Developing a Safe and Versatile Chemiluminescence Demonstration

Demonstration Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

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Developing a Safe and Versatile Chemiluminescence Demonstration for Studying Reaction Kinetics Abbas Eghlimi,* Hasan Jubaer, Adam Surmiak, and Udo Bach Department of Chemical Engineering, Monash University, Clayton 3800, Australia

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S Supporting Information *

ABSTRACT: Although chemiluminescent reactions are generally used in demonstrations to pique students’ interest in chemistry, they may serve as a great tool for studying reaction kinetics. In this paper, we briefly present an overview of the basics of chemiluminescent kinetics and introduce a safe and robust formulation for making chemiluminescent reactions using citratebased solvents suitable for chemical studies. The rates of chemiluminescence reactions were quantified using open-source Arduino-development-board projects and ubiquitous photoresistor-based sensors. The simple and versatile formulation as well as the data logging proposed in this work provide instructors with an easy, interesting, and cost-effective tool for teaching reaction kinetics at room temperature. The experiment can be tuned to accommodate for time constraints and various levels of complexity in postprocessing. On the basis of the proposed formulation, a procedure for model demonstration has been described. The proposed methodology was supported by providing an example of data collected and postprocessed by first-year undergraduate students. This work will contribute to improving the pedagogical applications of chemiluminescent reactions. KEYWORDS: First-Year Undergraduate/General, Second-Year Undergraduate, Chemical Engineering, Demonstrations, Organic Chemistry, Public Understanding/Outreach, Esters, Fluorescence Spectroscopy

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BACKGROUND INFORMATION Chemiluminescent reactions have proved to be intriguing chemical reactions that motivate students to learn numerous chemistry concepts in a variety of settings and demonstrations.1−3 These reactions also are fundamental to a popular commercial product called “glow sticks”. Although several other formulations exist, peroxyoxalate-based glow sticks have dominated the market, because they are the most efficient nonenzymatic chemiluminescent reactions.4 In these products, hydrogen peroxide (H2O2) reacts with a diaryl oxalate diester (e.g., bis(2-carbopentyloxy-3,5,6-trichlorophenyl) oxalate, CPPO) in the presence of a base acting as catalyst and produces oxalyl chloride. The unstable intermediate oxalyl chloride quickly converts into another high-energy intermediate, 1,2-dioxetanedione, which eventually decomposes into carbon dioxide (CO2), releasing energy. This released energy, which would otherwise heat up the mixture, can be absorbed by a fluorescer, generating light via chemiluminescence. The energy is used to excite electrons in the dye and consequently, the dye releases light upon the electrons’ relaxation back to ground state via radiative decay. In other words, the system extracts the energy released by the exothermic reaction to produce light. This is summarized in Scheme 1.

Scheme 1. Working Mechanism of the Indirect Chemiluminescence of Peroxyoxalate-Based Glow Sticks with CPPO and H2O2 Reagents

analytical tool in chromatography9 and to determine the kinetics of other chemical reactions.10,11 However, their innate kinetics at room temperature can be utilized to study reaction kinetics in an intriguing manner. In order to discuss the reaction kinetics in detail, the efficiency of a chemiluminescent reaction must be elaborated first. The efficiency of a chemiluminescent reaction, ΦCL, is the number of light quanta emitted per molecule of reactants.12 In

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KINETICS OF PEROXYOXALATE CHEMILUMINESCENCE Both the wavelength (i.e., color, see Figure 1) and intensity of the light produced by the glow stick depend on the intrinsic properties of the dye (among other things, which will be discussed). However, by selecting any dye suitable for the application and not varying it, chemiluminescent reactions can be utilized to teach the basics of reaction kinetics at different levels.5−8 Chemiluminescent reactions are generally used as an © XXXX American Chemical Society and Division of Chemical Education, Inc.

