ACS Catalysis
Research Article
of 15 or 20 kV and used to determine crystal size. SEM images
Silicon/metal (Si/M) molar ratios were determined by
Galbraith Laboratories (GLI procedure ME-70).
Hamilton 5 μL GC injection syringe. Split injection mode was
used with a 7:1 split ratio. A typical oven temperature program
was as follows: Hold 75 °C for 0.3 min, ramp to 90 °C at
10 °C/min and hold for 4.5 min, ramp to 300 °C at 50 °C/min
and hold for 3 min.
2.3. Procedure for Diels−Alder Dehydration Reactions
Using Ethylene. Experiments were carried out in a 50 mL
high-pressure stainless steel batch reactor (Parr Series 4590)
equipped with a magnetic stirrer and heater. The reactor setup
allowed for ethylene gas (Matheson, 99.995% purity) or helium
to be charged to the reactor. In a typical experiment, 10 g of a
0.1 M diene [DMF (Sigma-Aldrich, 99%), MMF (Sigma-
Aldrich, 97%), or MMFC (Enamine, 95%)] solution in dioxane
(Sigma-Aldrich, 99.8%) and catalyst were loaded into the
reactor. For reactions quantified by GC/FID, triglyme (Sigma-
Aldrich, 99%) internal standard was also added at 0.1 M
concentration. The magnetic stirrer was operated at 200 rpm,
and the head space of the reactor was purged with helium gas
with a fill/vent cycle (10 times). Next, the reactor was
pressurized to 37 bar (room temperature) with ethylene gas,
the inlet valve was closed, and the reaction was performed in
batch operation. The reactor was heated to reaction temper-
ature (170−230 °C) while the pressure increased autogenously
(∼60−80 bar). At the end of the reaction time, the reactor was
allowed to cool to room temperature, and the reactor gases
were vented. The product was then collected for analysis.
MMFC and MMF reaction experiments for the 13C KIE
study were performed with larger reaction solutions and
catalyst amounts because multiple aliquots were taken during
these experiments. For the MMFC reaction, 12 g of a 0.1 M
MMFC solution and 100 mg of Zr-β were charged to the
reactor; for the MMF reaction, 14 g of a 0.1 M MMF solution
and 140 mg of Zr-β were charged to the reactor. Aliquots
2.6. Analysis of reaction products by GC/MS. GC/MS
analysis was performed on an Agilent 5890 GC interfaced with
a 5970 Mass Selective Detector. The column used was an DB-5
(30 m × 0.25 mm × 0.25 μm). The MSD was set to scan 50 to
550 m/z at 1.61 scans/s. The ionization mode was electron
ionization, and the instrument was tuned using standard
manufacturer autotune procedures using PFTBA (perfluoro-
tributylamine).
GC/TOF-MS analysis was performed by JEOL on a
AccuTOF GCv 4G system. The MS ion source was a EI/FI/
FD Combination Ion Source (EI+: 70 eV, 300 μA, 280 °C. FI+:
−10 kV, 40 mA(30 ms). JEOL emitter, heater off). A GC
interface temperature of 280 °C was used with 1 Hz data
acquisition rate.
2.7. Separation of Product Mixtures by Thin Layer
Chromatography. Preparatory thin-layer chromatography
(prep-TLC) on silica-gel plates was used to separate reaction
product mixtures. The product mixture was filtered to remove
spent catalyst, and the solution was deposited onto silica plates
using a needle syringe. Using a 1 ethyl acetate/3 hexanes v/v
mobile phase, the product mixture was separated into multiple
bands (visible under UV light). Analytes in each band were
collected by scraping the silica from the plates and extracting
with dichloromethane (DCM); the DCM was then filtered and
1
analyzed by GC/MS and GC/FID. If H NMR analysis was
desired, the DCM was removed by rotary evaporation, the
residual organics redissolved in CDCl3 NMR solvent, and a
NMR spectrum was collected at room temperature.
1
(∼0.5 g) for H NMR and GC/IR-MS analysis were collected
at various time points by cooling and opening the reactor.
When an aliquot was collected, the spent catalyst was removed
from the reaction solution by centrifugation, an equivalent
amount (100 mg for the MMFC reaction or 140 mg for the
MMF reaction) of freshly calcined Zr-β was added, and the
reactor was started again using the described protocol.
2.8. GC/Isotope Ratio MS Experiments. Carbon isotope
ratios (13C/12C) of analytes were determined using a
ThermoFinnigan TraceGC Ultra connected to a Deltaplus XP
isotope-ratio mass spectrometer (IRMS) via the ThermoFinni-
gan GC Combustion-III interface. Principle of operation of this
system is described by Sessions.23 Briefly, analytes in the GC
effluent are continuously combusted to CO2, which is dried
over a Nafion membrane then passed to the mass spectrometer.
Multicollector monitoring of m/z 45/44 then provides high-
precision measurement of the 13C/12C ratio, which is calibrated
to the international VPDB scale by comparison to a lab CO2
working gas standard.
2.4. Analysis of Reaction Products by 1H NMR.
Reaction results were quantified by 1H NMR as follows:
0.2 g of the starting diene solution and product solution were
added to separate 1 g DMSO-d6 solutions containing 5 mM
tetraethylsilane as an internal standard. The two mixtures were
transferred through filtering pipettes into NMR tubes, and the
1H NMR spectra were collected at room temperature. By
comparison with the tetraethylsilane peak, the concentrations
could be determined, and conversions and yields were
calculated. For example, the signals used for calculating the
conversion of MMFC and the yield of MMBC: tetraethylsilane
δ = 0.49 ppm (q, 8 H); MMFC δ = 4.42 ppm (s, 2 H), δ =
6.63 ppm (d, 1 H), and δ = 7.26 ppm (d, 1 H); MMBC δ =
4.50 ppm (s, 2 H), δ = 7.46 ppm (d, 2 H), and δ = 7.95 ppm
(d, 2 H).
Analytes were injected using a programmable-temperature
vaporization (PTV) injector operated in programmed temper-
ature mode (65 to 350 °C at 14.6°/s), and separated on a
Zebron ZB-5 ms column (30 m × 0.25 mm × 1.00 μm) with
He carrier gas at 1.4 mL/min. The oven temperature program
was 100 °C for 0.2 min, 7°/min up to 150°, 20°/min up to
310°, with a hold at 310 °C for 4 min. Analytes were oxidized
to CO2 in a reactor containing CuO, Ag, and Pt wires that was
reoxidized with O2 every night. 13C/12C ratios were calibrated
via CO2 reference gas peaks inserted at the beginning and end
of every chromatogram. Data were collected at 8 Hz and
processed using Isodat v2.1 software. Precision of replicate
measurements of unknowns averaged 5.8 ppm for the
13C/12C ratio of MMF (0.5‰ in δ 13C value), and 1.3 ppm
for MMFC (0.11‰ in δ 13C). Accuracy, measured as the mean
error for an external standard mixture containing eight fatty
acid methyl esters, was 3.5 ppm in 13C/12C ratio (0.31‰ in
2.5. Analysis of Reaction Products by GC/FID. GC/FID
analysis was performed on an Agilent 7890B GC system
equipped with a flame ionization detector (FID). The column
used was an Agilent HP-5 (30 m × 0.32 mm × 0.25 μm) with
N2 as carrier gas (6 mL/min flow through column). Samples
were typically prepared for injection by filtering a small aliquot
of the product solution through a filter pipet before diluting in
dichloromethane (DCM) in a ratio of 30 mg sample:170 mg of
DCM. Volumes of 1 μL were injected into the GC using a
δ
13C value).
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ACS Catal. 2015, 5, 5904−5913