In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...
, the high dilution principle is a strategy for some
macrocyclization reactions, i.e. the synthesis of
macrocycle
Macrocycles are often described as molecules and ions containing a ring of twelve or more atoms. Classical examples include the crown ethers, calixarenes, porphyrins, and cyclodextrins. Macrocycles describe a large, mature area of chemistry. ...
s. Unlike the synthesis of 5- and 6-membered rings, the preparation of larger rings competes unfavorably with polymerization reactions.
Polymer
A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...
s arise from coupling of long chain precursors. Such reactions are disfavored when the acyclic compounds are dilute. Although high dilution reactions can be conducted in a batch reactor with large volumes of
solvent
A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
, an alternative practical implementation entails slow addition of reactants, under conditions that the reactants are more rapidly consumed than the rate of addition. Typically, additions use one or more
syringe pumps. Illustrative is the synthesis of thiacyclopentadecane from 1,14-dibromotetradecane and sodium sulfide in 45% yield:
:BrCH
2(CH
2)
12CH
2Br + Na
2S → (CH
2)
14S + 2 NaBr
A range of specialized glassware
[{{cite journal , author=Lawrence T. Scott, Chris A. Sumpterdoi=10.15227/orgsyn.069.0180 , title=Diazo Ketone Cyclization Onto a Benzene Ring: 3,4-Dihydro-1(2H)-Azulenone , journal=Organic Syntheses , date=1990 , volume=69 , page=180 ] and instrumentation are often used, e.g.
syringe pumps.
References
Carbon-carbon bond forming reactions