A On water reaction is a group of organic reactions that take place as an emulsion in water and that exhibit a unusual reaction rate acceleration compared to the same reaction in an organic solvent or compared to the dry media reaction. This effect has been known for many years but in 2005 researchers in the group of K. Barry Sharpless presented a systematic study into this phenomenon. Organic reactions are chemical reactions between organic compounds. ... A. Two immisicble liquids, not emulsified; B. An emulsion of Phase B dispersed in Phase A; C. The unstable emulsion progressively separates; D. The (purple) surfactant positions itself on the interfaces between Phase A and Phase B, stabilizing the emulsion An emulsion is a mixture of two immiscible (unblendable) substances. ... The reaction rate for a reactant or product in a particular reaction is defined as the amount (in moles or mass units) per unit time per unit volume that is formed or removed. ... A solvent is a liquid that dissolves a solid, liquid, or gaseous solute, resulting in a solution. ... A dry media reaction or solid-state reaction is a chemical reaction system in the absence of a solvent. ... Karl Barry Sharpless (born April 28, 1941) is a chemist renowned for his work on organometallic chemistry. ...

The rate acceleration is found in Claisen rearrangements. In one typical example of this reaction at room temperature the chemical yield was found to be 100% on water after 120 hours compared to 16% with the same reaction in toluene or 73% in the neat reaction. Room temperature, in laboratory reports, is taken to be roughly 21–23 degrees Celsius (70–73 degrees Fahrenheit), or 294–296 kelvins. ...

Enhanced reactivity is also found in cycloadditions. The reaction of quadricyclane with DEAD is a 2σ + 2σ + 2π cycloaddition that on water takes place within 10 minutes at room temperature with 82% yield. The same reaction in toluene takes 24 hours at 80°C with 70 yield. A emulsion reaction in fluorinated cyclohexane takes 36 hours and the neat reaction takes even longer (48 hours). A Cycloaddition is a pericyclic reaction in which the net result is loss of two pi bonds and gain of two sigma bonds. ... A cyclohexane molecule in chair conformation, with hydrogen atoms in axial position in red, equatorial in blue. ...

Other reaction with apolar reactants such as Ene reactions and Diels-Alder reactions also exhibit rate accelerations. An explanation is not available but it involves hydrogen bonding and the presence of a small amount of dissolved solute. This reaction type is part of green chemistry because it does away with organic solvents and reaction product isolation is relatively easy. In chemistry, the reactants are the substances that exist at the start of a chemical reaction. ... Ene reactions are group transfer reactions between an alkyne or alkene, or similar double-bonded species and an allyl-like species. ... The Diels-Alder reaction is an organic chemical reaction (specifically, a cycloaddition) between a conjugated diene and a substituted alkene (commonly termed the dienophile) to form a substituted cyclohexene system. ... In chemistry, a hydrogen bond is a type of attractive intermolecular force that exists between two partial electric charges of opposite polarity. ... Green Chemistry is the design of chemical products and processes that reduce or eliminate the use and generation of hazardous substances. ...

References

• Unique Reactivity of Organic Compounds in Aqueous Suspension Sridhar Narayan, John Muldoon, M. G. Finn, Valery V. Fokin, Hartmuth C. Kolb, K. Barry Sharpless Angew. Chem. Int. Ed. 21/2005 p 3157 Abstract (http://www3.interscience.wiley.com/cgi-bin/abstract/110497267/ABSTRACT)