Transformation of Chitin and Waste Shrimp Shells into Acetic Acid and

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Transformation of Chitin and Waste Shrimp Shells into Acetic Acid and Pyrrole Xiaoyun Gao, Xi Chen, Jiaguang Zhang, Weimin Guo, Fangming Jin, and Ning Yan ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b00767 • Publication Date (Web): 12 May 2016 Downloaded from http://pubs.acs.org on May 21, 2016

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ACS Sustainable Chemistry & Engineering

Transformation of Chitin and Waste Shrimp Shells into Acetic Acid and Pyrrole Xiaoyun Gao,‡[a] Xi Chen,‡[b] Jiaguang Zhang,[b] Weimin Guo,[a] Fangming Jin,*[a] Ning Yan,*[b] [a]

School of Environmental Science and Engineering, State Key Lab of Metal Matrix

Composites, Shanghai Jiao Tong University, 800 Dongchuan Rd, Shanghai, China [b]

Department of Chemical and Biomolecular Engineering, National University of Singapore, 4

Engineering Drive 4, Singapore, 117585. Email: [email protected] ‡ X. G. and X. C. contributed equally to this work.

Abstract: Global shellfishery waste generation is around 6 to 8 million metric tons annually. Chitin, as a major component in crustacean shells, is the second most abundant biopolymer on earth holding the potential to supplement lignocellulosic biomass resource for renewable chemicals. Herein, we established direct transformation of chitin and raw shrimp shells into acetic acid (HAc) by a catalytic method using metal oxide and oxygen gas in basic water. The work showcased that chitin is a superior starting material to other major biomass resources for HAc production. 38.1% yield of HAc was produced from chitin, which was beyond 2-fold compared to that from cellulose. Moreover, 47.9% yield was directly obtained from crude shrimp shells. Another finding is that heterocyclic compound pyrrole was generated as the major

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nitrogen-containing (N-containing) product in the reaction system, which offers a potential chemical route for one-step pyrrole formation from sustainable resource. The study opens up new avenues to transform shellfishery waste into platform chemicals. Keywords: Chitin, Acetic acid, Pyrrole, Biomass, Bio-based chemical, Hydrothermal conversion Introduction In the long run, various biomass components can be utilized as sustainable carbon resource for manufacturing organic chemicals.1-4 While valorization of cellulose,5-11 lignin12-16 and lipids17-18 have been extensively investigated, chemical transformation of chitin is still at a nascent stage.1920

Chitin, naturally existing in crustacean shells (e.g. crabs, shrimps), insect exoskeletons (e.g.

ants), and fungi, represents the second most abundant biomass resource on earth with global reserves of 100 billion tons.21 Chitin22-25 and its monomer N-acetyl-D-glucosamine (NAG)

26-30

have been converted into value-added materials31-34 and several compounds including 3acetamido-5-acetylfuran (3A5AF), 5-hydroxymethylfurfural (5-HMF) and levulinic acid (LA), etc.35-38 These compounds were regarded as potential building blocks for other chemicals and synthetic polymers. However, feasible production routes of platform chemicals with direct and wide industrial applications such as acetic acid (HAc) and pyrrole have not yet been achieved from chitin. HAc is one of the most important organic acids with a global production of 12.9 million tons in 2014.39 In the chemical industry, HAc is mainly synthesized by methanol carbonylation via the Monsanto or Cativa processes.40 Meanwhile, exploration of new synthetic routes for acetic acid from alternative sources, such as methane41-44 and biomass,45 has received continued attention. Pioneering studies on renewable HAc production include using lignin model


