Total mineralization of carbon tetrachloride under basic phase transfer conditions

Article abstract of DOI:10.1021/op800012z

Complete dechlorination of carbon tetrachloride to the mineral level was realized under mild conditions in the presence of a solid caustic base, a quaternary ammonium phase transfer catalyst and a cocatalyst such as an alcohol which functioned also as a solvent The solvent and the catalyst could be readily recovered and recycled after completion of the process. The reaction is sufficiently fast to avoid neutralization of the formed carbon dioxide, and consequently the overall stoichiometry of the process is: CCl₄ + 4NaOH → 4NaCl + CO₂ + 2H₂O. The key step in the reaction mechanism is the extraction of alkoxide anion by the phase transfer catalyst followed by consecutive nucleophilic substitution and hydrolysis of the substrate.

Full text of DOI:10.1021/op800012z

Organic Process Research & Development 2008, 12, 765–770
Total Mineralization of Carbon Tetrachloride under Basic Phase Transfer Conditions
Elza Snir and Yoel Sasson*
Casali Institute of Applied Chemistry, Institute of Chemistry, The Hebrew UniVersity of Jerusalem, Jerusalem 91904, Israel
Abstract:
particularly when performed in the presence of hydrogen donor
molecules such as toluene or methane.
5
Complete dechlorination of carbon tetrachloride to the mineral
level was realized under mild conditions in the presence of a solid
caustic base, a quaternary ammonium phase transfer catalyst and
a cocatalyst such as an alcohol which functioned also as a solvent.
The solvent and the catalyst could be readily recovered and
recycled after completion of the process. The reaction is sufficiently
fast to avoid neutralization of the formed carbon dioxide, and
Numerous alternatives have been reported for alternative
destruction methods of CT and other chlorinated hydrocarbons
(CHC). Typical are catalytic oxidative, reductive or hydrolytic
degradation and reaction with zero-valent metal such as zero-
6
7
valent iron (ZVI). Electrochemical and photochemical methods
are less common.
consequently the overall stoichiometry of the process is: CCl
4
+
Destructive adsorption of CT was realized at 200–300 °C
in a gas-phase reaction in the presence of steam and solid
4
NaOH f 4NaCl + CO + 2H O. The key step in the reaction
2
2
mechanism is the extraction of alkoxide anion by the phase transfer
catalyst followed by consecutive nucleophilic substitution and
hydrolysis of the substrate.
8
alkaline-earth oxides (i.e., SrO, BaO) or lanthanide oxides (i.e.,
9
La
2
O
3
, Pr
2
O
3
), particularly when supported on alumina. It was
shown that the gaseous CT and the solid metal oxide form
carbon dioxide and a metal chloride. The latter simultaneously
reacts with steam to form HCl and regenerate the metal oxide.
The authors claimed an unprecedented destruction rate of 0.289
Introduction
-1
-1
Carbon tetrachloride (CT) is a perchlorinated biorefractory
contaminant that has been used in the past in a wide range of
commercial, industrial and military applications. It has been
applied as a solvent, heat transfer medium, cleaning solvent,
pesticide, refrigerant aerosol propellant, and as an intermediate
for the production of chlorofluorocarbons (CFC). Even though
CT was banned in 1990 at the London Conference due to its
potential impact on the ozone layer depletion, it is still being
formed as a byproduct in various chlorination processes. CT is
classified as a Group B2 carcinogen and is highly toxic to the
liver, lung and kidneys. CT does not degrade naturally (although
some anaerobic microorganisms, such as methanogens, are
4
g of CCl h g catalyst at 350 °C. This is a simple technology
that produces a useful byproduct (HCl), but since the intermedi-
ate in the catalytic cycle was phosgene, which in certain
instances turned up in the final product mixture, it is highly
unlikely to be applied in practice.
10
Degradation of CT using the modified Fenton reagent was
found to be principally suitable for in situ treatment of
contaminated soil and groundwater, particularly when dense
11
non-aqueous-phase liquid (DNAPL) was present. Interestingly,
it was established that the reactive species in these processes
was not the typical hydroxyl radical but rather the less reactive
12
1
superoxide anion.
capable of reductive dechlorination ) and thus accumulates in
Reductive dechlorination by zero-valent metals was advo-
cated as the technology of choice for treatment of CT-
the environment, causing heavy damage to the ecosystem. Clean
and effective methods for destruction of CT are hence being
sought by researchers.
