{"id":11813,"date":"2018-08-27T06:00:10","date_gmt":"2018-08-27T11:00:10","guid":{"rendered":"https:\/\/www.masterorganicchemistry.com\/?p=11813"},"modified":"2026-04-18T05:02:00","modified_gmt":"2026-04-18T10:02:00","slug":"the-wolff-kishner-clemmensen-and-other-sidechain-reductions","status":"publish","type":"post","link":"https:\/\/www.masterorganicchemistry.com\/2018\/08\/27\/the-wolff-kishner-clemmensen-and-other-sidechain-reductions\/","title":{"rendered":"The Wolff-Kishner, Clemmensen, And Other Carbonyl Reductions"},"content":{"rendered":"<p><strong>The Wolff-Kishner, Clemmensen, and Other Fun Reductions<\/strong><\/p>\n<p>In this post we go through 4 ways of reducing\u00a0 C=O to CH<sub>2<\/sub> including:<\/p>\n<ul>\n<li>The Wolff-Kishner reaction<\/li>\n<li>The Clemmensen reduction<\/li>\n<li>Catalytic hydrogenation<\/li>\n<li>Thioacetal formation and reduction<\/li>\n<\/ul>\n<p>But first: why might you want to do this? Well, it&#8217;s a key component in a common little synthesis problem I like to call &#8220;The Great Friedel-Crafts Workaround&#8221;.<\/p>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"alignnone wp-image-36130\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2018\/08\/0-summary-of-reduction-of-aromatic-carbonyls-clemmensen-wolff-kishner-hydrogenation-thioacetal.gif\" alt=\"summary of reduction of aromatic carbonyls clemmensen wolff kishner hydrogenation thioacetal\" width=\"640\" height=\"527\" \/><\/a><\/p>\n<p><strong>Table of Contents<\/strong><\/p>\n<ol>\n<li><a href=\"#one\">The Great Friedel-Crafts Workaround<\/a><\/li>\n<li><a href=\"#two\">The Wolff-Kishner Reduction Of Ketones<\/a><\/li>\n<li><a href=\"#three\">Mechanism Of The Wolff-Kishner Reaction<\/a><\/li>\n<li><a href=\"#four\">The Clemmensen Reduction of Ketones<\/a><\/li>\n<li><a href=\"#five\">Why Would You Prefer The Wolff-Kishner Over the Clemmensen, Or Vice Versa?<\/a><\/li>\n<li><a href=\"#six\">A Third Method For Carbonyl Reduction: Catalytic Hydrogenation<\/a><\/li>\n<li><a href=\"#seven\">Reduction of Thioacetals<\/a><\/li>\n<li><a href=\"#eight\">A Workaround Example<\/a><\/li>\n<li><a href=\"#nine\">A Final Note: Reversing Polarity<\/a><\/li>\n<li><a href=\"#notes\"><span class=\"s1\">Notes<\/span><\/a><\/li>\n<li><a href=\"#quiz\">Quiz Yourself!<\/a><\/li>\n<li><a href=\"#references\">(Advanced) References and Further Reading<\/a><\/li>\n<\/ol>\n<hr \/>\n<h2><strong><a id=\"one\"><\/a>1. The Great Friedel-Crafts Workaround<\/strong><\/h2>\n<p>A recent post covered <a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/06\/13\/reactions-on-the-benzylic-carbon-bromination-and-oxidation\/\">oxidations on the &#8220;benzylic&#8221; carbon<\/a> (i.e. on the carbon adjacent to the aromatic ring). We showed that benzylic C-H bonds are unusually weak, and can be converted relatively easily (and selectively!) to C\u2013Br or C\u2013O bonds.<\/p>\n<p>Today we&#8217;re going to go in the reverse direction and address <strong>reduction<\/strong> of the benzylic carbon, notably reduction of ketones (C=O) to alkyl (CH<sub>2<\/sub>).<\/p>\n<p>This is particularly important because of the <strong>Great Friedel-Crafts Workaround.\u00a0<\/strong><\/p>\n<p><em>What&#8217;s that<\/em>, you ask?<\/p>\n<p>You may recall that <a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/05\/17\/friedel-crafts-alkylation-acylation\/\">Friedel-Crafts alkylation<\/a>\u00a0of aromatic rings with primary alkyl halides can result in carbocation rearrangements. For example, attempting a Friedel-Crafts alkylation of benzene with propyl chloride results in isopropylbenzene, not propyl benzene.