
Total
95.700
0.135
0.004
0.103
0.003
1.190
0.004
0.021
0.004
0.041
0.065
0.098
0.046
0.081
0.072
0.124
0.170
0.450
0.500
00.000
aAnalyzed by gas chromatography/mass spectroscopy (GC/MS).
Source: U.S. Army, 1997a.
analyzed by GC with an electron-impact mass selec-
tive detector. Metal analysis was performed with in-
ductively-coupled plasma/atomic emission spectros-
copy (ICP/AES ). Mercury was analyzed by cold-vapor
atomic absorption.
The largest "impurity" listed is DICDI, which was
added to the VX as a stabilizer (antioxidant). Its con-
centration can be as high as 5 percent. The other
TABLE D-4 Results of the VX Ton Container Survey
Program (Metals~a
Metal
Analytical
Result (ppm)
Arsenic
Chromium
Lead
Selenium
Zinc
Mercury
Copper
Iron
Magnesium
Calcium
Barium
6.700
1.200
0.370
3.600
4.400
0.130
0.500
17.000
4.200
28.000
0.031
aAnalyzed by inductively coupled plasma (ICP) spectrometry.
Source: U.S. Army, 1997a.
207
impurities shown are present at large parts-per-million
(ppm) concentrations; many impurities in the parts-per-
billion (ppb) range would probably be found with more
sensitive analytic techniques.
The aqueous phase contains most of the product,
about 95 percent; the organic layer has approximately
5 percent of the total. The compositions of the two
product phases will, of course, be quite different. A
typical composition for the total mixture (obtained by
"homogenizing" the two phases) is shown in Table D-5.
The analysis was based on 13C and 3lP nuclear mag-
netic resonance spectrometry (NMR).
The major products are those expected from the re-
action sequence given in Figure D-1, together with
nonreacted impurities expected from the initial compo-
sition. Materials present at very low concentrations
(e.g., ppm range or less) are not, in general, differenti-
ated in the analysis. The exceptions are VX, shown
in Table D-6 to be remaining to the ppb range, and
EA 2192, in the ppm range.
The hydrolysis product has an unpleasant odor,
which can be mitigated by the addition of bleach after
the hydrolysis reaction is complete. This may or may
not be desirable, depending on the subsequent treat-
ment planned for the material.
OCR for page 208
208
ALTERNATIVE TECHNOLOGIES FOR DEMILITARIZATION OF ASSEMBLED CHEMICAL WEAPONS
TABLE D-5 Analysis of Homogenized VX Hydrolysate after 240-Minute Reaction Timea
Compound Formula Mole %
EMPA (Ethyl methlyphosphonic acid)
MPA (Methylphosphonic acid)
EMPSH (O-Ethyl methylphosphonothioic acid)
Other UP
RSH (Diisopropylaminoethanethiol)
RSSR (Bis [diisopropylaminoethyl] disulfide)
RS R (B is [diisopropylaminoethyl] sulfide)
RSCCSH (2- [diisopropylaminoethylthio] ethanethiol
DIPA (Diisopropylamine)
CDI (Dicyclohexylcarbodiimide)
Other RS-compounds
OP(CH3)(0 CH2 CH3) (OH)
OF (CH3)(0H)2
SP(CH3)(0 CH2 CH3)(0H)
Not applicable
R'- SH
R'- SS'R'
R'- S - R'
R1 - S1 - CH2 CH2SH
HN[CH(CH3)2]2
C6Hll - N = C = N - C6H
Not applicable
41.5
4.6
0.3
0.2
43.4
0.4
0.7
1.3
0.6
2.7
1.9
aAnalyzed by 13C and 31p nuclear magnetic resonance (NMR) spectroscopy.
Source: U.S. Army, 1997b.
VX was hydrolyzed at CAMDS to supply hydroly-
sate for the ACWA technology provider demonstra-
tions. This hydrolysate had a higher concentration than
the GB hydrolysate. Thirty-three gallons of VX were
mixed with 67 gallons of 20 percent NaOH solution in
water to produce the hydrolysate.
The primary purpose of the VX hydrolysis is to re-
duce the material toxicity. Animal tests have been car-
ried out to confirm the reduced toxicity. The intrave-
nous LD50 value of VX for mice was reported to be
0.0141 mglkg. The hydrolysis product was 4 to 6 or-
ders of magnitude less toxic. The characteristic signs
of nerve agent attack were not observed with the hy-
drolyzed material. The remaining toxicity is due to the
salt and organic content of the samples.
The major phosphorus products in the hydrolysate
are considered to be Schedule 2 compounds; they must
be irreversibly destroyed to meet the requirement of
the CWC.
In summary, the hydrolysis reaction can reduce the
toxicity of the original VX by a large factor, 5,000-fold
TABLE D-6 Residual VX and EA 2192 Concentrations
from 12-Liter Reactor Tests
Reaction Time
(minutes)
Homogenized Samples
vxa
EA 2192b
30
120
< 20 ppb
< 20 ppb
65 ppm
< 24 ppm
aAnalyzed by GC/ion trap mass spectrometry (ITMS).
bAnalyzed by 3~P NMR spec~oscopy.
