2
S. Rayati et al. / C. R. Chimie xxx (2018) 1e8
mechanistic study of these reactions. In addition, a great
deal of attention has been paid to developing the selectivity
and efficiency of the aforementioned reactions. As a
continuation of our work on the oxidation of various
organic substrates with green oxidants catalyzed by sup-
ported metalloporphyrins [8,14,26], herein, we report a
reusable, highly efficient catalyst for aerobic oxidation of
hydrocarbons under mild conditions.
this process, TBTU ((2-1H-benzotriazole-1-yl)-1,1,3,3-
tetramethyluronium tetrafluoroborate) as a highly effec-
tive uronium salt is used as an activation agent for car-
boxylic acids to prepare esters in the presence of DIPEA
(N,N-diisopropylethylamine) by the following procedure
[30,31]: GO (1.5 g), TBTU (0.4 g), and DIPEA (0.3 g) were
added to a solution of Mn(THPP)OAc (0.63 g) in DMF
(70 mL), and the reaction mixture was vigorously stirred at
room temperature for 48 h. The black solids were then
collected by filtration, washed thoroughly with ethanol,
and dried at 50 ꢂC for about 24 h. Mn-porphyrin was
immobilized onto the GO surface via the ester bond as re-
ported in our previous study. Preparation of the catalyst has
been schematically described in Scheme 1.
2. Experimental section
2.1. Materials and characterization
Analytical grade chemicals were purchased from Merck
and Fluka and used without further purification. Fourier
transform infrared (FT-IR) spectra were obtained using
potassium bromide pellets in the range 400e4000 cmꢀ1 on
an ABB Bomem FTLA 200-100 spectrophotometer. A Varian
AA240 atomic absorption spectrometer was used for
manganese determination. The UVevis spectra were
recorded using a Cam-Spec-M330 model. Scanning elec-
tron micrograph was taken using an EDf Oxford Mat 50
(Tescan vega3, lab6 model, magnification: 100,000). Gas
chromatography experiments were performed by an Agi-
lent 7890B instrument using an SAB-5 capillary column
2.5. General procedure for aerobic oxidation of hydrocarbons
Oxidation of hydrocarbons (0.192 mmol) was initiated
in a 5 mL test tube consisting of 1 mL acetone, 90 mL iso-
butyraldehyde (IBA) (0.960 mmol), 0.002 g catalyst, and
0.026 mmol imidazole (ImH) under the oxygen atmo-
sphere, where the reaction mixture was stirred for 120 min
at room temperature. The heterogenized catalyst was
separated from the reaction media by a simple filtration.
Gas chromatography was used to monitor the reaction
progress, and the oxidation products were identified by
comparison with the genuine samples.
(phenyl methyl siloxane 30 m ꢁ 0.32 mm ꢁ 0.25
mm) and a
flame ionization detector. The thermogravimetric analysis
(TGA) and Differential Scanning Calorimetry (DSC) was
carried out using Mettler Toledo (TGA-DSC), and X-ray
diffraction (XRD) was recorded by Philips PW3710 at the
3. Results and discussion
angle range of 5e150ꢂ using Cu K
a radiation.
3.1. Characterization of the [Mn(THPP)OAc@GO] catalyst
2.2. Preparation of Mn(THPP)OAc
Mn(THPP)OAc is anchored to the GO through covalent
bonding between the hydroxyl group of the Mn-porphyrin
and the carboxylic acid group of GO. The FT-IR spectra
confirmed the covalent anchoring of Mn(THPP)OAc to the
surface of GO (Fig. 1). An absorption band was observed at
856 cmꢀ1 in the spectra of GO, which is related to the
asymmetric epoxy on the GO surface [32]. Furthermore, the
two peaks appeared at 1155 and 1596 cmꢀ1 are respec-
tively, related to the CeO and C]O stretching bands
existing on the GO surface, and the broad peak observed at
3406 cmꢀ1 corresponds to the eOH stretching band of GO.
All these observations demonstrate that graphene was
successfully converted to GO. In addition, the sharp peak
5,10,15,20-Tetrakis(4-hydroxyphenyl)porphyrin
(H2THPP) was successfully prepared by the addition of 4-
hydroxybenzaldehyde (1.1 g, 14.5 mmol) and pyrrole
(0.62 mL, 14.46 mmol) to refluxing propionic acid as
described by Adler et al. [27]. Mn(THPP)OAc was also pre-
pared according to the procedure reported elsewhere [28].
2.3. Preparation of GO
GO was synthesized from natural graphite powder ac-
cording to the modified Hummers' method [15,29]. Briefly,
H2SO4 (360 mL) and H3PO4 (40 mL) were stirred and the
graphite powder (3 g) was added to the acidic solution and
sonicated for 30 min. Then, KMnO4 (18 g) was gradually
added to the mixture with stirring in an ice bath. After that,
the mixture was stirred for 24 h at 50 ꢂC to achieve GO.
Subsequently, the mixture was diluted with deionized ice
water (400 mL), and the oxidized product was treated with
H2O2 (6 mL) to remove the residual permanganate ions. The
ꢂ
GO product was collected by centrifuge and dried at 60 C
before further use.
2.4. Preparation of [Mn(THPP)OAc@GO]
Mn-porphyrin was covalently grafted to the GO nano-
sheets by the ester bond forming between the porphyrin
hydroxyl groups and carboxylic acid groups of the GO. In
Scheme 1. Preparation of [Mn(THPP)OAc@GO].
Please cite this article in press as: S. Rayati, et al., Mn(III)-porphyrin/graphene oxide nanocomposite as an efficient catalyst for the