Rapid Blue Bottle Experiment: Autoxidation of Benzoin Catalyzed by

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Rapid Blue Bottle Experiment: Autoxidation of Benzoin Catalyzed by Redox Indicators Urawadee Rajchakit and Taweetham Limpanuparb* Mahidol University International College, Mahidol University, Salaya, Phutthamonthon, Nakhon Pathom 73170, Thailand S Supporting Information *

ABSTRACT: Air oxidation of reducing sugar under alkaline conditions and air oxidation of ascorbic acid catalyzed by methylene blue are known as the classical and the green chemistry versions of the blue bottle experiment, respectively. We propose a faster alternative of the blue bottle experiment in which air oxidation of benzoin under an alkaline condition is the main reaction. In addition to methylene blue (for the blue bottle experiment), erioglaucine (FD&C Blue #1), indigo carmine (FD&C Blue #2, for the chemical traffic light experiment), resazurin (for the vanishing valentine experiment), safranine, phenanthrenequinone, and tetrazolium chloride also catalyze the autoxidation of benzoin. Similar to sugar/hydroxide and ascorbic acid/CuCl2 reactions, chemical pattern formations are observed in this benzoin/hydroxide system. Our colorful reactions and patterns open the possibilities for both pedagogical activities and future in-depth research. KEYWORDS: Graduate Education/Research, Upper-Division Undergraduate, Demonstrations, Interdisciplinary/Multidisciplinary, Dyes/Pigments, Kinetics, Mechanisms of Reactions, Oxidation/Reduction

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BLUE BOTTLE EXPERIMENT The classical blue bottle experiment, in which a transparent liquid turns blue when shaken and fades to colorless when left to stand, is a very popular reaction for both demonstration and practical activities.1−3 The classical blue bottle experiment is made of three chemicals: glucose, KOH, and methylene blue in water. The ingredients are not required to be accurately weighed, and they may be added to the solution until one gets the desired behavior.1 The origins of the blue bottle experiment are not welldocumented. To the best of our knowledge, the earliest publication of the experiment was in this journal by Dutton4 in 1960, while the name “blue bottle experiment” first appeared in Campbell’s 1963 paper.1 A number of authors attributed it to a 1954 catalogue at the University of Wisconsin,1,5 but there was also a suggestion that the experiment originated at the California Institute of Technology.1 Despite these claims, the reaction of reducing sugar and methylene blue (synthesized by Heinrich Caro6 in 1876) was well-known long before the introduction of the blue bottle experiment.7−9 It is also interesting to note that a similar reaction with a different dye has also been reported in this journal in 1946 by Michaelis.10,11 Many variations and modifications to the classical blue bottle experiment have been proposed. Cook and co-workers12 and Chen13 independently pioneered the use of other reducing sugars and dyes to get a different reaction rate and visual behavior in the classical version. Wellman and Noble14 proposed the green chemistry version of the blue bottle © XXXX American Chemical Society and Division of Chemical Education, Inc.

experiment by replacing sugar and hydroxide by vitamin C and CuCl2. Many others reported detailed mechanistic study of the reaction5,12 and variation of dyes,10−13,15,16 presentation of the experiment,3,15,17,18 and pattern formation.19−25 In an attempt to understand the origin of the experiment, we encountered interesting reports by Chen on the catalytic effect of benzoin on the chemical traffic light and the vanishing valentine experiments13,16 and on a separate experiment of only benzoin and hydroxide.13,26 The nature of the experiment of benzoin and hydroxide is similar to that of the blue bottle experiment but has also been reported in the literature long before the blue bottle experiment.27,28 Inspired by the reports on benzoin reactions, we proposed new formulations for the blue bottle experiment and its variants, and the results are discussed in this paper.