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compound. guaiacol to form 9.6% HAc (carbon basis),46 and conversion of cellulose to 10.5% HAc at 673 K in an alkaline solution with hydrogen peroxide (H2O2) as oxidant.47 Subsequently, the yield of cellulose derived HAc was improved to 16.3% by a two-step strategy.48 Therefore, current production of HAc from lignocellulosic biomass is non-catalytic and suffers from low yield. Chitin is a linear polymer comprised of NAG monosaccharide units in pyranose ring conformation, linked together by β-glycosidic bonds (see Fig. 1). The major difference between chitin and cellulose is the acetyl amide group on C2 position in chitin, in contrast with a hydroxyl group in cellulose. As a result, we envisage that chitin is intrinsically more suitable for HAc production compared with other types of biomass. The hydrolysis of acetyl amide side chain alone could readily lead to 25% yield of HAc, and the yield will be enhanced by further decomposition and oxidantion of the pyranose ring. In the domain of N-heterocyclic compounds, pyrrole represents one of the most common core units in many natural products and synthetic drugs, and is a valuable building block for biologically active molecules and functional materials.49 Synthetic strategies such as the cyclization reaction between alkynes and diazenes,50 or between secondary alcohols and amino alcohols,51 have been developed for its productions. However, pyrrole synthesis directly from biomass polymers has not been reported considering the huge structural difference between the natural polymers and the product. In the paper, we demonstrated selective synthesis of HAc from chitin with high yields which has not been reported previously. A catalytic system was established using copper oxide (CuO) catalyst in the presence of oxygen gas in sodium hydroxide (NaOH) solution with the temperature range of 508 K to 573 K. 38.1% and 47.9% yields of HAc can be obtained from chitin and raw shrimp shells respectively. Apart from HAc, other products were carefully


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identified and examined. The reaction pathways were investigated by control experiements, kinetic studies and isotope-labelling tests. It has been proved that HAc was initially produced from hydrolysis of acetyl amide, and subsequently from the oxidation of intermediate compounds derived from pyranose ring fragmentation. Meanwhile, with biologically-fixed nitrogen in chitin, pyrrole was formed as the dominant N-containing product in this one-step transformation. By supplying extra ammonia, the yield of pyrrole was 6% (equal to 12 mol%) under optimal conditions. The new chemistry of pyrrole formation from chitin polymer has been discovered herein, which points out the possibility of synthesizing important heterocyclic chemicals from renewable chitin biomass.

Fig. 1 Two chemical routes for chitin conversion into HAc and pyrrole.

Experimental General reaction procedures Chitin conversion into HAc was conducted in an autoclave. The autoclave with gas valve was put into a steel holder with insulating jacket heated by a hotplate, with the thermal sensor


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inserted into the steel holder (Fig. S2). The temperature was pre-set to desired value prior to the reaction. In a typical reaction without catalyst/oxidant, 100 mg chitin (4 mmol carbon), 5 mL 2 M NaOH and a stirrer bar were loaded into the autoclave. In a typical reaction with catalyst and oxidant, 100 mg chitin (4 mmol carbon), 0.5 mmol or 5 mmol metal oxides, 5 bar O2 gas, 5 mL 2 M NaOH and a stirrer bar were loaded. After reaction, the autoclave was taken out and cooled down to room temperature with cooling water. The reaction solution was transferred into a volumetric flask and diluted to 10 mL. When catalyst was employed, or chitin was not fully converted, filtration was conducted to separate the solution and the spent catalyst/unconverted chitin. Chitin conversion into pyrrole was mainly conducted in a slim tube reactor (~1 cm diameter, 1 mm wall thickness, and 5.5 inch length, image shown below) heated by melting salt bath. The tube reactor is made of SUS 316 alloys with an internal volume of 5.7 mL. In a typical reaction to form pyrrole without ammonia, 100 mg chitin (4 mmol carbon) and 2 mL 1 M NaOH solution were loaded into the tube reactor and immersed in the salt bath that was preheated to the desired temperature. In a typical reaction to form pyrrole with ammonia, the procedures were similar but 0.5 mL 4 M NaOH solution and 1.5 mL 25 wt% ammonia solution were mixed together to a total volume of 2 mL as the reaction medium (in this case the ammonia concentration was 19 wt%). For lower ammonia concentration, smaller amount of ammonia solution was added, and deionized water was employed to ensure the total volume to be 2 mL. The agitation of solutions was achieved by mechanical shaking of the tube reactor by a robot arm. After reaction, the tube reactors were immediately immersed into water bath to cool down to room temperature. Then the reaction solutions were taken out for analysis.


