Lighting the Way to Greener Chemistry: Incandescent

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Lighting the Way to Greener Chemistry: Incandescent Floodlights as a Facile UV Light Source for Classic and Cutting-Edge Photoreactions Katelyn Randazzo, Zhihan Wang, Zijun D. Wang, Jonathan Butz, and Qianli Rick Chu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.6b01506 • Publication Date (Web): 25 Jul 2016 Downloaded from http://pubs.acs.org on July 31, 2016

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ACS Sustainable Chemistry & Engineering

Lighting the Way to Greener Chemistry: Incandescent Floodlights as a Facile UV Light Source for Classic and Cutting-Edge Photoreactions Katelyn Randazzo, Zhihan Wang, Zijun D. Wang, Jonathan Butz, and Qianli R. Chu* Department of Chemistry, University of North Dakota, 151 Cornell St, Grand Forks, ND 58202‐9024, United States *E‐mail: [email protected] Supporting Information Placeholder

ABSTRACT: While ultraviolet light is hailed for its renewability, non‐toxicity, and lack of resulting waste products, photochem‐ istry is relatively out of reach for many researchers and industries because conventional ultraviolet radiation sources are not always accessible. For example, the availability of sunlight varies with weather conditions, geographical location, and daylight duration. The use of commercial incandescent light as an alternative to conventional ultraviolet radiation was explored in this article. The classic [2+2] photocycloaddition of trans‐cinnamic acid was tested under controlled conditions in the solid state, and it was found that 150 W light bulbs provided satisfactory results and 1.5 cm away from the light source was a viable distance for the photoreac‐ tion. A [2+2] cycloaddition of 10 milligrams trans‐cinnamic acid finished in as few as four hours. Gram‐scale synthesis was also achieved in 40 hours by using a 500 W floodlight bulb. The incandescent floodlight also effectively facilitated a cutting‐edge photopolymerization in 24 hours to produce a two‐dimensional (2D) polymer. The use of reliable, inexpensive, and non‐hazardous incandescent light in place of sunlight or even ultraviolet lamps for certain photoreactions will allow for the wider study and development of photochemistry.

Key words: Sunlight alternative, Polycyclobutane, 2D polymer, Cinnamic acid, Photocycloaddition, Green photochemistry, Frugal engineering, Frugal innovation INTRODUCTION Over a century ago, nature’s safe and efficient synthesis through the use of light as a reagent inspired the pioneers of green chem‐ istry to turn to photochemistry in search of greener methods.1, 2 At the heart of green chemistry, and by extension photochemistry,

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is the desire to reduce or eliminate hazardous substances associated with chemical synthesis.3‐6 Due to light’s renewability, non‐

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toxicity, and lack of resultant waste products, photochemistry continues to appeal to both researchers and industry alike, with recent advances observed in diverse applications ranging from synthesis to ecology.7‐17 Pharmaceutical companies in particular have recently embraced photochemical innovation due to the capability of photochemistry to yield unique products that cannot be achieved through thermal techniques.18 For those cases in which thermal and photochemical reagents do obtain identical products, the photochemical route is often much simpler and less expensive than its thermal equivalent.19 The long‐term cost‐ effectiveness of photochemistry may serve to advance efforts in frugal engineering, an emerging concept which aims to diminish the complexity and cost associated with a product’s manufacture.20, 21, 22 Despite the mass appeal of photochemistry and all that it has to offer, lack of facile and reliable equipment prevents many researchers and industries from realizing the full potential of photochemical techniques. Sunlight represents the most abundant source of ultraviolet radiation, but the availability of sunlight is dependent upon a number of uncontrollable factors including weather conditions, daylight duration, and latitudinal location.6 Ultraviolet lamps are a reliable alternative, however their costli‐ ness, hazardousness, and resulting inconvenience constitute hindrances in their popularity with many research groups and busi‐ nesses. In this article, incandescent light is demonstrated to be a promising candidate in the facilitation of photoreactions, which have been conventionally executed via sunlight or UV lamp. It is hypothesized that incandescent light’s effectiveness can be attributed to its emission of a continuous distribution of wavelengths of light, which resembles that of sunlight. The tail of the wavelength distribution lies in the range of wavelengths smaller than 400 nm, which corresponds to the ultraviolet region.23 The incandescent lights proved to be effective in the facilitation of both a classic photoreaction and for the cutting‐edge synthesis of a recently developed two‐dimensional (2D) polymer. Furthermore, the lights were reliable, inexpensive, and generally non‐hazardous. It is our hope that the adoption of incandescent lights as a facile alternative to traditional UV radiation sources for certain photoreac‐ tions will make photochemistry a more accessible discipline to researchers and industries seeking green, inexpensive solutions. EXPERIMENTAL PROCEDURES General Reagents and Methods: The incandescent floodlights used in this article are readily available at residential lighting sources. The incandescent floodlights were purchased from either local retail outlets or online. Trans‐cinnamic acid and 1,2,4,5‐ tetrakis(bromomethyl)benzene and other chemicals used in the experiments were purchased through Alfa Aesar, Sigma Aldrich and used without further purification. Thin layer chromatography (TLC) was performed on silica gel W/UV 200 μm precoated plates. The solution phase nuclear magnetic resonance spectra (NMR) were recorded with Bruker AVANCE (1H: 500MHz, 13C: 125 MHz). All spectra were obtained in deuterium dimethyl sulfoxide (DMSO‐d6). For DMSO‐d6 solution, the chemical shifts were reported as parts per million (ppm) with tetramethylsilane as a standard. Coupling constants were reported in hertz (Hz). Data for 1H NMR spectra were reported as follows: chemical shift (ppm: referenced to parts per million), brs = broad singlet, s = singlet,


