{"id":7268,"date":"2013-05-08T11:59:45","date_gmt":"2013-05-08T15:59:45","guid":{"rendered":"https:\/\/www.masterorganicchemistry.com\/?p=7268"},"modified":"2026-04-22T12:20:04","modified_gmt":"2026-04-22T17:20:04","slug":"nanh3-partial-reduction-of-alkynes","status":"publish","type":"post","link":"https:\/\/www.masterorganicchemistry.com\/2013\/05\/08\/nanh3-partial-reduction-of-alkynes\/","title":{"rendered":"Partial Reduction of Alkynes With Na\/NH3 To Obtain Trans Alkenes"},"content":{"rendered":"<p><b>Partial Reduction of Alkynes to <em>trans<\/em>-Alkenes (olefins) With Sodium in Ammonia (Na\/NH<sub>3<\/sub>)<\/b><\/p>\n<ul>\n<li>Alkynes can be hydrogenated to alkanes with Pd\/C and excess H<sub>2<\/sub>, or partially reduced to cis alkenes with Lindlar&#8217;s catalyst and H<sub>2\u00a0<\/sub>(<span style=\"color: #800080;\"><a style=\"color: #800080;\" href=\"https:\/\/www.masterorganicchemistry.com\/2013\/05\/08\/lindlar-nanh3-partial-reduction-of-alkynes\/\"><em>See article &#8211; Partial Hydrogenation of Alkynes With Lindlar&#8217;s Catalyst<\/em><\/a><\/span>)<\/li>\n<li>Alkynes can also be partially reduced to\u00a0<em>trans<\/em> alkenes through reduction with sodium metal (Na) in ammonia (NH<sub>3<\/sub>) at low temperature. This is sometimes referred to as a &#8220;dissolving metal reduction&#8221;.<\/li>\n<li>In this reaction, two electrons (from sodium metal) sequentially add to the alkyne, resulting in carbanions that are protonated by the solvent (NH<sub>3<\/sub>).<\/li>\n<li>The resulting <em>trans<\/em> alkenes can then undergo all the normal reactions of alkenes. It&#8217;s important to be able to properly draw the all stereoisomers resulting from the partial reduction of alkynes (with Na\/NH<sub>3<\/sub> or Lindlar&#8217;s catalyst) followed by stereospecific reactions such as dihydroxylation (OsO<sub>4<\/sub>), halogenation (Cl<sub>2<\/sub>, Br<sub>2<\/sub>), epoxidation (<em>m<\/em>-CPBA) and others.<\/li>\n<li>In the forward direction, it&#8217;s also important to be able to apply the partial reduction of alkynes toward the synthesis of various target compounds.<\/li>\n<\/ul>\n<p><img fetchpriority=\"high\" decoding=\"async\" class=\"alignnone wp-image-35903\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2024\/01\/0-summary-of-sodium-in-ammonia-reduction-of-alkynes-to-give-trans-alkenes.gif\" alt=\"summary of sodium in ammonia reduction of alkynes to give trans alkenes\" width=\"640\" height=\"540\" \/><\/a><\/p>\n<p><strong>Table of Contents<\/strong><\/p>\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\n<li><a href=\"#one\">Partial Reduction of Alkynes With Sodium In Ammonia<\/a><\/li>\n<li><a href=\"#two\">Reduction with Na\/NH3 Is Selective For\u00a0<em>trans-\u00a0<\/em>Alkenes<\/a><\/li>\n<li><a href=\"#three\">Mechanism for Reduction of Alkynes With Na\/NH3<\/a><\/li>\n<li><a href=\"#four\">A Few Synthesis Problems\u00a0<\/a><\/li>\n<li><a href=\"#five\">Summary<\/a><\/li>\n<li><a href=\"#notes\">Notes<\/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<\/li>\n<\/ol>\n<hr \/>\n<h2><a id=\"one\"><\/a>1. Partial Reduction of Alkynes with Sodium in Ammonia (Na\/NH<sub>3<\/sub>)<\/h2>\n<p>Previously we&#8217;ve seen that catalytic hydrogenation of <strong>alkynes<\/strong> with Pd\/C and excess hydrogen gas (H<sub>2<\/sub>) gives <strong>alkanes<\/strong> (four C-H bonds formed, two C-C pi bonds broken). We&#8217;ve also seen that alkynes can be <strong>partially<\/strong> <strong>hydrogenated<\/strong> by using <strong>Lindlar&#8217;s catalyst<\/strong>, a hydrogenation catalyst where the Pd has intentionally been rendered less active (&#8220;poisoned&#8221;) through the addition of Pb (lead) salts. [<span style=\"color: #993366;\"><em>See article &#8211; <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2011\/08\/19\/lindlars-catalyst-partial-cis-reduction\/\">Partial Hydrogenation of Alkynes With Lindlar&#8217;s Catalyst<\/a><\/em><\/span>]<\/p>\n<p>When alkynes are hydrogenated with Lindlar&#8217;s catalyst,\u00a0<em>cis<\/em> alkenes are formed preferentially:<\/p>\n<p><img decoding=\"async\" class=\"alignnone wp-image-35890\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/1-review-of-the-lindlar-reduction-of-alkynes-to-give-cis-alkenes-and-full-hydrogenation-of-alkynes-to-give-alkanes.gif\" alt=\"review of the lindlar reduction of alkynes to give cis alkenes and full hydrogenation of alkynes to give alkanes\" width=\"640\" height=\"419\" \/><\/a><\/p>\n<p><span style=\"color: #993366;\"><em>We call these hydrogenations &#8220;reductions&#8221; since each carbon is swapping a C-C bond for a C-H bond. In the oxidation state formalism, each C-H bond decreases the oxidation state of carbon by 1. For more, see article: <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2011\/07\/25\/calculating-the-oxidation-state-of-a-carbon\/\">How to calculate the oxidation state of a carbon<\/a>).