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Blue bottle experiment
Blue bottle experiment
Blue bottle experiment
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Blue bottle reaction video

The blue bottle experiment is a color-changing redox chemical reaction. An aqueous solution containing glucose, sodium hydroxide, methylene blue is prepared in a closed bottle containing some air. Upon standing, it spontaneously turns from blue to colorless due to reduction of methylene blue by the alkaline glucose solution. However, shaking the bottle oxidizes methylene blue back into its blue form. With further shaking, this color-change cycle can be repeated many times.[1] This experiment is a classic chemistry demonstration that can be used in laboratory courses as a general chemistry experiment to study chemical kinetics and reaction mechanism.[2] The reaction also works with other reducing agents besides glucose[3] and other redox indicator dyes besides methylene blue.[4]

Reactions

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History and general concept

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Blue Bottle Reaction Scheme[5][6]

The mechanism of the blue bottle experiment requires an understanding of rates and mechanisms of complex interacting chemical reactions. In complex chemical reactions, individual sub-reactions can occur simultaneously but at significantly different rates. These, in turn, can be affected by reagent concentration and temperature. In most cases, the overall reaction rate is determined by the fastest single component reaction. However, when some processes form intermediate molecules which then react in other processes to form the end product, the rate of the overall reaction is determined by the rate of the slowest reaction. In such circumstances the intermediate products are usually in a steady state at low concentrations because they are highly reactive.[7] Equilibrium state requires that all reaction forward and backward mechanism happens at the same rate.[8] Thus, the overall net reaction is determined by the sum of all the mechanism steps where the rate depends on the concentration and temperature. The blue bottle experiment illustrates this principle of interacting reactions with different rates.[4]

The blue bottle experiment requires only three reagents: potassium hydroxide solution, dextrose solution, and dilute methylene blue solution. These reagents are added to a flask, mixed, and the flask is stoppered. The initial color of the solution is blue, but upon standing for a short interval it spontaneously fades to colorless, as the alkaline dextrose solution reduces the methylene blue to colorless leuco-methylene blue. Shaking the flask causes oxygen present in the head space air to dissolve in the solution and oxidize the leuco-methylene blue back to its colored form again.[9] Another variation uses methylene blue in water, glucose, and caustic soda (NaOH).[10] There are many versions of the experiment, however, unlike the classical version where dye is necessary to use as a catalyst for the reaction, the green and rapid versions undergo autoxidation even in the absence of the dye.[11]

In the past, it was thought that the reaction occurred by the oxidation of an aldehyde group to a carboxylic acid under alkaline conditions. For instance, glucose would be oxidized to gluconate by oxygen.[12] However, the experiment also works with compounds such as vitamin C and benzoin, which do not contain an aldehyde group.[4] Thus, the reaction is actually the oxidation of an acyloin or related α-hydroxycarbonyl group, which is a structural feature of glucose, to a 1,2-diketone.[13] The reduced redox dye (colorless state) is formed from oxidized redox dye (blue). The color-change that occurs in the blue bottle experiment has features of a clock reaction, in which a visible change in the concentration of one or more reagents suddenly occurs upon the exhaustion of a limiting reagent. For example, the limiting reactant, oxygen, is consumed by another reactant, benzoin, with the help of safranin as a catalyst. Once the limited amount of oxygen has been used up, the catalyst is unable to change forms, and as a result, the solution changes color.

Blue Bottle in Different Temperature Time-lapse Coldest (left) to Warmest (right)
Blue Bottle with Manometer Video
Blue Bottle with Manometer

Classical version

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The aqueous solution in the classical reaction contains glucose, sodium hydroxide and methylene blue.[14] In the first step an acyloin of glucose is formed. The next step is a redox reaction of the acyloin with methylene blue in which the glucose is oxidized to diketone in alkaline solution[6] and methylene blue is reduced to colorless leucomethylene blue. If there is enough oxygen available (i.e., after shaking the bottle), leucomethylene blue is immediately re-oxidized to methylene blue and the blue color of the solution persists. However, when the solution is left to rest, the dissolved oxygen is gradually irreversibly[11] consumed, and at the point where it has been completely exhausted, the glucose reduction of methylene blue proceeds unopposed and the color of the solution rapidly disappears.[15] The reaction is first order in glucose, methylene blue and hydroxide ion and zero-order in oxygen. The process can be described as a pseudo first order reaction, and can be used to illustrate the changing concentrations of the reagents over the course of the reaction as the solution changes from blue back to colorless.[1]