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d = doublet, t = triplet, q = quartet, dd = doublet of doublets, dt = doublet of triplets, ddd = doublet of doublet of doublets, p =

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pentet, h = heptet, m = multiplet, coupling constant (Hz), and integration. Single crystal X‐ray data were recorded on Bruker Kappa Apex II Duo X‐ray diffractometer with Mo Kα (λ = 0.710 73Å) or Cu Kα (λ = 1.541 78Å). Melting points were measured on a MEL‐TEMP device without correction. Infrared spectroscopy (IR) was recorded on Thermo Scientific Nicolet iS5 FT‐IR spectrom‐ eter. UV/Vis was recorded on Beckman DU 640 Spectrophotometer. The emission spectra for the light bulbs was obtained using a Thorlabs CCS200USB spectrometer coupled with a fiber‐optic CCSA2 cosine corrector in an open‐air setup. The obtained spectra were corrected for the CCSA2s transmittance (provided by manufacturer). The spectra were processed using Thor Labs publishing software. The mass spectrometric analyses were performed using a high‐resolution time‐of‐flight G1969A with electrospray (at‐ mospheric pressure chemical) ionization (Agilent, Santa Clara, CA) and reported as m/z (relative intensity). Accurate masses are reported for the molecular ion [M + Na]+, [M + H]+, [M + NH4]+, or [M]+. Photoreaction of trans‐cinnamic acid: Trans‐cinnamic acid powder was irradiated via residential incandescent light on a transparent glass slide. About 10 or 50 mg of powder was evenly scattered on a glass slide, and the sample was placed beneath the bulb inside of a vented fumehood. The progress of the photoreaction was monitored by FT‐IR. Reaction completion time varied for different bulbs and distances tested. For the optimized trials, cinnamic acid was ground to a fine powder by scattering it evenly between two glass slides which were rubbed together. Stirring the powder sample with a spatula or a small knife every a few hours to generate fresh surface increased the dimerization progress. Figure S1 in the supporting information depicts the experimental apparatus. Gram‐scale photoreaction of trans‐cinnamic acid: Trans‐cinnamic acid powder was irradiated via 500 W quartz halogen bulb of UTILITECH residential incandescent light on a transparent glass slide.24 About 1 gram of powder was evenly scattered on a glass slide, and the sample was placed beneath the exposed bulb with a distance of 6 cm inside of a vented metal cabinet. Another glass slide was placed about 1 cm above the sample to block part of the heat generated by the bulb and a copper pipe with cooling water was introduced into the cabinet to further cool the reaction environment. The progress of the photoreaction was monitored by 1H NMR. Reaction completion time was 40 h, and it varied for distances between the sample and bulb tested. Photoreaction of trans‐cinnamic acid using ambient sunlight: Trans‐cinnamic acid powder was irradiated via ambient sunlight on a transparent glass slide for comparison. About 50 mg of powder was evenly scattered on a glass slide in exactly the same manner as was done for the procedure using incandescent bulbs. The slide was placed outside to be exposed to sunlight from 11 am until reaction completion, corresponding to the hours when direct sunlight was most readily available. All experiments using sunlight were conducted during peak daylight hours on sunny days during the month of May in Grand Forks, North Dakota, USA. The supporting information contains additional data for the weather conditions. Synthesis of monomer: The monomer synthesis is similar to the reported literature procedure.25 Cinnamic Acid (3.3 g, 22.2 mmol), 1,2,4,5‐tetrakis(bromomethyl)benzene (2.0 g, 4.4 mmol), and K2CO3 (3.7 g, 26.7 mmol) were added to DMSO (50 mL). The mixture was stirred at room temperature for 17 h. White precipitate was formed. Then the mixture was poured into 300 mL of