Received: August 20, 2018 Revised: January 17, 2019

A

DOI: 10.1021/acs.jchemed.8b00614 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

Demonstration

Figure 1. Conventional peroxyoxalate-based-glow-stick dyes showing the color of their glow.

case of indirect chemiluminescence, this is a product of the following: • the chemical yield, Φchem (i.e., the ratio of the number of molecules that go through the chemiluminescence route to the total number of reacted molecules); • the excitation yield, Φex (i.e., the ratio of the number of molecules that lead to the formation of an excited intermediate to the number of molecules that go through the chemiluminescence route); • the energy-transfer yield, ΦFRET (i.e., the efficiency of energy transfer from the initially chemiexcited intermediate to the acceptor fluorescer through Förster resonance-energy transfer, FRET); and • the fluorescence quantum yield of the fluorescer, Φfl (i.e., the ratio of photons absorbed by the fluorescer to the photons fluoresced by it). ΦCL = ΦchemΦex ΦFRETΦfl

Figure 2. Typical rise−decay curve from a chemiluminescent reaction with indications of its characteristic parameters.

(1)

as shown in Figure 2, which are derived from two-step, consecutive, pseudo-first-order, irreversible reactions:13,14

In a direct (type I) chemiluminescent reaction, illuminance (I) is mainly governed by the rate of the chemical reaction, whereas in indirect (type II) chemiluminescence, such as peroxyoxalate-based processes, I is primarily controlled by the concentration of the high-energy intermediate (i.e., the compound responsible for the energy transfer to the fluorescer). Because the generation and dissipation of the high-energy intermediate is the main rate-controlling parameter, the rise−decay curve of an indirect chemiluminescence reaction illustrates how the concentration of the rate-limiting intermediate changes over time. In case of peroxyoxalate chemiluminescence, this rate-limiting intermediate is the result of the first nucleophilic substitution of H2O2 in the oxalate ester.4 Chemiluminescent processes are inherently dynamic (i.e., the illuminance of the produced light changes as a function of time). As exemplified in Figure 2, a typical illuminance profile for a chemiluminescent reaction comprises a very fast rise in the emission followed by a significantly slower illuminance decay. Typically, this behavior is manifested in a rise−decay curve. The rise curve can be characterized by a first-order riserate constant, krise; the maximum illuminance, Imax; and the time to reach Imax, tmax. The exponential decay can be modeled with the first-order rate constant, kfall. Thus, the rise and decay of the illuminance can be characterized by two first-order rate constants, krise and kfall,

k rise

k fall

reactants ⎯→ ⎯ intermediates ⎯→ ⎯ products

(2)

Considering this path, the observed illuminance over time for a curve like the one shown in Figure 2 can be expressed as I (t ) =

I0k fall [exp( −k fallt ) − exp( −k riset )] k rise − k fall

= Imax exp( −k fallt ) − Imax exp(−k riset )

(3)

where I0 is a theoretical maximum level of intensity for the case where the reactants were entirely converted to the excited Ik intermediate, and Imax = k 0−fallk is the maximum practical rise

fall

intensity. Because the rise of the illuminance is much faster than its fall (kfall ≪ krise), these expressions can be simplified to an exponential-decay form to describe the major part of the reaction profile: I(t ) = Imax exp( −k fallt )

(4)

Moreover, the following equation also stands: I(t ) = k[intermediate] = ΦCL

12,13

−d[rate − limiting reagent] dt (5)

B



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Demonstration

PRINCIPAL HAZARDS AND SAFETY MEASURES For the entire duration of the experiment, gloves, lab coats, and safety glasses ought to be worn. The following principal hazards were identified for the individual chemicals: • Concentrated (>3 wt %) H2O2 solutions can cause burns and hence should be handled with gloves. • Sodium salicylate is an eye-irritant. The byproduct pentyl 3,5,6-trichlorosalicylate may cause an allergic skin reaction and should be handled with gloves. • Because of the production of CO2 as a byproduct, the tube size needs to be larger than the total volume of the chemicals added into the tubes to avoid pressurization. According to the safety data sheets of major manufacturers like Sigma-Aldrich, Merck Millipore, Alfa Aesar, Chem-lab, and Fluka, CPPO, TEC, and ABTC are not hazardous or dangerous substances.

where brackets represent concentration, and k is the rate constant. The unit of k depends on the units chosen for concentration and illuminance. According to eq 5, the intensity of the chemiluminescent reaction depends solely on the concentration of the high-energy intermediate (oxalyl chloride or 1,2-dioxetane in the case of the example shown in Scheme 1), which in turn is limited by the rate of the reaction controlled by the consumption rate of the rate-limiting reagent (CPPO in this example).