\u00a0<\/em><\/span><\/p>\n<p>A method for the conversion of alkynes into\u00a0<em>trans<\/em> alkenes has also been developed. Instead of catalytic hydrogenation with palladium and H<sub>2<\/sub>, the alkyne is added into a solution of sodium (or lithium) metal dissolved in liquid ammonia (NH<sub>3<\/sub>).<\/p>\n<p><img decoding=\"async\" class=\"alignnone wp-image-35891\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2-reduction-of-alkynes-with-sodium-and-ammonia-gives-trans-alkenes-with-good-selectivity.gif\" alt=\"reduction of alkynes with sodium and ammonia gives trans alkenes with good selectivity\" width=\"640\" height=\"510\" \/><\/a><\/p>\n<p>When sodium is dissolved in NH<sub>3<\/sub>, the loosely-held valence electron of Na dissociates from the metal, resulting in a solution of\u00a0 &#8220;solvated electrons&#8221;. These &#8220;free&#8221; electrons are the reducing agent in the conversion of alkynes to alkenes and are also responsible for the deep blue color of the solution.<\/p>\n<p><em>This clip from\u00a0 <a href=\"https:\/\/www.youtube.com\/@NileRed\">@<strong>NileRed <\/strong><\/a>shows the addition of lithium, not sodium, but Na is very similar.\u00a0<\/em><\/p>\n<p><img decoding=\"async\" src=\"https:\/\/media.giphy.com\/media\/v1.Y2lkPTc5MGI3NjExbmllajVvNnY0NGQ2M3BmeHMxN2wzMzN1c29zNTVjdWFmZzZyMGc4NyZlcD12MV9pbnRlcm5hbF9naWZfYnlfaWQmY3Q9Zw\/rtNIBOihqGOZTpZatj\/giphy.gif\" \/><\/p>\n<p><em><span style=\"color: #993366;\">NH<sub>3<\/sub> is a gas at room temperature. Using liquid NH<sub>3<\/sub> as a solvent requires cooling it down to -33\u00b0C with an external cooling bath.\u00a0<\/span><\/em><\/p>\n<p>Alkynes are reduced to <em>trans<\/em> alkenes in good yields. Here are a few more examples.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35892\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/4-examples-of-reduction-of-alkynes-with-sodium-and-ammonia-na-nh3-to-give-trans-alkenes.gif\" alt=\"examples of reduction of alkynes with sodium and ammonia na nh3 to give trans alkenes\" width=\"640\" height=\"367\" \/><\/a><\/p>\n<p>Since Na only has one valence electron, it&#8217;s important to add at least <strong>two<\/strong> molar equivalents of Na.<\/p>\n<p>Make sure you don&#8217;t confuse Na\/NH<sub>3<\/sub> with NaNH<sub>2<\/sub>\/NH<sub>3<\/sub>.<\/p>\n<ul>\n<li>NaNH<sub>2<\/sub> is a <strong>strong base<\/strong> dissolved in its conjugate acid (ammonia). Useful for deprotonating terminal alkynes.<\/li>\n<li>Na is metallic <strong>sodium<\/strong>, a source of electrons (reducing agent) dissolved in ammonia.<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35893\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/5-avoid-the-common-mistake-of-confusing-sodium-in-ammonia-for-nanh2-in-ammonia.gif\" alt=\"avoid the common mistake of confusing sodium in ammonia for nanh2 in ammonia\" width=\"640\" height=\"365\" \/><\/a><\/p>\n<p>Lithium can be used in place of sodium.<\/p>\n<p><span style=\"color: #993366;\"><em> In practice, there are other ways of running this reaction that don&#8217;t involve liquid NH<sub>3<\/sub>, but we need not discuss them here.<\/em> <\/span>[<span style=\"color: #ff0000;\">Note 1<\/span>].<\/p>\n<h2><a id=\"two\"><\/a>2. The Consequences of Stereochemistry<\/h2>\n<p>It&#8217;s very useful to have a method for the partial reduction of alkynes to alkenes in your back pocket, since it allows us to employ the huge number of useful reactions of alkenes we have learned previously (<span style=\"color: #993366;\"><em>See article &#8211; <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2014\/01\/21\/synthesis-reactions-of-alkenes\/\">Reactions of Alkenes<\/a><\/em><\/span>) .<\/p>\n<p>Before we get too far ahead of ourselves, however, let&#8217;s just examine some consequences of the <strong>stereochemistry<\/strong> of this reaction.