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Product identification HAc, LA, formic acid (FA), glycolic acid (GA), oxalic acid (OxA), C4-1 and C4-5 (see Fig. 2) were identified by gas chromatography mass spectrometry (GC-MS, an Agilent 7890A GC system with 7693 Autosampler and 5975C inert MSD with triple-axis detector) by using a HP-5 capillary column, and double confirmed by high performance liquid chromatography (HPLC, an Agilent 1200 Series LC system with Diode-Array detector by using two Agilent Hi-Plex H columns in series with a working temperature of 333 K) analysis by comparing retention time and UV absorption spectra with authentic standard samples. HPLC method: the mobile phase was 0.005 M H2SO4. The flow rate was kept at 0.6 mL/min with a run-time of 60 min. The wavelength at 210 nm was used to analyze the products. Other C4 to C6 organic acids or alcohols were identified by GC-MS analysis. Prior to GC-MS analysis, the reaction solutions were freeze dried and a silylation step was applied. The silylation step was as follows: 1 mL of the reaction solution was freeze dried in a glass vial. Then, pyridine (700 µL), hexamethyldisililazane (700 µL), trifluoreacetic acid (60 µL) and a small stirring bar were added. The closed vial was put in a water bath at 60 °C for 1 h. After heating, the sample was cooled down to room temperature and filtered for GC analysis. Pyrrole and other N-containing compounds were identified by GC-MS (an Agilent 5890 Series II GC system with 5898B mass spectrometer) by using a HP-Innowax capillary column with direct injection of the reaction solutions. Pyrrole was also confirmed using the authentic standard by comparing the retention time in GC.

Product quantification


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The total organic carbon (TOC) and inorganic carbon (IC) in liquid phase was analysed by using a TOC analyzer (Shimadzu TOC 5000A). HAc product was quantified on GC-FID (Agilent 7890A GC with a flame ionization detector) by using BP-5 capillary column. After reactions, 1 mL of the solution was acidified by adding 150 µL 37% HCl solution. Then the solution was filtered by polyethersulfone (PES) membrane filters with 0.45 µm pore size prior to GC-FID analysis. Both external calibration curve and internal standard (propionic acid) were used to quantify HAc. LA, GA, FA, OxA and HIA were quantified by HPLC analysis using external calibration curve. Other C4 to C6 organic acids or alcohols were quantified on GC-FID with HP-5 capillary column after freeze dry and silylation, with n-dodecane as the internal standard. The effective carbon numbers were calculated according to the literature.52 Pyrrole was quantified on GC-FID with HP-Innowax capillary column by using external calibration curve (direct injection). The yields of other N-containing chemicals were estimated by using the relative peak area ratio to pyrrole. The yields of all products were calculated based on carbon by using the following equation: Yield% = the mass of carbon in the product/the mass of carbon in chitin * 100%

(1)

Unconverted chitin was collected by centrifugation, washing for three times with deionized water and dried in an oven overnight. The conversion of chitin was determined as follow: Conversion% = (mass of starting chitin – mass unconverted)/mass of starting chitin * 100% (2)

Isotope labelling tests 13

C-labelled NAG (acetyl amide group labelled) was used for isotope labelling tests. 100 mg

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C-labelled NAG (4 mmol carbon), none or 5 mmol metal oxides and 5 bar O2 gas, 5 mL 2 M

NaOH and a stirrer bar were loaded into an autoclave. After the desired reaction time at a pre-set


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temperature, the autoclave was taken out and cooled down to room temperature by cooling water. The reaction solution was freeze dried. Part of the sample was silylated for GC-MS analysis and a second part was dissolved in D2O for nuclear magnetic resonance (NMR) analysis. NMR was conducted on a Bruker ultrashield 400 plus spectrometer by using tetramethylsilane (TMS) as the standard.