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CHEMICALS Commercial products work mainly on the basis of the reactions of bis(2,4,6-trichlorophenyl)oxalate (TCPO), CPPO, and bis(2,4-dinitrophenyl) oxalate (DNPO) with hydrogen peroxide. Despite the attempts undertaken to make peroxyoxalate-based glow sticks safer by using alternative oxidants15 such as urea−hydrogen peroxide or sodium percarbonate, the parent phenol, which is generated as a byproduct, poses the highest health risk. Therefore, not only are these chemicals unsuitable for use in schools, but their commercial application also needs to be reconsidered because of their cytotoxicity.16 The byproduct of the reaction between TCPO and hydrogen peroxide, 2,4,6-trichlorophenol, is a proven carcinogen.17 The reaction between DNPO and H2O2 results in the byproduct 2,4-dinitrophenol, which causes acute toxicity and may also cause explosions.18 Although the risk of these hazardous compounds can be contained during demonstrations, having student run chemiluminescent experiments in a lab or performing indoor demonstrations, particularly where ventilation could prove an issue, still requires careful consideration. In contrast, the byproduct of CPPO reactions with H2O2, pentyl 3,5,6-trichlorosalicylate, although not entirely free of hazards, is nonetheless safer than the other two alternatives.19 Furthermore, compared with even safer oxalate alternatives such as divanillyl oxalate (DVO)20 and dimethylsalicyl oxalate (DMO)21 and activated amides like 1,1′-oxalyldiimidazole (ODI) and 1,1′-oxalyldibenzotriazole (ODBT),22 CPPO produces a brighter glow and has much better solubility in nonhazardous organic solvents, which evidently makes it a better candidate for demonstrations. Furthermore, it obviates the need for local ventilation apparatus such as fume-cupboard, which is required for chemiluminescence systems based on oxalyl chloride23 and 1,2-dioxetane.24 In addition, if desired, it empowers students with a hands-on experience by ruling out the necessity of doing the experiment just as a demonstration. Moreover, the experiment does not require a dark environment, as in the case of luminol.25 Commercial products rely on phthalate plasticizers such as dibutyl, dimethyl, and diethyl phthalate for providing good solubility for the oxalate ester and fluorophore. These phthalates have been identified as reproductive and developmental toxicants that can leach out into the environment very easily.26,27 Hence, there has been a tremendous effort to replace them with safer and greener alternatives.28 Citratebased plasticizers offer solutions to these issues. Even though they cannot accommodate high solubility for conventional polycyclic aromatic hydrocarbon based dyes, as phthalate derivates can, they are still capable of achieving a reasonable outcome. Therefore, two citrate-based solvents, acetyl tributyl citrate (ATBC) and triethyl citrate (TEC), were selected.

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CHEMICAL PREPARATION AND DEMONSTRATION The chemiluminescent component is made by preparing three stock solutions: • 0.05 wt % BPEA solution in ATBC (It is noteworthy that other dyes can be used as alternative to the BPEA, especially rubrene and 1-chloro-9,10-bis(phenylethynyl)anthracene (1-CBPEA), which have better solubilities in ATBC, i.e., 0.3 and 0.2 wt %, respectively, compared with ∼0.05 wt % in the case of BPEA.) • 10 wt % CPPO solution in ATBC • pure ATBC for diluting the concentrated CPPO solution The activator component is made by preparing the following stock solutions: • 2 wt % sodium salicylate solution in TEC • 18 wt % H2O2 aqueous solution • pure water for diluting concentrated 18 wt % H2O2 solutions down to 6 and 2 wt % Demonstrators start by preparing the chemiluminescent component required for all runs in separate tubes. Vigorous stirring is required for proper dissolution of BPEA and CPPO salts in ATBC and sodium salicylate in TEC. Aqueous H2O2 solutions at different concentrations are to be prepared by diluting hydrogen peroxide solutions with concentrations higher than 18 wt %. If different concentrations are considered for the runs, the required amount of each solution should be selected in such a way that there will always be a surplus of H2O2. This will ensure the kinetics to follow the suggested two-step, consecutive, pseudo-first-order, irreversible reaction path as described by eq 2. Furthermore, the effect of temperature on kinetics can be examined by mixing reagents at different temperatures. In that case, demonstrators mix both components and measure the illuminances of the formulations formulations at different temperatures.