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water. The precipitate was filtered out to give crude product. The crude product was added into 100 mL of EtOAc and sonicatored

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for 1 h. Then, the solid was filtered to give pure product (2E,2’E,2’’E,2’’’E)‐benzene‐1,2,4,5‐tetrayltetrakis‐(methylene) tetrakis(3‐ phenyl acrylate) (2.2 g, 68%) as a white solid; mp 188‐189 °C.25 TLC (hexanes:ethyl acetate, 3:1 v/v): Rf = 0.54. 1H NMR (500 MHz, DMSO‐d6): δ 7.62‐7.68 (m, 14H), 7.31‐7.40 (m, 12H), 6.64 (d, J = 16 Hz, 4H), 5.38 (s, 8H). 13C NMR (125 MHz, DMSO‐d6): δ 166.2, 145.4, 135.5, 134.2, 131.7, 130.9, 129.2, 128.7, 117.9, 63.5. IR: 1707, 1635, 1575, 1495, 969 cm‐1. UV/Vis: λmax 275 nm. HRMS (m/z): [M + Na]+ calcd. for C46H38O8Na, 741.24643; found 741.23698. Photoreaction of stereoregular two‐dimensional (2D) polycyclobutane: About 5 mg of powder was added to about 10 mL of solvent ethyl acetate. The vial of the suspended mixture was put in an ultrasonic cleaner (Bransonic, Models 1200) for two minutes. Drops of the suspended mixture were scattered evenly on a quartz plate, which was placed 1.5 cm beneath a 150W General Electric Floodlight w/ Saf‐t‐Gard inside of a vented fumehood. The ethyl acetate evaporated, leaving very thin films of monomer where each droplet was placed. After twelve hours, the quartz plate was flipped over to allow the incandescent light’s radiation to reach the unreacted underside of the monomer films. Reaction progress was monitored by FT‐IR. The reaction completed in 24 h. RESULTS AND DISCUSSION Commercially available light bulbs were screened for their efficacy in facilitating the dimerization of trans‐cinnamic acid to α‐ truxillic acid, a classic photoreaction which has been studied for over a century.26 The photoreaction of cinnamic acid and its derivatives continues to attract the attention of researchers,27‐30 with recent studies suggesting that α‐truxillic acid possesses anti‐ inflammatory and anti‐nociceptive prop‐ erties.31 32, 33 The mechanism for the dimerization of cinnamic acid is [2+2] cycloaddition, which is shown in Scheme 1. In order for a species to undergo [2+2] cycloaddition in the solid state, its geometry must adhere to the principles famously outlined by Schmidt, namely, there must exist parallel double bonds that are separated by 4.2 or fewer angstroms.9, 34‐37 Upon sufficient exposure to ultraviolet radiation, cinnamic acid’s pi bonds close to form a cyclobutane ring, resulting in a stable stereospecific dimer in the solid state.

HO O

hv

O OH

HO O

O OH

Scheme 1. The synthesis of α‐truxillic acid from trans‐cinnamic acid via [2+2] cycloaddition. Dimerization is accessible through this mechanism because double bonds in adjacent molecules are a) parallel and b) separated by fewer than 4.2Å.


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During the screening process, about 50 milligrams of trans‐cinnamic acid powder was spread evenly on a glass plate and posi‐

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tioned beneath an incandescent lightbulb. The time necessary to for the dimerization to complete was monitored by FT‐IR and 1H NMR. The results of the screening process are compiled in Table 1.

Decreasing the distance between the bulb surface and the sample had a dramatic effect on dimerization rate. For example, trials of both the 150W Sylvania Utility bulb and the 150W General Electric Floodlight w/ Saf‐T‐Gard demonstrated that decreasing the reaction distance from 3 cm to 1.5 cm reduced the dimerization time by about a third (entry 1 vs. 8 and 4 vs. 9). This is most likely because light emitted by the bulbs becomes increasingly scattered in many directions as it travels further from its source. Therefore, samples closer to the bulb received a more concentrated dosage of light, and those which were positioned farther received only a fraction of the same dosage, with the difference lost to the surroundings.

Table 1. Summary of results from the screening process: Variances in manufacturer, wattage, and distance between the bulb sur‐ face and the sample affected the photodimerization rate of trans‐cinnamic acid.

