Supporting Information for Visible-Light Induced Thiol Ene Reaction on Natural Lignin Hailing Liu and Hoyong Chung * Department of Chemical and Biomedical Engineering, Florida State University, Tallahassee, Florida 32310, United States 2525 Pottsdamer Street, Building A, Suite A131, Tallahassee, Florida, 32310-6046, USA *E-mail: hchung@fsu.edu Contents I. General Information.S2 II. Synthesis Procedure S3 - Synthesis of lignin-alkene: S3 - General procedure of photoredox catalyzed thiol-ene reaction:...s3 - Temporal and spatial control of the thiol-ene reaction: S8 - PEG-thiol synthesis:.s9 - Graft copolymerization of lignin-alkene and PEG:.S10 - Sunlight induced thiol-ene reaction on lignin:.s11 III. References S11 Number of pages: 11 Number of figures: 7 Number of schemes: 2 S1
I. General Information Materials Lignin was purchased from TCI America (Product number: L0045, softwood lignin, kraft lignin). Poly(ethylene glycol) was purchased from TCI America (Mn: 550 g/mol, Product number: P2184) All other chemicals were purchased from TCI America and used without further purification unless otherwise stated. All organic solvents were degassed before use with bubbling dry nitrogen gas in the presence of 4Å molecular sieves. Instrumentation NMR Nuclear magnetic resonance experiments were carried out on a Bruker Avance 400 MHz spectrometer. All spectra were internally referenced to tetramethylsilane. FT-IR The FTIR-ATR spectra were obtained from a PerkinElmer spectrum 100 FT-IR spectrometer. Light source A LED light bulb was equipped to household desk lamp for irradiation. The light bulb (3W A19/B/LED A19 Blue LED, Feit electric) was purchased from amazon.com and household desk lamp (allen+roth table lamp Model No. ETL01BNK, Foshan Lvzhicai Printing Co,.Ltd.) was purchased from local Lowe s store. UV irradiation source was Luzchem LCZ-4X photoreactor that is equipped with 14 bulbs of 8-watt UVA light bulbs (Hitachi FL8BL-B). S2
II. Synthesis procedure Synthesis of lignin-alkene Supplementary Scheme S1. Lignin modification to prepare lignin-alkene. Lignin was chemically functionalized with 4-Pentenoic acid as shown in supplementary scheme S1. In a 250 ml flask, lignin (4 g), N,N -Dicyclohexylcarbodiimide (DCC, 9.5 g), and 4- Pentenoic acid (4.7 ml) were added to 100 ml of DMF. Then 0.56 g 4-(Dimethylamino)pyridine in 8 ml DMF solution was dropped into the reaction solution. The solution was vigorously stirred at room temperature for 48 hours. After that, the reaction was filtered to collect dark brown filtrate. The filtrate was concentrated by vacuum rotary evaporator. The concentrated solution was precipitated in cold aqueous 1M hydrochloric acid solution. The formed dark brown slurrylike solid was collected by vacuum filtering. The obtained solid was further dried in a vacuum oven for 3 hours at 70. After drying, the solid was dissolved in dichloromethane followed by precipitation in cold hexane. The precipitated product was vacuum filtered and dried in a vacuum oven overnight at 70 to obtain the final purified lignin-alkene. General procedure of photoredox catalyzed thiol-ene reaction S3
Supplementary Scheme S2. Thiol-ene reaction of lignin and 1-decanethiol; various thiolcontaining substrates were tested under the same experimental condition. Supplementary scheme S2 demonstrates graft copolymerization of lignin-alkene and PEG. Lignin-alkene, 6.62 mg, was put in a 4 ml glass vial and sealed with a Teflon cap. The vial was degassed by evacuation and nitrogen refill three times. Then another degassed solution that contains Ru(bpy) 3 Cl 2 (2.5%, 0.376 mg) and p-toluidine (0.5 eq. 1.04 mg) in 1 ml dry DMF was added to the initial degassed lignin-alkene containing vial. Tetramethylsilane (TMS) (2 µl) was added as internal standard to monitor reaction