Communication Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX
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Low-Cost Equipment for Photochemical Reactions Heiko Hoffmann*,† and Michael W. Tausch‡ †
Provadis-Hochschule, Industriepark Höchst, Gebäude B 835, D-65926 Frankfurt am Main, Germany Bergische Universität Wuppertal, Fakultät für Mathematik und Naturwissenschaften, Gebäude V.11.027, Gaußstraße 20, D-42119 Wuppertal, Germany
‡
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S Supporting Information *
ABSTRACT: An inexpensive self-made apparatus for photochemical experiments was developed and has been tested to facilitate the inclusion of photoreactions in undergraduate teaching laboratories despite budget constraints. The core setup allowing the selection of defined wavelengths in the visible and UV regions is made of commercially available components for less than $500, including an enclosure providing a high safety standard. By choice of the reaction glassware, both reactions on micro scale as well as on preparative scale can be conducted easily in an appropriate time frame. In the Supporting Information, ideas for further optional equipment expanding the setup and enhancing its applicability are presented. KEYWORDS: Photochemistry, Laboratory Equipment/Apparatus, Microscale Lab, Second-Year Undergraduate, Hands-On Learning/Manipulatives
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INTRODUCTION In comparison to classical chemistry, the experimental equipment for photochemical reactions requires different additional devices, e.g., light sources with selectable wavelengths, shielding of the experimentalist from hazardous radiation, and often special glassware made of quartz glass. In addition, equipment including inert gas inlets and outlets for gas flushing and arrangements for maintaining temperature such as cooling circuits for isothermal reactions are commonly used. The core of an experimental setup for photochemistry is the light source and the reaction vessel. Different immersion well photoreactors, which are classic tools for photochemical investigations, are commercially available but quite expensive (typically more than $2000). Most of them are designed for working at the 200−400 mL reaction volume scale.1−3 However, photoreactions in smaller volumes with smaller amounts of material are sufficient for teaching experiments. Such smaller devices are commercially available but expensive, e.g., the micro photochemical reaction assembly from Aldrich.4,5 In science education, microscale experiments6,7 and low-cost experimental techniques8−13 are preferred. One has to distinguish between immersion well reactors with light sources inside the reaction mixture and setups with external light sources. Because of the fact that the light emitted by the source penetrates directly into the reaction volume, the immersion well reactors are more energy efficient. However, because of the geometry and the size of the light source and reaction vessel, the need for light filters of specific wavelengths,14 and cooling systems, the whole immersion well setup is complicated and consequently more expensive. Devices made for © XXXX American Chemical Society and Division of Chemical Education, Inc.
irradiation from outside are well established and commercially available but also expensive.15,16 Other setups including falling film reactors, simple tubular reactors, and microreactor parts have been described17 and reviewed.18,19 Different attempts have successfully been made to use cheaper equipment for photochemistry using devices originally made for other purposes6,20−22 as well as simple handmade light-emitting diode (LED)-based light sources.23 The advantages of using LED-based light sources are high light intensities and no necessity of waiting between turning the lamps off and on again, but the disadvantage is that the user only has ultravioletA (UVA) and longer wavelengths available via LEDs in the low-cost range.23 To overcome budget limitations in hands-on photochemical education, we report a detailed description of the construction of self-build low-cost equipment for approximately $500. It enables a high safety standard and enhances the inclusion of photochemical experiments into educational laboratories. Examples demonstrating the effectiveness and flexible usability of the proposed equipment are given. Details concerning the equipment as well as teaching recommendations are presented in the Supporting Information (SI).
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PHOTOREACTION SETUP The core of the self-made low-cost photoreaction setup is shown in Figure 1. A simple but effective self-built light source Received: June 12, 2018 Revised: October 19, 2018
A
DOI: 10.1021/acs.jchemed.8b00442 J. Chem. Educ. XXXX, XXX, XXX−XXX
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Figure 1. (A,B) The low-cost photochemistry setup provides flexible usability in terms of the geometry between lamp and reaction flask. (C) Several reaction volumes can be irradiated in parallel. (D) Qualitative emission lines of three different UV lamps.