<\/p>\n<p><img decoding=\"async\" class=\"alignnone wp-image-16010\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/1-friedel-crafts-alkylation-example-of-rearranged-product-isopropyl-benzene.gif\" alt=\"friedel crafts alkylation example of rearranged product isopropyl benzene\" width=\"600\" height=\"189\" \/><\/p>\n<p>The Great Friedel-Crafts Workaround solves this issue. We begin with a Friedel-Crafts\u00a0<em>acylation<\/em>, which proceeds without rearrangement, and follow by reducing the ketone down to CH<sub>2<\/sub>.<\/p>\n<p><img decoding=\"async\" class=\"alignnone wp-image-31216\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2018\/08\/2-great-friedel-crafts-workaround-use-fridel-crafts-acylation-to-get-around-rearrangements-in-friedel-crafts-alkylation.gif\" alt=\"great friedel crafts workaround use fridel crafts acylation to get around rearrangements in friedel crafts alkylation\" width=\"600\" height=\"368\" \/><\/a><\/p>\n<p>So how can we reduce the ketone down to an alkane? Four ways.<\/p>\n<h2><a id=\"two\"><\/a>2. The Wolff-Kishner Reduction Of Ketones<\/h2>\n<p>The Wolff Kishner reduction of ketones utilizes hydrazine (NH<sub>2<\/sub>NH<sub>2<\/sub>) as the reducing agent in the presence of strong base (KOH) in a high-boiling protic solvent (ethylene glycol, HO-CH<sub>2<\/sub>CH<sub>2<\/sub>-OH, boiling point 197 \u00b0C).<\/p>\n<p>The driving force for the reaction is the conversion of hydrazine to nitrogen gas.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-16012\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/3-wolff-kishner-reduction-of-ketones-using-hydrazine-and-koh-in-ethylene-glycol.gif\" alt=\"wolff kishner reduction of ketones using hydrazine and koh in ethylene glycol\" width=\"600\" height=\"210\" \/><\/p>\n<p>This is not exactly a <em>gentle<\/em> process; heating to almost 200 \u00b0C is required to make the reaction occur at a reasonable rate. [<a href=\"#noteone\">Note 1<\/a>]<\/p>\n<p>The first step is formation of a hydrazone from the ketone (hydrazones are a cousin of<a href=\"https:\/\/www.masterorganicchemistry.com\/2010\/05\/24\/imines-and-enamines\/\"> imines<\/a>, which we cover later in the course).\u00a0 \u00a0Hydrazine (NH<sub>2<\/sub>NH<sub>2<\/sub>) adds to the carbonyl, and following a series of proton transfer steps, water is expelled.\u00a0 <a href=\"\" class=\"custom-tooltip\" data-image=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/Supp-1-Full-wolff-kishner-mechanism-for-formation-of-hydrazone-from-aldehyde-or-ketone.gif\" data-link=\"\" data-title=\"\" data-text=\"\">Click here to see an image of the mechanism for hydrazone formation<\/a>.<a href=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/Supp-1-Full-wolff-kishner-mechanism-for-formation-of-hydrazone-from-aldehyde-or-ketone.gif\"> (link to image)<\/a><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-16013\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/4-first-step-of-wolff-kishner-reaction-is-formation-of-hydrazone-intermediate.gif\" alt=\"first step of wolff kishner reaction is formation of hydrazone intermediate\" width=\"600\" height=\"205\" \/><\/p>\n<p>Once the hydrazone is formed, the real action in the Wolff-Kishner begins!<\/p>\n<h2><a id=\"three\"><\/a>3. Mechanism Of The Wolff-Kishner Reaction<\/h2>\n<p>The NH<sub>2<\/sub> of the hydrazone is reasonably acidic (pK<sub>a<\/sub> about 21) and can be deprotonated by strong base at a high enough temperature (the base is likely the conjugate base of ethylene glycol, not KOH). This deprotonation appears to be the rate-limiting step.