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Can. J. Chem. Vol. 77, 1999
for the hydrolysis of various alkanesulfates (6–10). Although
CE has already been used to study reaction kinetics (12–15),
its utility in this regard is yet to be fully exploited, and the
demonstration that we could use CE for this purpose was an
important facet of our work. Thermodynamic calculations
were also done.
prior to use. Prior to each run the capillary (52 cm to
detector) was rinsed for 2 min with each of 0.1 M sodium
hydroxide, water, and buffer.
The water bath was a HAAKE G water circulator employ-
ing a digital HAAKE D8 thermostat and containing a 1:1 so-
lution of ethylene glycol and water. A Digi-Sense digital
pH͞mV͞ORP meter was used to record and adjust all pH’s.
Hydrolyses
Reagents
A sulfuric acid solution was prepared from concentrated
sulfuric acid and standardized to be 1.002 M using 8.2168 M
sodium hydroxide in a Hach model 16900–01 digital titrator
(Loveland, Colo.). A 10 mL aliquot was pipetted into a large
test tube sealed with a rubber stopper. A balloon on a sy-
ringe needle was inserted to allow for expansion and the
tube was equilibrated for 10 min at the desired temperature
(60, 75, or 90°C). Surfactant solutions of concentrations be-
tween 2 and 35 mM were also equilibrated at the chosen
temperature for 10 min before a 10 mL aliquot was added to
the acid and the time and initial pH recorded. Approximately
2 mL aliquots were taken via syringe from the reaction mix
at recorded time intervals. Each aliquot was placed in a
15 mL beaker. From this, 1 mL was pipetted into 30 mL wa-
ter, the time was noted and the pH was recorded. The 30 mL
solutions were neutralized using 1 M and 0.1 M sodium hy-
droxide and diluted to 50 mL. Samples were analyzed by
taking 100 µL of the above solution and running it in the CE
as described above. The peak areas and migration times
were recorded and the concentration was determined by ref-
erence to a standard curve of peak area͞migration time ver-
sus concentration. This standard curve was prepared by
diluting surfactant with sulfuric acid at room temperature
and immediately neutralizing and diluting samples as done
in the actual hydrolyses experiments.
Chlorosulfonic acid and diethylbarbituric acid were from
BDH, Mississauga, Ont.; 1,2-tetradecanediol, anhydrous di-
ethyl ether, and n-butanol were from Aldrich, Mississauga,
Ont., and sodium hydroxide was from J.T. Baker Chemical
Co., Phillisburg, N.J. Ethanol was obtained from Commer-
cial Alcohols, Boucherville, Que., and concentrated sulfuric
acid and pure cellulose Soxhlet extraction thimbles were
from Fisher Scientific, Nepean, Ont. Sodium chromate
tetrahydrate was from Anachemia, Mississauga, Ont.
CIA-PakTM OFM Anion-BT solution was obtained from
Waters (Millipore), Milford, Mass.The reverse-phase columns
were 15g Supelclean Envi-Carb solid phase extraction
columns from Supelco, Bellefonte, Pa.
All water used was 10 MΩ cm resistivity (Millipore
4000S purification system).
Preparation of TDDS: 1,2-Tetradecanediol (2.3 g,
10 mmol) was dissolved in 50 mL ether cooled in an ice
bath, and chlorosulfonic acid (1.5 mL, 22 mmol) was added
dropwise. The reaction mixture was stirred for 10 min and
then neutralised with 8 M sodium hydroxide. The white pre-
cipitated surfactant was collected and vacuum dried. A por-
tion (0.083g) was diluted to 25 mL and checked for purity
by CE.
Purification by reverse phase extraction columns: The
crude product was dissolved in 100 mL water and loaded
onto the column, which was then washed with water in
10 50-mL aliquots.
Purification by Soxhlet extraction: Crude product was
placed in a thimble and extracted with n-butanol. The prod-
uct remaining in the thimble was then extracted with etha-
nol.
Reaction rates of substances are greatly changed when the
substances in question are incorporated into micelles. These
substances may enter the micelle and thus be held in a more
hydrophobic environment where the reagent is more or less
soluble, or, as in the case of TDDS, the substance of interest
may be the surfactant actually forming the micelles. The
charge on the surface of a micelle will strongly attract or re-
pel charged reagents. In the case of acid hydrolysis we
would expect the protons to be attracted to the negatively
charged surface of the micelle, thus producing rate enhance-
ment at surfactant concentrations above the cmc. Such a
phenomenon has been well documented in the case of
alkanesulfate hydrolysis (8, 9, 11). Some investigators of
alkanesulfate hydrolysis have only used concentrations
above the cmc (7) while others have conducted studies at
lower concentrations (9–11). It was our intention to carry
out our study in a concentration region considerably lower
than the cmc in order to avoid micellar rate enhancement.
We chose our experimental setup to mimic conditions used
by El Sawy et al. (3), so that comparisons would be valid.
To this end, we chose TDDS as the substrate because it was
the shortest-chain disulfate reported in their paper. Because
of having the shortest chain, it was found to have the lowest
surface tension and be the best emulsifying agent of the
Instrumentation
Capillary zone electrophoresis (CZE) was carried out on a
Waters Quanta 4000 capillary electrophoresis system using a
75 µm fused silica capillary (Polymicro Technologies Inc.,
Phoenix, Ariz.), hydrostatic injection mode for 30 s, and in-
direct photometric detection at 254 nm. The data were col-
lected using LabCalc software (Galactic, Salem, N.H.) with
1 V equal to 1 au.
For anion analysis (to check salt content of surfactant
preparations), the applied voltage was –20 kV, and the buffer
was a chromate solution containing CIA-PakTM OFM-BT
solution, prepared as described by Waters (16). The capillary
was 58 cm to the detector.
For surfactant analysis, the applied voltage was +25 kV,
and the buffer was a diethylbarbiturate solution prepared by
dissolving 0.0554 g diethylbarbituric acid in 30 mL water,
adjusting the pH to 8.6, then making the volume up to 50 mL.
The pH was readjusted to 8.6 (17), and the buffer was fil-
tered through a 45 µL syringe filter and sonicated for 3 min
© 1999 NRC Canada