13
contaminated water. Indeed, rapid conversion of highly diluted
CT (µM level) could be measured, particularly under anaerobic
conditions, but unfortunately the dehalogenation process came
Simple adsorption of CT, such as by activated carbon, is
not practical mainly because the regeneration of the saturated
actived carbon is not straightforward and subsequent replace-
2
ment of the adsorbent would be frequently required. Incinera-
(5) (a) Gervasini, A.; Pirola, C.; Ragaini, V. Appl. Catal., B 2002, 38,
17. (b) Gervasini, A.; Pirola, C.; Zilio, S. Ragaini, V. Appl. Catal., B
3
tion is thus currently the most widely used solution, but the
2
004, 47, 257.
high temperatures required (>1300 °C) result in formation of
highly toxic byproducts such as dioxins and furans. Catalytic
incineration provides a partial solution to this problem,
(
6) He, J.; Saez, E. J.; Ela, W. P.; Batterton, E. A.; Arnold, R. G. Ind.
Eng. Chem. Res. 2004, 43, 913.
4
(7) Wiltowski, T. S.; Howerton, R. D.; Lalvani, S. B.; Zamansky, V.
Energy Sources 2001, 23, 845.
(
8) Weckhuysen, B. M.; Mestl, G.; Rosynek, M. P.; Krawietz, T. R.; Haw,
*
Author to whom correspondence may be sent. E-mail: ysasson@huji.ac.il.
1) (a) Chun, P.-C.; Reinhard, M. EnViron. Sci. Technol. 1996, 30, 1882.
b) Novak, P. J.; Daniels, L.; Parkin, G. F. EnViron. Sci. Technol.
J. F.; Lunsford, J. H. J. Phys. Chem. B 1998, 102, 3773.
(
(
(
(
(9) (a) Van der Avert, P.; Podkolzin, S. G.; Manoilova, O.; de Winne,
H.; Weckhuysen, B. M. Chem.-Eur. J. 2004, 10, 1637. (b) Van der
Avert, P.; Weckhuysen, B. M. Phys. Chem. Chem. Phys. 2004, 6, 5256.
(10) Teel, A. L.; Watts, R. J. J. Hazard. Mater. 2002, B94, 179.
(11) Smith, B. A.; Teel, A. L.; Watts, R. J. J. Contam. Hydrol. 2006, 85,
229.
(
1
998, 32, 3132.
2) (a) Armand, B. L.; Uddholm, H. B.; Vikstroem, P. T. Ind. Eng. Chem.
Res. 1990, 29, 436. (b) Salvador, S.; Kara, Y.; Crussol, J. M. Appl.
Therm. Eng. 2005, 25, 1871.
3) (a) Bose, D.; Senkan, S. Combust. Sci. Technol. 1983, 35, 187. (b)
Josephson, J. EnViron. Sci. Technol. 1984, 18, 222. (c) Huang, S. L.;
Pfefferle, L. D. EnViron. Sci. Technol. 1989, 23, 1085.
4) Lester, G. R. Catal. Today 1999, 53, 407.
(12) Roberts, J. L.; Calderwood, T. S.; Sawyer, D. T. J. Org. Chem. 1983,
105, 7691.
(13) Helland, B. R.; Alvarez, P. J. J.; Schnoor, J. L. J. Hazard. Mater.
1995, 41, 205.
1
0.1021/op800012z CCC: $40.75

2008 American Chemical Society
Vol. 12, No. 4, 2008 / Organic Process Research & Development
•
765
Published on Web 05/21/2008

to a standstill at dichloromethane, although some improvement
14
was realized when a Cu/Al bimetallic alloy was applied.
The best technology for detoxification of CT (and other
CHCs) in bulk is catalytic hydrogenolysis using hydrogen or
hydrogen donors as primary reducing agents. Palladium is the
15
catalyst of choice for both gas- or liquid-phase reactions, but
16
other transition-metal catalysts have been used as well. An
identical process has been the foundation of the transformation
of CFCs to the more ozone-friendly derivatives HCFCs via
Figure 1. Extraction of alkoxide anions in the presence of phase
17
catalytic hydrodechlorination. When applied to CT destruction,
the main shortcoming of catalytic hydrodehalogenation is its
selectivity which, with any metallic catalyst (with very few
transfer catalysts.