Results and Discussion Product identification of chitin conversion in alkaline water We first tested the reaction behavior of chitin in 2 M NaOH for 35 min at 573 K in an autoclave under oxidant-free conditions. A yellow, transparent solution was obtained after the reaction, indicating complete conversion of chitin into soluble products (Fig. S4). TOC suggested over 90% carbon remained in the liquid phase (Table S2). Via elaborated analysis using combined instrumentations, > 60% of carbon distributed across more than twenty products were identified. Among these HAc was the most dominant with a yield of 23.5%, followed by LA (14.9% yield) (Fig. 2a). A series of other organic chemicals, mainly acids, were also identified, including FA (4.8%), GA (2.3%), OxA (0.6%), C4 compounds (4.8%), C5 compounds (0.6%) and C6 compounds (1.1%) (structures shown in Fig. 2c). 3.4% of the carbon in solution stayed in inorganic form. Besides, a range of N-containing compounds with combined yield of 3.9% was observed with pyrrole being most abundant. When starting with NAG (monomer of chitin), glucosamine (deacetylated NAG), glucose (monomer of cellulose), and cellulose, only NAG gave high yield of HAc under the same condition (Table S3), suggesting the acetyl amide group on the side chain is associated with the superior performance in HAc production.


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The evolution of major products was followed during chitin conversion (Fig. S5). HAc, LA and FA were generated in parallel, along with increased chitin conversion in the first 25 min of the reaction. Afterwards chitin was fully consumed whereas the yields of HAc, LA and FA reached plateaus. Gel permeation chromatography (GPC) was employed to monitor the molecular weight evolution of the liquid solution in the first 25 min, and the presence of oligomers in the early stage of the reaction was identified (Fig. S6). Unconverted solid was isolated from the system after 5, 10, 15, and 25 min respectively, and all of the samples fully retained chitin structure as suggested by X-ray diffraction (XRD, Fig. S7) and Fourier transform infrared spectroscopy (FTIR, Fig. S8).


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Fig. 2 The product distributions for chitin conversion (a) in the absence of oxidants; (b) in the presence of 5 mmol ball milled CuO (BM CuO) and 5 bar O2. Reaction conditions: 100 mg chitin (4 mmol carbon), 5 mL 2 M NaOH solution, 573 K, 35 min; (c) the structures of identified organic products. N-containing chemicals were listed separately in Table S5. Table 1 Oxidative conversion of chitin and shrimp shell into HAc.

a

Substrate

Catalyst & oxidant

Ratioa

T/K

t / min

HAc %

Chitin

none

-

573

35

23.5

Chitin

CuO

1.25

573

35

28.2

Chitin

BM CuO

1.25

573

35

32.3

Chitin

BM CuO + O2b

1.25

573

35

38.1

Chitin

BM CuO + O2b

0.125

573

35

32.6

Chitin

BM CuO + O2b

0.125

508

90

35.1

Shrimp

BM CuO + O2b

1.25

573

35

47.9

Shrimp

BM CuO + O2b

0.125

508

90

47.1

The ratio refers to the mole of CuO catalyst to the mole of carbon in chitin in the substrate; b 5

bar. Reaction conditions: 100 mg chitin (4 mmol carbon) or 400 mg shrimp shell, 5 mL 2 M NaOH solution.

Catalytic, oxidative conversion of chitin and shrimp shell In an attempt to further enhance HAc yield, different oxidants were employed as additives (Fig. S9). WO3 and Fe2O3 were not effective, while others exhibited positive effects following the order of H2O2 < V2O5 < CuO < CeO2. Since CuO was only slightly less effective than CeO2 but significantly cheaper, it was selected for further optimization. CuO powder was ground by ball mill (termed as BM CuO). This immediately led to enhanced HAc yield of 32.3% (Table 1), which can be explained by the decrease in CuO particle size after ball mill treatment (see XRD


