- Source: Dry media reaction
A dry media reaction or solid-state reaction or solventless reaction is a chemical reaction performed in the absence of a solvent. Dry media reactions have been developed in the wake of developments in microwave chemistry, and are a part of green chemistry.
The drive for the development of dry media reactions in chemistry is:
economics (save money on solvents)
ease of purification (no solvent removal post-synthesis)
high reaction rate (due to high concentration of reactants)
environmentally friendly (solvent is not required), see green chemistry
Drawbacks to overcome:
reactants should mix to a homogeneous system
high viscosity in reactant system
unsuitable for solvent assisted chemical reactions
problems with dissipating heat safely; risk of thermal runaway
side reactions accelerated
if reagents are solids, very high energy consumption from milling
In one type of solventless reaction a liquid reactant is used neat, for instance the reaction of 1-bromonaphthalene with Lawesson's reagent is done with no added liquid solvent, but the 1-bromonaphthalene acts as a solvent.
A reaction which is closer to a true solventless reaction is a Knoevenagel condensation of ketones with (malononitrile) where a 1:1 mixture of the two reactants (and ammonium acetate) is irradiated in a microwave oven.
Colin Raston's research group have been responsible for a number of new solvent free reactions. In some of these reactions all the starting materials are solids, they are ground together with some sodium hydroxide to form a liquid, which turns into a paste which then hardens to a solid.
In another development the two components of an aldol reaction are combined with the asymmetric catalyst S-proline in a ball mill in a mechanosynthesis. The reaction product has 97% enantiomeric excess.
A reaction rate acceleration is observed in several systems when a homogeneous solvent system is rapidly evaporated in a rotavap in a vacuum, one of them a Wittig reaction. The reaction goes to completion in 5 minutes with immediate evaporation whereas the same reaction in solution after the same 5 minutes (dichloromethane) has only 70% conversion and even after 24 hours some of the aldehyde remains.
References
Kata Kunci Pencarian:
- Kalium permanganat
- Aluminium klorida
- Sitagliptin
- Asam klorida
- Magnesium
- Klorin
- Dakwaan terhadap Donald Trump di New York
- Astatin
- Molibdenum
- Daftar pemenang Hadiah Ig Nobel
- Dry media reaction
- On-water reaction
- Microwave chemistry
- Thermite
- Maillard reaction
- ABC dry chemical
- Dry ice
- Voltaic pile
- Zinc–carbon battery
- Freeze drying
