A dry media reaction or solid-state reaction or solventless reaction is a

chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking ...

system in the absence of a

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

. The drive for the development of dry media reactions in

chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...

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 uni ...

(due to high

concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', ''number concentration'', ...

of reactants) * environmentally friendly (solvent is not required), see

green chemistry Green chemistry, also called sustainable chemistry, is an area of chemistry and chemical engineering focused on the design of products and processes that minimize or eliminate the use and generation of hazardous substances. While environmental che ...

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 The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the int ...

in reactant system * unsuitable for solvent assisted chemical reactions * problems with dissipating heat safely; risk of

thermal runaway Thermal runaway describes a process that is accelerated by increased temperature, in turn releasing energy that further increases temperature. Thermal runaway occurs in situations where an increase in temperature changes the conditions in a way t ...

* 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, ...

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 th ...

, 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 prep ...

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 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 b ...

with (

malononitrile Malononitrile is an organic compound nitrile with the formula . It is a colorless or white solid. It can be prepared by dehydration of cyanoacetamide. Malononitrile is relatively acidic, with a p''K''a of 11 in water. This allows it to be used ...

) where a 1:1 mixture of the two reactants (and ammonium acetate) is irradiated in a

microwave oven A microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce ...

. 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 al ...

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 The aldol reaction is a means of forming carbon–carbon bonds in organic chemistry. Discovered independently by the Russian chemist Alexander Borodin in 1869 and by the French chemist Charles-Adolphe Wurtz in 1872, the reaction combines two ...

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 molec ...

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 p ...

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. A

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

vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often ...

, one of them a

Wittig reaction The Wittig reaction or Wittig olefination is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide called a Wittig reagent. Wittig reactions are most commonly used to convert aldehydes and ketones to alkenes. Mos ...

. 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 wit ...

) 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