Preparation of Copper Phosphate from Naturally Occurring Phytic Acid

Subscriber access provided by NAGOYA UNIV

Letter

Preparation of Copper Phosphate from Naturally Occurring Phytic Acid as an Advanced Catalyst for Oxidation of Aromatic Benzyl Compounds Haoran Wu, Jinliang Song, Chao Xie, Yue Hu, Shuaishuai Liu, and Buxing Han ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04193 • Publication Date (Web): 29 Sep 2018 Downloaded from http://pubs.acs.org on October 1, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Preparation of Copper Phosphate from Naturally Occurring Phytic Acid as an Advanced Catalyst for Oxidation of Aromatic Benzyl Compounds Haoran Wu,†,‡ Jinliang Song,*,† Chao Xie,†,‡ Yue Hu,†,‡ Shuaishuai Liu,†,‡ and Buxing Han*,†,‡ †

Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Colloid and Interface

and Thermodynamics, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China. ‡

School of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, Beijing

100049, China.

E-mails: [email protected], [email protected].

ABSTRACT: Both direct oxidation of aromatic benzyl compounds to aromatic ketones and utilization of naturally occurring chemicals to prepare functional catalysts are highly attractive. Herein, copper phosphate was successfully synthesized by using naturally occurring phytic acid as the phosphorus source. The obtained copper phosphate showed excellent performance for the direct oxidation of aromatic benzyl compounds to aromatic ketones with N-hydroxyphthalimide (NHPI) as the radical promoter using O2 as the oxidant. Additionally, the synthesized copper phosphate was stable in the reaction system, and could be used at least four cycles without considerable decrease in catalytic performance. This work provides a new way to prepare efficient heterogeneous catalysts using naturally occurring chemicals for the highly efficient oxidation of aromatic benzyl compounds to aromatic ketones. KEYWORDS: Naturally occurring phytic acid, copper phosphate, oxidation, aromatic benzyl compounds, aromatic ketones

ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

INTRODUCTION Aromatic ketones are an important class of intermediates in pharmaceuticals and fine chemicals.1-8 Direct oxidation of aromatic benzyl compounds has been regarded as an attractive route for the synthesis of aromatic ketones. However, it is still highly challenging for the production of aromatic ketones via direct oxidation of aromatic benzyl compounds owing to the inert nature of C-H bonds and poor product selectivity.9 Conventionally, the transformation can be realized using hazardous oxidants such as manganese dioxide, chromium trioxide or potassium dichromate, resulting in large amounts of highly toxic waste and by-products.10 Besides, expensive tert-butyl hydroperoxide (TBHP) or H2O2 were also widely employed as the oxidants for the direct oxidation of aromatic benzyl compounds.11-16 Compared with the above oxidants, O2 is an inexpensive and green oxidant due to its economic and environmentally benign features.17-20 However, direct oxidation of aromatic benzyl compounds using O2 as the oxidant is still seen as one of the main challenges because O2 is an inert oxidant.21 To dates, tremendous efforts have been devoted to developing efficient catalytic systems for direct oxidation of aromatic benzyl compounds to produce aromatic ketones,22 and several catalysts have been developed including mesoporous MnCeOx,23 ferric-based catalyst,24 and chromium-based mesoporous molecular sieve,25 etc. Despite these achievements, it is still a highly desired task to develop efficient and selective catalysts for oxidation of aromatic benzyl compounds to aromatic ketones using O2 as the oxidant. Utilization of naturally occurring chemicals to prepare functional catalysts is highly attractive,26 which is an important content of Green Chemistry.27 Phytic acid (denoted as


Page 2 of 16

Page 3 of 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


PhyA hereafter), a natural chemical obtained from seeds and grains, has been widely used as food additives.28 Due to the existence of six phosphate groups in its structure (Scheme S1), it can coordinate with metal ions and provide rich phosphorus source.29,30 Inspired by this character, interest was paid on the preparation of functional catalysts based on the rich phosphorus source in PhyA and its coordination ability with metal ions. For direct oxidation of aromatic benzyl compounds with O2, herein, copper phosphate was synthesized using naturally occurring PhyA as the phosphorus source. The as-prepared copper phosphate as a heterogeneous catalyst showed good catalytic performance for the direct oxidation of aromatic benzyl compounds to aromatic ketones using O2 as the oxidant. To be best of our knowledge, this is the first work on both the synthesis of copper phosphate from PhyA and oxidation of aromatic benzyl compounds over this bio-derived copper phosphate.