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POSTPROCESSING After data-logging is completed, students can fit exponential equations in the form of eq 3 and extract the values of the coefficients. These values (i.e., the various reaction-kinetic C



Demonstration

parameters determined for each run) may be compared to evaluate the reaction kinetics (see Figure 2). Learning the principles of pseudo-first-order reactions29 can also be an objective at higher education levels. Systematically increasing the concentration of each reactant while keeping the others constant will provide the students with the opportunity to clearly identify the effect of each reagent and easily draw conclusions. Among the many possibilities,3 by fitting exponential curves to the data, students can compare Imax-, half-life (t1/2)-, kfall-, and t∞-versusconcentration curves. In more advanced courses, they can find the concentration of the rate-limiting intermediate or the rate-limiting reagent over time. If the goal of the demonstration is to study the effect of temperature on reaction kinetics, students can find the trend of change in the rate constants, κ, as a function of temperature, T, with the goal of finding the activation energy, Ea, by plotting the illuminance-versus-temperature curve6 following eq 6. Further information can be found elsewhere.3 i E y κ = A expjjj− a zzz k RT {

(6)

From the demonstration executed in the above-mentioned manner, students should be able to achieve the following objectives: • learn how experiments can be systematically designed to study the effect of each reagent on the reaction rate, • explain how an indirect method of measurement can be utilized to quantify the reaction rate, and • show how reaction kinetics of relatively complex reactions can be described using simplified mathematical models. Obviously, students need advanced knowledge in the concepts of reaction kinetics to fully understand and appreciate this experiment and exploit its full potential. Consequently, this experiment can be adapted for a second- or third-year undergraduate course. However, even with basic knowledge in chemical-reaction kinetics (i.e., knowledge limited to firstorder reactions and some basic mathematical concepts such as the linearization of exponential curves), they should be able to achieve the above-mentioned objectives.

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Figure 3. Examples of (a) decay curves plotted by students on the basis of the data given to them and (b,c) postprocessing done to find the effects of the reagent concentrations on (b) maximum intensity,

EXAMPLE PROCEDURE Table 1 provides an example of the design of an experiment suitable for studying the effects of reagent concentrations on

(

Imax, and (c) half-life It = t1/2 =

Imax 2

). The dashed lines in b and c are

added to guide the eye of the reader.

Table 1. Example Experimental Design for Investigating the Effects of Reagent Concentrations on Kinetics reagent A solutions: chemiluminescent components (μL) run no.

BPEA

1.1 1.2 1.3 2.1 2.2 2.3

1000 1000 1000 1000 1000 1000

CPPO ATBC 300 300 300 100 300 900

600 600 600 800 600 0

chemiluminescence kinetics. The concentrations of the 9,10bis(phenylethynyl)anthracene (BPEA)-dye solution in reagent A and the sodium salicylate buffer solution in reagent B are kept constant, whereas those of the CPPO and H2O2 reagents are varied by the addition of solvents (ATBC in reagent A and water in reagent B). In order to ensure this, the total volume of the dye and catalyst components are kept constant. Also, in this example, the total volume of chemiluminescent and activator components is fixed at 1900 and 1200 μL for each run, respectively. Hence, the concentrations of dye and catalyst in the final reaction medium are also not varied among different runs. It should be noted that the concentrations of the buffer and dye are always in excess, so they do not affect the output.

reagent B solutions: activator components (μL) sodium salicylate

aqueous H2O2 (wt %)a

1000 1000 1000 1000 1000 1000

200 (2) 200 (6) 200 (18) 200 (6) 200 (6) 200 (6)

a The total volume of the H2O2 solution remains unchanged in all runs, but the concentration of the solution differs.

D



Demonstration

ORCID

The proposed variations in the concentrations of the principal reactants will result in different kinetics. As there are only two major reactants, the variation in concentration was divided into two sets. Each set examines the impact of one reactant on the reaction. The chemiluminescent reaction starts by the addition of catalyst and H2O2 solutions to activate the reaction. One part of the chemiluminescent component is mixed with 1000 μL of the catalyst solution, followed by 200 μL of the H2O2 solution at the desired concentration in a 10 mL centrifuge tube. Right after the addition of H2O2 solution, the tube is to be capped and shaken mildly for 2 s. After activating the reaction, the tube must be placed immediately in the holder equipped with a sensor (see the Supporting Information for further details on the setup of such a measurement device) to measure the illuminance over a certain period. As discussed in the Supporting Information, logging can be done either manually at different intervals or automatically using a computer or even a mobile phone. Examples of the results obtained and the postprocessing performed following the above-mentioned procedure can be found in Figure 3. As can be seen in Figure 3a, increasing the concentration of H2O2 while keeping the concentration of CPPO constant in runs 1.1 to 1.3 increases the reaction kinetics, resulting in a higher maximum intensity (Figure 3b) but with a faster exponential decay, ultimately causing a shorter half-life (Figure 3c).

