World Library  
Flag as Inappropriate
Email this Article

Phase-transfer catalyst

Article Id: WHEBN0002885779
Reproduction Date:

Title: Phase-transfer catalyst  
Author: World Heritage Encyclopedia
Language: English
Subject: Flow chemistry, PTC, Catalysts, Sodium hypochlorite
Collection: Catalysts
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Phase-transfer catalyst

In detergent for solubilizing the salts into the organic phase. Phase-transfer catalysis refers to the acceleration of the reaction upon the addition of the phase-transfer catalyst.

By using a PTC process, one can achieve faster reactions, obtain higher conversions or yields, make fewer byproducts, eliminate the need for expensive or dangerous solvents that will dissolve all the reactants in one phase, eliminate the need for expensive raw materials and/or minimize waste problems. Phase-transfer catalysts are especially useful in

  1. ^ J. O. Metzger (1998). "Solvent-Free Organic Syntheses".  
  2. ^ Mieczyslaw Makosza (2000). "Phase-transfer catalysis. A general green methodology in organic synthesis".  
  3. ^ a b Marc Halpern "Phase-Transfer Catalysis" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a19_293
  4. ^ Starks, C.M. (1971). "Phase-transfer catalysis. I. Heterogeneous reactions involving anion transfer by quaternary ammonium and phosphonium salts".  
  5. ^ Herriott, A.W.; Picker, D. (1975). "phase-transfer catalysis. Evaluation of catalysis".  
  6. ^ Takuya Hashimoto and Keiji Maruoka “Recent Development and Application of Chiral Phase-Transfer Catalysts” Chem. Rev. 2007, 107, 5656-5682. doi:10.1021/cr068368n

References

See also

PTC is widely exploited industrially.[3] Polyester polymers for example are prepared from acid chlorides and bisphenol-A. Phosphothioate-based pesticides are generated by PTC-catalyzed alkylation of phosphothioates. One of the more complex applications of PTC involves asymmetric alkylations, which are catalyzed by chiral quaternary ammonium salts derived from cinchona alkaloids.[6]

Applications

An alternative to the use of "quat salts" is to convert alkali metal cations into hydrophobic cations. In the research lab, crown ethers are used for this purpose. Polyethylene glycols are more commonly used in practical applications. These ligands encapsulate alkali metal cations (typically Na+ and K+), affording large lipophilic cations. These polyethers have a hydrophilic "interiors" containing the ion and a hydrophobic exterior.

Subsequent work demonstrated that many such reactions can be performed rapidly at around room temperature using catalysts such as tetra-n-butylammonium bromide or methyltrioctylammonium chloride in benzene/water systems.[5]

[4] Via the quaternary phosphonium cation,

C8H17Br(org) + NaBr(aq) (catalyzed by a R4P+Cl PTC)

For example, the nucleophilic aliphatic substitution reaction of an aqueous sodium cyanide solution with an ethereal solution of 1-bromooctane does not readily occur. The 1-bromooctane is poorly soluble in the aqueous cyanide solution, and the sodium cyanide does not dissolve well in the ether. Upon the addition of small amounts of hexadecyltributylphosphonium bromide, a rapid reaction ensues to give nonyl nitrile:

Phase-transfer catalysts for anionic reactants are often phosphonium salts are also used, e.g., hexadecyltributylphosphonium bromide. The phosphonium salts tolerate higher temperatures, but are unstable toward base, degrading to phosphine oxide.[3]

Types of phase-transfer catalysts

Contents

  • Types of phase-transfer catalysts 1
  • Applications 2
  • See also 3
  • References 4

Contrary to common perception, PTC is not limited to systems with hydrophilic and hydrophobic reactants. PTC is sometimes employed in liquid/solid and liquid/gas reactions. As the name implies, one or more of the reactants are transported into a second phase which contains both reactants.

[2][1]

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 


Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.