<\/p>\n<p>The next step is the trickiest: protonation on the <em>carbon<\/em>. With the caveat that\u00a0resonance forms don&#8217;t really exist, it can be helpful to imagine forming the resonance form of this species that has a negative charge on the carbon, and <em>then<\/em> protonating it with solvent (ethylene glycol).<\/p>\n<p>This gives a species with a nitrogen-nitrogen double bond\u00a0, which , after deprotonation by base, decomposes irreversibly to give nitrogen gas and a carbanion (i.e. a negatively charged carbon).<\/p>\n<p>Protonation of the carbon completes the process.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26261\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2022\/08\/5-wolff-kishner-mechanism-deprotonation-of-hydrazone-followed-by-protonation-deprotonation-loss-of-n2-formation-of-anion-and-protonation-at-carbon.gif\" alt=\"wolff kishner mechanism deprotonation of hydrazone followed by protonation deprotonation loss of n2 formation of anion and protonation at carbon\" width=\"640\" height=\"456\" \/><\/a><\/p>\n<p><a href=\"\" class=\"custom-tooltip\" data-image=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2022\/08\/Supp-2-Full-wolff-kishner-arrow-pushing-mechanism-for-reduction-of-hydrazone-using-strong-base-and-ethylene-glycol.gif\" data-link=\"\" data-title=\"\" data-text=\"\">Hover for full arrow-pushing mechanism <\/a> or click on this <a href=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2022\/08\/Supp-2-Full-wolff-kishner-arrow-pushing-mechanism-for-reduction-of-hydrazone-using-strong-base-and-ethylene-glycol.gif\">link<\/a>.<\/p>\n<p>&nbsp;<\/p>\n<h2><a id=\"four\"><\/a>4. The Clemmensen Reduction of Ketones<\/h2>\n<p>A second way to go about reducing the carbonyl of an aromatic ketone is to use a reaction known as the <a href=\"https:\/\/www.masterorganicchemistry.com\/reaction-guide\/clemmensen-reduction-of-ketonesaldehydes-to-alkanes\/\">Clemmensen Reduction<\/a>. The reductant here is &#8220;zinc amalgam&#8221; (Zn-Hg) which is used under acidic conditions; one method calls for the presence of aqueous HCl, for example:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-16015\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/6-example-of-the-clemmensen-reduction-of-ketones-with-zinc-amalgam-zn-hg-and-aqueous-hcl.gif\" alt=\"example of the clemmensen reduction of ketones with zinc amalgam zn hg and aqueous hcl\" width=\"450\" height=\"185\" \/><\/p>\n<p>This process works best for aromatic ketones; non-aromatic ketones, not so much.\u00a0 The mechanism has not been thoroughly worked out; it&#8217;s thought to occur through a series of one-electron transfers from zinc amalgam.<\/p>\n<h2><strong><a id=\"five\"><\/a>5. Why Would You Prefer The Wolff-Kishner Over the Clemmensen, Or Vice Versa?<\/strong><\/h2>\n<p>It&#8217;s somewhat rare to encounter conditions in an introductory class where a Wolff Kishner would be called for over a Clemmensen, or vice versa, but here are some things to think about.<\/p>\n<ul>\n<li>The Wolff-Kishner is done under strongly <strong>basic<\/strong> conditions using high heat in a polar protic solvent.<\/li>\n<li>The Clemmensen is performed in strongly <strong>acidic<\/strong> conditions. If you have a protecting group somewhere which can be removed with acid, such as an acetal or silyl ether, consider an alternative.<\/li>\n<\/ul>\n<p>Two other methods deserve mention, although you might not seen them covered until later in the course when ketone chemistry is addressed.<\/p>\n<h2><strong><a id=\"six\"><\/a>6. A Third Method For Carbonyl Reduction: Catalytic Hydrogenation<\/strong><\/h2>\n<p>The first is catalytic hydrogenation, i.e. using a metal catalyst such as Pd\/C or Pt\/C with hydrogen gas (H<sub>2<\/sub>).