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AUTOXIDATION OF BENZOIN

First, the Chen autoxidation of benzoin demonstration26−28 was investigated. With respect to the blue bottle experiment, the visual effect of the benzoin demonstration without a dye is relatively poor as it requires vigorous shaking to change to pale yellow, and it turns back to pale violet instantly (see Figure 1S). The use of methanol as a solvent is also an additional hazard. Received: January 9, 2016 Revised: May 2, 2016

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DOI: 10.1021/acs.jchemed.6b00018 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

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In our experiments to verify Chen’s claim of benzoin catalytic activity,13,16 it was found that Chen’s formula for the chemical traffic light and the vanishing valentine experiments can work without adding the sugar. The formulation without sugar is then modified so that other dyes can be used and the organic solvent component is minimal. Seven families of dyes10−13,15,16 were reported to work as a catalyst under classical blue bottle conditions. Background color dyes18 are not viable to act as catalysts and were not employed for this study. One representative dye was selected for each family, with the exception of the indophenol family. Because sodium salt of indophenol as reported by Chen13 was not available, both indophenol and dichlorophenolindophenol were used instead. However, the two compounds did not result in a reversible color change. Tetrazolium chloride, a common redox indicator for seed viability tests, was introduced for the first time to this experiment. The next two sections discuss new formulations for flask and Petri dish reactions.

The oxidized color fully developed in a few vigorous shakes and returned to reduced color in 10−30 s, with the exception of tetrazolium chloride, which required ∼2 min to return. The color change cycle may be repeated many times but not as many as the classical and green chemistry versions. After a number of cycles, the rapid formulation is more likely to run out of reactants, and benzoin may be added to the solution to allow more cycles.

RAPID BLUE BOTTLE EXPERIMENT Table 1 shows a list of concentrations of stock solutions. Methanol is the solvent suggested by Chen16 as benzoin is

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HAZARDS Hazards similar to the classical version of the experiment pertain: NaOH is corrosive, and most dyes may stain and cause irritation. In addition to these, acetone is highly flammable and volatile. Gloves and chemical splash goggles are recommended. To avoid staining, care should also be taken at all times, and it may be convenient to use disposable plasticware (e.g., syringe, PETE bottle) for this experiment. Table 1S in the Supporting Information shows detailed safety information for all chemicals.

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PATTERN FORMATION Adamcikova et al.19−21 reported that patterns form in the classical blue bottle solution when poured onto a Petri dish. Limpanuparb and co-workers later discovered that chemical patterns occur in both classical and green versions of the blue bottle experiment and for a variety of redox dyes.17,22,23 Because chemical pattern formations were reported in both glucose and vitamin C systems,17,22,23 it is natural to test our new benzoin system for pattern formation. Glass Petri dishes (internal diameter = 9.6 cm) were used without a cover. Stock solutions were added in the same order as the experiment in a flask. In agreement with the observation in vitamin C,23 a relatively higher concentration of the dye was required to induce pattern formation. However, for convenience, more diluted stock solutions for benzoin and sodium hydroxide were used instead (see Table 1). Table 3 shows formulations and resulting patterns. Full-sized images of Petri dishes can be found in Table 3S. Dot and line patterns were observed, similar to earlier reports in the classical and green chemistry versions. The pattern develops in less than 5 min, but the time to disappear varies greatly from 2 to 30 min. Pons et al. proposed a quantitative diffusion model for pattern formation in a methylene blue−glucose system based on gluconate as an autoxidation product.24,25 Gluconate is relatively denser, and its fall to the bottom of the solution leads to convection cells and thus chemical patterns on the surface of the solution. The gluconate model should be reconsidered based on results of the green23 and the rapid versions of the blue bottle experiment and the recent work of Anderson and co-workers,5 in which the production of gluconate is not applicable or disputed. The only common chemical species in all three versions is oxygen gas, and perhaps the attention to describe blue bottle chemical patterns should focus on that. Cellular automata models for pattern formation have been reported for chemical and biological systems. Many of them, for example, CO oxidation hodge podge model29 (which is similar to the famous Belousov−Zhabotinskii reaction30) and reaction−diffusion model for bird feathers,31 possess similar patterns found in the blue bottle reactions. Comprehensive information on computer modeling for patterns found in nature and various experiments can be found in Gaylord and Nishidate’s book.32

Table 1. Stock Solutions for the Experimentsa Common Name (CAS#)

Concentration/mM

Methylene blue (122965-43-9) Safranine (477-73-6) Resazurin (62758-13-8) Indigo carmine (860-22-0) Phenanthrenequinoneb (84-11-7) Erioglaucine (3844-45-9) Tetrazolium chloride (298-96-4) Benzoinb (119-53-9) Sodium hydroxide (1310-73-2)

0.10 0.10 0.10 20.00 4.80 0.10 1.00 47.00,c 4.70d 10,000.00,c 1000.00d

a

Note: See Table 1S in the Supporting Information for the mg/L preparation. bSolvent is acetone. cFor experiment in a flask. dFor pattern formation in a Petri dish.