Abbas Eghlimi: 0000-0003-3178-8147 Hasan Jubaer: 0000-0001-6372-125X Udo Bach: 0000-0003-2922-4959 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Jonathan Li, Department of Electrical and Computer Systems Engineering, Monash University, for his abundant support. We also gratefully acknowledge financial support provided by the Faculty of Engineering at Monash University.

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(1) McCapra, F. Demonstrations of chemiluminescence. Methods Enzymol. 2000, 305, 633−659. (2) Gafney, H. D.; Adamson, A. W. Chemiluminescence. An illuminating experiment. J. Chem. Educ. 1975, 52 (7), 480. (3) Kuntzleman, T. S.; Rohrer, K.; Schultz, E. The Chemistry of Lightsticks: Demonstrations To Illustrate Chemical Processes. J. Chem. Educ. 2012, 89 (7), 910−916. (4) Hadd, A. G.; Lehmpuhl, D. W.; Kuck, L. R.; Birks, J. W.; Mell, G. P. Chemiluminescence Demonstration Illustrating Principles of Ester Hydrolysis Reactions. J. Chem. Educ. 1999, 76 (9), 1237. (5) Carmel, J. H.; Ward, J. S.; Cooper, M. M. A Glowing Recommendation: A Project-Based Cooperative Laboratory Activity To Promote Use of the Scientific and Engineering Practices. J. Chem. Educ. 2017, 94 (5), 626−631. (6) McCluskey, C. L.; Roser, C. E. Lightstick Kinetics. J. Chem. Educ. 1999, 76 (11), 1514. (7) Bindel, T. H. Lightstick Magic: Determination of the Activation Energy with PSL. J. Chem. Educ. 1996, 73 (4), 356. (8) The Effects of Temperature on Lightsticks. J. Chem. Educ. 1999, 76(1), 40A−40B. (9) Kuntzleman, T. S.; Comfort, A. E.; Baldwin, B. W. Glowmatography. J. Chem. Educ. 2009, 86 (1), 64. (10) Jain, V. K. Chemiluminescence: A tool to determine the rate constant and order of chemical reactions. Asian J. Res. Chem. 2013, 6 (5), 495−497. (11) Dean, M. L.; Miller, T. A.; Brückner, C. Egg-Citing! Isolation of Protoporphyrin IX from Brown Eggshells and Its Detection by Optical Spectroscopy and Chemiluminescence. J. Chem. Educ. 2011, 88 (6), 788−792. (12) Fereja, T. H.; Hymete, A.; Gunasekaran, T. A Recent Review on Chemiluminescence Reaction, Principle and Application on Pharmaceutical Analysis. ISRN Spectrosc. 2013, 2013, 230858. (13) El Seoud, O. A.; Baader, W. J.; Bastos, E. L. Practical Chemical Kinetics in Solution. In Encyclopedia of Physical Organic Chemistry; Wang, Z., Wille, U., Juaristi, E., Eds.; John Wiley & Sons: Hoboken, NJ, 2016. (14) Hadd, A. G.; Seeber, A.; Birks, J. W. Kinetics of Two Pathways in Peroxyoxalate Chemiluminescence. J. Org. Chem. 2000, 65 (9), 2675−2683. (15) Smellie, I. A.; Aldred (née Prentis), J. K. D.; Bower, B.; Cochrane, A.; Macfarlane, L.; McCarron, H. B.; O’Hara, R.; Patterson, I. L. J.; Thomson, M. I.; Walker, J. M. Alternative Hydrogen Peroxide Sources for Peroxyoxalate “Glowstick” Chemiluminescence Demonstrations. J. Chem. Educ. 2017, 94 (1), 112− 114. (16) de Oliveira, T. F.; da Silva, A. L. M.; de Moura, R. A.; Bagattini, R.; de Oliveira, A. A. F.; de Medeiros, M. H. G.; Di Mascio, P.; de Arruda Campos, I. P.; Barretto, F. P.; Bechara, E. J. H.; de Melo Loureiro, A. P. Luminescent threat: toxicity of light stick attractors used in pelagic fishery. Sci. Rep. 2015, 4, 5359. (17) Pay, A. L.; Kovash, C.; Logue, B. A. General Chemistry Laboratory Experiment To Demonstrate Organic Synthesis, Fluo-