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patterns in Fig. S10). According to X-ray photoelectron spectroscopy (XPS) and XRD analysis, CuO acted as a stoichiometric oxidant that was converted into Cu2O (Fig. 3, a and b). We next targeted to develop the reaction into a catalytic mode by introducing 5 bar of O2 gas as the oxidant, assuming that O2 could oxidize Cu2O back to CuO to complete a catalytic cycle. HAc yield was further enhanced to 38.1% (Table 1), and much narrower product distribution was observed (Fig. 2b). In addition to HAc, FA (7.1%) and OxA (5.0%) exhibited pronounced increase in yields, while the yield of LA dropped drastically from 14.9 % to 1.6 %, C4 acids from 4.8% to 0.9%, and C5 and C6 acids were no longer detected. In XPS spectra, peaks for BM CuO were broad and contained satellite peaks (Fig. 3a). CuO was converted into Cu2O after reaction when oxygen was absent, as evidenced by the disappearance of satellite peaks. With added O2, the XPS spectrum of BM CuO after reaction was nearly identical with unreacted BM CuO, indicating its catalytic role. XRD data were in full agreement with XPS analysis that BM CuO was recovered in the presence of O2 (Fig. 3b). In addition, the catalyst before and after reaction have been characterized by scanning electron microscope (SEM, Fig. S11) and Brunauer– Emmett–Teller (BET) techniques. BM CuO showed irregular shapes at low magnifications and layered structures at high magnifications. After reaction, some octahedral shaped CuO particles were formed. The change of morphology indicated that CuO was actively involved in the reaction. Meanwhile, BET analysis suggested that CuO were non-porous displaying negligible surface areas. A series of CuO catalysts including CuO nanoleaves,53 CuO microspheres,54 CuO/TiO2, CuO/HAP and CuO/CeO2 were prepared and evaluated (XRD data shown in Fig. S12). Over CuO/TiO2 catalyst and 5 bar of O2 gas, 35.3% HAc was obtained within 60 min even when CuO


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amount was reduced by a factor of ten, highlighting the potential for catalyst design (Table S4). Again, CuO acted as a catalyst that was recovered back to CuO after the reaction (Fig. S13). Up to this point, only commercially available, purified chitin has been used as the starting material. It is a refined product extracted from crustacean shells via multiple steps. We do not see it as an economically viable starting point for HAc synthesis, unless cheap methods of extracting chitin from crustacean shells can be developed in the future. As such, the applicability of the process to untreated tiger shrimp shell powder (Penaeus monodon, values ca. 0.1 USD/kg)19 consisting of 24.4% chitin, 17.5% protein and 43.2% calcium carbonate (CaCO3), was tested. HAc yield, on chitin basis, reached a remarkable 47.9% in 2 M NaOH at 573 K in the presence of BM CuO and O2 after 35 min. A comparable yield (47.1%) can be obtained in 90 min when the temperature was reduced to 508 K. The HAc yield is higher over raw shrimp shells than purified chitin, indicating some carbon present in protein may contribute to HAc formation. Product separation is often an issue for biomass-derived chemicals. HAc has a higher boiling point than water so that conventional purification by distillation will be energy intensive. Therefore, we envisage membrane separation (pervaporation, etc.) to be a potentially viable solution that is efficient and cost effective.55-57


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Fig. 3 (a) XPS Cu 2p spectra and (b) XRD patterns of BM CuO before and after reaction (both in the presence and absence of 5 bar of O2).

Isotope labelling tests The relative ratio of HAc coming from the amide side chain and the pyranose ring was quantified using acetyl group labeled NAG (both carbons on carbonyl group and on methyl group were labeled by

13

C) with GC-MS analysis. When unlabeled NAG was employed, the

main peak of silylated HAc was located at m/z 117 (Fig. 4a). When isotope-labelled NAG was reacted for 5 min at 573 K, the signal at m/z 117 was barely detectable while the peak at m/z 119 was predominant, indicating HAc was almost exclusively generated from the hydrolysis of acetyl amide group at the initial stage of reaction (Fig. 4b). After 25 min in the presence of catalyst and oxidant (see Fig. 4c), both signals at m/z 117 and m/z 119 were pronounced, with a ratio close to


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0.4. This ratio translates to 60% HAc generated from the side chain and 40% from the C6 pyranose ring.

Fig. 4 MS spectra of silylated HAc from (a) unlabeled NAG reacted for 25 min without catalyst; (b)

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C-labelled NAG reacted for 5 min without catalyst; (c)

min with 5 mmol BM CuO, 5 bar O2.