Entry

Bulb

Light Color Temp (K)

Dis‐ tance (cm)

Reaction Temp (ºC)

1st Result (h)

2nd Result (h)

3rd Result (h)

Average (h)

Not speci‐ fied

1.5

50

20

16

18

18

1

150W Sylvania Utility

2

150W Sylvania Soft White

2850

1.5

45

50

48

48

49

3

150W General Electric Rough Service Garage Light

2800

1.5

52

80

84

78

81

4

150W General Electric Flood‐ light w/ Saf‐T‐Gard

2700

1.5

50

24

25

20

23

5

100W Westinghouse Amber

Not speci‐ fied

1.5

40

100

‐

‐

100

6

120W Aero Tech Indoor Flood Light

2800

1.5

41

96

‐

‐

96

7

250W Sylvania Halogen Flood Capsylite

3025

3.0

85

(Melted after 3 hours)

‐

‐

(Melted after 3 hours)

8

150W Sylvania Utility

Not speci‐ fied

3.0

49

30

28

36

31

9


2700

3.0

48

30

36

35

34

10

150W General Electric Rough Service Garage Light

2800

5.0

46

60

‐

‐

60

11


2700

6.0

44

36

41

40

39



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Dimerization progressed more rapidly when the bulbs were of a higher wattage. Among the lower wattage bulbs screened were the 100W Westinghouse Amber light (entry 5) and the 120W Aero Tech Indoor Floodlight (entry 6), both of which required at least four days to complete the dimerization. This is in contrast to bulbs of a higher wattages which achieved the dimerization from the same distance in less than a day (entries 1 and 4). These results were consistent with the expectation that bulbs which release light at a higher rate would more rapidly facilitate the reaction.

trans-cinnamic acid starting material

After 12 hours

After 24 hours

Figure 1. The photodimerization of trans‐cinnamic acid: 1H NMR spectra demonstrate that the dimerization was completed within 24 hours. Dimerization rate also varied with bulb manufacturer, even when wattage and the distance between the bulb surface and the sample were held constant. The screening process results identified the 150W Sylvania Utility bulb and the 150W General Electric Floodlight w/ Saf‐T‐Gard as the most effective bulbs surveyed. Due to its longer lifetime, the latter was selected for further study. Figure 1 shows the progression of the dimerization reaction for trans‐cinnamic acid as facilitated by the selected bulb. Over the


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course of the 24‐hour reaction, the cyclobutane ring transformed the alkene alpha and beta hydrogens of the trans‐cinnamic acid starting material into the cyclobutane hydrogens present in the α‐truxillic acid dimer. This is evidenced by the disappearance of the peaks at 6.5 ppm and 7.7 ppm, respectively, and the emergence of the peaks at 4.3 ppm and 3.8 ppm, corresponding to the cyclobutane hydrogens. Furthermore, the upfield shift in the remaining peaks is consistent with the loss of conjugation in the molecule. Following the screening process, the reaction conditions were further optimized for the dimerization of trans‐cinnamic acid facilitated by the 150W General Electric Floodlight w/ Saf‐T‐Gard. By grinding the cinnamic acid to a fine powder, the dimerization rate was drastically increased. Figure 2 shows that at a distance of 1.5 cm between the sample and the bulb surface, about 10 milligrams of cinnamic acid was completely dimerized within four hours. Even at a distance as great as 14 cm, the dimerization was completed in less than 80 hours. 300

Completion time (h)

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

250 200 150 100 50 0 0

5

10

15

Distance (cm)

20

25

Figure 2. The time‐distance relationship for the dimerization of finely ground trans‐cinnamic acid. Gram‐scale synthesis of α‐truxillic acid from cinnamic acid was achieved by within 40 hours by using a 500 W residential floodlight bulb. The spectra presented in Figure 3 offers insight as to why the floodlights were effective. Cinnamic acid’s absorp‐ tion of light as solid film and methanol solution are shown as black line and blue line, respectively. While the solution absorption has a peak with wavelengths of 220‐320 nm, the solid spectrum shows clear red shift and a broader absorption peak reaching near 400 nm. Because glass surface of the General Electric Floodlight w/ Saf‐T‐Gard allows for the transmission of light with wave‐ lengths greater than 280 nm (green line in Figure 3a),24 there exists a range of ultraviolet wavelengths which correspond to light that is both absorbed by trans‐cinnamic acid and transmitted through the bulb surface. It is the light that falls within this distinct range of wavelengths that makes the photodimerization via incandescent floodlight possible. No reaction was observed when an optical filter was used to block the radiation below 400 nm (purple line in Figure 3), confirming that the dimerization is induced by UV light that is present in the emission spectra of the incandescent bulbs. Figure 3b show the UV emission spectra for each