<\/p>\n<p>Starting with an alkyne, partial reduction via Lindlar\/H<sub>2<\/sub> will give you the <em>cis<\/em> alkene and reduction with Na\/NH<sub>3<\/sub> will give the\u00a0<em>trans<\/em> alkene.<\/p>\n<p>What happens when those respective alkenes are then subjected to a reaction known to be stereospecific, such as OsO<sub>4<\/sub> for the dihydroxylation of alkenes?<\/p>\n<p>How are those products related?<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35881\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35881\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"35881\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"35881\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35881\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35881 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35881\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-hdn52\" data-id=\"hdn52\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2648-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2648-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>The result should be <em>diastereomers<\/em>.<\/p>\n<p>You might rightfully ask whether or not it\u00a0<em>truly\u00a0<\/em>matters whether you use Na\/NH3 or Lindlar in the first step. After all, don&#8217;t you still end up with a vicinal diol in the end? Those products look\u00a0<em>pretty much\u00a0<\/em>the same, don&#8217;t they?<\/p>\n<p>They are\u00a0<em>not\u00a0<\/em>the same products! They have different melting points, different boiling points, different configurations in space. They will interact with chiral molecules (like proteins and enzymes!) in different ways. Not to get overly dramatic, but if a major pharmaecutical company sold a product to the public that had one stereocenter with the wrong configuration, the consequences could be death or <a href=\"https:\/\/en.wikipedia.org\/wiki\/Thalidomide\">disfigurement<\/a> for thousands of its customers, with the attendant billions of dollars in lawsuits.<\/p>\n<p>That&#8217;s why we care about stereochemistry. If we have the ability to control it, we should control it.<\/p>\n<p>Here&#8217;s another example.\u00a0 Try drawing the product of these two reactions:<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35882\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35882\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"35882\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"35882\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35882\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35882 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35882\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-dbn41\" data-id=\"dbn41\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2649-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2649-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>Final example. Draw the product!<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35883\"><style type=\"text\/css\" id=\"wq-flip-custom-css\">.wq-quiz-wrapper[data-id=\"35883\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-font-color: #444;\n}\n\n\t\t\t.wq-quiz-wrapper[data-id=\"35883\"] {\n\t\t\t\t--wq-question-width: 600px;\n\t\t\t}\n\n\t\t\t@media screen and (max-width: 600px) {\n\t\t\t\t.wq-quiz-wrapper[data-id=\"35883\"] .wq_singleQuestionWrapper { width:100% !important; height:auto !important; }\n\t\t\t}\n\t\t<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35883\" class=\"wq_quizCtr single flip_quiz wq-quiz wq-quiz-35883 wq-quiz-flip wq-layout-single wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35883\">\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-4uh96\" data-id=\"4uh96\">\n\n\t\n\t<div class=\"item_top\">\n\t\t<div class=\"title_container\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4 class=\"wq-question-title\"><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n\n\t<div class=\"card \">\n\t\t<div class=\"front\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2650-Front.gif\" \/>\n\t\t\n\t\t\n\t\n\t\n\t\t\t<span class=\"top-desc\">Click to Flip<\/span>\n\t<\/div>\n\t\t<div class=\"back\" >\n\t\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-images\/2650-Reverse.gif\" \/>\n\t\t\n\t\t\n\t\n\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>These are examples of questions that tie together topics in multiple chapters &#8211; stereochemistry, alkenes, and alkynes &#8211; and therefore make for excellent questions on final exams.