<\/p>\n<p>We&#8217;ve mostly seen catalytic hydrogenation used for reducing alkenes and alkynes, but it can also be used for ketones if you crank on it enough (i.e. higher temperatures, with higher pressure of H<sub>2<\/sub>).<\/p>\n<p>One subtle tweak in conditions, sometimes not mentioned,\u00a0 is that platinum on carbon (Pt-C) or platinum oxide (PtO<sub>2<\/sub>)\u00a0 is often used instead of palladium (Pd).<\/p>\n<p>Normally, reduction of ketones usually stops at the alcohol stage.\u00a0<strong> However, in the case where the alcohol is on a benzylic position,\u00a0<\/strong>(i.e. on a carbon adjacent to an aromatic ring)\u00a0reduction with can occur further to the alkane (recall that bonds at benzylic positions tend to be easier to break, since the adjacent aromatic ring can donate electron density to them).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-16016\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/7-catalytic-hydrogenation-of-aromatic-ketones-with-platinum-on-carbon-hydrogen-and-high-pressure.gif\" alt=\"catalytic hydrogenation of aromatic ketones with platinum on carbon hydrogen and high pressure\" width=\"630\" height=\"213\" \/><\/p>\n<h2><strong><a id=\"seven\"><\/a>7. Reduction of Thioacetals<\/strong><\/h2>\n<p>The second method that sees use is conversion of the ketone to a &#8220;thioacetal&#8221; with HS-CH<sub>2<\/sub>CH<sub>2<\/sub>-SH and a Lewis acid such as BF<sub>3\u00a0<\/sub>. [<a href=\"#notetwo\">Note 2<\/a>] This is followed by treating the thioacetal with a reducing agent known as Raney Nickel: it&#8217;s a form of finely divided nickel containing adsorbed hydrogen that cleaves C-S bonds to give C-H bonds, through a somewhat mysterious process also thought to involve free-radicals. [See: <em><a href=\"https:\/\/www.masterorganicchemistry.com\/2011\/09\/30\/reagent-friday-raney-nickel\/\">Reagents &#8211; Raney Nickel<\/a>]<\/em><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-16017\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/8-reduction-of-thioacetals-with-raney-nickel-formation-of-thioacetals.gif\" alt=\"reduction of thioacetals with raney nickel formation of thioacetals\" width=\"600\" height=\"422\" \/><\/p>\n<p>Unlike the Clemmensen and catalytic hydrogenation,\u00a0 thioacetal\/Raney nickel method isn&#8217;t limited merely to benzylic ketones. It can be used to completely &#8220;disappear&#8221; an aldehyde or ketone, as was part of the strategy in <a href=\"https:\/\/www.synarchive.com\/syn\/17\">Woodward&#8217;s synthesis of erythromycin<\/a>.<\/p>\n<h2><strong><a id=\"eight\"><\/a>8. A Workaround Example<\/strong><\/h2>\n<p>With these methods in our toolbox, we can now fill in the vague description &#8220;reduction&#8221; over the arrow with something a lot more specific.<\/p>\n<p>Here&#8217;s a concrete example of a Friedel-Crafts Workaround:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-16018\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2019\/12\/9-specific-example-of-friedel-crafts-workaround-using-friedel-crafts-acylation-followed-by-wolff-kishner.gif\" alt=\"specific example of friedel crafts workaround using friedel crafts acylation followed by wolff kishner\" width=\"600\" height=\"208\" \/><\/p>\n<h2><a id=\"nine\"><\/a>9. A Final Note: Reversing Polarity<\/h2>\n<p>A final thing to note here is that reduction of a benzylic ketone to the alkane reverses the polarity of the substituent. It converts an electron-withdrawing\u00a0<em>meta<\/em>-director (an acyl group) into an electron-donating\u00a0<em>ortho-, para-\u00a0<\/em>director. We&#8217;ll have more to say about this when we address synthesis in aromatic compounds, but just take a gander at these two examples&#8230;.