Source: U.S. Army, 1997b.
to 25,000-fold. The product retains a low level of toxic-
ity and will require further treatment before being re-
leased to the environment.
HYDROLYSIS OF HD
The mustard stored at Aberdeen, Maryland, will be
detoxified by hydrolysis with hot water (90°C; 194°F)
followed by the addition of caustic.
The overall desired reaction is:
S\
,CH, CH, C1
CH2 CH2 C1
+ 20H- ~ S\
,CH3 CH2 CH
'CH3 CH2 CH
+ 2C1
This overall reaction follows a complex series of steps,
however, leading to several products. In addition, mili-
tary grade mustard is usually impure (as low as 80 per-
cent purity), and the impurities contribute to the com-
plexity of the neutralized mix.
There are several reasons for the two-step reaction
sequence (hot water hydrolysis followed by addition of
caustic). Hydrolysis with water is preferred because
caustic produces vinyl compounds, which are consid-
ered toxic and resist further treatment. The products of
the aqueous hydrolysis are strongly acidic, and the pH
must be adjusted for the subsequent treatment proposed
for Aberdeen (biodegradation). Finally, the added caus-
tic will react with a small amount of sulfonium salts,
which are themselves toxic.
A typical analysis of liquid mustard is shown in
Table D-7 (based on GC/MS analysis). There are
probably many more components present at lower
OCR for page 209
APPENDIX D
TABLE D-7 Typical Composition of HD Agenta
209
TABLE D-8 Concentration of Metals in HD Agenta
Compound Mole %c Metal Content (ppm)
HD
Qb
2-chloroethyl 4-chlorobutyl sulfide
1, 4-dithiane
1, 2-dichloroethane
Bis 3-chloropropyl sulfide
2-chloropropyl 3'-chloropropyl sulfide
2-chloroethyl 3-chloropropyl sulfide
1-chloropropyl 2-chloroethyl sulfide
1, 4-thioxane
91.38
6.08
0.86
0.81
0.35
0.18
0.18
0.14
0.02
<0.01
aAnalyzed by GC/MS.
bQ is the following cyclic sulfonium compound:
/ CH2 CH2
\
CH2 CH2/
CImpurities may vary widely among ton containers containing HD.
For example, in a survey of ton containers at Aberdeen (U.S. Army,
1996), the mole percent of 2-chloroethyl 4-chlorobutyl sulfide ranged
from 0 to 2.32, for trichlorethylene it varied between 0 and 0.02.
, S+ CH2 CH2 C1
Source: U.S. Army, 1996.
concentrations (e.g., at the ppm level). The mustard
also conta~ns small concentrations of metals (see Table
D-8) the exact forms of which are not known.
There is generally a residual "heel" in mustard con-
tainers a gel that will not flow but that can be washed
out. The heel can amount to more than 10 percent of
the stored agent. Analyses of three heel samples are
given in Table D-9. The heel also contains metals, in-
cluding a large amount of iron (e.g., > 10,000 ppm as
iron sulfide).
Clean out of the ton containers containing HD leads
to a small vapor stream that requires treatment prior to
release. An analysis of a vapor sample is shown in
Table D-10. Sim~lar vapors should be expected when
cleaning out mustard-filled weapons.
Aluminum
Antimony
Arsenic
Barium
Beryllium
Bismuth
Cadmium
Calcium
Chromium
Cobalt
Copper
Iron
Lead
Magnesium
Manganese
Nickel
Phosphorus
Selenium
Silicon
Silver
Sodium
Sulfur
Thallium
Thorium
Tin
Vanadium
Zinc
< 13.0
<9.0
18.9
<0.3
<0.2
< 12.0
<3.0
9.6
<2.0
<2.0
91.8
5,035.0
<7.0
<0.4
0.6
<4.0
32.6
< 14.0
110.9
<4.0
< 16.0
264,420.0
< 13.0
< 11.0
<6.0
<3.0
<0.7
aAnalyzed by ICP spectrometry.
Source: U.S. Army, 1996.
Mustard is relatively insoluble in water, so the hy-
drolysis reaction must occur at the interface. High-
shear mixing has been used to speed up the reaction.
The rate-determining step of the reaction with water
was found to be the formation of an intermediate cyclic
ethylene sulfonium ion:
S\
CH2 CH2 C1 /CH2
+ H+ + C1- ~ C1~H2~H2 S\ | + C1
CH2
CH2 CH2 C1
TABLE D-9 Complex Organic Compounds in HD Heel by NMR (mole percent~a
Sample #
Location
HD Cyclic Sulfonium Ionb 1, 4-Dithiane Other
C-03-04-HH-1936 Top of heel 53 42
C-03-05-HH-1936 Bottom of heel 33 60
C-03-06-HH-1936 Middle portion 14 86
aAnalyzed by ~H and ~3C NMR.
bThe cyclic sulfonium ion is
CH2 CH2\
\
CH2 CH2/
Source: U.S. Army, 1996.
