Eco-friendly Catalytic Conversion of Fructose into 5-Hydroxymethylfurfural and 2,5-Diformylfuran : 과당으로부터 5-Hydroxymethylfurfural 및 2,5-Diformylfuran 전환을 위한 친환경적 촉매반응

다국어 초록 (Multilingual Abstract)

Catalytic conversions of fructose to platform chemicals such as 5-hydroxymethylfurfural (5-HMF) and its furanic derivative, 2,5-diformylfuran (2,5-DFF), were investigated under mild conditions using homogeneous and heterogeneous catalysts. The effects of various factors in the catalytic reactions were evaluated.
Mild and homogeneous dehydration systems were examined for the conversion of fructose in the presence of acid catalysts such as phosphorous pentoxide (P2O5) and earth abundant metal chlorides in the ionic liquids. The acidic nature of P2O5 along with its hygroscopic properties has been successfully utilized to afford 81.2 % yield of 5-HMF at 50 oC in 60 min. Different metal chlorides were examined as Lewis acid catalysts for production of 5-HMF from fructose. Among tested metal chlorides, niobium pentachloride (NbCl5) exhibited the highest 5-HMF yield. NbCl5 (0.20 mmol) afforded 79.3 % yield of 5-HMF at 80 oC only within 30 min. It was found that no degradation products were generated under these conditions resulting, while high selectivity for the target product was achieved. FT-IR studies indicated that the moderate Lewis acidity of NbCl5 was possibly responsible for the selective formation of 5-HMF. Besides, an aerobic oxidation system was investigated for derivatization of 5-HMF to 2,5-DFF using 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl (4-hydroxy-TEMPO) radical as a catalyst with [bis(acetoxy)-iodo]benzene (BAIB) and acetic acid (CH3COOH) as co-oxidants. The highest yield (65.0 %) of 2,5-DFF was achieved in the optimized TEMPO/BAIB/CH3COOH system at 30 oC within 45 min in ethyl acetate. It was found that the presence of BAIB facilitated in-situ regeneration of hydroxylamine form of TEMPO and acetic acid addition assisted in initial formation of oxoammonium form of TEMPO, which was responsible for facile 5-HMF oxidation. It is projected that the proposed reaction system in this study is environmentally benign (metal-free) and highly energy efficient.
In order to recycle TEMPO catalyst effectively, immobilization of 4-hydroxy-TEMPO on SBA-15 was carried out and then, TEMPO-SBA-15 was characterized by XRD, N2 physisorption, thermo-gravimetric analyses (TGA), SEM and FT-IR. TEMPO-SBA-15 efficiently oxidized 5-HMF to 2,5-DFF with 72.5 % yield at only 40 oC in ethyl acetate with the aid of BAIB and acetic acid as co-oxidants in an oxygen-rich environment. It indicated that the pore size distribution and architecture of SBA-15 played important roles for the diffusive transport of reactants and products, which resulted in improved selectivity. In addition, the catalyst was reused for five times with negligible decrease in terms of its catalytic activity.
A novel bi-functional catalyst (WO3HO-VO(Salten)-SiO2@Fe3O4) with silica encapsulated magnetic nanoparticles was prepared by anchoring oxovanadium complex and tungstic acid onto the surface of silica coated Fe3O4 nanoparticles. The prepared catalyst and its precursors were characterized by FT-IR, XRD, HRTEM and N2 physisorption, and (TGA). The WO3HO-VO(Salten)-SiO2@Fe3O4 catalyst facilitated a remarkable activity for the one-pot; i.e. direct conversion of fructose to 2,5-DFF in one step. In this manner, tedious separation and purification steps of intermediate compound 5-HMF could be eliminated. Conversion yield (70.4 %) of 2,5-DFF was obtained in an one-pot reaction of fructose at mild reaction temperature of 50 oC. After a reaction, catalyst can simply be recovered by using an external magnet.