<\/p>\n<h2><a id=\"three\"><\/a>3. Mechanism For Reduction of Alkynes With Na\/NH3<\/h2>\n<p>If Na is a source of electrons &#8211; a reducing agent &#8211; then where do those electrons <em>go<\/em> when the alkyne is added?<\/p>\n<p>The electrons will go into the<strong> lowest<\/strong>-energy <strong>empty\u00a0<\/strong>orbital available on the alkyne!<\/p>\n<p>This can&#8217;t be a bonding orbital, however, because all the bonding orbitals are already occupied with electrons.<\/p>\n<p>The lowest-energy unoccupied molecular orbital &#8211; often abbreviated LUMO &#8211; is actually the <strong>antibonding<\/strong> orbital of one of the pi bonds &#8211; in other words, a pi* orbital.<\/p>\n<p>When the alkyne accepts an electron from solution, a pi-pi bond breaks, resulting in the formation of an intermediate which contains both an anion and a radical. Unsurprisingly, these types of species are called &#8220;radical anions&#8221;.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35894\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/9-mechanism-of-na-nh3-reduction-of-alkynes-step-1-addition-of-elctron-to-alkyne-gives-radical-anion.gif\" alt=\"mechanism of na nh3 reduction of alkynes step 1 - addition of elctron to alkyne gives radical anion\" width=\"640\" height=\"283\" \/><\/a><\/p>\n<p>The next step is protonation of the anion by the strongest acid available, which in this case happens to be the solvent NH<sub>3.\u00a0<\/sub><\/p>\n<p>Anions on sp<sup>2 <\/sup>hybridized carbons such as alkenes are extremely basic.\u00a0 Although we don&#8217;t generally think of NH<sub>3<\/sub> as an acid (pK<sub>a<\/sub> 38), it is in fact a stronger acid than an alkene C-H (pK<sub>a<\/sub> about 42).<\/p>\n<p>Since this acid-base reaction results in a weaker acid (NH<sub>3<\/sub>) and a weaker base (NaNH<sub>2<\/sub> is a weaker base than the conjugate base of an alkene), the acid-base reaction is <strong>favorable<\/strong> overall. [<span style=\"color: #993366;\"><em>See article &#8211; <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2010\/09\/29\/how-to-use-a-pka-table\/\">How To Use A pK<sub>a<\/sub> Table<\/a><\/em><\/span>] [<a href=\"#notetwo\"><span style=\"color: #ff0000;\">Note 2<\/span><\/a>]<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35895\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/10-mechanism-of-na-nh3-reduction-step-2-protonation-of-vinyl-anion-with-NH3-gives-vinyl-radical.gif\" alt=\"mechanism of na nh3 reduction step 2- protonation of vinyl anion with NH3 gives vinyl radical\" width=\"640\" height=\"238\" \/><\/a><\/p>\n<p>After protonation, we are left with a radical on the sp<sup>2<\/sup> hybridized carbon of the alkene, a species known as a vinyl radical. [<a href=\"#notethree\"><span style=\"color: #ff0000;\">Note 3<\/span><\/a>]<\/p>\n<p>This vinyl radical rapidly accepts a <strong>second\u00a0<\/strong>electron from solution, resulting in another anion.<\/p>\n<p>It is generally thought that the preference for\u00a0<em>trans\u00a0<\/em>products is set at this stage. \u00a0[<span style=\"color: #ff0000;\">Note 4<\/span>]<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35896\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/11-mechanism-of-na-nh3-alkyne-reduction-step-3-reduction-of-vinyl-radical-to-give-vinyl-anion.gif\" alt=\"-mechanism of na nh3 alkyne reduction step 3 - reduction of vinyl radical to give vinyl anion\" width=\"640\" height=\"209\" \/><\/a><\/p>\n<p>This anion is then protonated by solvent, giving us our alkene product.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35897\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/12-mechanism-of-na-nh3-reduction-of-alkynes-step-4-protonation-to-give-trans-alkene.gif\" alt=\"mechanism of na nh3 reduction of alkynes step 4 - protonation to give trans alkene\" width=\"640\" height=\"226\" \/><\/a><\/p>\n<h2><a id=\"four\"><\/a>4. Some Synthesis Problems Involving Na\/NH3 Reduction<\/h2>\n<p>In a previous article, we saw that acetylides (the conjugate bases of alkynes) undergo S<sub>N<\/sub>2 reactions with alkyl halides to give substituted acetylenes. (<span style=\"color: #993366;\"><a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2013\/05\/01\/the-2-most-important-reactions-of-alkynes\/\"><em>See article &#8211; Substitution Reactions of Acetylides<\/em><\/a><\/span>). This is an extremely important reaction for forming carbon-carbon bonds.