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26263\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2022\/08\/10-reduction-of-ketone-reverses-polarity-of-side-chain-group-results-in-changing-meta-director-to-ortho-para-director.gif\" alt=\"reduction of ketone reverses polarity of side chain group results in changing meta director to ortho para director\" width=\"600\" height=\"409\" \/><\/a><\/p>\n<p>Two more examples of reversing the polarity of a substituent is reduction of the nitro group and Baeyer-Villiger oxidation of a ketone to an ester. We&#8217;ll cover those next!<\/p>\n<hr \/>\n<h2><a id=\"notes\"><\/a>Notes<\/h2>\n<div class=\"related-articles\"><p><strong>Related Articles<\/strong><\/p><ul><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/10\/08\/nitration-baeyer-villiger\/\" class=\"\"><span>More Reactions on the Aromatic Sidechain: Reduction of Nitro Groups and the Baeyer Villiger<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2010\/05\/28\/acetals-hemiacetals-hydrates\/\" class=\"\"><span>Hydrates, Hemiacetals, and Acetals<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/10\/22\/aromatic-synthesis-2-polarity-reversal\/\" class=\"\"><span>Synthesis of Benzene Derivatives (2) \u2013 Polarity Reversal<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/10\/15\/aromatic-synthesis-1-order-of-operations\/\" class=\"\"><span>Aromatic Synthesis (1) \u2013 \u201cOrder Of Operations\u201d<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2022\/03\/07\/imine-formation-reactions-mechanisms\/\" class=\"\"><span>Clemmensen Reduction (MOC Membership) of Ketones\/Aldehydes to Alkanes<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2011\/09\/24\/reagent-friday-hydrazine-nh2nh2\/\" class=\"\"><span>Wolff Kishner Reaction (MOC Membership)<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/reaction-guide\/conversion-of-thioacetals-to-alkanes-using-raney-nickel\/\" class=\"\"><span>Conversion of thioacetals to alkanes using Raney Nickel<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2018\/05\/17\/friedel-crafts-alkylation-acylation\/\" class=\"\"><span>EAS Reactions (3) \u2013 Friedel-Crafts Acylation and Friedel-Crafts Alkylation<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/organic-chemistry-practice-problems\/aromatic-reactions-and-synthesis-practice\/\" class=\"\"><span>Aromatic Reactions and Synthesis Practice (MOC Membership)<\/span><\/a><\/li><\/ul><\/div>\n<p><a id=\"noteone\"><\/a><strong>Note 1<\/strong>.\u00a0 One way of getting around the requirement for high heat in the Wolff-Kishner is to use a strong base like <em>t<\/em>-BuOK in DMSO, which can be done around room temperature. [<a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/ja00868a048\">Ref<\/a>: <em>J. Am. Chem. Soc<\/em>,\u00a0<strong>1962<\/strong>,\u00a0<em>84,\u00a0<\/em>1734-1735.]<\/p>\n<p><strong><a id=\"notetwo\"><\/a>Note 2.\u00a0<\/strong>, Lewis acids such as BF<sub>3<\/sub> or ZnCl<sub>2<\/sub> are commonly used for this reaction [<a href=\"http:\/\/www.orgsyn.org\/demo.aspx?prep=cv6p0556\">see this Org Syn reference<\/a>] although in practice, protic acids such as HCl are perfectly fine if the starting material is an aldehyde or ketone [<a href=\"http:\/\/www.orgsyn.org\/demo.aspx?prep=CV6P0109\">see this Org Syn reference<\/a>]<\/p>\n<p>In Corey and Seebach&#8217;s method for making 1,3-dithiane, the starting materials are 1,3-propanedithiol and dimethoxymethane (CH<sub>3<\/sub>OCH<sub>2<\/sub>OCH<sub>3<\/sub>), an equivalent of formaldehyde.