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New Journal of Chemistry
Page 2 of 7
DOI: 10.1039/C7NJ04958G
ARTICLE
Journal Name
has been proposed based on the reaction results combining (λ=1.5406 Å) with a scanning angle (2θ) range of 5-80°.
with the density functional theory (DFT) calculation results.
Samples were carefully dried with a vacuum dryer under
nitrogen (99.999%) before testing.
Solid-state 13C NMR spectra were recorded on a Bruker
AVANCE-III 9.4
T
(13C Larmor frequency of 100 MHz)
2. Experimental
spectrometer at room temperature. Samples were packed into
a 4.0 mm rotor and were spinning at 8 kHz. 1H-13C cross-
polarization (CP) was employed with radio-frequency field of
π/2 and contact pulse optimized on Glycine sample. All spectra
were obtained with 2 s recycle delay, a contact time of 4 ms,
2.1 Materials and reaction procedure.
MA, DMC, DMM, and dimethyl sulfoxide (DMSO) (>99.0%
purity by GC analysis) were dried with 5A molecular sieves to
water content less than 0.005% determined by coulometric
Karl Fisher titration. Sodium methoxide (CH3ONa) and
potassium methoxide (CH3OK) solutions in DMSO were titrated
using literature methods18. All the reactions were conducted in
a 250 mL bath-type flask under nitrogen (99.999%) at ambient
pressure. Gas-tight syringes were employed to transfer
moisture-sensitive solutions.
1
and two-pulse phase modulation H decoupling. The chemical
shifts were referenced to tetramethylsilane by using glycine as
an external reference.
2.3 Computational methods.
All electronic structure simulation calculations were performed
with the Gaussian 09 program package19 using its default
criteria. Ab initio density functional B3LYP were employed with
a standard 6-31+G (d) basis set using the PCM solvent model20.
Optimal structures at B3LYP/6-31+G (d) theory level of each
transition state and intermediate are demonstrated in Fig. S1.
Frequency calculations were carried out for all stationary
points at the same level of theory as the geometry
optimization. No imaginary vibrational frequencies were
acquired for all local minimum structures, while only one
single imaginary frequency was presented for the transition
state that corresponded to the expected motion along the
reaction coordinate. Single-point calculations at the MP2/6-
31+G(d) level for the optimized structures were then carried
out incorporating thermal corrections to Gibbs free energy as
achieved at the B3LYP/6-31+G(d) level of theory and PCM
corrections for dimethyl sulfoxide (DMSO) as the solvent (ΔG,
298.15 K, 1.0 atm).
Typically, the condensation of MA and DMC catalyzed by
sodium methoxide was carried out as follows: solution of 5.4 g
CH3ONa dissolved in 50 mL DMSO was introduced to the flask
which has been pre-charged with N2 at an ambient pressure,
then the flask was placed in an oil-bath. After the system
reached the reaction temperature (typically 341 K), MA/DMC
(14.8 g /90 g) solution (which has been pre-heated to the
reaction temperature) was introduced into the reactor by a
gas-tight syringe, and the reaction was initiated instantly with
vigorous stirring. After 12 h, the reaction was instantly
terminated by cooling the reactor to room temperature (RT) in
iced water and stood still for 12 h before analyzing. The liquid
products were analyzed by gas chromatography (GC 9560,
Shanghai Huaai) equipped with an FID detector and a DB-200
capillary column (30 m×0.32 mm×0.25 μm). The same
experiment were carried out at least in triplicate for each run
to make sure the relative error was <5%.
2.2 Product characterization.
3. Results and discussion
GC-MS system consisted of an Agilent 7890A gas
chromatograph and an Agilent 7863B auto injector coupled
with an Agilent 5975C mass selective detector. The mass
spectral scan rate was 2.86 scan s-1. The GC was operated in
splitless injection mode with a helium (ultra-high purity,
99.999%) flow rate of 0.7 mL min-1 and the injection volume
was 1 μL. The MS was operated in the electron ionization (EI)
mode with an ionization voltage of 70 eV and a source
temperature of 503 K. The GC-MS chromatographic
separations were carried out on a HP-5 capillary column (30
m×0.25 mm × 0.25 µm).
3.1 The protonation for DMM formation after the condensation.
The condensation reaction of MA and DMC in DMSO solution
was conducted under 341 K for 12 h, then cooled to RT
immediately and stood still for 12 h. The reacted system split
into 2 phases-a white solid phase and a translucent liquid
phase, as demonstrated in Fig. S2 (A). Sampling of the liquid
phase was analyzed by a GC-MS spectrometer and only
unreacted MA, DMC, and newly-formed methanol were
detected besides the solvent DMSO. Surprisingly, the
expecting product DMM has not been examined (refer to the
GC-MS spectra in Fig. S3 (A)).
Liquid
chromatography-electrospray
ionization-
high
resolution mass spectrometry (LC/ESI-HRMS) measurements
were carried out on a Shimadzu LCMS-8030 triple quadrupole
Since methanol, as one of the condensation products, has
been confirmed in the product mixture, it is natural to
speculate that the condensation did occur in the reaction
system. And another expecting product of condensation
probably exist in certain form. Thus acetic acid (HAc), H2O, and
HCl acid, serving as proton-donors, were introduced into the
reaction system after the condensation reaction in order to
extract the objective product DMM. Interesting phenomena
were observed that the reaction system turned into a white
solid phase and a transparent organic liquid phase when HAc
mass spectrometer connected to
a Shimadzu LC-20AD
chromatograph (Kyoto, Japan). The ionization was performed
under normal electrospray conditions (flow rate: 4 ml min-1,
4.5 kV, dry temperature: 473 K) in positive mode. Methanol
(Merck LCMS Grade) was adopted as the mobile phase, and
samples were diluted with methanol at a ratio of 1:80 (V/V)
before analysis and the injection volume was set at 5 µL.
The XRD measurements were carried out using a Rigaku
C/max-2500 diffraectometer employing the Cu Kα radiation
2 | J. Name., 2012, 00, 1-3
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Zheng, Sainan