<\/p>\n<p>In the quizzes below,\u00a0 your job is to combine this reaction along with partial reduction and various reactions of alkenes to make several different products.<\/p>\n<p>Sometimes doing a bond rotation will make the process of working backwards more clear. (<span style=\"color: #800080;\"><em>See article &#8211; <a href=\"https:\/\/www.masterorganicchemistry.com\/2023\/11\/06\/bond-rotation-how-to-draw\/\">How To Do A Bond Rotation<\/a><\/em><\/span>).<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35884\"><style type=\"text\/css\" id=\"wq-personality-custom-css\">.wq-quiz-wrapper[data-id=\"35884\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-bar-color: #00c479;\n--wq-font-color: #444;\n--wq-background-color: #f2f2f2;\n}\n<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35884\" class=\"wq_quizCtr multiple personality_quiz wq-quiz wq-quiz-35884 wq-quiz-personality wq-layout-multiple wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35884\">\n<!-- Progress bar -->\n<div class=\"wq-progress-bar-container wq_quizProgressBarCtr\">\n\t<div class=\"wq_quizProgressBar\">\n\t\t<span class=\"wq_quizProgressValue\" style=\"width: 0%;\">0%<\/span>\n\t<\/div>\n<\/div>\n<!-- \/\/ Progress bar-->\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-ad51r\" data-index=\"0\">\n\n\t\n\t<div class=\"wq_singleQuestionCtr\">\n\t\t<div class=\"wq_questionTextWrapper quiz-pro-clearfix\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4> <\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\n\t\t<div class=\"wq_questionMediaCtr\">\n\t\t\t<div class=\"wq_questionImage wq-question-image\">\n\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"874\" height=\"420\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2651-Front-na-nh3-synth-1.gif\" class=\"attachment-full size-full\" alt=\"\" \/>\t\n\t<\/div>\n\t\t<\/div>\n\n\t\t<div class=\"wq-question-answers wq_questionAnswersCtr\">\n\t\t\t<div class=\"wq-answers wq_answersWrapper\">\n\t<div class=\"row\">\n\t\t\n\t\t\t<div class=\"col-md-wq-4\">\n\t\t\t\t<div class=\"wq-answer wq_singleAnswerCtr wq_hasImage\" data-id=\"b71gz\">\n\n\t\t\t\t\t\t\t\t\t\t\t<div class=\"wq_answerImgCtr\">\n\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"874\" height=\"700\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2651-Reverse-1-na-nh3-synth-1-2.gif\" class=\"attachment-full size-full\" alt=\"\" \/>\t\t\t\t\t\t<\/div>\n\t\t\t\t\t\n\t\t\t\t\t\t\t\t\t\t\t<label class=\"wq_answerTxtCtr\">2-Working backwards<\/label>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t<\/div>\n\n\t\t\t\n\t\t\t<\/div>\n<\/div>\n\t\t<\/div>\n\n\t\t\n\t\t<div class=\"wq-personality-question-explanation wq_personalityQuestionExplanation\">\n\t\t\t<div class=\"wq-explanation-head wq_ExplanationHead\"><\/div>\n\t\t\t<p class=\"wq-explanation-text wq_QuestionExplanationText\">Work backwards from the product<\/p>\n\t\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<div class=\"wq-question wq_singleQuestionWrapper wq-question-3trrc\" data-index=\"1\">\n\n\t\n\t<div class=\"wq_singleQuestionCtr\">\n\t\t<div class=\"wq_questionTextWrapper quiz-pro-clearfix\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\n\t\t<div class=\"wq_questionMediaCtr\">\n\t\t\t<div class=\"wq_questionImage wq-question-image\">\n\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"874\" height=\"700\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2651-Reverse-1-na-nh3-synth-1-2.gif\" class=\"attachment-full size-full\" alt=\"\" \/>\t\n\t<\/div>\n\t\t<\/div>\n\n\t\t<div class=\"wq-question-answers wq_questionAnswersCtr\">\n\t\t\t<div class=\"wq-answers wq_answersWrapper\">\n\t<div class=\"row\">\n\t\t\n\t\t\t<div class=\"col-md-wq-4\">\n\t\t\t\t<div class=\"wq-answer wq_singleAnswerCtr wq_hasImage\" data-id=\"7ojq8\">\n\n\t\t\t\t\t\t\t\t\t\t\t<div class=\"wq_answerImgCtr\">\n\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"874\" height=\"694\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2651-Reverse-2-na-nh3-synth-1-2-2.gif\" class=\"attachment-full size-full\" alt=\"\" \/>\t\t\t\t\t\t<\/div>\n\t\t\t\t\t\n\t\t\t\t\t\t\t\t\t\t\t<label class=\"wq_answerTxtCtr\">Final