progress. The reaction was started by irradiation of blue LED light at a distance of 6 cm with vigorous stirring. The light source was a 3 W blue light manufactured from Feit electric company as described above. The reaction progress was determined by alkene conversion. In order to verify the alkene conversion, aliquots of reaction solution was taken with designated frequency followed by 1 H NMR characterization in DMSOd 6. The conversion was calculated from the relative integration of alkene compared to initial integration of the reaction. An equation below was used to obtain numerical values of alkene conversion. In the equation, I t,alkene / I t,tms is ratio between alkene integration and internal standard, TMS, integration at reaction time t. I 0,alkene / I 0,TMS is the ratio at reaction time 0, i.e. initial time. The obtained conversion (conversion of olefin %) was specified in Figure S5 as a function of reaction time. The same procedure was conducted for Eosin Y catalyzed reaction with the only change of catalyst Eosin Y instead of Ru(bpy) 3 Cl 2. No additives were used for S4
Eosin Y experiments. For 2,2-Dimethoxy-2-phenylacetophenone (DMPA), the same experimental procedure was used except light source, Luzchem UV photoreactor. No other chemicals were added to DMPA experiments.,,, /, 100%, /, Supplementary Figure S1- S6 shows 1 H NMR spectra of various thiol-ene reactions that are listed in Table 1. The rectangular area of the spectra displays conversion of alkene on lignin. Supplementary Figure S1. 1 H NMR spectra of 1-decanethiol and lignin-alkene thiol-ene reactions in d-dmso. The top spectrum is the kinetics study at initial time, and the bottom spectrum is the kinetics study when the reaction was finished at 60 minutes. Alkene peaks from lignin at 5.79 and 4.97 ppm was consumed during the reaction. A series of detailed 1 H NMR spectra of the same reaction is shown in Figure S6(a). S5
Supplementary Figure S2. The 1 H NMR spectra of cyclohexanethiol and lignin-alkene thiolene reactions in d 6 -DMSO. The top spectrum is the kinetics study at initial time, and the bottom spectrum is the kinetics study when the reaction was finished at 60 minutes. Alkene peaks from lignin at 5.79 and 4.97 ppm was consumed during the reaction. Supplementary Figure S3. The 1 H NMR spectra of Methyl Thiolglycolate and lignin-alkene thiol-ene reactions in d 6 -DMSO. The top spectrum is the kinetics study at initial time, and the S6
bottom spectrum is the kinetics study when the reaction was finished at 60 minutes. Alkene peaks from lignin at 5.79 and 4.97 ppm was consumed during the reaction. Supplementary Figure S4. The 1 H NMR spectra of 1-Thiolglycerol and lignin-alkene thiol-ene reactions in d 6 -DMSO. The top spectrum is the kinetics study at initial time, and the bottom spectrum is the kinetics study when the reaction was finished at 90 minutes. Alkene peaks from lignin at 5.79 and 4.97 ppm was consumed during the reaction. S7
Supplementary Figure S5. The 1 H NMR spectra of Thioacetic acid and lignin-alkene thiol-ene reactions in d 6 -DMSO. The top spectrum is the kinetics study at initial time, and the bottom spectrum is the kinetics study when the reaction was finished at 180 minutes. Alkene peaks from lignin at 5.79 and 4.97 ppm was consumed during the reaction. Supplementary Figure S6. The 1 H NMR spectra of Tert-Butyl Mercaptan and lignin-alkene thiol-ene reactions in d 6 -DMSO. The top spectrum is the kinetics study at initial time, and the bottom spectrum is the kinetics study when the reaction was finished at 180 minutes. Alkene peaks from lignin at 5.79 and 4.97 ppm was consumed during the reaction. Temporal and spatial control of the thiol-ene reaction Lignin-alkene and 1-decanethiol (or PEG-thiol) were mixed in 2.5 ml DMF according to general reaction procedure. All other reagents were used more due to the scale-up. Briefly, 16.55 mg lignin-alkene and stir bar were added in a Teflon cap-sealed 4 ml vial. The solid lignin-alkene in S8