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bulb tested during the screening process. Significant concentrations of ultraviolet light appear in the range of 360 nm to 400 nm in the bulbs’ emission spectra. In this range, 70‐80% of the light is transferred through the bulb glass (green line in Figure 3a). Therefore, not only do the incandescent bulbs emit a non‐negligible amount of UV light, but a significant portion of this light reaches the sample unimpeded. It is also worthwhile to mention that the two most efficient 150W bulbs in table 1, General Electric Floodlight w/ Saf‐T‐Gard and Sylvania Utility, showed highest UV emission in Figure 3b. a)

100

Transmittance(%)

80 60 40

Cinnamic acid solution GogglesFilter Optical Floodlight glass Cinnamic acid solid film

20 0 200

300

400

500

600

700

800

Wavelength (nm) b) 1.0

Relative Intensity

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

150W GE Floodlight w/ Saf-T-Gard 100W Westinghouse Amber

0.8

120W Aerotech Indoor Floodlight 150W GE Rough Service Garage Light

0.6

150W Sylvania Soft White 150W Sylvania Utility

0.4 0.2 0.0 200

250

300

350

Wavelength (nm)

400

Figure 3. a) The UV‐Vis spectra for trans‐cinnamic acid, 150W General Electric Floodlight w/ Saf‐T‐Gard glass, and plastic optical filter. A range of wavelengths exists that is both absorbed by the trans‐cinnamic acid and transmitted by the floodlight glass. b) Ultraviolet emission spectra for screened bulbs. Emission was measured from a distance of 3 cm for all bulbs. Unlike the conventional mercury UV lamp, incandescent floodlight intrinsically lacks the strong sharp peaks in the UV range. However, its emission of a continuous distribution of wavelengths of light offered a facile and reliable alternative to sunlight as a UV source. In addition, incandescent floodlight can be readily combined with other lab techniques to control temperature of the reaction, accomplish transformation under an inert atmosphere, and achieve slow addition of starting material etc. Meanwhile, the reactions can be visualized and easily monitored by multiple means such as FT‐IR, NMR, and TLC (Thin Layer Chromatog‐ raphy). For comparative purposes, the dimerization was also carried out using ambient sunlight. While sunlight during peak daylight hours on a clear day only required an average of 5 hours for completion, the inherent disadvantages associated detracted from its practicality. For example, the three trials with sunlight conducted were performed on the only three days in the month


8

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of May in which there were sufficiently clear skies during peak daylight hours in Grand Forks, North Dakota, USA. Therefore,

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while sunlight promoted the most expedient reaction time, the incandescent floodlight proved to be a viable alternative, trumping sunlight in terms of reliability. Having demonstrated that incandescent floodlights may facilitate the efficient dimerization of a classic photoreaction, we en‐ deavored to further extend the usefulness of the floodlights to other applications. The synthesis of a 2D polycyclobutane recently developed by our research team represents a cutting‐edge opportunity for the practical implementation of the floodlights.25 A novel monomer consisting of four cinnamic acid arms linked by 1,2,4,5‐tetrakis‐(bromomethyl)benzene was synthesized and the monomer readily self‐assembled into a crystalline solid. The chemical and crystal structure of the symmetric monomer are depicted in Figure 4. All of the C=C double bonds of the monomer structure in the solid state satisfy the requirements for [2+2] cycloaddition,25, 34 and upon sufficient exposure to incandescent floodlight adjacent monomers were locked into a covalently‐ bonded 2D stereoregular polycyclobutane.32 The locally confined topochemical photopolymerization process in the solid‐state led to the stereoregularity and avoided cross‐linking. Monomer conversion with respect to time was monitored via FT‐IR, and is summarized in Figure 5. The absorption peak at 1637 cm‐1 typical of C=C stretching grew smaller and ultimately disappeared within 24 hours of exposure to the 150W General Electric Floodlight w/ Saf‐T‐Gard, as did the peak at 980 cm‐1 corresponding to the out‐of‐plane twist of the carbon‐hydrogen single bonds in the starting material. Completion of the polymerization was further evidenced by the shift of the C=O peak to a higher energy wavenumber, consistent with the deconjugation of the carbonyl group. The IR spectrum of 2D polymeric product was nearly identical to the ones obtained by using sunlight and UV mercury lamp that were reported, confirming the success of photopolymerization.32 a)

b) O

O

O O

O O

O

O

c)

Figure 4. The structure of the cinnamic acid‐derived monomer: a) chemical structure of the symmetric monomer; b) Oak Ridge Thermal Ellipsoid Plot (ORTEP) representation at 50% electron density of the monomer crystal structure; c) packing of the mon‐ omer in the solid state showing parallel double bonds that are fewer than 4.2Å apart (the red dotted lines showing where the new C‐C bonds form; monomer colors introduced arbitrarily for illustrating the packing).