/ S+ CH2 CH2 C1
OCR for page 210
210
TABLE D-10 Content of HD Agent and Volatile
Organic Compounds in Initial Ton Container Vapora
Compound
1, 2-dichloroethane
Bis-(2-chloroethyl) sulfide (HD)
1, 4-dithiane
2-Chlorobutane
Tetrachloroethene
aAnalyzed by GC/MS.
Source: U.S. Army, 1996.
ALTERNATIVE TECHNOLOGIES FOR DEMILITARIZATION OF ASSEMBLED CHEMICAL WEAPONS
Concentration (mg/L)
6.000
0.830
0.600
0.210
0.083
This intermediate then reacts further, and a series of
materials other than the expected thiodiglycol are
formed. A suggested reaction pathway is shown in
Figure D-2.
In early work on mustard hydrolysis, HD could not
be detoxified by hydrolysis. The rate of reaction was
slow and was controlled by the rate of mass transfer.
As shown in the reaction scheme of Figure D-2, sulfo-
nium ion aggregates H-TG, CH-TG, and H-2TG were
formed and could be stable; also, H-2TG was believed
Main reaction
CH2 CH2CI CH2 CH2
S/ - S+
CH2 CH2CI CH2CH2CI
HD CH
(Sulfur mustard) I (Chlorohydrin)
Side reaction ~ +Thiodiglycol ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
/CH2 CH2CS+
S\
\ CH2CH2OH
CH2 CH2CI
H-TDG
HOCH2CHp
HOCH2 CH2
, CH2CH2OH / CH2 CH2OH
~H2O / CH2 CH2 C S\
· S CH2 CH2OH
CH2 CH2 OH
\ ~Thiodiglycol
/
/
\ /
S+CH2 CH2 CH2 CH2S+
/ \ / \
CH-TDG
,CH2 CH2OH
\ /
S CH2CH2OH
H-2TDG
*Brackets indicate transition states that are not directly observable.
to be quite toxic. All of these observations were based
on low-temperature hydrolysis with moderate stirring.
With very vigorous high-shear m~xing and high tem-
perature (90°C; 194°F), very complete hydrolysis, pri-
marily to the desired thiodiglycol, has been achieved.
Work at ERDEC using hot water for hydrolysis with
NaOH solution added at the end of the reaction has
reduced mustard to less than 20 ppb (the detection
level); 99 percent of the mustard was converted to the
thiodiglycol.
The organic compounds in the hydrolysate at differ-
ent times during the reaction after agent addition to
the hot water, and after subsequent addition of NaOH-
are shown in Table D- 1 1. (Only the major components
were analyzed; there are undoubtedly many others at
ppm-levels). The analysis of Table D- 1 1 does not show
the chlorinated hydrocarbons present in the original
mustard, which go through the hydrolysis reaction es-
sentially unchanged.
The hydrolyzed product remains toxic to some ani-
mal species. For example, fathead minnows (a fresh-
water species) showed an EC50 of 12 percent vol./volt
~H2OCH2CH2OH CH2-CH2 ~H2O CH2CH2OH
·S. ~S+ ~ S
CH2CH2 Cl CH2CH2 OH CH2 CH2 OH
TDG
(Thiodiglycol)
FIGURE D-2 Reversible formations of the sulfonium ion aggregates in the hydrolysis of mustard. Source: Yang et al., 1992; NRC,
1996.
OCR for page 211
APPENDIX D
TABLE Dell Organic Compounds in HD Hydrolysate (Mole Percent)
Analysis of Residuals
Compound 79 Minutes after End of HD Feed 63 Minutes after End of NaOH Addition
TDG 90.70 91.20
CHTGb 1.70 0.05
Q OHC 2.50 3.40
1, 4-dithiane 0.50 0.80
Glycol o.so o.5o
C6H~2SO2 compounds 2.10 2.20
Acetone 0.02 Not detected
Other 2.00 1.80
aAnalyzed by OH NMR.
bCHTG=HOCH2CH2-S-CH2CH2-S+-(CH2CH2OH)2
CQ-OH = HO CH2 CH2-S- CH2 CH2-S- CH2 CH2OH
Source: U.S. Army, 1996.
(i.e., a concentration of 12 vol. percent hydrolysate in
water led to the death of half the test population.)
Sheepshead minnows, a saltwater species, had a higher
tolerance: EC50 of 80 percent vol./volt The difference
in the tolerance level of the two species is probably due
to the high salt content of the hydrolysate.
The hydrolysis product is not acceptable for direct
discharge and must be further treated. The major prod-
uct (the thiodiglycol) is considered a Schedule 2 com-
pound and must be irreversibly reacted to meet the re-
quirements of the CWC.
Recent work on HD has shown that hydrolysis at
high temperature (90°C; 194°F) with vigorous mixing
can successfully destroy the mustard. The product is
not acceptable for discharge, however, without further
treatment.
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Representative terms from entire chapter:
alternative technologies