RESULTS AND DISCUSSIONS The detailed preparation information of copper phosphate was shown in Supporting Information. The obtained blue solid material from PhyA was characterized by X-ray diffraction (XRD), FT-IR spectra, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The SEM and TEM image showed that the prepared solid material has the irregular coral-like structure (Figure 1A, B and Figure S1). XRD pattern showed very sharp peaks, indicating the highly crystalline nature of the synthesized material (Figure 1C), and meanwhile, the pattern well agreed with that for the standard copper phosphate (JCPDS card No. 21-0298). FT-IR spectrum showed the strong absorptions at



947-1137 cm-1 and 1628 cm-1 belonging to the phosphate group (Figure 1D).31 Furthermore, X-ray photoelectron spectrum (XPS) showed the characteristic binding energy of Cu2+ and P5+ in the prepared material (Figure 1E and F).32-34 Additionally, from the analysis of ICP-AES, the contents of Cu and P were 51.46% and 15.27%, respectively, in the obtained solid material. Therefore, its molecular formula could be inferred as Cu3(PO4)2. On the basis of the above analysis, the synthesized blue solid was copper phosphate.

Figure 1. Characterization of the prepared copper phosphate. (A, B) SEM images, (C) XRD pattern, (D) FT-IR spectrum, and (E, F) XPS spectrum of Cu 2p and P 2p.


Page 4 of 16

Page 5 of 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The oxidation of diphenylmethane to diphenylmethanone was selected as a model reaction to evaluate the effect of various reaction parameters using the as-prepared copper phosphate as the heterogeneous catalyst. Generally, for direct oxidation of diphenylmethane,

N-hydroxyphthalimide (NHPI) was needed as a radical promoter.35 Therefore, the effect of NHPI amount on the oxidation of diphenylmethane was firstly determined (Figure 2A). It was clear that no reaction happened in the absence of NHPI. The increase of NHPI amount could result in the rising of the conversion, indicating the significant role of NHPI, and 10 mol% NHPI showed the best performance. Meanwhile, it was found that the conversion was very low in the absence of copper phosphate, suggesting the synergistic effect of copper phosphate and NHPI. Subsequently, the influence of reaction temperature on the reaction efficiency was investigated (Figure 2B). Lower reaction temperature was not helpful for the reaction, and a lower conversion of 40.4% was obtained at 40 oC. It was found that the conversion increased with the increase of reaction temperature from 40 to 100 oC (Figure 2B). The reaction could be almost completed at 100 oC with a diphenylmethane conversion of about 96% and a diphenylmethanone selectivity of 99%. Apart from reaction temperature, O2 pressure is another key parameter to influence the reaction efficiency. As shown in Figure 2C, the diphenylmethane conversion increased with the improvement of O2 pressure from 0.5 MPa to 4.0 MPa, and 4.0 MPa provided the best result. However, a conversion of 71.9% could still be achieved at a lower O2 pressure (0.5 MPa). Finally, the reaction kinetics was studied (Figure 2D). It was clear that the conversion of diphenylmethane steadily increased with the prolonging reaction time, and the reaction was completed with a reaction time of 12 h to provide a diphenylmethane conversion of about 96%. Additionally, in all above experiment,



the selectivity of diphenylmethanone maintained at 99%, suggesting copper phosphate/NHPI was a highly efficient and selective catalytic system for oxidation of diphenylmethane using O2 as the oxidant.

Figure 2. Effect of various parameters on the oxidation of diphenylmethane. (A) NHPI amount, (B) reaction temperatue, (C) O2 pressure, and (D) reaction time. Reaction conditions: diphenylmethane, 1 mmol; copper phosphate, 0.1 g; acetonitrile, 2 g; NHPI, 10 mol% in B to D; temperature, 100 °C in A, C, and D; pressure, 4.0 MPa in A, B, and D; time, 12 h in A to C.

The activity of several copper salts were further examined to show the role of Cu and P in the achieved Cu3(PO4)2 (Table 1, entries 1-3). All the examined copper salts showed good performance, and the anions showed no obvious impact on the catalytic activity. Meanwhile, Na3PO4 exhibited poor activity (Table 1, entry 4). These results suggested that Cu was the catalytic active site for the reaction, while PO43- played the role to combing Cu2+ to generate a heterogeneous catalyst. Although the prepared Cu3(PO4)2 showed similar catalytic activity


Page 6 of 16

Page 7 of 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


with the commercial one (Table 1, entries 3 and 5), the utilization of naturally occurring phytic acid as the phosphorus source made the prepared Cu3(PO4)2 to be an attractive sustainable catalyst form the viewpoint of green chemistry. In addition, the synthesized copper phosphate had better performance than other reported heterogeneous catalysts or comparable activity with some homogeneous catalysts (Table S1).

Table 1. Catalytic activity of various catalysts for the oxidation of diphenylmethane to diphenylmethanone.a Entry

Catalyst

Conversion (%)b

Yield (%)b

1

Cu(NO3)2·3H2O

96.7

95.1

2

CuCl2·2H2O

94.2

92.5

3

The prepared Cu3(PO4)2

96.3

95.9

4

Na3PO4

3.2

Preparation of Copper Phosphate from Naturally Occurring Phytic Acid

Recommend Documents