The final glucose oxidation products besides sodium gluconate have been identified as D-arabino-hexos-2-ulose (glucosone), the anion of D-arabinonate after splitting off of a formate anion and arabinonic acid.[13]

Green version

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Wellman and Noble proposed a new formulation for the Blue Bottle experiment in which vitamin C serves as a reducing agent instead of glucose; the methylene blue and oxygen are still used.[16] Copper is added as a catalyst for the reoxidation of leucomethylene blue to methylene blue. These modifications give an experiment that generates a smaller amount of waste that is less corrosive and easier to neutralize, and therefore is an example of green chemistry modification.[17]

Rapid version

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The Chen[18] autoxidation of benzoin had performed a similar experiment with respect to the classical and green versions. It was found that the traffic light and vanishing valentine experiments can become successful regardless of whether a sugar is added. One variation is more rapid, with the number of color change cycles do not last as long as the classical and green versions because the reactants are present in smaller amounts; also, the reducing agent for this experiment is benzoin, which is added to help increase the number of cycles in the solution. Moreover, the usable period in this experiment is quite short. Although the experiment is prepared overnight, the reducing agent can be added at any time to be able to observe the solution more.[19]

Enzymatic version

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Zhang, Tsitkov, and Hess from Columbia University[20] proposed an enzymatic version of the "blue bottle experiment". They named it the "green bottle experiment", since the system is colored green and the reagents are safer than classical approaches. The experiment is performed in a clear glass vial containing two common enzymes (glucose oxidase and horseradish peroxidase), glucose, and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (abbreviated as ABTS) in PBS buffer. A thin layer of oil is used to block the solution from the air. The solution initially turns green and then turns colorless with the depletion of dissolved oxygen. Shaking the solution introduces fresh oxygen and colors the solution green again until the oxygen is consumed.

This version relies on three enzymatic reactions. First, the glucose oxidase catalyzes the oxidation of glucose in the presence of oxygen and produces hydrogen peroxide. Second, the horseradish peroxidase utilizes the hydrogen peroxide to oxidize ABTS to its radical cationic form, ABTS+•. As the dissolved oxygen is consumed in the solution, the third reaction occurs: glucose oxidase catalyzes the reduction of ABTS+• back to ABTS in the presence of glucose. This system can also form beautiful patterns arising from reaction-driven Rayleigh–Bénard convection.[21]

Variation of dyes

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The chemical reactions and mechanism in the blue bottle experiment rely on the oxidation of a sugar with the aid of air and a redox dye in a basic solution. Other variations of this reaction have been reported that use four families of redox dyes: thiazines, oxazines, azines, and indigo carmine have all been reported to work with glucose and caustic soda.[19]

Chemical traffic light experiment

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The chemical traffic light is a color-changing redox reaction that is related to the blue bottle experiment. One of the early formulas consists of glucose, sodium hydroxide, indigo carmine (dye), and water. Another formula consists of indigo carmine, ascorbic acid (Vitamin C), sodium bicarbonate, sodium chloride, copper(II) sulfate, sodium hydroxide and water.[17] By doing so, chemical waste and the level of corrosive chemicals is reduced. The amount of solid chemicals dissolved in the experiment could be reduced from 60 grams to 6 grams. And the pH could be lowered from 13 to 3 which is easier to neutralize the pH to 7 by adding baking soda before disposal.[16] Also, it is safer and the reactions also occur faster and are easier to perform.

At first, all chemicals are added together and the color appears yellow. After shaking, the color turns green and then changes to red after it is left untouched. When further observed, the color turns back to yellow, which is why the solution is called the chemical traffic light. This reaction can be repeated many times, but it needs additional oxygen or indigo carmine.