18
hydrolytic destruction of carbon tetrachloride under mild
conditions.
exceptions ), is mainly directed to the formation of chloroform
19
although a small amount of methane is also formed. Chloro-
form is the only product obtained also when a hydrogen donor
such as isopropanol is applied in the presence of a homogeneous
Results and Discussion
20
When CT (neat or in a solvent such as toluene) was heated
to reflux in the presence of 6 equiv of a concentrated aqueous
solution of sodium hydroxide, no reaction was observed after
several hours. Addition of 5 mol% of a typical phase transfer
Ru(II) catalyst. If total mineralization is required, a successive
step is necessary for the decomposition of chloroform, e.g. via
basic hydrolysis.
In this study we have developed conditions for the direct
aqueous hydrolysis of CT in the presence of sodium hydroxide.
The main tool for this unexpected reaction is quaternary
ammonium phase transfer catalysis combined with an alcohol
cocatalyst. It was previously proven that the direct extraction
of hydroxide anion in phase transfer systems is practically
24
catalyst such as Aliquat 336 or tetra-n-butylammonium
bromide (TBAB) initiated a very slow hydrolytic reaction.
Conversely, upon addition of a small amount of alcohol such
as isopropanol or n-hexanol to the above mixture, a highly
exothermic transformation (∆H ) -949 kJ/mol CT) was
realized according to the following stoichiometry: (eq 3)
21
unfeasible (eq 1).
PTC, toluene
alcohol, 70 °C, 16 h8
+
-
-
+
-
(org)
-
(org)
Q X( + OH h Q OH
+ X
(1)
CCl + 6NaOH
(aq)
org)
(aq)
4
4
NaCl + Na CO + 3H O (3)
2 3 2
However, upon addition of alcohols, basicity could be trans-
ferred into the organic phase via the extractable alkoxide anions
8
5% conversion,100% selectivity
22
(eq 2).
Reaction 3 achieved 85% conversion after 16 h. When
isopropanol was used in excess in the above experiment, in the
presence of solid sodium hydroxide and 5 mol% TBAC at
ambient temperature, a rapid autothermal reaction developed
+
-
-
+
-
(org)
-
(org)
Q X( + OH + ROH h Q OR
+ X
+ H O
org)
(aq)
2
(2)
(
reaching 75 °C) with a different stoichiometry: (eq 4)
This phenomenon has been used in several phase transfer
PTC
23
systems. The efficacy of the extraction is determined by the
pK of the alcohol and the extraction coefficient of the alkoxide
CCl + 4NaOH
isopropanol, 20 – 75 ° C, 3 h8
4
(aq)
a
4
NaCl + CO + 2H O (4)
2 2
anion (see Figure 1). In this study we have explored the
cocatalytic effect of alcohols on the phase transfer catalyzed
9
8% conversion, 100% selectivity
In the latter faster reaction, 4 equiv of sodium hydroxide was
sufficient to almost completely convert the CT into carbon
dioxide. The latter was formed so rapidly that it did not have
the time to react with the base to form sodium carbonate. The
enthalpy change in the latter reaction was calculated to be -778
kJ/mol CT. A very slow reaction was observed in this case even
in the absence of the phase transfer catalyst.
One can actually direct the process either to reaction 3, in
the presence of toluene as a solvent, or to reaction 4 when
isopropanol was used as the solvent.
(
(
(
(
14) Lien, H.-L.; Zhang, W. Chemosphere 2002, 49, 371.
15) Urbano, F. J.; Marinas, M. J. J. Mol. Catal., A 2001, 173, 329.
16) Alonso, F.; Beletskaya, I. P.; Yus, M. Chem. ReV. 2002, 102, 4009.
17) (a) Cho, O.-J.; Lee, I.-M.; Park, K.-Y.; Kim, H.-S. J. Fluor. Chem.
1
995, 71, 107. (b) Wiersema, A.; ten Cate, A.; van de Sandt, E. J. A.
X; Makkee, M. Ind. Eng. Chem. Res. 2007, 46, 4158.
(
(
18) Golubina, E. V.; Lokteva, E. S.; Lunin, V. V.; Turakulova, A. O.;
Simagina, V. I.; Stoyanova, I. V. Appl. Catal., A 2003, 241, 123.