9


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1637

Monomer

980

1.5 cm 16 h

Trasmittance

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

1.5 cm 24 h

Hg Lamp Polymer

1703

2400

2200

2000

1800

1600

1400

1200

1000

800

-1

Wavenumber (cm )

Figure 5. Photopolymerization of a stereoregular 2D polycyclobutane facilitated by incandescent floodlight: FT‐IR spectra confirm that polymerization was completed within 24 hours. The IR spectrum of 2D polymeric product (blue) was nearly identical to the one obtained by UV mercury lamp (magenta). The key starting material used in this article is cinnamic acid, a naturally occurring compound in plants that has been widely used in flavorings, synthetic indigo, plastic, and pharmaceuticals.38 Recently, cinnamic acid was adequately derived from a by‐ product of growing biofuel production39,40 and from other renewable substrates such as glucose by using engineered E. coli.41‐43 Biomass‐based cinnamic acid is a likely prospect for the production of styrene by decarboxylation to make environmentally‐ friendly polystyrene.41‐44 In this work, cinnamic acid has been used in an atomically economical way, as only one hydrogen atom was lost during the transformations to the novel 2D polymer. The photopolymerization via incandescent floodlight was solvent‐ free and resulted in a 2D polycyclobutane comprised of 81% biomass by mass, such that both the reactants and the reagents involved in the reaction were sustainable. This cutting‐edge application of the incandescent floodlights constitutes merely one opportunity for the transformation of an already environmentally‐friendly reaction into a holistically greener process. CONCLUSIONS Incandescent floodlights were successfully demonstrated to be effective in facilitating both a classic photoreaction and the cutting‐ edge polymerization of a recently developed 2D polymer. The solid‐state [2+2] cycloaddition of trans‐cinnamic acid to yield α‐ truxillic acid was completed in a timely manner as confirmed by NMR spectroscopy when factors such as the thickness of the sample powder and the distance between the sample and the bulb surface were controlled. Synthesis of a stereoregular 2D poly‐ cyclobutane was monitored via FT‐IR spectroscopy and completed within 24 hours of exposure to incandescent light. As exem‐ plified in the article, photoreactions that do not require hazardous deep UV sources may be carried out with the commercially available inexpensive incandescent floodlight. Although the incandescent lights are not attractive in terms of energy efficiency,


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they are reliable, inexpensive, convenient, safe, and can be easily combined with other lab techniques and industrial operations.

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The implementation of incandescent floodlights as an alternative to sunlight or other conventional UV radiation sources for cer‐ tain photoreactions may allow for the wider execution of photochemistry by academia and industry alike, granting greater acces‐ sibility to what has traditionally been a relatively inaccessible discipline. ASSOCIATED CONTENT

Supporting Information

Experimental details and spectra are available free of charge via the Internet at http://pubs.acs.org. Photo of the polymerization apparatus, reaction details with ambient sunlight; 1H NMR spectra of cinnamic acid start‐ ing materials, dimerization progress after 12 h, and α‐truxillic acid product after 24 h; UV/Vis spectra of starting ma‐ terials, FT‐IR spectra of cinnamic acid dimerization, time‐distance relationship data for the dimerization, emission spectra of bulbs

AUTHOR INFORMATION Corresponding Author

*E‐mail: [email protected] (Q. Rick Chu). Notes

The authors declare no competing financial interests.

ACKNOWLEDGMENT This material is based upon work supported by the Doctoral New Investigator grants of the American Chemical Society Petroleum Research Fund (PRF 52705‐DNI7) and the National Science Foundation Grant (NSF EPSCoR Award IIA‐ 1355466).