poorly soluble in water and ethanol. Due to toxicity concerns, acetone is used instead for benzoin and phenanthrenequinone solutions. There are two concentrations for benzoin and NaOH for two different experiments. Solutions were freshly prepared a few hours before the experiment by using commercially available chemicals as received. All experiments were conducted in an air-conditioned room set to 25 °C (∼77 °F). Table 2 shows the dye structure, its color (in acidic, neutral, and alkaline solutions), formulation, and color in the benzoin autoxidation reaction. In a similar vein that hydroxide should not be added directly to sugar in the classical formulation, care was taken to not mix stock solutions directly to avoid undesirable reactions. To make up the blue bottle solution, 95 mL of water, 2.0 mL of 10 M NaOH solution, 2.0 mL of 0.10 mM methylene blue solution, and 1.0 mL of 47 mM benzoin solution were added to a 125 mL Erlenmeyer flasks. All other solutions were made in a similar manner. Table 2 shows that the new formulation has the same visual appeal as the classical formulation. Most of the dyes have a colorless reduced form in the rapid blue bottle experiment with only two exceptions, indigo carmine and phenanthrenequinone. Phenanthrenequinone is also the only dye with a colorless oxidized form. B



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Table 2. Dye Structures and Their Colors in the Rapid Blue Bottle Experiment

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PEDAGOGICAL AND OTHER USES

may be prepared overnight in advance, but it is not recommended to mix them long before experiment. The main advantages of the new reaction include the following:

Table 4 shows the comparison of the key features of the new reaction and the two published versions. For laboratory demonstration, our rapid version presented here can replace or complement the classical version of the experiment without deterioration of the usual visual behavior. The stock solutions

• Experiment/demonstration time can be reduced • More colors can be produced from different redox indicators C



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Table 3. Formulations and Chemical Patterns in the Rapid Blue Bottle Experimenta

a Note: The numbers listed are for stock solutions in Table 1. For example, 13.0/2.0/3.0/2.0 in the methylene blue column stands for 13.0 mL of water, 2.0 mL of 1.0 M NaOH, 3.0 mL of 0.10 mM methylene blue, and 2.0 mL of 4.7 mM benzoin.

Table 4. Comparison of 100 mL of the Three Versions of the Blue Bottle Experiment Classical Version1,14

Property/Reaction Mass of reducing agent Mass of other reagents (including organic solvent) O2 consumptiona Visual behavior Usable period Size of patterns

Green Version14

2.0−3.3 g 2.0−2.7 g of hydroxide salts

0.4−0.8 g 0.19−0.20 g of mainly NaCl 124−205 mL 25−51 mL Standard Slow color change and relatively pale color ∼1−3 h due to deterioration of sugar; brown Overnight preparation is solution should be discarded possible Medium (see ref 22) Large (see ref 23)

Rapid Version (This Work) 0.010−0.020 g 1.6−2.4 g of NaOH and acetoneb 0.53−1.1 mL Rapid color change and comparable color to the classical experiment ∼1 h due to depletion of reducing agent; benzoin can be added even if it is left overnight Small (see Table 3)

a

O2 consumption comparison is based on the following assumption: four-electron pathway for O2 reduction, two-electron per a molecule of reducing agent22 (glucose, ascorbic acid, and benzoin), and the reaction goes to completion at STP. bExcluding the solvent to dissolve phenanthrenequinone.

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• Depletion of the reducing agent (benzoin) can be noticed easily in just a number of cycles • Though the rapid blue bottle experiment is still strongly alkaline, the amount of base and the mass of waste chemical are significantly reduced from the classical version Oxidation of benzoin to benzil is a classical reaction reported elsewhere.33−36 However, this is the first to consider the use of redox indicators as a catalyst in the autoxidation reaction that may be of interest to organic chemists for further investigation. Application of the classical blue bottle reaction as an oxygen sensor37 and reagent for high-resolution/millimeter-scale imaging38 may also benefit from this rapid formulation.

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful for a generous research grant from the Mahidol University International College (Contract No. 004/2558). We also thank Rattha Noorat for his helping hands in the lab, Dianne Przytula for obtaining a rare reference (ref 13) from the SA State library, Australia, Punchalee Montriwat for formatting assistance, Supaporn Phomsurin for laboratory support, and four anonymous reviewers for comments and suggestions.