This reaction occurs by oxidation and reduction of the solution where alkaline glucose solution is acting as a reducing agent. The glucose solution is added to the solution containing indicator (dye indigo carmine) the color changes occur. This reaction is also known as chemical clock experiment because concentrations of the products and reactants changed over the specific period.[22] When the solution is shaken, oxygen dissolves in the solution and oxidizes indigo carmine. Solution becomes red if a small amount of oxygen is dissolved, and green if all of indigo carmine is oxidized.[23] The solution will turn back to original yellow color when the concentration of oxygen level drops.[24]

  • Chemical traffic light reaction time-lapse
  • Chemical traffic light reaction (yellow)
    Chemical traffic light reaction (yellow)
  • Chemical traffic light reaction (red)
    Chemical traffic light reaction (red)
  • Chemical traffic light reaction (green)
    Chemical traffic light reaction (green)

Vanishing valentine experiment

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The vanishing valentine experiment is another chemical reaction related to the blue bottle experiment. This reaction occurs when water, glucose, sodium hydroxide, and resazurin is mixed in a flask. When the solution is shaken, it turns from light blue to a reddish color. The solution turns back to a light blue after being left to stand for a while. This reaction can be repeated several times.[25]

After mixing all the components, shake the bottle and the color will turn to red or pink depend on the amount of resazurin in the solution. More resazurin will result in more time needed for the solution to turn back the color and the intensity of the red color.

Vanishing Valentine Equation

The chemical reaction stimulates glucose to reduce resazurin to resorufin. It would then be reduced again into a colorless compound called dihydroresorufin. When dihydroresorufin is shaken, it is oxidized back to resorufin. This is due to the fact that shaking it results oxygen in the bottle to oxidized dihydroresorufin back into resorufin.[26]

  • solution turn from colorless to red
  • reduced color of the experiment
    reduced color of the experiment
  • oxidized color of the experiment
    oxidized color of the experiment

Others

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Gatorade

Erioglaucine, a food colorant and a redox dye, was found to be an effective substitute for methylene blue in the blue bottle experiment. Since some candies and drinks such as Gatorade contain the dye and a reducing sugar, only sodium hydroxide need be added to turn these food products into a blue bottle solution.[27]

Purple flask

Thionine can be used in the green version of the experiment in combination with copper/iron catalyst to create the purple flask.[28]

Pattern formation

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Pattern formation is when a solution containing NaOH, glucose, and dye is poured into a Petri dish that is open to the atmosphere.[29] This will result in solution changing its structure over a period of time. Structures arise from molecular transport through diffusion and chemical kinetics. Patterns formed in the Petri dish can be described as a mosaic pattern; web-like, dynamic spiral, branching, and lines connecting to each others.[30]

Changes in pattern formation are not homogeneous and can be affected by several factors. Different types of dye in solution will give the same pattern because of the bond's formation and the dynamics remain the same, this is because the solution has the same colour as the dye. Different amounts of dye can result in density change in the solution and this results in changing of convective motion. Different amounts of dye can bring in different amounts of convention cells which are also formed by different amounts of glucose and oxidized product. This can result in an interesting spatial phenomena. Time can also affect pattern formation. As the time passed, one pattern gradually faded away. Spirals and branches started to disappear and eventually disappeared fully. These facts indicate that oxygen affects the chemical reaction and this plays a fundamental role in the pattern formation. Pattern formation may also form from a chemically driven convective instability. This means that matter is exchanged across the air-reaction mixture interface, due to the fluctuations in the molecular nature of chemical systems.[31] The temperature can affect the formation of pattern.[6] Colder temperature formed a clearer pattern than hot temperature. The shape of the Petri dish also contributed to the pattern formation.[6]

  • Pattern Formation from Blue Bottle Experiment in Ice Water Bath Time-lapse
  • Pattern Formation from Blue Bottle Experiment in Ice Water Bath
    Pattern Formation from Blue Bottle Experiment in Ice Water Bath
  • Pattern Formation from Blue Bottle Experiment in Cold Water Bath Time-lapse
  • Pattern Formation from Blue Bottle Experiment in Cold Water
    Pattern Formation from Blue Bottle Experiment in Cold Water
  • Pattern Formation from Blue Bottle Experiment in Room Temperature Time-lapse
  • Pattern Formation from Blue Bottle Experiment in Room Temperature
    Pattern Formation from Blue Bottle Experiment in Room Temperature
  • Pattern Formation from Blue Bottle Experiment in Warm Water Bath Time-lapse
  • Pattern Formation from Blue Bottle Experiment in Warm Water Bath
    Pattern Formation from Blue Bottle Experiment in Warm Water Bath
  • Chemical Traffic Light Experiment Pattern Formation In Different Shape Containers Time-lapse
  • Chemical Traffic Light Experiment Pattern Formation In Different Shape Containers
    Chemical Traffic Light Experiment Pattern Formation In Different Shape Containers