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8. Hoffmann, N., Photochemical Reactions as Key Steps in Organic Synthesis. Chem. Rev. 2008, 108 (3), 1052-1103. 9. Wang, Z.; Kastern, B.; Randazzo, K.; Ugrinov, A.; Butz, J.; Seals, D. W.; Sibi, M. P.; Chu, Q. R., Linear polyester synthesized from furfural-based monomer by photoreaction in sunlight. Green Chem. 2015, 17 (10), 4720-4724. 10. Hou, X.; Wang, Z.; Lee, J.; Wysocki, E.; Oian, C.; Schlak, J.; Chu, Q. R., Synthesis of polymeric ladders by topochemical polymerization. Chem. Commun. 2014, 50 (10), 1218-1220. 11. Chu, Q.; Swenson, D. C.; MacGillivray, L. R., A single-crystal-to-single-crystal transformation mediated by argentophilic forces converts a finite metal complex into an infinite coordination network. Angew. Chem. Int. Ed. 2005, 44, 3569-3572. 12. Burnworth, M.; Tang, L.; Kumpfer, J. R.; Duncan, A. J.; Beyer, F. L.; Fiore, G. L.; Rowan, S. J.; Weder, C., Optically healable supramolecular polymers. Nature 2011, 472 (7343), 334-337. 13. Meng, J.; Li, J.; Zhang, Y.; Ma, S., A novel controlled grafting chemistry fully regulated by light for membrane surface hydrophilization and functionalization. J. Membr. Sci. 2014, 455, 405-414. 14. Wihodo, M.; Moraru, C. I., Effect of Pulsed Light treatment on the functional properties of casein films. Food Sci. Technol. 2015, 64 (2), 837-844. 15. Fukuhara, G., Polymer-based supramolecular sensing and application to chiral photochemistry. Polym J 2015, 47 (10), 649-655. 16. Altınok, E.; Smith, Z. C.; Thomas, S. W., Two-Dimensional, Acene-Containing Conjugated Polymers That Show Ratiometric Fluorescent Response to Singlet Oxygen. Macromolecules 2015, 48 (19), 6825-6831. 17. Vaiano, V.; Sacco, O.; Pisano, D.; Sannino, D.; Ciambelli, P., From the design to the development of a continuous fixed bed photoreactor for photocatalytic degradation of organic pollutants in wastewater. Chem. Eng. Sci. 2015, 137, 152-160. 18. Kemsley, J., Celebrating The International Year Of Light. C&EN 2015, 93 (40), 13-19. 19. Protti, S.; Dondi, D.; Fagnoni, M.; Albini, A., Photochemistry in synthesis: Where, when, and why. Pure Appl. Chem. 2007, 79 (11), 1929-1938. 20. Basu, R. R.; Banerjee, P. M.; Sweeny, E. G., Frugal Innovation: Core Competencies to Address Global Sustainability. 2013 2013, 1 (2), 20. 21. Smith, A.; Fressoli, M.; Thomas, H., Grassroots innovation movements: challenges and contributions. J. Clean Prod. 2014, 63, 114-124. 22. http://salt.strikingly.com/ (accessed Mar. 2016). 23. Nuzum-Keim, A.; Sontheimer, R., Ultraviolet light output of compact fluorescent lamps: comparison to conventional incandescent and halogen residential lighting sources. Lupus 2009, 18 (6), 556-560. 24. Quartz is used in making the 500 W halogen bulb of UTILITECH residential floodlight. Please read and understand the entire manual of the manufactory before attempting to assemble, operate, or install the product. 25. Wang, Z.; Randazzo, K.; Hou, X.; Simpson, J.; Struppe, J.; Ugrinov, A.; Kastern, B.; Wysocki, E.; Chu, Q. R., Stereoregular Two-Dimensional Polymers Constructed by Topochemical Polymerization. Macromolecules 2015, 48 (9), 2894-2900. 26. Liebermann, C.; Bergami, O., Ueber die Einwirkung der Schwefelsäure auf γ- und δ-Isatropasäure. Berichte der deutschen chemischen Gesellschaft 1889, 22 (1), 782-786. 27. Benedict, J. B.; Coppens, P., Kinetics of the Single-Crystal to Single-Crystal Two-Photon Photodimerization of αtrans-Cinnamic Acid to α-Truxillic Acid. J. Phys. Chem. A 2009, 113 (13), 3116-3120. 28. Khan, M.; Brunklaus, G.; Enkelmann, V.; Spiess, H.-W., Transient States in [2 + 2] Photodimerization of Cinnamic Acid: Correlation of Solid-State NMR and X-ray Analysis. J. Am. Chem. Soc. 2008, 130 (5), 1741-1748. ACS Paragon Plus Environment