sequence<\/label>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t<\/div>\n\n\t\t\t\n\t\t\t<\/div>\n<\/div>\n\t\t<\/div>\n\n\t\t\n\t\t<div class=\"wq-personality-question-explanation wq_personalityQuestionExplanation\">\n\t\t\t<div class=\"wq-explanation-head wq_ExplanationHead\"><\/div>\n\t\t\t<p class=\"wq-explanation-text wq_QuestionExplanationText\">Final sequence<\/p>\n\t\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<div class=\"wq-results wq_resultsCtr\">\n\t<span class=\"wq-result-quiz-title wq_quizTitle\">Quiz 2651<\/span>\n<div class=\"wq-result wq_singleResultWrapper\" data-id=\"gjwfm\">\n\n\t<div class=\"wq-result-score wq_resultScoreCtr\"><\/div>\n\n\t<div class=\"wq-result-title wq_resultTitle\"><\/div>\n\n\t\t\t<p><img loading=\"lazy\" decoding=\"async\" width=\"874\" height=\"694\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2651-Reverse-2-na-nh3-synth-1-2-2.gif\" class=\"wq-result-img wq_resultImg\" alt=\"\" \/><\/p>\n\t\n\t<div class=\"wq_resultDesc\"><\/div>\n<\/div>\n<\/div><!-- End .wq-results -->\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>In this synthesis question, show how to build this vicinal diol starting from acetylene.<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35886\"><style type=\"text\/css\" id=\"wq-personality-custom-css\">.wq-quiz-wrapper[data-id=\"35886\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-bar-color: #00c479;\n--wq-font-color: #444;\n--wq-background-color: #f2f2f2;\n}\n<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35886\" class=\"wq_quizCtr multiple personality_quiz wq-quiz wq-quiz-35886 wq-quiz-personality wq-layout-multiple wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35886\">\n<!-- Progress bar -->\n<div class=\"wq-progress-bar-container wq_quizProgressBarCtr\">\n\t<div class=\"wq_quizProgressBar\">\n\t\t<span class=\"wq_quizProgressValue\" style=\"width: 0%;\">0%<\/span>\n\t<\/div>\n<\/div>\n<!-- \/\/ Progress bar-->\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-gr5jx\" data-index=\"0\">\n\n\t\n\t<div class=\"wq_singleQuestionCtr\">\n\t\t<div class=\"wq_questionTextWrapper quiz-pro-clearfix\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\n\t\t<div class=\"wq_questionMediaCtr\">\n\t\t\t<div class=\"wq_questionImage wq-question-image\">\n\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"900\" height=\"838\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2652-Reverse-1-na-nh3-synth-2-2.gif\" class=\"attachment-full size-full\" alt=\"\" \/>\t\n\t<\/div>\n\t\t<\/div>\n\n\t\t<div class=\"wq-question-answers wq_questionAnswersCtr\">\n\t\t\t<div class=\"wq-answers wq_answersWrapper\">\n\t<div class=\"row\">\n\t\t\n\t\t\t<div class=\"col-md-wq-4\">\n\t\t\t\t<div class=\"wq-answer wq_singleAnswerCtr wq_hasImage\" data-id=\"wrs7y\">\n\n\t\t\t\t\t\t\t\t\t\t\t<div class=\"wq_answerImgCtr\">\n\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"970\" height=\"646\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2652-Reverse-2-na-nh3-synth-2-2-2.gif\" class=\"attachment-full size-full\" alt=\"\" \/>\t\t\t\t\t\t<\/div>\n\t\t\t\t\t\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t<\/div>\n\n\t\t\t\n\t\t\t<\/div>\n<\/div>\n\t\t<\/div>\n\n\t\t\n\t\t<div class=\"wq-personality-question-explanation wq_personalityQuestionExplanation\">\n\t\t\t<div class=\"wq-explanation-head wq_ExplanationHead\"><\/div>\n\t\t\t<p class=\"wq-explanation-text wq_QuestionExplanationText\">Work backwards from the product!<\/p>\n\t\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<div class=\"wq-question wq_singleQuestionWrapper wq-question-dv9t8\" data-index=\"1\">\n\n\t\n\t<div class=\"wq_singleQuestionCtr\">\n\t\t<div class=\"wq_questionTextWrapper quiz-pro-clearfix\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\n\t\t<div class=\"wq_questionMediaCtr\">\n\t\t\t<div class=\"wq_questionImage wq-question-image\">\n\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"970\" height=\"646\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2652-Reverse-2-na-nh3-synth-2-2-2.gif\" class=\"attachment-full size-full\" alt=\"\" \/>\t\n\t<\/div>\n\t\t<\/div>\n\n\t\t<div class=\"wq-question-answers wq_questionAnswersCtr\">\n\t\t\t<div class=\"wq-answers wq_answersWrapper\">\n\t<div class=\"row\">\n\t\t\n\t\t\t<div class=\"col-md-wq-4\">\n\t\t\t\t<div class=\"wq-answer wq_singleAnswerCtr wq_hasImage\" data-id=\"mc57y\">\n\n\t\t\t\t\t\t\t\t\t\t\t<div