\u00a0 BF<sub>3<\/sub>, a strong Lewis acid, gave better yields in this procedure than did anhydrous acid,\u00a0 subsequently BF<sub>3<\/sub> seems to be the Lewis acid of choice in organic chemistry textbooks despite the fact that most thioacetal formation reactions seen in introductory courses are from aldehydes or ketones, not acetals.<\/p>\n<hr \/>\n<h2><a id=\"quiz\"><\/a>Quiz Yourself!<\/h2>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/0539-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <br \/>\n<\/p>\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/0540-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <br \/>\n<\/p>\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/0541-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/2110-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <br \/>\n<\/p>\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/2202-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <br \/>\n<\/p>\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/2030-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <br \/>\n<\/p>\n<p class=\"p1\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-26714\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/1979-Front-Image-Only.png\" alt=\"\" width=\"640\" height=\"616\" \/><\/p>\n<p><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a\u00a0 MOC member<\/strong><\/a> to see the clickable quiz with answers on the back. <\/p>\n<hr \/>\n<p><strong><a id=\"references\"><\/a>(Advanced) References and Further Reading<\/strong><\/p>\n<ol>\n<li><strong>Chemischen Institut der Universit\u00e4t Jena: Methode zum Ersatz des Sauerstoffatoms der Ketone und Aldehyde durch Wasserstoff. [Erste Abhandlung.]<\/strong><br \/>\nWolff, L.<br \/>\n<em> Lieb. Ann. Chem. <\/em><strong>1912\u00a0<\/strong><em>394\u00a0<\/em>(1), 86<br \/>\n<strong>DOI<\/strong>: <a href=\"http:\/\/doi.wiley.com\/10.1002\/jlac.19123940107\">10.1002\/jlac.19123940107<\/a><br \/>\nThe original paper by Ludwig Wolff on the reduction of aldehydes and ketones with hydrazine.<\/li>\n<li><strong>The Wolff-Kishner Reaction of Hydrazones<br \/>\n<\/strong>Szmant, H. H.; Harmuth, C. H.<br \/>\n<em>J. <\/em><em>Am. Chem. Soc.<\/em><strong>1964, <\/strong><em>86\u00a0<\/em>(14), 2909<br \/>\n<strong>DOI:\u00a0<\/strong><a href=\"http:\/\/pubs.acs.org\/doi\/abs\/10.1021\/ja01068a028\">10.1021\/ja01068a028<\/a><br \/>\nA very nice Physical Organic study on the decomposition of hydrazones, involving Hammett plots (a classic tool in Physical Organic Chemistry), determining the relationship between the electron density of the carbonyl carbon and the mechanism.<\/li>\n<li><strong>Reduction of Steroid Ketones and other Carbonyl Compounds by Modified Wolff-Kishner Method<br \/>\n<\/strong>Huang-Minlon<br \/>\n<em>J.<\/em><em> Am. Chem. Soc.<\/em><strong>1949<\/strong>, <em>71\u00a0<\/em>(10), 3301<br \/>\n<strong>DOI:\u00a0<\/strong><a href=\"https:\/\/pubs.acs.org\/doi\/abs\/10.1021\/ja01178a008\">10.1021\/ja01178a008<\/a><br \/>\nA one-pot modification for the Wolff-Kishner reaction that involves distilling off the excess water and hydrazine before heating the hydrazine. This results improved yields and significantly shorter reaction times.<\/li>\n<li><strong>REDUCTION OF KETONES BY USE OF THE TOSYLHYDRAZONE DERIVATIVES: ANDROSTAN-17 \u03b2-OL<br \/>\n<\/strong> Caglioti<br \/>\n<em>Org. Synth<\/em>. <strong>1972,<\/strong><em>52<\/em>, 122<br \/>\n<strong>DOI: <\/strong><a href=\"http:\/\/www.orgsyn.org\/demo.aspx?prep=CV6P0062\">10.15227\/orgsyn.052.0122<\/a><br \/>\nDue to the harsh conditions involved in the standard Wolff-Kishner reduction, a number of variations have been developed with milder conditions more amenable for organic synthesis. The use of tosylhydrazide instead of hydrazine allows much gentler reaction conditions \u2013 the tosylhydrazone can be reduced with NaBH4 in refluxing methanol (68 \u00b0C vs. 200 \u00b0C!).