13

13

C-labelled NAG reacted for 25

C-labelled atoms were denoted by *. Reaction

conditions: 100 mg substrate (4 mmol carbon), 5 mL 2 M NaOH solution, 573 K. Note: the sole role of the acetyl amide on

13

C1,2-labelled NAG is to form HAc, since HAc was the only

13

C

enriched species identified by NMR and GC-MS (Fig. S14-15) analysis.


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Reaction pathway illustration Chitin monomer NAG was employed under milder conditions without catalyst/oxidant to trap intermediate species. After treating for 5 min in 2 M NaOH at 120 ̊C, glucosamine was detected suggesting hydrolysis of acetyl amide chain is the first step. After 10 min, the yield of compound C6-1–an alkaline degradation product of glucose45–significantly increased. Some C3 and C4 compounds were also identified (structures shown in Fig. S16). They were derived from glyceraldehyde and erythrose which are common intermediates in the retro-aldol reaction of glucose.58-60 These evidences suggest the formation of glucose as a secondary intermediate from the deamination of glucosamine, which was further transformed into C6-1 or fragmented into a series of C2-C5 chemicals such as LA. A UV-Vis protocol61 was employed to quantify the amount of deaminated ammonia (Fig. S17). As expected, a considerable portion of glucosamine underwent deamination. Reactions of NAG were further conducted at 473 K and 573 K (Fig. S18). The GC-MS chromatogram at 473 K for 5 min highly resembled the chromatogram at 393 K for 30 min, confirming the reaction pathways remained unchanged at higher temperatures despite of accelerated reaction rate. By comparing the reaction in the presence and absence of O2 and catalyst, we suspect that a number of C3-C6 intermediate compounds can be converted into HAc through a catalytic oxidation pathway. To verify this, LA was treated with BM CuO catalyst and O2 gas, whereupon a gradual increase of HAc in a period of 35 min was indeed observed. In fact, compounds C4-1 and C4-4 can also be transformed into HAc (in yield of 13.7% and 8.8% respectively) under oxidative conditions. Based on these observations, the reaction network of chitin conversion in alkaline water has been proposed (Fig. 5). Chitin is depolymerized, deacetylated and deaminated into glucose, liberating HAc from the side chain. Following that, several parallel reaction


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pathways involving a number of reactions such as retro-aldol condensation, isomerization, deamination, oxidation, Cannizzaro reaction and benzilic acid rearrangement, are entangled forming a highly complex reaction network. Many intermediate species are not stable under catalytic oxidative conditions so that the product stream gradually converges into several stable, simple organic acids as reaction progresses.

Fig. 5 Proposed reaction networks of chitin conversion into HAc and other organic acids. Solid line: plausible pathway with experimental evidence; dash line: speculated pathway.

Formation of N-containing compounds in chitin conversion After chitin conversion in 2 M NaOH at 573 K in the absence of catalysts/oxidants, a variety of N-containing compounds were detected by GC-MS, including pyrrole and its derivatives,


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pyrazine derivatives, pyridine derivatives, and amides (Table S5). Among these, pyrrole was dominant. Since these N-containing compounds were not stable under applied reaction conditions, a slim tube reactor (diameter ~1 cm) using melting salt as the heating source was subsequently employed, where the reaction mixture could reach the desired temperature within seconds. Parameters such as the species and concentration of alkali (see Fig. S19 & S20), reaction temperature, time (see Fig. 6a & 6b) and the substrate types (see Table S6) were optimized. The major findings include: 1) pyrrole formation is favored at high temperature (in the range of 523 K to 598 K); 2) Group I bases perform far better than other bases, of which 1 M NaOH was most suitable; 3) the reaction kinetics is very fast (maximum yield of pyrrole reached within 5 min). Nevertheless, the pyrrole yield is no more than 2% after optimization. We realized that the nitrogen inherently presented in chitin may not be adequate for pyrrole formation. Therefore, ammonia as an external nitrogen source was introduced, and the yield of pyrrole improved accordingly with increasing ammonia concentration (Fig. S21). After further optimization of reaction temperature (Table S7), 6% pyrrole was obtained from chitin after only 1 min at 598 K. Note that 6% refers to carbon yield; it translates to 12 mol% yield considering every NAG unit in chitin (which contains 8 carbon atoms) could only be converted into one pyrrole (which contains 4 carbon atoms). Currently, the yield was insignificant. However, in industry, pyrrole is normally synthesized via multiple steps when employing petroleum as the carbon source: the first step is steam cracking of naphtha into 1,3-butadiene in ca. 5% yield (1023-1173 K).62 1,3-butadiene can then be converted to furan with < 40% yield (363-393 K or 753-863 K, depending on the catalyst).63-65 Finally, the reaction between furan with ammonia leads to 90% yield of pyrrole (623-673 K).66 Another industry route for pyrrole production via the catalytic dehydrogenation of pyrrolidine involves even more steps. The overall yield is