국문 초록 (Abstract)

균일 및 불균일 촉매군을 사용하여 탄수화물 과당으로부터 플랫폼 화학물질인 5-Hydroxymethylfurfural (5-HMF) 및 퓨란 유도체인 2,5-Diformylfuran (2,5-DFF) 등으로의 화학전환반응에 관한 연구를 수행하면서 다양한 반응조건 및 촉매가 반응에 미치는 영향을 조사하였다.
이온성 액체상에서 P2O5 및 금속염화물과 같은 균일계 산촉매를 사용함으로써 온화한 조건에서 과당의 탈수반응을 연구하였다. P2O5의 흡습성 및 산특성을 활용하여 50 oC에서 60분 반응 시 81.2 % 의 5-HMF 수율을 얻었다. 또한, 다양한 금속염화물을 루이스산 촉매로서 적용해 본 결과 오염화니오븀 (NbCl5)이 과당으로부터 5-HMF 합성에 있어서 최고 수율을 나타내었다. 80 oC에서 NbCl5 (0.20 mmol)을 사용한 결과 단 30분 만에 79.3 % 의 5-HMF 수율을 얻을 수 있었을 뿐만 아니라, 부반응물도 전혀 생성되지 않았기에 매우 선택적인 촉매로 확인되었다. FT-IR 분석에 의하면, 이는 NbCl5의 온화한 루이스 산성도에 기인한다. 또한, 촉매로서 4-히드록시-2,2,6,6,-테트라메틸-피페리딘-1-옥실 (4-히드록시-TEMPO) 라디칼을 보조 산화제로서 [비스(아세톡시)-아이오도]벤젠 (BAIB), 아세트산 (CH3COOH)을 사용하여 5-HMF의 2,5-DFF로의 호기성 산화반응을 연구하였다. 반응온도 30 oC 및 최적화된 TEMPO/BAIB/CH3COOH 조건하에서 45분만에 에틸 아세테이트 상에서 65.0 % 의 2,5-DFF 수율을 얻을 수 있었다. BAIB로 인하여 TEMPO의 히드록실아민 형태를 반응 중에 재생할 수 있었으며, 아세트산 첨가는 5-HMF 산화의 활성상인 옥소암모늄 형태의 TEMPO로의 변환을 촉진하였다. 본 반응시스템은 금속을 사용하지 않았기에 친환경적이며 에너지 효율적이다.
TEMPO 촉매의 반복 회수 및 재생을 위하여 4-히드록시-TEMPO를 SBA-15에 고정화하였으며 (TEMPO-SBA-15), 제조된 촉매의 특성은 XRD, 질소흡탈착 등온곡선, TGA, SEM 및 FT-IR 등을 통해서 분석하였다. 5-HMF로부터 2,5-DFF 전환용 산화반응 촉매로 TEMPO-SBA-15, 보조 산화제로서 BAIB 및 아세트산을 사용한 결과 40 oC의 에틸 아세테이트 상에서 72.5 % 의 2,5-DFF수율을 얻었다. SBA-15의 기공 크기 분포 및 구조적 특성이 반응물과 생성물의 확산 이동을 촉진시켜 선택성이 향상된 것으로 판단된다. 뿐만 아니라 촉매는 여러 번의 반복 회수 및 재생 시에도 활성이 손실되지 않았다.
자성 나노입자가 실리카로 밀폐된 신규 이원기능성 촉매 (WO3HO-VO(Salten)-SiO2@Fe3O4)를 제조하기 위해서 Fe3O4 나노입자 표면을 실리카로 코팅한 후, 그 표면에 옥소바나듐 복합체 및 텅스텐산을 고정하였다. 제조된 촉매와 전구체들은 FT-IR, XRD, HR-TEM 질소 흡탈착 등온곡선 및 열중량분석 (TGA) 등을 통해서 분석되었다. WO3HO-VO(Salten)SiO2@Fe3O4 촉매는 과당으로부터의 탈수 및 산화반응의 두 단계에 모두 작용함으로써 과당으로부터 단일공정으로 2,5-DFF를 생성할 수 있게 하였다. 이를 통해서 중간화합물인 5-HMF의 복잡한 분리 및 정제 작업을 피할 수 있었다. 50 oC의 온화한 반응조건에서 과당으로부터 70.4 % 수율의 2,5-DFF를 단일공정으로 얻을 수 있었으며, 반응 후에는 외부자성체를 이용하여 촉매를 쉽게 회수할 수 있었다.