19) (a) Gomez-Sainero, L. M.; Cortes, A.; Seoane, X. L.; Arcoya, A. Ind.
Eng. Chem. Res. 2000, 39, 2849. (b) Gomez-Sainero, L. M.; Seoane,
X. L.; Arcoya, A. Appl. Catal., B 2004, 53, 101. (c) Bae, J. W.; Jang,
E. J.; Lee, B. I.; Lee, J. S.; Lee, K. H. Ind. Eng. Chem. Res. 2007, 46,
1
721. (d) Cassez, A.; Ponchel, A.; Bricout, H.; Fourmentin, S.; Landy,
D.; Monflier, E. Catal. Today 2006, 108, 209.
In both reactions, assay of CCl
4
(by gas chromatography),
(by titration) and of CO (volumetric
analysis and capture with Ba(OH) followed by titration) in the
(
(
20) Sasson, Y.; Rempel, G. L. Tetrahedron Lett. 1974, 3221.
21) (a) Gordon, J. E.; Kutina, R. E. J. Am. Chem. Soc. 1976, 99, 3903.
-
-
-2
of OH , Cl , CO
3
2
(
b) De la Zerda, H.; Sasson, Y. J. Chem. Soc., Perkin Trans. II 1987,
147.
22) Demlow, E. V.; Thieser, R.; Sasson, Y.; Pross, E. Tetrahedron 1985,
972.
23) Maskoza, M.; Chesnokov, A. A. Tetrahedron 2002, 58, 7291.
2
1
(
(
2
(24) Tri-capryl-methylammonium chloride. Aliquat 336 is the trademark
of the Cognis Corporation.
7
66
•
Vol. 12, No. 4, 2008 / Organic Process Research & Development

cocatalyst. Interestingly, the mixing rate had only a negligible
effect on the reaction rate.
Effect of the Base Concentration. Table 1 displays the
conversion of CT after 80 min (reaction 3) and 30 min (reaction
4
) as function of the initial aqueous sodium hydroxide concen-
tration. Figure 4 presents the measured initial rates in reaction
as function of the initial aqueous NaOH concentration (weight
). Practically no reaction was observed, in both cases, when
4
%
the aqueous NaOH concentration was below 10%. The rate
sharply increased above 50% w/w concentration up to 100%
concentration (solid NaOH). Phase transfer systems in the
presence of bases are known to be strongly dependent on the
base concentration. Weaker bases such as potassium carbonate
or potassium phosphate were totally inactive in reaction 4.
Application of molar excess of sodium hydroxide beyond 50%
excess (up to 12:1 NaOH/CT molar ratio) had only a negligible
effect on the reaction rate and the final conversion.
Figure 2. Reaction profile (eq 4). Experimental conditions
CCl - 10.4 mmol, NaOH - 62.4 mmol, TBAC - 5 mol%, IPA
50 mmol, magnetically stirred open flask. Initial temper-
4
-
ature: 25 °C.
25
Nature and Concentration of the Phase Transfer Cata-
lyst. Figure 5 displays the activity of several phase transfer
catalysts in reaction 3 in the presence of 1-hexanol (conversion
achieved after 1 h). It is clear that the chloride and hydrogen
sulfate catalysts are superior to the bromide catalysts. This lower
activity of bromide salts can be attributed to partial “poisoning”
of the catalyst by the bromide anion which has a relatively high
Figure 3. Temperature profile of catalytic and noncatalytic
reaction 4. Experimental conditions for catalytic system: CCl
4
26
extraction coefficient. Tetrabutylammonium catalysts are more
-
10.4 mmol, NaOH - 62.4 mmol, TBAC - 0.52 mmol, 5 mol%
active than tetraethyl- and tetrahexylammonium catalysts,
probably due to the most favorable balance between lipophilicity
relative to CT, IPA - 50 mmol, magnetically stirred open
flask. Initial temperature: 25 °C. Noncatalytic system: same
conditions, but without TBAC.
27
and accessibility of the catalyst’s cation. Polyethylene glycol
PEG) 600 has shown some activity as well.
