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<title>Phase-transfer catalyst</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Phase-transfer catalyst</span></span>

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<p>In <a href="Chemistry" title="Chemistry">chemistry</a>, a <b>phase-transfer catalyst</b> or <b>PTC</b> is a <a href="Catalyst" class="mw-redirect" title="Catalyst">catalyst</a> that facilitates the <a href="Phase_transition" title="Phase transition">transition</a> of a <a href="Reactant" class="mw-redirect" title="Reactant">reactant</a> from one <a href="Phase_(matter)" title="Phase (matter)">phase</a> into another phase where reaction occurs. Phase-transfer catalysis is a special form of catalysis and can act through <a href="Homogeneous_catalysis" title="Homogeneous catalysis">homogeneous catalysis</a> or <a href="Heterogeneous_catalysis" title="Heterogeneous catalysis">heterogeneous catalysis</a> methods depending on the catalyst used. <a href="Ionic_compound" class="mw-redirect" title="Ionic compound">Ionic</a> reactants are often <a href="Soluble" class="mw-redirect" title="Soluble">soluble</a> in an <a href="Aqueous" class="mw-redirect" title="Aqueous">aqueous</a> phase but insoluble in an organic phase in the absence of the phase-transfer catalyst. The catalyst functions like a <a href="Detergent" title="Detergent">detergent</a> for solubilizing the <a href="Salts" class="mw-redirect" title="Salts">salts</a> into the organic phase. Phase-transfer catalysis refers to the acceleration of the reaction upon the addition of the phase-transfer catalyst. PTC is widely exploited industrially.<sup id="cite_ref-Ullmann_1-0" class="reference"><a href="#cite_note-Ullmann-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> <a href="Polyester" title="Polyester">Polyesters</a> for example are prepared from acyl chlorides and <a href="Bisphenol_A" title="Bisphenol A">bisphenol-A</a>. Phosphothioate-based pesticides are generated by PTC-catalyzed <a href="Alkylation" title="Alkylation">alkylation</a> of phosphothioates.

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<p>In ideal cases, PTC can be fast and efficient, minimizing the need for expensive or dangerous solvents and simplifying purification<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> Phase-transfer catalysts are <a href="Green_chemistry" title="Green chemistry">"green"</a>—by allowing the use of water, the need for <a href="Organic_solvent" class="mw-redirect" title="Organic solvent">organic solvents</a> is lowered.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading2"><h2 id="Types">Types</h2></div>

<p>Phase-transfer catalysts for anionic reactants are often <a href="Quaternary_ammonium_salt" class="mw-redirect" title="Quaternary ammonium salt">quaternary ammonium salts</a>. Commercially important catalysts include benzyltriethylammonium chloride, <a href="Aliquat_336" title="Aliquat 336">methyltricaprylammonium chloride</a> and methyltributylammonium chloride. Organic <a href="Phosphonium_salt" class="mw-redirect" title="Phosphonium salt">phosphonium salts</a> are also used, e.g., hexadecyltributylphosphonium bromide. The phosphonium salts tolerate higher temperatures.

</p><p>An alternative to the use of "quat salts" is to convert alkali metal cations into hydrophobic cations. <a href="Crown_ether" title="Crown ether">Crown ethers</a> are used for this purpose on the laboratory scale. <a href="Polyethylene_glycol" title="Polyethylene glycol">Polyethylene glycols</a> and their amine derivatives are common in practical applications. One such catalyst is <a href="Tris(2-(2-methoxyethoxy)ethyl)amine" title="Tris(2-(2-methoxyethoxy)ethyl)amine">tris(2-(2-methoxyethoxy)ethyl)amine</a>. These ligands encapsulate alkali metal cations (typically <style data-mw-deduplicate="TemplateStyles:r1123817410">

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</style><span class="chemf nowrap">Na<sup class="template-chem2-sup">+</sup></span> and <span class="chemf nowrap">K<sup class="template-chem2-sup">+</sup></span>), affording lipophilic cations. Polyethers have a <a href="Hydrophilic" class="mw-redirect" title="Hydrophilic">hydrophilic</a> "interiors" containing the ion and a <a href="Hydrophobic" class="mw-redirect" title="Hydrophobic">hydrophobic</a> exterior.