the vial was degassed by evacuation and nitrogen refill three times. Then separately prepared solution of Ru(bpy) 3 Cl 2 (2.5 mole %, 0.94 mg) and p-toluidine (0.5 eq. 2.60 mg) in 2.5 ml of dry DMF was added to the degassed vail that contains lignin-alkene. During the OFF stage of the reaction, the reaction solution-containing vial was covered by aluminum foil to avoid any light exposure. For the ON stage, the aluminum foil was removed and the prepared light was used for irradiation. Progress of the thiol-ene reaction was monitored by integration change of alkene groups. Aliquots, 0.1 ml, were taken during the reaction at designated times for 1 H NMR analysis in DMSO-d 6. The ON-OFF study results are demonstrated in Figure S7 and S8 (d). PEG-thiol synthesis PEG-thiol was prepared by previously reported synthesis method. 1 A reaction scheme of the synthesis is shown in Scheme 1 (c). Poly(ethylene glycol) methyl ether (4.59 ml, 9 mmol), 3- mercaptopropionic acid (3.9 ml, 45 mmol), and p-toluenesulfonic acid (171 mg, 0.9 mmol) were dissolved in 50 ml toluene. The solution was refluxed overnight at 150 o C using Dean-stark apparatus. Next, the solvent was removed by rotary evaporator; and then the obtained transparent viscous liquid was dissolved in chloroform. The product was washed with aqueous NaHCO 3 saturated solution twice and then brine. After the washing process, the organic layer was dried over MgSO 4 followed by filtering to collect liquid solution. A transparent viscous liquid was obtained as a product after removal of chloroform with rotary evaporator. The product was stored in nitrogen atmosphere in dark. The product PEG-thiol was characterized by 1 H NMR in CDCl 3 as shown in the Supplementary Figure S1. The shift of two protons e from 3.70 ppm (proton adjacent to hydroxyl group) to 4.29 ppm (proton adjacent to newly formed ester group) S9
and appearance of two protons f, two protons g, and a proton h confirm the success thiolene reaction. Supplementary Figure S7. 1 H NMR of PEG-thiol in CDCl 3 Graft copolymerization of lignin-alkene and PEG Lignin-alkene and 5 equivalent of PEG-thiol were reacted as described in model reaction. After 1 hour, the reaction was finished. Product solution was reduced by rotary evaporator to remove DMF. The residual dark brown liquid was precipitated in a cold ether. It was observed that the precipitated dark brown slurry-like solids was stick on a beaker wall. After decant solvents, the product solid was further dried for 1 hour at 40 in a vacuum oven. Then the dried solid was dissolved in DCM followed by second precipitation in cold ether. The precipitated solid product was dried for 5 hours at 40 in a vacuum oven. The final product was characterized by 1 H NMR in DMSO-d 6 (Figure S8 (a)). S10
Sunlight induced thiol-ene reaction on lignin A thiol-ene reaction with lignin-alkene and 1-decanethiol (or PEG-thiol) was prepared as described in the general procedure above. The only difference to the general procedure was light source, natural sunlight. The prepared reaction vials were exposed under natural sunlight (location: 5 th floor south-face window in Chemical Science Laboratory of FSU) for 4 hours. The irritation time was from 1:00 pm to 5:00 pm on January 5 th 2017. A photo of the sunlight reaction is presented in Figure S8 (b). III. References (1) Oberg, K.; Hed, Y.; Rahmn, I. J.; Kelly, J.; Lowenhielm, P.; Malkoch, M., Dual-Purpose Peg Scaffolds for the Preparation of Soft and Biofunctional Hydrogels: The Convergence between Cuaac and Thiol-Ene Reactions. Chem Commun 2013, 49 (62), 6938-6940. S11