(
The effect of the catalyst concentration on the rate of reaction
is shown in Figure 6. The rate is increasing linearly up to 3
mol% of catalyst and then levels off to reach saturation above
0 mol % of catalyst. This can be rationalized by the limited
interfacial area in the system that can transfer only certain
amount of anions per unit time. Above a particular concentration
of catalyst, further addition would not increase the reaction rate
further.
Structure and Concentration of the Cocatalyst. Figure 7
compares the impact of different alcohols as cocatalysts on
reaction 3. Evidently phenol acts as a catalyst poison, giving a
lower rate than the blank experiment. Aliphatic primary alcohols
and diols had a clear cocatalytic effect on the process, with
1-hexanol showing the highest activity. Increasing the concen-
tration of the added alcohol in reaction 3 augmented the reaction
rate almost linearly. The obvious conclusion has been to apply
the cocatalyst as a solvent in order to achieve maximum rate.
In a series of experiments where various alcohols were used as
solvents we concluded that isopropanol is by far the best
cocatalyst in these systems. This is shown in Figure 8 where
the cocatalytic effect of isopropanol is compared with the effects
of 1-hexanol, benzyl alcohol, and 1-propanol. These results
suggest that the cocatalytic effect of the alcohol is governed
course and at the end of each process, confirmed the stoichi-
ometry and the mass balance of reactions 3 and 4. We
established that both the consumption of NaOH and the
formation of NaCl, as functions of time, are linear with the
rate of destruction of CT.
IR spectroscopy of both reaction mixtures, at various levels
of CT conversion, unequivocally rejects the presence of any
oxidation products such as aldehydes or ketones, thus eliminat-
ing the possibility of a redox reaction taking place in these
systems.
3
1
A typical nonisothermal reaction profile (eq 4) is shown in
Figure 2. Figure 3 presents the temperature profile of reaction
4
in the presence and in the absence of the phase transfer
catalyst.
At the end of reaction 4 the mixture was filtered, the aqueous,
concentrated brine phase was separated from the mother liquor,
and the remaining organic phase was analyzed to contain all
the initial isopropanol, the phase transfer catalyst, and the
nonreacted CT. After addition of a fresh batch of CT this
mixture could be recycled as-is for a second reaction batch
without any loss in activity.
In a series of experiments we have assessed the effect of
some critical parameters on the rate of the isothermal reaction
(
(
25) Solaro, R.; D’Antone, S.; Chiellini, E. J. Org. Chem. 1980, 45, 4179.
26) Bar, R.; de la Zerda, H.; Sasson, Y. J. Chem. Soc., Perkin Trans. II
1984, 1875.
(eq 3). We found that the reaction rate was strongly influenced
by the concentration of the alkali, the characteristics and
concentration of the quaternary ammonium phase transfer
catalyst, and the nature and concentration of the alcohol
(
27) Halpern, M. E. Phase Transfer Catalysis Mechanism and Syntheses.
In ACS Symposium Series, 659; Halpern, M. E., Ed.; American
Chemical Society: Washington, D.C., 1996. p 97.
Vol. 12, No. 4, 2008 / Organic Process Research & Development
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767

Table 1. Effect of the initial NaOH concentration on the reaction rate (eqs 3 and 4)
NaOH] w/w %
[
4
0
50
60
19
35.0
70
80
90
100
a
reaction 3 CT conversion (%)after 80 min
3.7
15.0
7.4
23.0
35.1
48.5
48.3
72.0
58.7
76.6
64.8
84.8
b
reaction 4CT conversion (%)after 30 min
a
Reaction conditions: reaction 3: CT 6.25 mmol, toluene 3.5 mL, 1-hexanol 2.94 mmol, Aliquat 336 0.312 mmol in a sealed tube. 80 min at 60 °C, magnetic stirring.
Reaction conditions: reaction 4: CT, 10.4 mmol; NaOH, 41.6 mmol; isopropanol, 85 mmol; TBAC, 0.52 mmol. In an open flask equipped with a reflux condenser; 25 °C
b
initial temperature; magnetic stirring for 30 min.
by its acidity and by the extractability and nucleophilicity of
the corresponding alkoxide anion. Finally, Figure 9 presents
the effect of the concentration of 1-hexanol on the rate
(conversion after 1 h) of reaction 3. Some conversion is
observed even in the absence of the alcohol cocatalyst (15%
conversion), but evidently the cocatalytic effect is strongly
dependent on the 1-hexanol concentration, thus substantiating
the conclusion to use the alcohol as a solvent in this process.
