A dry media reaction or solid-state reaction or solventless reaction is a chemical reaction system in the absence of a solvent. The drive for the development of dry media reactions in

chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...

is * economics (save money on solvents) * ease of purification (no solvent removal post-synthesis) * high

reaction rate The reaction rate or rate of reaction is the speed at which a chemical reaction takes place, defined as proportional to the increase in the concentration of a product per unit time and to the decrease in the concentration of a reactant per unit ...

(due to high concentration of reactants) * environmentally friendly (solvent is not required), see green chemistry Drawbacks to overcome: * reactants should mix to a

homogeneous Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, siz ...

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 A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...

reactant is used

neat Neat may refer to: * Neat (bartending), a single, unmixed liquor served in a rocks glass * Neat, an old term for horned oxen * Neat Records, a British record label * Neuroevolution of augmenting topologies (NEAT), a genetic algorithm (GA) for the ...

, for instance the reaction of

1-bromonaphthalene 1-Bromonaphthalene is an organic compound with the formula C10H7Br. It is one of two isomeric bromonaphthalenes, the other being 2-bromonaphthalene. Under normal conditions, the substance is a colorless liquid. Synthesis and reactions It is pre ...

with

Lawesson's reagent Lawesson's reagent (LR) is a chemical compound used in organic synthesis as a thiation agent. Lawesson's reagent was first made popular by Sven-Olov Lawesson, who did not, however, invent it. Lawesson's reagent was first made in 1956 during a sys ...

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 In organic chemistry, the Knoevenagel condensation () reaction is a type of chemical reaction named after German chemist Emil Knoevenagel. It is a modification of the aldol condensation. A Knoevenagel condensation is a nucleophilic addition of ...

ketones In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bon ...

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 Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...

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 Enantioselective synthesis, also called asymmetric synthesis, is a form of chemical synthesis. It is defined by IUPAC as "a chemical reaction (or reaction sequence) in which one or more new elements of chirality are formed in a substrate molecul ...

S-

proline Proline (symbol Pro or P) is an organic acid classed as a proteinogenic amino acid (used in the biosynthesis of proteins), although it does not contain the amino group but is rather a secondary amine. The secondary amine nitrogen is in the prot ...

in a

ball mill A ball mill is a type of grinder used to grind or blend materials for use in mineral dressing processes, paints, pyrotechnics, ceramics, and selective laser sintering. It works on the principle of impact and attrition: size reduction is done ...

in a mechanosynthesis. The reaction product has 97%

enantiomeric excess In stereochemistry, enantiomeric excess (ee) is a measurement of purity used for chiral substances. It reflects the degree to which a sample contains one enantiomer in greater amounts than the other. A racemic mixture has an ee of 0%, while a sin ...

. A

acceleration is observed in several systems when a homogeneous solvent system is rapidly evaporated in a

rotavap A rotary evaporator (rotovap) is a device used in chemical laboratories for the efficient and gentle removal of solvents from samples by evaporation. When referenced in the chemistry research literature, description of the use of this technique an ...

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 Dichloromethane (DCM or methylene chloride, methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odour is widely used as a solvent. Although it is not miscible with ...

) has only 70% conversion and even after 24 hours some of the aldehyde remains.

Bibliography

* Kidway, M. (2001)
Dry Media Reactions
Pure and Applied Chemistry 73 (1),147-151 {{DEFAULTSORT:Dry Media Reaction Chemical reactions