Figure 2. (A) Simple quartz glass-made test tubes equipped with a small rubber stopper pierced by two cannulas. (B) The cannulas can be closed using truncated syringes. (C) GL14 thread with melted bottom, equipped with screw cap, septum, and magnetic stirrer. (D,E) A 100 mL quartz glass Erlenmeyer flask equipped with a rubber stopper pierced by cannulas.
Scheme 1. Sample Reactions Conducted Using the Equipment and Reaction Parameters: (1) Photoreduction of Benzophenone and (2) Photoinitiation of Radical Polymerization of Methylmethacrylate
well. Prices and the detailed assembly of the light source are explained in the SI together with ideas comprising additional low-cost equipment emphasizing safety and the affordability of the building parts. Test tubes of quartz glass, with a small rubber stopper pierced by two cannulas, can serve as reaction vessels (Figure 2A). Both can be flushed with inert gas by connecting a syringe to the inlet cannula as described in the SI. A second short cannula serves as outlet and has to be open during gas flushing. Afterward, both cannulas can be closed with 1 mL syringes,
can be positioned in different ways relative to the reaction vessel, providing flexibility in terms of the geometry between lamp and reaction flask (Figure 1A,B). If necessary, up to four reaction volumes can be irradiated in parallel (Figure 1C). The spectral region of radiation can easily be chosen by changing the UV lamp (Figure 1D). Here, we focus on UVA, UVB, and UVC lamps due to their importance in organic photochemistry of nonconjugated functional groups or of small conjugated systems. Additional lamps emitting at longer wavelengths are commercially available as B
DOI: 10.1021/acs.jchemed.8b00442 J. Chem. Educ. XXXX, XXX, XXX−XXX
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C
Polymer precipitated, ∼50% (gravimetric) on ice no 30 min 2-benzyl-2,2-dimethoxy-acetophenone (0.01 M) and methylmethacrylate (0.7 M) in ethanol−water mixture photoinitiation of radical polymerization 2
1d
1b 1c
The temperature of the reaction flasks can be maintained around the ambient temperature using a simple air fan. bThe conversions were determined by gravimetry and TLC. a
UVA
50 mL 4 test tubes in parallel, 3 mL each 4 flasks in parallel, 100 mL each ∼40 mL
100 mL benzophenone (0.1 M), 2-propanol (solvent and reactant) photoreduction 1a
The provided low-cost option to employ UVA, UVB, and UVC light in photochemical teaching experiments enables the instructor to focus on model compounds with small chromophors (e.g., simple olefins, dienes, ketones, aromatic ketones, and enones) in educational laboratories. These molecules exhibit, when irradiated, less diverse and easier to predict photochemical behavior than more complex and wider conjugated species, and their photoreactions are easier to retrace by a freshman (in terms of the basic photochemical mechanisms discussed in typical textbooks).19,24,25 Typical working techniques and safety considerations for prevention of hazards related to experimental organic photochemistry, which are among the possible learning outcomes of undergraduate laboratory courses, can be practiced and retraced using the equipment in teaching laboratories. Students from the author’s school have worked for several weeks using the equipment and have been asked for their perception regarding its handiness and suitability for undergraduate
Reactants
Educational Relevance in Undergraduate Teaching Laboratories
Reaction
Table 1. Sample Photoreactions Conducted with the Low-Cost Equipment
Volume Scale
UVA
The low-cost photochemistry equipment has been successfully used on a range of photochemical reactions during the development of teaching experiments for undergraduate laboratories by the author at Provadis School. Sample reactions are shown in Scheme 1 and summarized in Table 1, demonstrating its effectiveness regarding different reaction types, reaction volume scales, concentrations, conversions, and irradiation times in the teaching laboratory. The authors are planning to publish further reactions conducted with the equipment in the future. We would like to especially emphasize the general usability of the setup regarding many diverse photoreactions, which is demonstrated by the sample photoreactions. Because of the relatively high degrees of freedom regarding the choice of wavelength and glassware, the potential range of applications is diverse. Further experimental details and a comparison with other low-cost proposals published in the literature20,22 (indicating the advantages of our equipment regarding its flexibility and safety) are given in the SI.
UVB UVA
Light
Examples of the Broad Applicability in Different Photoreactions and of the Equipment’s Performance
UVA and aluminum foil reflector
∼50% (by TLC) 24 °C (air fan) yes 3h
23 °C (air fan)
29 °C (without fan) 23 °C (air fan) yes yes 2h 2h
O2 excluded Time
DISCUSSION
No.