</p><p><a href="Chirality_(chemistry)" title="Chirality (chemistry)">Chiral</a> phase-transfer catalysts have also been demonstrated.<sup id="cite_ref-phipps_5-0" class="reference"><a href="#cite_note-phipps-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup>

Asymmetric alkylations are catalyzed by chiral quaternary ammonium salts derived from <a href="Cinchona_alkaloid" class="mw-redirect" title="Cinchona alkaloid">cinchona alkaloids</a>.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup>

</p><p>A variety of functionalized catalysts have been evaluated for PTC. One example is the Janus interphase catalyst, applicable to organic reactions on the interface of two phases via the formation of Pickering emulsion.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading3"><h3 id="Limitations">Limitations</h3></div>

<p>Quaternary ammonium cations degrade by <a href="Hofmann_degradation" class="mw-redirect" title="Hofmann degradation">Hofmann degradation</a> to amines, especially at higher temperatures preferred by process chemists. The resulting amines can be difficult to remove from the product. Phosphonium salt are unstable toward base, degrading to <a href="Phosphine_oxide" title="Phosphine oxide">phosphine oxide</a>.<sup id="cite_ref-Ullmann_1-1" class="reference"><a href="#cite_note-Ullmann-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading3"><h3 id="Laboratory_examples">Laboratory examples</h3></div>

<p>For example, the <a href="Nucleophilic_substitution" title="Nucleophilic substitution">nucleophilic substitution</a> reaction of an <a href="Aqueous" class="mw-redirect" title="Aqueous">aqueous</a> <a href="Sodium_cyanide" title="Sodium cyanide">sodium cyanide</a> solution with an <a href="Ether" title="Ether">ethereal</a> solution of 1-bromooctane does not readily occur. The 1-bromooctane is poorly soluble in the aqueous <a href="Cyanide" title="Cyanide">cyanide</a> 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:

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<annotation encoding="application/x-tex">{\displaystyle {\ce {C8H17Br_{(org)}{}+ NaCN_{(aq)}->[{\ce {R4P+Br-}}] C8H17CN_{(org)}{}+ NaBr_{(aq)}}}}</annotation>

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</math></span><img src="./03c57dfb73a0ce7aa2e2bafdd89165361d9aaee7.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.505ex; margin-top: -0.301ex; width:60.142ex; height:5.509ex;" alt="{\displaystyle {\ce {C8H17Br_{(org)}{}+ NaCN_{(aq)}->[{\ce {R4P+Br-}}] C8H17CN_{(org)}{}+ NaBr_{(aq)}}}}" loading="lazy"></span></dd></dl>

<p>By the quaternary phosphonium cation, cyanide ions are "ferried" from the aqueous phase into the organic phase.<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup>

</p><p>Subsequent work demonstrated that many such reactions can be performed rapidly at around room temperature using catalysts such as <a href="Tetra-n-butylammonium_bromide" class="mw-redirect" title="Tetra-n-butylammonium bromide">tetra-n-butylammonium bromide</a> and <a href="Methyltrioctylammonium_chloride" class="mw-redirect" title="Methyltrioctylammonium chloride">methyltrioctylammonium chloride</a> in benzene/water systems.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading2"><h2 id="Phase-boundary_catalysis">Phase-boundary catalysis</h2></div>

<p><b>Phase-boundary catalysis</b> (PBC) is a type of PTC wherein catalysis occurs at a <a href="Phase_boundary" title="Phase boundary">phase boundary</a>. Some <a href="Zeolite" title="Zeolite">zeolites</a> can be modified to operate by PBC: they are <a href="Hydrophobic" class="mw-redirect" title="Hydrophobic">hydrophobic</a> on the inside and <a href="Hydrophilic" class="mw-redirect" title="Hydrophilic">hydrophilic</a> on the outside.<sup id="cite_ref-:4_10-0" class="reference"><a href="#cite_note-:4-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> In some sense, PBC resemble <a href="Enzyme" title="Enzyme">enzymes</a>. The major difference between this system and <a href="Enzyme" title="Enzyme">enzyme</a> is lattice flexibility. The lattice of <a href="Zeolite" title="Zeolite">zeolite</a> is rigid, whereas the <a href="Enzyme" title="Enzyme">enzyme</a> is flexible. Phase-boundary catalytic (PBC) systems can be contrasted with conventional catalytic systems. PBC is primarily applicable to reactions at the <a href="Interface_(chemistry)" class="mw-redirect" title="Interface (chemistry)">interface</a> of an aqueous phase and organic phase. In these cases, an approach such as PBC is needed due to the <a href="Miscible" class="mw-redirect" title="Miscible">immiscibility</a> of aqueous phases with most organic substrate. In PBC, the catalyst acts at the interface between the aqueous and organic phases. The reaction medium of phase boundary catalysis systems for the catalytic reaction of immiscible aqueous and organic phases consists of three phases; an organic liquid phase, containing most of the substrate, an aqueous liquid phase containing most of the substrate in <a href="Aqueous_phase" class="mw-redirect" title="Aqueous phase">aqueous phase</a> and the solid catalyst.

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<div class="mw-heading mw-heading3"><h3 id="Design_of_phase-boundary_catalyst">Design of phase-boundary catalyst</h3></div>

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<p>A zeolite is treated with <a href="Organosilicon_chemistry" title="Organosilicon chemistry">alkylsilane</a> to render its surface hydrophobic.<sup id="cite_ref-:4_10-1" class="reference"><a href="#cite_note-:4-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> For examplex n-octadecyltrichlorosilane (OTS) has been used to modify W-Ti-NaY materials Due to the <a href="Hydrophilicity" class="mw-redirect" title="Hydrophilicity">hydrophilicity</a> of the w-Ti-NaY surface.