A group of researchers of the University of Glasgow named Pons, Batiste and Bees came up with a small conclusion about pattern formation in the methylene blue-glucose system. They came up with a conclusive statement that a similar pattern can be formed in a container with accessible oxygen. This resulting surface tension effect isn't required to produce the instability. Small holes were also found in the lid of container that oxygen can't access resulting in a thin, blue, and lower amount of oxygen. Pattern length and time scale had been explored in one of their experiments due to the variation in viscosity and fluid depth. The experiment reveals that the wavelength is formed as a pattern starts to form quickly. Then wavelength or pattern can be maintained or oscillate for a while.[32]

References

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Blue bottle experiment

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from Grokipedia
The Blue Bottle experiment is a classic demonstration in chemistry education that showcases a reversible reaction through a vivid color change in an . At rest, the solution appears colorless, but vigorous shaking causes it to turn deep blue, after which it gradually returns to colorless when left undisturbed; this cycle can be repeated numerous times until the reagents are depleted. The experiment typically involves preparing a solution with glucose (a reducing sugar), a strong base such as sodium hydroxide or potassium hydroxide, and methylene blue as a redox indicator. A common formulation includes 10 g glucose, 8 g potassium hydroxide, and 0.05 g methylene blue dissolved in water to a volume of about 1 L, often with a small amount of ethanol to aid solubility. The solution is placed in a flask or bottle, initially appearing colorless due to the reduction of methylene blue to its leuco (colorless) form by glucose under alkaline conditions. Shaking introduces dissolved oxygen from the air, which rapidly oxidizes the leuco-methylene blue back to the intensely blue oxidized methylene blue. Upon standing, the reaction reverses as the alkaline glucose solution reduces the methylene blue, effectively removing the dissolved oxygen and restoring the colorless state. The underlying chemistry highlights catalyzed by the indicator, with facilitating between oxygen and glucose. The process follows kinetics influenced by factors such as base concentration, temperature, and oxygen availability, with an change of approximately 23 kJ mol⁻¹ for the reduction step. First introduced in the chemical education literature in by J. A. Campbell as a simple illustration of reaction kinetics, the experiment originated from demonstrations at institutions like Caltech and the University of Wisconsin, though its precise historical roots remain undocumented beyond educational contexts. Widely used in classrooms, it effectively teaches concepts of oxidation-reduction, , and the effects of physical agitation on reaction rates, with safe, low-hazard materials that make it accessible for student-led inquiries. Variations include photochemical versions using light instead of shaking and adaptations with different indicators or sugars to produce other colors, such as green or red.

Background

History and Discovery

The blue bottle experiment was first described in 1960 by F. B. Dutton as a simple demonstration of the reversible reduction and oxidation of in an alkaline medium containing a . Although first documented in the literature in 1960, the demonstration was known earlier at institutions such as the , with origins attributed to Caltech. This setup highlighted the color change from blue to colorless and back, driven by oxygen exposure, using basic laboratory materials. In 1963, J. A. Campbell expanded on the demonstration in the Journal of Chemical Education, applying it to teach chemical kinetics early in the curriculum. The experiment's initial purpose was to illustrate oxidation-reduction processes and reaction rates without requiring complex equipment, making it accessible for introductory chemistry instruction. The experiment gained popularity in classroom settings through adaptations by educators and suppliers like Flinn Scientific, which provides pre-packaged materials to facilitate safe and repeatable demonstrations. These developments emphasized its role as an engaging tool for demonstrating redox kinetics.