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29. Park, I.-H.; Chanthapally, A.; Lee, H.-H.; Quah, H. S.; Lee, S. S.; Vittal, J. J., Solid-state conversion of a MOF to a metal-organo polymeric framework (MOPF) via [2+2] cycloaddition reaction. Chem. Commun. 2014. 30. Macgillivray, L. R.; Papaefstathiou, G. S.; Friščić, T.; Hamilton, T. D.; Bučar, D.-K.; Chu, Q.; Varshney, D. B.; Georgiev, I. G., Supramolecular control of reactivity in the solid state: from templates to ladderanes to metal− organic frameworks. Acc. Chem. Res. 2008, 41 (2), 280-291. 31. Chi, Y.-M.; Nakamura, M.; Zhao, X.-Y.; Yoshizawa, T.; Yan, W.-M.; Hashimoto, F.; Kinjo, J.; Nohara, T.; Sakurada, S., Antinociceptive Activities of α-Truxillic Acid and β-Truxinic Acid Derivatives. Biol. Pharm. Bull. 2006, 29 (3), 580-584. 32. Berger, W. T.; Ralph, B. P.; Kaczocha, M.; Sun, J.; Balius, T. E.; Rizzo, R. C.; Haj-Dahmane, S.; Ojima, I.; Deutsch, D. G., Targeting Fatty Acid Binding Protein (FABP) Anandamide Transporters – A Novel Strategy for Development of Anti-Inflammatory and Anti-Nociceptive Drugs. PLoS ONE 2012, 7 (12), e50968. 33. Liu, S. X.; Jin, H. Z.; Shan, L.; Zeng, H. W.; Chen, B. Y.; Sun, Q. Y.; Zhang, W. D., Inhibitory effect of 4,4′dihydroxy-α-truxillic acid derivatives on NO production in lipopolysaccharide-induced RAW 264.7 macrophages and exploration of structure–activity relationships. Bioorg. Med. Chem. Lett. 2013, 23 (7), 2207-2211. 34. Schmidt, G. M. J., Photodimerization in the solid state. Pure Appl. Chem. 1971, 27 (4), 647-678. 35. Abdelmoty, I.; Buchholz, V.; Di, L.; Guo, C.; Kowitz, K.; Enkelmann, V.; Wegner, G.; Foxman, B. M., Polymorphism of Cinnamic and α-Truxillic Acids: New Additions to an Old Story. Cryst. Growth Des. 2005, 5 (6), 2210-2217. 36. Medishetty, R.; Husain, A.; Bai, Z.; Runčevski, T.; Dinnebier, R. E.; Naumov, P.; Vittal, J. J., Single Crystals Popping Under UV Light: A Photosalient Effect Triggered by a [2+2] Cycloaddition Reaction. Angew. Chem. Int. Ed. 2014, 53 (23), 5907-5911. 37. Weerasinghe, M. S.; Karlson, S. T.; Lu, Y.; Wheeler, K. A., Crystal Photodimerization Reactions of Spatially Engineered Isocoumarin Assemblies. Cryst. Growth Des. 2015. 38. Garbe, D., Cinnamic Acid. In Cinnamic Acid, Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH & Co. KGaA: 2000. 39. Dried Distillers Grains with Solubles (DDGS) is generated as a side product of dry mill ethanol production on a large scale and used as livestock feed. The DDGS typically contains about 30% proteins by weight. Phenylalanine, one of the common building blocks of proteins and a precursor of cinnamic acid, can be obtained from the DDGS. Using enzyme phenylalanine ammonia lyase (PAL) or recombinant E. coli strains under alkaline conditions, phenylalanine can be converted into cinnamic acid. 40. https://en.wikipedia.org/wiki/Distillers_grains (Accessed in Mar. 2016) 41. Scott, E.; Peter, F.; Sanders, J., Biomass in the manufacture of industrial products—the use of proteins and amino acids. Appl. Microbiol. Biotechnol. 2007, 75 (4), 751-762. 42. Goodman, C., Metabolic engineering: A plastic pathway. Nat. Chem. Biol. 2011, 7 (9), 576-576. 43. McKenna, R.; Nielsen, D. R., Styrene biosynthesis from glucose by engineered E. coli. Metab. Eng. 2011, 13 (5), 544-554. 44. Spekreijse, J.; Le Notre, J.; van Haveren, J.; Scott, E. L.; Sanders, J. P. M., Simultaneous production of biobased styrene and acrylates using ethenolysis. Green Chem. 2012, 14 (10), 2747-2751.


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For Table of Contents Use Only

Lighting the Way to Greener Chemistry: Incandescent Floodlights as a Facile UV Light Source for Classic and Cutting-Edge Photoreactions Katelyn Randazzo, Zhihan Wang, Zijun D. Wang, Jonathan Butz, and Qianli R. Chu

Synopsis: Incandescent lamps are effective in facilitating certain photoreactions, providing a reliable, inexpensive, and non-hazardous alternative to sunlight.

Ar Ar Ar Ar

O

O

O

O

O

O

O

O

Ar HO O

Ar Ar Ar Ar

O OH Ar

Lighting the Way to Greener Chemistry


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Graphical Abstract:


Ar Ar Ar Ar

O

O

O

O

O

O

O

O

Ar HO O

Ar Ar Ar Ar

O OH Ar

Lighting the Way to Greener Chemistry



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Figure 4b


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Figure 4c



Lighting the Way to Greener Chemistry: Incandescent

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