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<div class="mw-heading mw-heading2"><h2 id="Phase_transfer_agents_(PTAs)">Phase transfer agents (PTAs)</h2></div>

<p>Not all phase transfer processes involve catalysis. A distinction can be made between phase-transfer catalysts (PTCs), which facilitate catalytic turnover between immiscible phases, and phase transfer agents (PTAs), which operate in stoichiometric or excess amounts to assist the movement of solutes between phases without participating in a catalytic cycle.

</p><p>Phase transfer agents are typically surfactant-like molecules or ligands that aid in the extraction, stabilisation, or dispersion of compounds—particularly nanoparticles, ions, or polymers—between immiscible media such as water and organic solvents. Unlike PTCs, these agents are not regenerated and are often retained in the final product or dispersion medium.

</p><p>Examples of PTAs include:

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<ul><li><b>Cetyltrimethylammonium bromide (CTAB)</b> – often used to transfer metal nanoparticles from aqueous to organic media via bilayer or micellar encapsulation.</li>

<li><b>Oleylamine (OAm) and octadecylamine (ODA)</b> – long-chain primary amines used in nanochemistry for transferring and stabilising hydrophilic nanoparticles in nonpolar organic solvents.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup></li>

<li><b>Crown ethers and polyethylenglycol (PEG) derivatives</b> – in specific stoichiometric applications, these compounds can also act as phase transfer agents, especially in inorganic or polymer-related systems.</li></ul>

<p>Phase transfer agents play a crucial role in the synthesis and processing of colloidal nanomaterials, hybrid polymers, and functional coatings. They are especially relevant in materials science contexts such as electrospinning, thin-film fabrication, and surface functionalisation, where precise control over dispersion and compatibility between components is essential.

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<ul><li><a href="Ionic_transfer" title="Ionic transfer">Ionic transfer</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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<li id="cite_note-Ullmann-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-Ullmann_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Ullmann_1-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text">Marc Halpern "Phase-Transfer Catalysis" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. <style data-mw-deduplicate="TemplateStyles:r1238218222">

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</style><a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1002%2F14356007.a19_293">10.1002/14356007.a19_293</a></span>

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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text">Katole DO, Yadav GD. Process intensification and waste minimization using liquid-liquid-liquid triphase transfer catalysis for the synthesis of 2-((benzyloxy)methyl)furan. Molecular Catalysis 2019;466:112–21. <a rel="nofollow" class="external free" href="https://doi.org/10.1016/j.mcat.2019.01.004">https://doi.org/10.1016/j.mcat.2019.01.004</a></span>

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<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><cite id="CITEREFMieczyslaw_Makosza2000" class="citation journal cs1">Mieczyslaw Makosza (2000). <a rel="nofollow" class="external text" href="https://doi.org/10.1351%2Fpac200072071399">"Phase-transfer catalysis. A general green methodology in organic synthesis"</a>. <i><a href="Pure_Appl._Chem." class="mw-redirect" title="Pure Appl. Chem.">Pure Appl. Chem.</a></i> <b>72</b> (7): <span class="nowrap">1399–</span>1403. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1351%2Fpac200072071399">10.1351/pac200072071399</a></span>.</cite></span>

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<li id="cite_note-phipps-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-phipps_5-0">^</a></b></span> <span class="reference-text"><cite id="CITEREFPhippsHamiltonToste2012" class="citation journal cs1">Phipps, Robert J.; Hamilton, Gregory L.; Toste, F. Dean (2012). "The progression of chiral anions from concepts to applications in asymmetric catalysis". <i>Nature Chemistry</i>. <b>4</b> (8): <span class="nowrap">603–</span>614. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2012NatCh...4..603P">2012NatCh...4..603P</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1038%2Fnchem.1405">10.1038/nchem.1405</a>. <a href="PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/22824891">22824891</a>.</cite></span>

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<li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text">Takuya Hashimoto and Keiji Maruoka "Recent Development and Application of Chiral Phase-Transfer Catalysts" Chem. Rev. 2007, 107, 5656-5682. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1021%2Fcr068368n">10.1021/cr068368n</a></span>

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<li id="cite_note-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-8">^</a></b></span> <span class="reference-text"><cite id="CITEREFStarks,_C.M.1971" class="citation journal cs1">Starks, C.M. (1971). "Phase-transfer catalysis. I. Heterogeneous reactions involving anion transfer by quaternary ammonium and phosphonium salts". <i><a href="J._Am._Chem._Soc." class="mw-redirect" title="J. Am. Chem. Soc.">J. Am. Chem. Soc.</a></i> <b>93</b> (1): <span class="nowrap">195–</span>199. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1971JAChS..93..195S">1971JAChS..93..195S</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1021%2Fja00730a033">10.1021/ja00730a033</a>.</cite></span>

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