Proposed Reaction Mechanism. The destruction processes
3
and 4 can proceed via one of the following three mechanisms
28
formerly proposed by Sawyer:
1] A single electron transfer (SET) from hydroxide or
alkoxide anion to CT to form a radical anion:
[
Figure 4. Initial rates of reaction3 as function of initial NaOH
concentration; CT, 6.25 mmol; toluene, 3.5 mL; 1-hexanol, 2.95
mL; Aliquat 336, 5 mol % relative to CT; NaOH, 37.5 mmol
at different concentrations in water; 60 °C in a magnetically
stirred, sealed tube.
-
-•
OH + CCl f •OH + CCl
4
4
-
-•
4
OR + CCl f •OR + CCl
4
carbonates instantly decompose under our reaction conditions
to yield carbon dioxide and release the original alcohol which
enters a new catalytic cycle (eq 5):
[
2] A nucleophilic attack of hydroxide or alkoxide on the carbon
of CT:
-
-
3
RO + CCl f RO + CCl
C(OR) + 4NaOH f CO + 4RONa + 2H O (5)
4
4
2
2
where R ) H, alkyl.
3] A nucleophilic attack of alkoxide on chlorine:
On the basis of our results we propose the following
conceptual flowchart for the continuous destruction of CT to
carbon dioxide with consumption of only sodium hydroxide
[
-
-
3
(Figure 10). One equivalent of fresh CT and four equivalents
OR + CCl f ROCI + CCl
4
of solid sodium hydroxide are fed into an adiabatic reactor
maintained at 75 °C and mixed with recycled isopropanol
solvent and Aliquat 336 catalyst. The reactor has a residence
where R ) H, alkyl.
Both routes 1 and 3 would result in formation of alcohol
oxidation products such as aldehyde or ketone. These could
not be detected in any of the reaction mixtures that we have
studied. In addition, mechanism 5 would be strongly influenced
time of 1 h in which CT and NaOH are converted to CO
NaCl. The reaction is sufficiently fast to prevent the neutraliza-
tion of the CO by the base as was demonstrated on the
2
and
2
29
laboratory scale. At the following stage the mixture is transferred
to a settler where the aqueous and solid sodium chloride are
separated from the organic phase containing the isopropanol
and the Aliquat 336 catalyst. The latter mixture is recycled to
the reactor and the sodium chloride is discarded.
In a similar manner we were able to decompose hexachlo-
roethane, tetrachloroethylene and trichloroethylene although at
a slower rate. We thus propose this method as a general
technique for the destruction of polyhalomethanes, -ethanes and
by the presence of radical scavengers such as p-dinitrobenzene.
Addition of the latter to reactions 3 and 4 had no perceptible
effect on the measured rate. The possible presence of hydroxyl
radical was excluded in view of our failure to trap it with
30
salicylic acid. We thus conclude that the destruction processes
and 3 proceed via a four-step consecutive nucleophilic
2
substitution reactions. Since no intermediate could be identified
in our process, we presumed that all the intermediary products
decompose faster than their formation rate. This probably
includes the putative ortho carbonate ester formed by substitu-
tion of all the chlorine atoms in CT with alkoxides. The ortho
-ethylenes.
Conclusions
We explored and developed a simple, novel and autothermal
method for the total destruction of bulk carbon tetrachloride
under remarkably mild conditions using solid sodium hydroxide
(
(
(
28) Sawyer, D. T.; Roberts, J. L. Acc. Chem. Res. 1988, 21, 469.
29) Orvik, J. A. J. Org. Chem. 1996, 61, 4933.
30) Jen, J.-F; Leu, M.-F; Yang, T. C. J. Chromatogr., Sect. A 1998, 796,
2
83.
7
68
•
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Figure 5. Effect of different phase transfer catalysts on the
conversion of reaction 3. Experimental conditions: CT, 6.25
mmol; solid NaOH, 37.5 mmol; toluene, 3.5 mL; 1-hexanol, 2.95
mmol; catalyst 5 mol% relative to CT; 60 °C in a magnetically
stirred, sealed tube; 1 h.