General Concept

The is a classic chemistry demonstration featuring a reversible color-changing reaction in an . It consists of an alkaline containing a , such as glucose, and a indicator, like , which initially appears colorless due to the reduction of the indicator. When the solution is shaken, atmospheric oxygen dissolves into the liquid, oxidizing the indicator and producing a vivid color; upon standing, the color gradually fades back to colorless as the restores the indicator to its reduced state, allowing the cycle to repeat multiple times. This experiment serves key educational goals by illustrating fundamental chemical principles through a visually engaging process. It demonstrates reaction kinetics by showing how the rate of color change depends on factors like oxygen incorporation, dynamic equilibrium as the system oscillates between oxidized and reduced forms, and the critical role of dissolved gases in driving the reaction forward or backward. Suitable for high school or introductory chemistry courses, it encourages students to observe phenomena and form hypotheses about underlying processes without requiring advanced equipment. The significance of the blue bottle experiment lies in its ability to highlight reversible processes, where the indicator undergoes repeated oxidation and reduction, in contrast to typical irreversible reactions encountered in basic chemistry. It promotes hands-on learning of , as external disturbances like shaking shift the equilibrium toward the colored state by increasing oxygen concentration. To fully appreciate the demonstration, participants need a basic understanding of oxidation as the loss of electrons and reduction as the gain of electrons, concepts central to the color transitions observed.

The Classical Experiment

Materials

The standard blue bottle experiment requires the following materials: 10 g of glucose (dextrose), 8 g of (NaOH) or (KOH), 5–6 drops of a 1% solution, and approximately 300 distilled water. A 500-mL flask equipped with a stopper is used as the reaction vessel to allow for vigorous shaking while containing the solution. These quantities are scaled for a demonstration and can be adjusted proportionally for smaller setups, ensuring the solution remains effective for multiple cycles.

Preparation

To prepare the solution, first dissolve 8 g of NaOH or KOH in ~300 mL of distilled water in the 500-mL flask, stirring until fully dissolved; this step generates heat, so allow the solution to cool if necessary. Next, add 10 g of glucose and stir to dissolve completely. Then, incorporate 5–6 drops of the 1% methylene blue solution. The resulting solution initially appears blue but turns colorless or pale yellow upon standing for a short period, typically within 1 minute, due to the initial redox reaction in the presence of residual oxygen. For optimal results, prepare the solution fresh and allow it to settle for up to 24 hours if needed to ensure a clear, colorless state before use, though immediate decolorization is common.

Procedure

Begin by allowing the prepared solution to stand undisturbed in the stoppered flask until it is fully colorless. Secure the stopper and shake the flask vigorously for 10–20 seconds to dissolve atmospheric oxygen into the solution, causing it to turn deep blue almost immediately. Set the flask down and let it stand still for 1–2 minutes, during which the color fades back to colorless as the reaction proceeds. This shaking and settling cycle, which demonstrates a reversible redox color change, can be repeated 10–20 times until the glucose is depleted and the solution no longer responds effectively, often turning permanently yellow after extended use. Perform the demonstration in a well-lit area against a white background to enhance visibility of the color transitions.

Safety Considerations

Wear protective gloves, safety goggles, and a lab coat throughout the preparation and procedure, as NaOH and KOH are strong bases that can cause severe burns and eye damage upon contact. Avoid ingestion or inhalation of the solution, and perform the experiment in a well-ventilated area to minimize exposure to , which is harmful if swallowed. Dispose of the used solution as by neutralizing the alkali with a dilute before dilution and flushing down a drain, following local regulations. Keep the flask stoppered to prevent spills during shaking.

Tips for Success

Use fresh, oxygen-deprived —such as boiled and cooled water—to minimize premature oxidation and extend the number of cycles. Avoid direct during preparation and demonstration, as it can accelerate unwanted oxidation of the components. If the color change is slow, warm the solution gently to at least 20°C to enhance reaction kinetics, but do not overheat to prevent decomposition. Test the concentration dropwise if the initial color is too intense, aiming for a vivid but not opaque blue upon shaking.