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CONCLUDING REMARKS We present a completely new version of the blue bottle experiment and discovered that a new dye, tetrazolium chloride, also works for this experiment. The rapid blue bottle reaction accommodates more variety of redox dyes and forms chemical patterns in all cases. It opens possibilities to expand these preliminary results into in-depth research and various teaching activities and demonstrations.

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AUTHOR INFORMATION

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REFERENCES

(1) Campbell, J. Kinetics−Early and Often. J. Chem. Educ. 1963, 40, 578−583. (2) Engerer, S. C.; Cook, A. G. The Blue Bottle Reaction as a General Chemistry Experiment on Reaction Mechanisms. J. Chem. Educ. 1999, 76, 1519−1520. (3) Limpanuparb, T.; Hsu, S. The Colorful Chemical Bottle Experiment Kit: From School Laboratory to Public Demonstration. Pure and Applied Chemistry International Conference, Jan 21−23, Bangkok, Thailand 2015; pp 470−473. Available at http://arxiv.org/ abs/1504.02604 (accessed Apr 2016). (4) Dutton, F. Methylene Blue-Reduction and Oxidation. J. Chem. Educ. 1960, 37, A799. (5) Anderson, L.; Wittkopp, S. M.; Painter, C. J.; Liegel, J. J.; Schreiner, R.; Bell, J. A.; Shakhashiri, B. Z. What Is Happening When the Blue Bottle Bleaches: An Investigation of the Methylene BlueCatalyzed Air Oxidation of Glucose. J. Chem. Educ. 2012, 89, 1425− 1431.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.6b00018. Figure 1S showing Chen’s autoxidation of benzoin demonstration, Table 1S reporting stock solution formulas for the experiments, and Table 3S showing chemical pattern formation in the rapid blue bottle experiment (PDF) D



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(33) Weiss, M.; Appel, M. The Catalytic Oxidation of Benzoin to Benzil. J. Am. Chem. Soc. 1948, 70, 3666−3667. (34) Ueyama, N.; Kamabuchi, K.; Nakamura, A. Catalytic Air Oxidation of Benzoin in the Presence of Dioxomolybdenum (VI) Complexes with Sulphur Chelate Ligands. J. Chem. Soc., Dalton Trans. 1985, 635−639. (35) Skobridis, K.; Theodorou, V.; Weber, E. A Very Simple and Chemoselective Air Oxidation of Benzoins to Benzils Using Alumina. Arkivoc 2006, 10, 102−106. (36) Safari, J.; Zarnegar, Z.; Rahimi, F. An Efficient Oxidation of Benzoins to Benzils by Manganese (II) Schiff Base Complexes Using Green Oxidant. J. Chem. 2013, 765376. (37) Jang, N. Y.; Won, K. New Pressure-Activated Compartmented Oxygen Indicator for Intelligent Food Packaging. Int. J. Food Sci. Technol. 2014, 49, 650−654. (38) (a) Schafer, P.; van de Linde, S.; Lehmann, J.; Sauer, M.; Doose, S. Methylene Blue- and Thiol-Based Oxygen Depletion for SuperResolution Imaging. Anal. Chem. 2013, 85, 3393−3400. (b) Dietrich, N.; Loubiere, K.; Jimenez, M.; Hebrard, G.; Gourdon, C. A New Direct Technique for Visualizing and Measuring Gas−Liquid Mass Transfer around Bubbles Moving in a Straight Millimetric Square Channel. Chem. Eng. Sci. 2013, 100, 172−182.

