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The blue bottle experiment is a chemical reaction. An aqueous solution containing glucose, sodium hydroxide, methylene blue and some air is shaken in a closed bottle; it turns from colorless to blue and then decolorizes again after a while. With further shaking, the cycle can be repeated many times. This experiment is a classic chemistry demonstration and can be used in laboratory courses as a general chemistry experiment to study chemical kinetics and reaction mechanisms. The reaction also works with other reducing agents besides glucose and other redox indicator dyes besides methylene blue.

Reactions
It was originally believed that the total reaction was the oxidation of an aldehyde group to a carboxylic acid under alkaline conditions, for example, glucose being oxidized to gluconate by oxygen. However, the experiment also works for compounds such as vitamin C and benzoin, which do not contain an aldehyde. The reaction is actually the oxidation of an acyloin or related α-hydroxy-carbonyl group, which is a feature of glucose, to a 1,2 diketone. The rate of the reaction is also affected by the temperature. The reduced redox dye (colorless state) is formed from oxidised redox dye (blue) at faster rate in high temperature when compared to its formation in low temperature.



Classical version
The aqueous solution in the classical reaction contains glucose, sodium hydroxide and methylene blue. In the first step the enolate of glucose is formed. The next step is a redox reaction of the enolate with methylene blue. The glucose is oxidized to gluconic acid which, in alkaline solution is in the sodium gluconate form. Methylene blue is reduced to colorless leucomethylene blue. The process can be described by as a pseudo first order reaction, using it as an example to understand the changing concentration of the chemicals over the course of the solution going from blue back to colorless.

If there is enough available oxygen, leucomethylene blue is then re-oxidized to methylene blue and the blue color of the solution is restored. The availability of oxygen is increased by shaking the solution. When the solution comes to rest, glucose reduction of the redox dye again takes the upper hand and the color of the solution disappears. The reaction is first order in glucose, methylene blue and hydroxide ion and zero-order in oxygen. Other glucose oxidation products besides sodium gluconate that are reported are D-arabino-hexos-2-ulose (glucosone), the anion of D-arabinonate after splitting of a formate anion and finally arabinonic acid.

Green version
Wellman and Noble proposed a new formulation for the Blue Bottle experiment, vitamin C is used instead of glucose, while methylene blue and oxygen are still used. 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.

Rapid version
The Chen 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 not lasting as long as the classical and green versions because the reactants are used 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.

Enzymatic version
Zhang, Tsitkov, and Hess from Columbia University 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.

A movie can be found here: Green bottle experiment

Variation of dyes
Four (families) of dyes are used in the oxidation thiazines, oxazines, azines, and indigo carmine, reported to work with glucose and caustic soda. It is also noted that the observation of ascorbic acid is achieved in a wider range of pH.


 * Chemical traffic light experiment
 * Vanishing valentine experiment

Pattern formation
Pattern formation is when a solution containing NaOH, glucose, and dye is poured into an open Petri dish which is open to the atmosphere. 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.

There are factors that can affect pattern formation. Changes in pattern formation are not homogeneous and can be caused 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 cell 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. The temperature can affect the formation of pattern. Colder temperature formed a clearer pattern than hot temperature. The shape of the Petri dish also contributed to the pattern formation.

A small 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.