<\/li>\n<li><strong>\u03b3-PHENYLBUTYRIC ACID<br \/>\n<\/strong> L. Martin<br \/>\n<em>Org. Synth<\/em>. <strong>1935,<\/strong> <em>15<\/em>, 64<br \/>\n<strong>DOI: <\/strong><a href=\"http:\/\/www.orgsyn.org\/demo.aspx?prep=CV2P0499\">10.15227\/orgsyn.015.0064<\/a><br \/>\nA reliable, tested procedure for a simple Clemmensen Reduction that demonstrates how this reaction can be used to reduce a ketone in the presence of a carboxylic acid.<\/li>\n<li><strong>Elrik Clemmensen: Reduktion von Ketonen und Alahyden su den entspcechenden Kohlenwaaserstoflbn unter Anwendung von amalgamiertem Zink und Salesaure.<\/strong><br \/>\nClemmensen, E.<br \/>\n<em>Chem. Ber. <\/em><strong>1913<\/strong> <em>46<\/em> (2), 1837-1843<br \/>\n<strong>DOI: <\/strong><a href=\"https:\/\/onlinelibrary.wiley.com\/doi\/abs\/10.1002\/cber.19130460292\">10.1002\/cber.19130460292<\/a><br \/>\nThe original paper by Clemmensen on the reduction of aldehydes and ketones with Zn metal in acid. Note that even though this was submitted to a German journal and written in German, Clemmensen was working at Parke-Davis, in the U.S.Two reviews on the Clemmensen Reduction:<\/li>\n<li><strong>THE CLEMMENSEN REDUCTION<br \/>\n<\/strong>Martin, E. L.<br \/>\n<em>Org. React. <\/em><strong>1942, <\/strong><em>1<\/em>, 155<br \/>\n<strong>DOI: <\/strong><a href=\"https:\/\/onlinelibrary.wiley.com\/doi\/10.1002\/0471264180.or001.07\">10.1002\/0471264180.or001.07<\/a><\/li>\n<li><strong>CLEMMENSEN REDUCTION OF KETONES IN ANHYDROUS ORGANIC SOLVENTS<br \/>\n<\/strong>Vedejs, E.<br \/>\n<em>Org. React. <\/em><strong>1975<\/strong>, <em>22<\/em>, 401<br \/>\n<strong>DOI: <\/strong><a href=\"https:\/\/onlinelibrary.wiley.com\/doi\/10.1002\/0471264180.or022.03\">10.1002\/0471264180.or022.03<\/a><\/li>\n<li><strong>Stereoselective total synthesis of (\u2013)-pumiliotoxin C by an aqueous intramolecular acylnitroso Diels\u2013Alder approach<br \/>\n<\/strong>Masaichi Naruse, Sakae Aoyagi and Chihiro Kibayashi<strong><br \/>\n<\/strong><em>J. Chem. Soc., Perkin Trans<\/em>. <em>1<\/em>, <strong>1996<\/strong>, 1113-1124<br \/>\n<strong>DOI: <\/strong><a href=\"https:\/\/pubs.rsc.org\/en\/content\/articlelanding\/1996\/P1\/P19960001113#!divAbstract\">10.1039\/P19960001113<\/a><br \/>\nClemmensen reductions can be used in total synthesis due to the mild conditions \u2013 in this case <strong>34<\/strong> to <strong>35<\/strong> is a Clemmensen reduction that selectively reduces a ketone in the presence of an amide.<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"<p>The Wolff-Kishner, Clemmensen, and Other Fun Reductions In this post we go through 4 ways of reducing\u00a0 C=O to CH2 including: The Wolff-Kishner reaction The <\/p>\n","protected":false},"author":1,"featured_media":31036,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1297],"tags":[1356,303,321,506,1355,484,266,1354,505],"post_folder":[],"class_list":["post-11813","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-aromatic-reactions","tag-benzylic","tag-clemmensen","tag-friedel-crafts","tag-hydrazine","tag-platinum","tag-raney-nickel","tag-reduction","tag-thioacetal","tag-wolff-kishner"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>The Wolff-Kishner, Clemmensen, And Other Carbonyl Reductions<\/title>\n<meta name=\"description\" content=\"What are the Wolff-Kishner and Clemmensen reductions useful for? 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