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Temp.a
HAZARDS Hazards related to photochemical experiments using the described equipment could be (besides general hazards arising from the chemical compounds used and formed) the radiation, the formation of an explosive atmosphere in a nonair-exchanged housing, potential inert gas release, injuries when working with cannulas, and potential peroxide formation during irradiation. A detailed discussion of the hazards, including measures and precautions to control them and to maintain a high safety standard using the proposed equipment, is provided in the SI.
yes
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2.5 h
Conversionb
which were truncated above the piston and fixed using some tape and cable tie (Figure 2B). Alternatively, quartz glass GL14 threads can be melted and closed at their bottom (by a glassblower) to obtain 10 cm test tubes with a GL14 thread. It can be used with screw caps containing a septum (Figure 2C). If a bigger reaction scale is desired, Erlenmeyer flasks, also closed with a rubber stopper pierced by cannulas, can be employed (Figure 2D,E). Quartz versions of these flasks are also commercially available.
≳40% (by TLC and gravimetric) at least 34% (gravimetric) ≳95% (by TLC)
Communication
DOI: 10.1021/acs.jchemed.8b00442 J. Chem. Educ. XXXX, XXX, XXX−XXX
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de®ion=DE&cm_sp=Insite-_-prodRecCold_xviews-_prodRecCold10-5 (accessed Sep 2, 2018). (6) Tausch, M. W. Teaching Photochemistry with Microscale Experiments. Educ. Quim. 2018, 16 (4), 529−533. (7) Thompson, M. P.; Agger, J.; Wong, L. S. Paternò−Büchi Reaction as a Demonstration of Chemical Kinetics and Synthetic Photochemistry Using a Light Emitting Diode Apparatus. J. Chem. Educ. 2015, 92 (10), 1716−1720. (8) Albert, D. R.; Todt, M. A.; Davis, H. F. A Low-Cost Quantitative Absorption Spectrophotometer. J. Chem. Educ. 2012, 89 (11), 1432− 1435. (9) Bohrmann-Linde, C.; Tausch, M. W. Photogalvanic Cells for Classroom Investigations: A Contribution for Ongoing Curriculum Modernization. J. Chem. Educ. 2003, 80 (12), 1471−1473. (10) Gros, N.; Vrtačnik, M. A Small-Scale Low-Cost Gas Chromatograph. J. Chem. Educ. 2005, 82 (2), 291−293. (11) Romero, A.; Hernández, G.; Suárez, M. F. Photocatalytic Oxidation of Sulfurous Acid in an Aqueous Medium. J. Chem. Educ. 2005, 82 (8), 1234−1236. (12) Lab-guide for low-cost-experiments. University of Bremen. Dept. of Chemistry Education. SALiS-project homepage. http://www. idn.uni-bremen.de/chemiedidaktik/salis/index.php/teachingressouries/lab-guide-for-low-costs-experiments (accessed Sep 2, 2018). (13) Zhang, F.; Hu, Y.; Jia, Y.; Lu, Y.; Zhang, G. Assembling and Using a Simple, Low-Cost, Vacuum Filtration Apparatus That Operates without Electricity or Running Water. J. Chem. Educ. 2016, 93 (10), 1818−1820. (14) Wöhrle, D.; Stohrer, W.-D.; Tausch, M. W. Photochemie Konzepte, Methoden, Experimente, 1st ed.; Wiley-VCH: Weinheim, Germany, 1998; pp 325−334. (15) Xenon (Full Spectrum) Photoreactors. Several different model numbers. Luzchem Research Inc. homepage. http://www.luzchem. com/ (accessed Sep 2, 2018). (16) Rayonet Reactor©. Several different model numbers. Southern New England Ultraviolet Company homepage. https://rayonet.org/ reactors.php (accessed Sep 2, 2018). (17) Knowles, J. P.; Elliott, L. D.; Booker-Milburn, K. I. Flow photochemistry: Old light through new windows. Beilstein J. Org. Chem. 2012, 8, 2025−2052 and references cited therein . (18) Braun, A. M.; Maurette, M. T.; Oliveros, E. Photochemical Technology, 1st ed.; John Wiley & Sons Ltd.: Chichester, U.K., 1991; pp 107−199 and references therein. (19) Kopecký, J. Organic Photochemistry - A visual approach, 1st ed; VCH Publishers, Inc.: New York, 1992; pp 222−226 and references therein. (20) Aung, T.; Liberko, C. A. Bringing Photochemistry to the Masses: A Simple, Effective, and Inexpensive Photoreactor, Right Out of the Box. J. Chem. Educ. 2014, 91 (6), 939−942. (21) Freie Universität Berlin homepage. Institute of Chemistry and Biochemistry. http://www.bcp.fu-berlin.de/chemie/chemie/studium/ ocpraktikum/ressourcen/laborpraxis/laborpraxis_webinfos/ apparaturen/photochemie/index.html (accessed Sep 2, 2018). (22) Tatarko, M.; Tricker, J.; Andrzejewski, K.; Bumpus, J. A.; Rhoads, H. Remediation of Water Contaminated with an Azo Dye: An Undergraduate Laboratory Experiment Utilizing an Inexpensive Photocatalytic Reactor. J. Chem. Educ. 1999, 76 (12), 1680−1683. (23) Photochemical light source for preparative irradiations. No model number mentioned. Sahlmann Photochemical Solutions homepage. http://www.sahlmann-ps.de/pages_en/forscher_praep. html (accessed Sep 2, 2018). (24) Klán, P.; Wirz, J. Photochemistry of Organic Compounds, 1st ed.; John Wiley & Sons Ltd, Chichester, U.K., 2009. (25) Turro, N. J.; Ramamurthy, V.; Scaiano, J. C. Modern Molecular Photochemistry of Organic Molecules, 1st ed.; University Science Books, Sausalito, CA, 2010.
laboratories from a hands-on perspective of the learners. The students gave predominantly positive feedback (see details in SI).
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CONCLUSIONS Photoreactions both on microscale as well as on preparative scale can be conducted in a flexible way in undergraduate educational laboratories using our proposed equipment or parts of it. Thus, a low-cost option is provided to facilitate the inclusion of hands-on photochemistry in teaching laboratories at institutions with small budgets. Microscale reactions exhibit improved safety and far lower long-term cost, especially if expensive reactants and solvents are desired. On the basis of the successful use in sample reactions and on the positive feedback given by learners regarding its suitability in undergraduate education, we suggest its integration into teaching settings and learning laboratories. Research projects with small budgets might also benefit from considering the design of the equipment.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.8b00442. Detailed presentation of the whole equipment together with approximate pricing and other aspects mentioned above (PDF) Detailed presentation of the whole equipment together with approximate pricing and other aspects mentioned above (DOCX)
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AUTHOR INFORMATION
Corresponding Author
*E-mail: heiko.hoff
[email protected]. ORCID
Heiko Hoffmann: 0000-0002-4845-3688 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Heiko Hoffmann would like to thank his colleagues from Provadis’ workshop unit, Hartmut Kilb, Stephan Zoerb, and Claus Berger, for support in building the prototypes of the equipment.
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REFERENCES
(1) Normag Photoreactor. Catalogue No. SAA09316. NORMAG Labor- und Prozesstechnik GmbH homepage. http://www.normagglas.de/en/pdf/12_2_units.pdf (accessed Sep 2, 2018). (2) MPDSBASIC Photoreactors. Several different model numbers. Peschl Ultraviolet GmbH homepage. http://peschl-ultraviolet.com/ english_n/products/photochemistry/preparative-photochemistry/ standard-photoreactor-system/mpdsbasic-standard-laboratoryphotoreactors.html (accessed Sep 2, 2018). (3) Immersion Well Reactors. Several different model numbers. Photochemical Reactors Ltd. homepage. http://www. photochemicalreactors.co.uk/html/immersion-well-reactors.html (accessed Sep 2, 2018). (4) Penn, J. H.; Orr, R. D. A microscale immersion well for photochemical reactions. J. Chem. Educ. 1989, 66 (1), 86−88. (5) Micro photochemical reaction assembly. Model No. Z214558 Aldrich. Sigma-Aldrich Co. LLC. homepage. http://www. sigmaaldrich.com/catalog/product/aldrich/z214558?lang= D
DOI: 10.1021/acs.jchemed.8b00442 J. Chem. Educ. XXXX, XXX, XXX−XXX