(6) Caro, H. Improvement in the Production of Dye-Stuffs from Methyl-Aniline. U.S. Patent 204,796, 1878. (7) DuBois, M.; Gilles, K. A.; Hamilton, J. K.; Rebers, P. A.; Smith, F. Colorimetric Method for Determination of Sugars and Related Substances. Anal. Chem. 1956, 28, 350−356. (8) Lane, J. H.; Eynon, L. Determination of Reducing Sugars by Means of Fehling’s Solution with Methylene Blue as Internal Indicator. J. Soc. Chem. Ind. 1923, 42, 32T−37T. (9) Ling, A. R.; Carter, W. A. The Volumetric Determination of Reducing Sugars. Part IV. Invert Sugar. Analyst 1930, 55, 730−734. (10) Michaelis, L. J. Chem. Educ. 1946, 23, 317. (11) Michaelis, L. To the Editor. J. Chem. Educ. 1947, 24, 149. (12) Cook, A. G.; Tolliver, R. M.; Williams, J. E. The Blue Bottle Experiment Revisited: How Blue? How Sweet? J. Chem. Educ. 1994, 71, 160−161. (13) Chen, P. S. Entertaining and Educational Chemical Demonstrations; Chemical Elements Publishing Company: Camarillo, CA, 1974. (14) Wellman, W. E.; Noble, M. E.; Healy, T. Greening the Blue Bottle. J. Chem. Educ. 2003, 80, 537−540. (15) Staiger, F. A.; Peterson, J. P.; Campbell, D. J. Variations on the Blue-Bottle Demonstration Using Food Items That Contain FD&C Blue# 1. J. Chem. Educ. 2015, 92, 1684−1686. (16) (a) Chen, P. S. Oxidation and Reduction of Indigo Carmine Aided by Benzoin. J. Chem. Educ. 1970, 47, A335. (b) Chen, P. S. ResazurinReduction and Oxidation. J. Chem. Educ. 1970, 47, A335. (17) Hsu, S. Beyond the Blue Bottle Experiment. B.Sc. Senior Project in Chemistry, Mahidol University, Nakhon Pathom, Thailand, 2014. (18) Vandaveer, W. R., IV; Mosher, M. The Blue Bottle Revisited. J. Chem. Educ. 1997, 74, 402. (19) Adamcikova, L.; Sevcik, P. The Blue Bottle Experiment and Pattern Formation in This System. Z. Naturforsch., A: Phys. Sci. 1997, 52a, 650−654. (20) Adamcíková, L.; Sevcík, P. The Blue Bottle ExperimentSimple Demonstration of Self-Organization. J. Chem. Educ. 1998, 75, 1580. (21) Adamcíková, L.; Pavlíková, K.; Ševcík, P. The Methylene BlueD-Glucose-O2 System. Oxidation of D-glucose by Methylene Blue in the Presence and the Absence of Oxygen. Int. J. Chem. Kinet. 1999, 31, 463−468. (22) Rajchakit, U.; Limpanuparb, T. The Blue Bottle Experiment. Thai Science and Technology Journal 2016, 24, 1−11. (23) Rajchakit, U.; Limpanuparb, T. Greening the Traffic Light: Air Oxidation of Vitamin C Catalyzed by Indicators. J. Chem. Educ. 2015, DOI: 10.1021/acs.jchemed.5b00630. (24) Pons, A.; Sagués, F.; Bees, M.; Sørensen, P. G. Pattern Formation in the Methylene-Blue Glucose System. J. Phys. Chem. B 2000, 104, 2251−2259. (25) Pons, A.; Sagués, F.; Bees, M.; Sørensen, P. G. Quantitative Analysis of Chemoconvection Patterns in the Methylene-Blue-Glucose System. J. Phys. Chem. B 2002, 106, 7252−7259. (26) Chen, P. S. Autoxidation of Benzoin. J. Chem. Educ. 1970, 47, A67. (27) Fieser, L.; Fieser, M. Organic Chemistry, 3rd ed.; Reinhold: New York, 1956. (28) Michaelis, L.; Fetcher, E., Jr. Two-Step Oxidation of Benzoin to Benzil. J. Am. Chem. Soc. 1937, 59, 1246−1249. (29) Gerhardt, M.; Schuster, H. A Cellular Automaton Describing the Formation of Spatially Ordered Structures in Chemical Systems. Phys. D 1989, 36, 209−221. (30) Muller, S. C.; Plesser, T.; Hess, B. The Structure of the Core of the Spiral Wave in the Belousov−Zhabotinskii Reaction. Science 1985, 230, 661−663. (31) Prum, R. O.; Williamson, S. Reaction−Diffusion Models of within-Feather Pigmentation Patterning. Proc. R. Soc. London, Ser. B 2002, 269, 781−792. (32) Gaylord, R.; Nishidate, K. Modeling Nature: Cellular Automata Simulations with Mathematica; Springer-Verlag TELOS: Santa Clara, CA, 1996. E


Rapid Blue Bottle Experiment: Autoxidation of Benzoin Catalyzed by

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