class=\"wq_answerImgCtr\">\n\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"970\" height=\"646\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2652-Reverse-2-na-nh3-synth-2-2-2.gif\" class=\"attachment-full size-full\" alt=\"\" \/>\t\t\t\t\t\t<\/div>\n\t\t\t\t\t\n\t\t\t\t\t\t\t\t\t\t\t<label class=\"wq_answerTxtCtr\">Final sequence<\/label>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t<\/div>\n\n\t\t\t\n\t\t\t<\/div>\n<\/div>\n\t\t<\/div>\n\n\t\t\n\t\t<div class=\"wq-personality-question-explanation wq_personalityQuestionExplanation\">\n\t\t\t<div class=\"wq-explanation-head wq_ExplanationHead\"><\/div>\n\t\t\t<p class=\"wq-explanation-text wq_QuestionExplanationText\">Final sequence<\/p>\n\t\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<div class=\"wq-results wq_resultsCtr\">\n\t<span class=\"wq-result-quiz-title wq_quizTitle\">Quiz 2652<\/span>\n<div class=\"wq-result wq_singleResultWrapper\" data-id=\"lfqdc\">\n\n\t<div class=\"wq-result-score wq_resultScoreCtr\"><\/div>\n\n\t<div class=\"wq-result-title wq_resultTitle\"><\/div>\n\n\t\t\t<p><img loading=\"lazy\" decoding=\"async\" width=\"880\" height=\"492\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2652-Front-na-nh3-synth-2.gif\" class=\"wq-result-img wq_resultImg\" alt=\"\" \/><\/p>\n\t\n\t<div class=\"wq_resultDesc\"><\/div>\n<\/div>\n<\/div><!-- End .wq-results -->\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<p>In the question below, show how you would make this vicinal dibromide.<\/p>\n<div class=\"wq-quiz-wrapper\" data-id=\"35888\"><style type=\"text\/css\" id=\"wq-personality-custom-css\">.wq-quiz-wrapper[data-id=\"35888\"] {\n--wq-question-width: 100%;\n--wq-question-color: #009cff;\n--wq-question-height: auto;\n--wq-bar-color: #00c479;\n--wq-font-color: #444;\n--wq-background-color: #f2f2f2;\n}\n<\/style><!-- wp quiz -->\n<div id=\"wp-quiz-35888\" class=\"wq_quizCtr multiple personality_quiz wq-quiz wq-quiz-35888 wq-quiz-personality wq-layout-multiple wq-skin-traditional wq-should-show-correct-answer\" data-quiz-id=\"35888\">\n<!-- Progress bar -->\n<div class=\"wq-progress-bar-container wq_quizProgressBarCtr\">\n\t<div class=\"wq_quizProgressBar\">\n\t\t<span class=\"wq_quizProgressValue\" style=\"width: 0%;\">0%<\/span>\n\t<\/div>\n<\/div>\n<!-- \/\/ Progress bar-->\n<div class=\"wq-questions wq_questionsCtr\">\n\t<div class=\"wq-question wq_singleQuestionWrapper wq-question-l1shs\" data-index=\"0\">\n\n\t\n\t<div class=\"wq_singleQuestionCtr\">\n\t\t<div class=\"wq_questionTextWrapper quiz-pro-clearfix\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\n\t\t<div class=\"wq_questionMediaCtr\">\n\t\t\t<div class=\"wq_questionImage wq-question-image\">\n\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"882\" height=\"496\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2653-Front-na-nh3-synth-3.gif\" class=\"attachment-full size-full\" alt=\"\" \/>\t\n\t<\/div>\n\t\t<\/div>\n\n\t\t<div class=\"wq-question-answers wq_questionAnswersCtr\">\n\t\t\t<div class=\"wq-answers wq_answersWrapper\">\n\t<div class=\"row\">\n\t\t\n\t\t\t<div class=\"col-md-wq-4\">\n\t\t\t\t<div class=\"wq-answer wq_singleAnswerCtr wq_hasImage\" data-id=\"78ljt\">\n\n\t\t\t\t\t\t\t\t\t\t\t<div class=\"wq_answerImgCtr\">\n\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"880\" height=\"820\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2653-Reverse-1-na-nh3-synth-3-2.gif\" class=\"attachment-full size-full\" alt=\"\" \/>\t\t\t\t\t\t<\/div>\n\t\t\t\t\t\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t<\/div>\n\n\t\t\t\n\t\t\t<\/div>\n<\/div>\n\t\t<\/div>\n\n\t\t\n\t\t<div class=\"wq-personality-question-explanation wq_personalityQuestionExplanation\">\n\t\t\t<div class=\"wq-explanation-head wq_ExplanationHead\"><\/div>\n\t\t\t<p class=\"wq-explanation-text wq_QuestionExplanationText\">Work backwards from the final product<\/p>\n\t\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<div class=\"wq-question wq_singleQuestionWrapper wq-question-l0si3\" data-index=\"1\">\n\n\t\n\t<div class=\"wq_singleQuestionCtr\">\n\t\t<div class=\"wq_questionTextWrapper quiz-pro-clearfix\">\n\t\t\t<div class=\"wq_questionTextCtr\">\n\t\t\t\t<h4><\/h4>\n\t\t\t<\/div>\n\t\t<\/div>\n\n\t\t<div class=\"wq_questionMediaCtr\">\n\t\t\t<div class=\"wq_questionImage