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Dry media reaction

A dry media reaction or solid-state reaction or solventless reaction is a chemical reaction system in the absence of a solvent[1] . The drive for the development of dry media reactions in chemistry is

  • economics (save money on solvents)
  • ease of purification (not required to remove a solvent 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

One type of solventless reaction is one where 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 irradated in a microwave oven[2]

Collin Raston's research group have been responsible for a number of new solvent free reactions[3][4] 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 together with the asymmetric catalyst S-proline in a ball mill in a mechanosynthesis. The reaction product has 97% enantiomeric excess.[5]

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[6] :

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.


  1. ^ Dry media reactions M. Kidwai Pure Appl. Chem., Vol. 73, No. 1, pp. 147–151, 2001. Link
  2. ^ Solvent-free and aqueous Knoevenagel condensation of aromatic ketones with malononitrile Guan-Wu Wang and Bo Cheng Arkivoc 1 May 2004 Link
  3. ^ 'Towards benign synthesis of pyridines involving sequential solvent free aldol and Michael addition reactions', Gareth W. V. Cave and Colin L. Raston, Chem. Commun., 2000, 2119 - 2120 doi:10.1039/b007431o
  4. ^ Efficient synthesis of pyridines via a sequential solventless aldol condensation and Michael addition Gareth W. V. Cave, Colin L. Raston, J. Chem. Soc., Perkin Trans. 1, 2001, (24),3258-3264 doi:10.1039/b107302h .
  5. ^ Solvent-Free Asymmetric Organocatalysis in a Ball Mill Belén Rodríguez, Toni Rantanen, Carsten Bolm Angewandte Chemie International Edition Volume 45, Issue 41 , Pages 6924 - 6926 2006 doi:10.1002/anie.200602820
  6. ^ Rate acceleration of organic reaction by immediate solvent evaporation Akihiro Orita, Genta Uehara, Kai Miwa and Junzo Otera Chem. Commun., 2006, 4729–4731 doi:10.1039/b609567d


This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Dry_media_reaction". A list of authors is available in Wikipedia.
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