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Solvent-Less Organic Synthesis

  1. Gerd Kaupp

Published Online: 13 APR 2012

DOI: 10.1002/0471238961.solvkaup.a01

Kirk-Othmer Encyclopedia of Chemical Technology

Kirk-Othmer Encyclopedia of Chemical Technology

How to Cite

Kaupp, G. 2012. Solvent-Less Organic Synthesis. Kirk-Othmer Encyclopedia of Chemical Technology. 1–43.

Author Information

  1. University of Oldenburg

Publication History

  1. Published Online: 13 APR 2012

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Abstract

Solvent-less reactions realize 100% yield of one product without involvement of any added solvent for reaction and workup. They occur in virtually all reaction types by proper choice of the states of aggregation and reaction technique. This article is subdivided into melting, kneading, dry milling, gas–solid reactions, and gas–liquid reactions. The choice depends on the crystal packing, melting points, and eutectic temperatures during a reaction. Temperature control is essential for achieving the full benefit of crystal packing or the maximal concentration in the absence of deactivating solvation. The reaction temperatures are decreased as a result of the most favorable kinetics that lead to complete conversions and mostly avoid catalysis. An additional advantage is the direct and perfect exclusion of moisture. A decreased reaction temperature often enables staying below the eutectic temperature, or allows for obtaining otherwise nonaccessible new products that directly crystallize without involving a liquid phase. If the yield is also quantitative with the product directly crystallizing from the melt, it may be easier to perform melt reactions with slight heating. The so-called “solvent-free” (rather than solvent-less) reactions are mostly not quantitative and often not free of auxiliaries, which requires solvent-consuming chromatography and separation of the auxiliary with usually difficult recovery (eg, catalysts or supports). The hype surrounding catalysis from “green chemistry” to perform reactions in “green-solvents” or “solvent-free” is counterproductive. Solvent-less reactions without catalyst and with 100% yield of pure product are the better choice. It is therefore necessary to report the broad application and variability of solvent-less techniques, for the sake of sustainability.

Keywords:

  • Solvent-less;
  • kneading;
  • solid–solid milling;
  • gas–solid reaction;
  • gas–liquid reaction;
  • cascade reaction;
  • quantitative yield;
  • sustainable