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CONCLUSION Chemiluminescence has been the focus of many works studying the chemical-reaction kinetics as well as pedagogical applications. In this work, a safer set of chemicals based on citrate solvents for conventional peroxyoxalate-based chemiluminescence has been described. These chemicals along with the utilization of simple photodetectors provide instructors with a quick and robust way to introduce reaction kinetics in a visually appealing manner. Measuring the illuminance of different runs with different concentrations of reagents or at different temperatures with the prescribed setup provides a cheap yet versatile way to teach students the basics of reaction kinetics while maintaining a safe environment during the demonstration. In addition, because of the visually appealing nature of the experiment, the interest of the students in this study can be enhanced. Last but not least, the same setup can also potentially be developed into a rigorous lab experiment to unravel further aspects of relevant chemical reactions, which are hitherto poorly understood.

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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.8b00614. Details of the data-logging procedure (PDF, DOC)

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REFERENCES

Stereolithography (STL) and drawing (PDF) files for further 3D printing of the tube holder and Arduino enclosure and assembly (ZIP)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. E



Demonstration

rescence, and Chemiluminescence through Production of a Biphasic Glow Stick. J. Chem. Educ. 2017, 94 (10), 1580−1583. (18) Duarte, R.; Nielsen, J. T.; Dragojlovic, V. Synthesis of Chemiluminescent Esters: A Combinatorial Synthesis Experiment for Organic Chemistry Students. J. Chem. Educ. 2004, 81 (7), 1010. (19) Pentyl 3,5,6-trichlorosalicylate; ChemWatch Review SDS 421800, v2.1.1.1; ChemWatch, 2018. (20) Jilani, O.; Donahue, T. M.; Mitchell, M. O. A Greener Chemiluminescence Demonstration. J. Chem. Educ. 2011, 88 (6), 786−787. (21) Cambrea, L. R.; Davis, M. C.; Groshens, T. J.; Meylemans, H. A. A Soluble, Halogen-Free Oxalate from Methyl Salicylate for Chemiluminescence Demonstrations. J. Chem. Educ. 2013, 90 (9), 1253−1254. (22) Roncaglia, F. Designing and Using a Safer, Greener Azole Oxamide for Chemiluminescence Demonstrations. J. Chem. Educ. 2017, 94 (9), 1288−1290. (23) Bramwell, F. B.; Goodman, S.; Chandross, E. A.; Kaplan, M. A chemiluminescence demonstration - Oxalyl chloride oxidation. J. Chem. Educ. 1979, 56 (2), 111. (24) Meijer, E. W.; Wynberg, H. The synthesis and chemiluminescence of stable 1,2-dioxetane: An organic chemistry laboratory experiment. J. Chem. Educ. 1982, 59 (12), 1071. (25) Fuchsman, W. H.; Young, W. G. A simplified chemiluminescence demonstration using luminol and hypochlorite bleach. J. Chem. Educ. 1976, 53 (9), 548. (26) Lyche, J. L.; Gutleb, A. C.; Bergman, Å.; Eriksen, G. S.; Murk, A. J.; Ropstad, E.; Saunders, M.; Skaare, J. U. Reproductive and Developmental Toxicity of Phthalates. J. Toxicol. Environ. Health, Part B 2009, 12 (4), 225−249. (27) Kay, V. R.; Chambers, C.; Foster, W. G. Reproductive and developmental effects of phthalate diesters in females. Crit. Rev. Toxicol. 2013, 43 (3), 200−219. (28) Krauskopf, L. G. How about alternatives to phthalate plasticizers? J. Vinyl Addit. Technol. 2003, 9 (4), 159−171. (29) Rushton, G. T.; Criswell, B. A.; McAllister, N. D.; Polizzi, S. J.; Moore, L. A.; Pierre, M. S. Charting an Alternate Pathway to Reaction Orders and Rate Laws in Introductory Chemistry Courses. J. Chem. Educ. 2014, 91 (1), 66−73.

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Developing a Safe and Versatile Chemiluminescence Demonstration

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