목차 (Table of Contents)

• List of Figures i
• List of Tables v
• List of Schemes vi
• Abstract vii
• Chapter 1. Introduction 1
• 1.1. Motivation 1
• 1.2. Objectives 9
• Chapter 2. Review of related literature 11
• 2.1. Biomass as a renewable feedstock 11
• 2.2. 5-Hydroxymethylfurfural (5-HMF) 12
• 2.2.1. Structural and chemical properties of 5-HMF 12
• 2.2.2. Occurrence of 5-HMF 14
• 2.2.3. Significance of 5-HMF as a platform chemical 14
• 2.2.4. Synthesis of 5-HMF 20
• 2.3. 2,5-Diformylfuran (2,5-DFF) 34
• 2.3.1. Structural and chemical properties of 2,5-DFF 34
• 2.3.2. Significance of 2,5-DFF as a commodity chemical 36
• 2.3.3. Synthesis of 2,5-DFF 36
• Chapter 3. Homogeneous catalytic dehydration of fructose to 5-HMF 43
• 3.1. Introduction 43
• 3.2. Experimental 46
• 3.2.1. Materials 46
• 3.2.2. General procedure for dehydration of fructose 46
• 3.2.3. Extraction of 5-HMF 47
• 3.2.4. Analytical methods 47
• 3.2.5. Quantification method for 5-HMF 48
• 3.3. Results and discussion 50
• 3.3.1. P2O5 catalyzed dehydration of fructose 50
• 3.3.2. Fructose dehydration by various metal chlorides in ionic liquids 63
• 3.4. Conclusions 82
• Chapter 4. TEMPO mediated catalytic oxidation of 5-HMF to 2,5-DFF 83
• 4.1. Introduction 83
• 4.2. Experimental 85
• 4.2.1. Materials 85
• 4.2.2. General procedure for oxidation of 5-HMF 86
• 4.2.3. Isolation and purification of 2,5-DFF 87
• 4.2.4. Analytical methods 88
• 4.2.5. Quantification method for 2,5-DFF 88
• 4.3. Results and discussion 90
• 4.3.1. Oxidation of 5-HMF mediated by 4-hydroxy-TEMPO 90
• 4.3.2. Oxidation of 5-HMF by 4-hydroxy-TEMPO and BAIB 94
• 4.3.3. Oxidation of 5-HMF by 4-hydroxy-TEMPO/BAIB/CH3COOH 108
• 4.4. Conclusions 112
• Chapter 5. TEMPO radical functionalized SBA-15 as a heterogeneous catalyst for facile oxidation of 5-HMF to 2,5-DFF 113
• 5.1. Introduction 113
• 5.2. Experimental 117
• 5.2.1. Materials 117
• 5.2.2. Preparation of TEMPO-SBA-15 catalyst 117
• 5.2.3. Catalyst characterization 119
• 5.2.4. General procedure for oxidation of 5-HMF 120
• 5.2.5. Analytical methods 121
• 5.2.6. Recycling of the TEMPO-SBA-15 catalyst 122
• 5.3. Results and discussion 123
• 5.3.1. Synthesis of TEMPO-SBA-15 catalyst 123
• 5.3.2. Characterization of catalyst 123
• 5.3.3. Catalytic activity study of TEMPO-SBA-15 catalyst 134
• 5.3.4. Stability and recycling of TEMPO-SBA-15 148
• 5.3.5. One-Pot conversion of fructose to 2,5-DFF 151
• 5.4. Conclusions 154
• Chapter 6. One-pot, two-step conversion of fructose to 2,5-DFF by magnetic bi-functional heterogeneous catalyst 155
• 6.1. Introduction 155
• 6.2. Experimental 159
• 6.2.1. Materials 159
• 6.2.2. Catalyst preparation and characterization 160
• 6.2.3. Catalyst activity 168
• 6.2.4. Analytical methods 168
• 6.2.5. Recovery of the nanocatalyst 170
• 6.3. Results and discussion 171
• 6.3.1. Synthesis of bi-functional magnetic catalyst 171
• 6.3.2. Characterization of catalyst 173
• 6.3.3. Catalyst activity 187
• 6.4. Conclusions 193
• CHAPTER 7. Conclusions and recommendations 195
• 7.1. Conclusions 195
• 7.2. Recommendations 197
• References 199
• Appendices 235
• Academic Accomplishments 265
• Korean abstract 271