Figure 8. Effect of the nature of the alcohol cocatalyst on the
conversion of reaction 4. Experimental conditions: CT, 10.4
mmol; solid NaOH, 62.4 mmol; TBAC, 5 mol%; alcohol 50
mmol; 25 °C initial temperature in a stirred, open flask; 1 h.
Figure 9. Dependence of reaction 3 rate on 1-hexanol concen-
Figure 6. Conversion of reaction 3 after 1 h as function of the
phase transfer catalyst concentration. Experimental conditions:
CT, 6.25 mmol; solid NaOH, 37.5 mmol; toluene, 3.5 mL;
tration. Experimental conditions: CT, 6.25 mmol; solid NaOH,
3
7.5 mmol; toluene, 3.5 mL; Aliquat 336, 5 mol % relative to
CT; 60 °C in a magnetically stirred, sealed tube; 1 h.
1
-hexanol, 2.95 mmol; 60 °C in a magnetically stirred, sealed
tube; 1 h.
Figure 10. Conceptual design for a CT destruction unit based
on this study.
Figure 7. Effect of the nature of the alcohol cocatalyst on
conversion of reaction 3. Experimental conditions: CT, 6.25
mmol; solid NaOH, 37.5 mmol; alcohol, 2.95 mmol; Aliquat
Experimental Section
336, 5 mol %; toluene, 3.5 mL;. 60 °C in a magnetically stirred,
sealed tube, 1 h. pK ’s of each alcohol in parentheses.
a
Materials. All the materials, solvents and catalysts were
purchased from Aldich and were used without further
purification.
as sacrificial reagent. The system is based on a synergic
combination of a quaternary ammonium phase transfer catalyst
and a secondary alcohol which are both uncomplicatedly
recyclable.
Destruction of CT Using Isopropanol as Solvent (eq 4).
A mixture of 10.4 mmol of CT (1.6 g), 85 mmol isopropanol
(5 g, IPA solvent and cocatalyst), 62.4 mmol sodium hydroxide
(2.5 g of solid, granulated) and 5 mol % tetra-n-butylammonium
Vol. 12, No. 4, 2008 / Organic Process Research & Development
•
769

chloride (TBAC, 0.145 g), was stirred at room temperature in
an adiabatic glass reactor equipped with a reflux condenser.
The reaction started instantly, reaching reflux temperature within
minutes and started to cool down after 12 min. The stirring
was continued for 3 h. The progress of the reaction was
monitored by volumetric analysis of the released carbon dioxide.
The released carbon dioxide was captured in an aqueous barium
hyrdroxide trap. The precipitated barium carbonate was filtered,
dried and weighed to confirm the overall mass balance. After
completion of the reaction, 100 mL of water was added. The
phases were separated, and the aqueous solution was analyzed
Destruction of CT Using Toluene/1-Hexanol System (eq
3). A mixture of 6.25 mmol of CT (0.95 g), 3.5 mL of toluene,
37.5 mmol sodium hydroxide (1.5 g of solid, granulated), 2.94
mmol 1-hexanol (0.3 g) and 5 mol % methyl-tricapryl-
ammonium chloride (Aliquat 336, 0.31 mmol, 0.126 g), was
stirred in a sealed tube at 60 °C for 1 h. Water (100 mL) was
added to the mixture. The phases were separated, and the
-
aqueous solution was analyzed for Cl content by argentometric
3
titration (AgNO , 0.1 N for titrating chloride ions, using 5 w/w
% K CrO as indicator). The carbonate anion was assayed by
2
4
gravimetric analysis of the barium carbonate obtained by the
addition of barium hydroxide. Conversion of 59% of CT was
measured. Practically all the original 1-hexanol, Aliquat 336,
and toluene and the remaining CT were found in the organic
phase.
-
-
for Cl and OH content by volumetric titration (HCl, 0.01 N
-
for titrating OH using 0.5 w/w % phenolphthalein as indicator;
AgNO , 0.1 N, for titrating chloride ions, using 5 w/w %
4
CrO as indicator). A quantity of 9.8 mmol of carbon dioxide
3
K
2
was trapped as barium carbonate; 39.1 mmol chloride and 23
mmol hydroxide were assayed in the aqueous phase. The final
organic phase was found to contain 4.6 g of isopropanol and
Received for review January 18, 2008.
OP800012Z
0.138 g of TBAC.
7
70
•
Vol. 12, No. 4, 2008 / Organic Process Research & Development