Detailed Reaction Mechanism

The blue bottle experiment involves a redox cycle where glucose serves as the , converting from its oxidized blue form (MB⁺) to the reduced colorless leukomethylene blue (MBH₂) in an alkaline medium, while dissolved oxygen reoxidizes MBH₂ back to MB⁺ upon agitation. This process demonstrates the interplay between reduction and oxidation kinetics, with the color change driven by the relative rates of these reactions. The key reactions can be summarized as follows. In alkaline conditions, glucose enolizes to a reactive intermediate and undergoes oxidation primarily to arabinonic acid, releasing electrons: C6H12O6+2OH−→arabinonic acid intermediates+2H2O+2e−\text{C}_6\text{H}_{12}\text{O}_6 + 2\text{OH}^- \rightarrow \text{arabinonic acid intermediates} + 2\text{H}_2\text{O} + 2\text{e}^- These electrons reduce in a simplified : MB++2e−+2H+→MBH2\text{MB}^+ + 2\text{e}^- + 2\text{H}^+ \rightarrow \text{MBH}_2 Upon shaking, atmospheric oxygen dissolves into the solution and oxidizes the reduced form: 2MBH2+O2→2MB++2H2O2\text{MBH}_2 + \text{O}_2 \rightarrow 2\text{MB}^+ + 2\text{H}_2\text{O} Arabinonic acid formation contributes to gradual pH changes. The kinetics of the color change are governed by the slow reduction of MB⁺ by glucose in the absence of oxygen, which proceeds at a rate first-order with respect to hydroxide ion, methylene blue, and glucose concentrations (rate = k[MB⁺][glucose][OH⁻]), with an activation energy of approximately 23 kJ mol⁻¹. Shaking introduces dissolved oxygen to a concentration of about 8 mg/L (near air-saturated levels at room temperature), rapidly shifting the equilibrium toward oxidation and producing the blue color, which then fades as oxygen is depleted through diffusion-limited consumption by MBH₂. Alkaline conditions (pH 12–13) are essential, as they facilitate of glucose to form a reactive enediol intermediate that enhances its reducing capability, while the color of is tied to its —blue for the cationic MB⁺ and colorless for the neutral MBH₂. The system is limited to approximately 20 cycles of color change before glucose is sufficiently depleted, after which side reactions, including further oxidation to arabinonic acid, lower the and prevent sustained reactivity, often turning the solution yellow or brown.

Variations

Green Bottle Experiment

The Green Bottle Experiment represents a modification of the classical Blue Bottle Experiment, substituting for to achieve distinctive green-dominant color shifts in a demonstration. , or the disodium salt of indigo-5,5'-disulfonic acid, serves as the indicator; its oxidized form displays a hue, while the reduced leuco form is or colorless. In the adapted procedure, approximately 0.02 g of is dissolved in 20 cm³ water to form a deep blue solution, followed by the addition of 70 cm³ warm (40–50 °C) 0.4 M , which shifts the color to vibrant under alkaline conditions; dissolve 2.5 g glucose in 10 cm³ water and add the glucose solution, resulting in a different shade that spontaneously changes to then within seconds. When , shaking the flask dissolves atmospheric oxygen, oxidizing the dye first to then to a deeper , which fades back to over 1–2 minutes as the regenerates the leuco form. The underlying mechanism mirrors the classical process, where dissolved oxygen reoxidizes the reduced dye, and alkaline glucose acts as the reductant in a , but indigo carmine introduces pH-dependent color variations: green predominates at 11.4–13, shifting to blue below 11.4, with the yellow leuco form stable at higher . Key advantages include the dye's lower toxicity compared to —indigo carmine is an FDA-approved food colorant (FD&C Blue No. 2)—enhancing safety for educational use, alongside its capacity for vivid, traffic light-like color sequences that captivate audiences. Color cycles persist similarly to the original experiment but exhibit faster fading in subsequent iterations due to indigo carmine's relative stability under repeated oxidation-reduction.

Rapid Version

The rapid version of the blue bottle experiment, introduced in 2016, utilizes benzoin as the to achieve significantly faster color cycles compared to the classical glucose-based setup. This variant was developed by Rajchakit and Limpanuparb to demonstrate processes more efficiently in educational settings, leveraging benzoin's (C₆H₅CH(OH)COC₆H₅) inherent reactivity under alkaline conditions. In preparation, glucose is replaced with 5–10 g of benzoin dissolved in an aqueous solution, while retaining as the redox indicator; the mixture remains colorless initially until oxygen is introduced. Upon shaking to incorporate air, the solution rapidly turns within seconds due to the oxidation of leuco-methylene blue to its colored form, enabling multiple cycles in under 10 seconds as opposed to the minutes required in the original experiment. The mechanism involves the catalyzed autoxidation of benzoin to benzil (a yellow 1,2-diketone), where methylene blue facilitates the redox cycle by alternating between its oxidized (blue) and reduced (colorless) states, accelerated by benzoin's lower activation energy for oxidation relative to glucose. The key reaction can be represented as: Benzoin+O2→MBBenzil+H2O\text{Benzoin} + \text{O}_2 \xrightarrow{\text{MB}} \text{Benzil} + \text{H}_2\text{O}
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