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calculated to be around 3% starting from naphtha. Therefore, despite the low yield of pyrrole developed in our single step conversion, it is not inferior to the routes in current industry use, and has the potential to be further optimized.

Fig. 6 (a) Temperature optimization for pyrrole formation in the absence of ammonia. Reaction conditions: 0.2 mmol substrate, 2 mL 1 M NaOH solution, 573 K for 5 min; b) temperature optimization in the presence of 19 wt% ammonia. Other reaction conditions were the same; c) proposed reaction pathway of pyrrole formation. It is well established that furanic compounds can be generated from polysaccharides in water.7, 22, 28

Plausibly, pyrrole is formed via chitin derived furanic compounds, by exchanging oxygen

with nitrogen on the ring. To verify this, several compounds including furan, acetyl furan,


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chromogen III and 2,5-dimethyl furan (structures shown in Fig. S22) were reacted with base and ammonia in water (see Fig. S23 for GC-MS analysis). Furan can be transformed into pyrrole but only under harsh reaction conditions (598 K, 5 min). In sharp contrast, acetyl furan was converted into acetyl pyrrole at 523 K after only 2 min. After 5 min at 598 K, the peak for acetyl pyrrole decreased whereas the peak for pyrrole arose. Pyrrole was also observed starting from chromogen III at both 523 and 598 K but not from 2,5-dimethyl furan. Based on these, a possible pathway for pyrrole formation was proposed (Fig. 6b). NAG monomer released from chitin hydrolysis undergoes dehydration to afford a furanic compound with similar structure as chromogen III. Subsequently, oxygen-nitrogen exchange occurs, affording 2-acetyl pyrrole ring, which is converted to pyrrole by hydrolytic side chain cleavage.

Conclusion In summary, the present work exemplifies the possibility of chitin valorization to widely utilized platform chemicals such as HAc with high yields via simple, non-noble metal catalyzed processes. Encouragingly, HAc could also be generated in high yield from untreated shrimp shell powders which are low-cost shellfish waste. A catalytic system employing oxygen as oxidant was established, and the HAc yield obtained here is the highest among the synthesis routes of HAc from renewable biomass resources. Meanwhile, one step production of pyrrole from biomass polymer was achievable in the reaction providing an alternative route for the chemical from renewable resources. Associated Content


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The Supporting Information is available on the ACS Publications website. Other experimental details, characterizations, kinetic study were provided.

Acknowledgements The authors gratefully acknowledge the Green Chemistry for Life Grant from UNESCO. N.Y. thanks the Young Investigator Award from National University of Singapore (WBS: R-279-000464-133), and F.J. thanks the State Key Program of National Natural Science Foundation of China (No. 21436007), the National Natural Science Foundation of China (No. 21277091), and Key Basic Research Projects of Science and Technology Commission of Shanghai (14JC1403100) for the generous financial support.

Corresponding Author *Ning Yan, Email: [email protected] *Fangming Jin, Email: [email protected]

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For Table of Contents Use Only

Title: Transformation of Chitin and Waste Shrimp Shells into Acetic Acid and Pyrrole

Authors: Xiaoyun Gao, Xi Chen, Jiaguang Zhang, Weimin Guo, Fangming Jin,* Ning Yan,*

Synopsis: Transformations of chitin and raw shell waste into platform chemicals have been established, which contributes to the waste shell refinery.


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Transformation of Chitin and Waste Shrimp Shells into Acetic Acid and

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