wq-question-image\">\n\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"880\" height=\"820\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2653-Reverse-1-na-nh3-synth-3-2.gif\" class=\"attachment-full size-full\" alt=\"\" \/>\t\n\t<\/div>\n\t\t<\/div>\n\n\t\t<div class=\"wq-question-answers wq_questionAnswersCtr\">\n\t\t\t<div class=\"wq-answers wq_answersWrapper\">\n\t<div class=\"row\">\n\t\t\n\t\t\t<div class=\"col-md-wq-4\">\n\t\t\t\t<div class=\"wq-answer wq_singleAnswerCtr wq_hasImage\" data-id=\"eaozy\">\n\n\t\t\t\t\t\t\t\t\t\t\t<div class=\"wq_answerImgCtr\">\n\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"880\" height=\"706\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2653-Reverse-2-na-nh3-synth-3-2-2.gif\" class=\"attachment-full size-full\" alt=\"\" \/>\t\t\t\t\t\t<\/div>\n\t\t\t\t\t\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t<\/div>\n\n\t\t\t\n\t\t\t<\/div>\n<\/div>\n\t\t<\/div>\n\n\t\t\n\t\t<div class=\"wq-personality-question-explanation wq_personalityQuestionExplanation\">\n\t\t\t<div class=\"wq-explanation-head wq_ExplanationHead\"><\/div>\n\t\t\t<p class=\"wq-explanation-text wq_QuestionExplanationText\">Put the reactions in proper sequence<\/p>\n\t\t<\/div>\n\t<\/div>\n\n\t\n<\/div>\n<\/div>\n<div class=\"wq-results wq_resultsCtr\">\n\t<span class=\"wq-result-quiz-title wq_quizTitle\">Quiz 2653<\/span>\n<div class=\"wq-result wq_singleResultWrapper\" data-id=\"bj6ch\">\n\n\t<div class=\"wq-result-score wq_resultScoreCtr\"><\/div>\n\n\t<div class=\"wq-result-title wq_resultTitle\"><\/div>\n\n\t\t\t<p><img loading=\"lazy\" decoding=\"async\" width=\"878\" height=\"706\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2023\/12\/2653-Reverse-2-na-nh3-synth-3-2-2-1.gif\" class=\"wq-result-img wq_resultImg\" alt=\"\" \/><\/p>\n\t\n\t<div class=\"wq_resultDesc\"><\/div>\n<\/div>\n<\/div><!-- End .wq-results -->\n<\/div>\n<!-- \/\/ wp quiz-->\n<\/div><!-- End .wq-quiz-wrapper -->\n<h2><a id=\"five\"><\/a>5. Summary<\/h2>\n<p>Alkynes are partially reduced to <em>trans<\/em>-alkenes by metallic sodium (Na) dissolved in liquid ammonia. The reaction is complimentary to the Lindlar reduction of alkynes, which gives\u00a0<em>cis<\/em> products.<\/p>\n<p>The resulting alkenes can then undergo all the reactions of alkenes we&#8217;ve learned in a previous chapter. It&#8217;s extremely important to pay attention to stereochemical details, both in the reduction itself and also in all the subsequent reactions of alkenes. Expect to see lots of exam-type questions that ask you to to synthesize various molecules from alkynes that involve Na\/NH<sub>3<\/sub> as a key step.<\/p>\n<hr \/>\n<h2><strong><a id=\"notes\"><\/a>Notes<\/strong><\/h2>\n<div class=\"related-articles\"><p><strong>Related Articles<\/strong><\/p><ul><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2011\/08\/19\/lindlars-catalyst-partial-cis-reduction\/\" class=\"\"><span>Partial Reduction of Alkynes With Lindlar\u2019s Catalyst<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2024\/01\/23\/alkyne-hydroboration-with-r2bh\/\" class=\"\"><span>Alkyne Hydroboration With \u201cR2BH\u201d<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2013\/05\/14\/hydroboration-and-oxymercuration-of-alkynes\/\" class=\"\"><span>Hydroboration and Oxymercuration of Alkynes<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2013\/06\/24\/alkynes-are-a-blank-canvas\/\" class=\"\"><span>Alkynes Are A Blank Canvas<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2014\/01\/29\/synthesis-5-reactions-of-alkynes\/\" class=\"\"><span>Synthesis (5) \u2013 Reactions of Alkynes<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2013\/05\/01\/the-2-most-important-reactions-of-alkynes\/\" class=\"\"><span>Acetylides from Alkynes, And Substitution Reactions of Acetylides<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/reaction-guide\/partial-reduction-of-alkynes-with-lindlars-catalyst-to-give-cis-alkenes\/\" class=\"\"><span>Partial reduction of alkynes with Lindlar\u2019s catalyst (MOC Membership)<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/reaction-guide\/partial-reduction-of-alkynes-to-trans-alkenes-using-sodium-and-ammonia\/\" class=\"\"><span>Partial reduction of alkynes to trans alkenes using sodium and ammonia (MOC Membership)<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2011\/11\/25\/palladium-on-carbon-pdc\/\" class=\"\"><span>Palladium on Carbon (Pd\/C) for Catalytic Hydrogenation<\/span><\/a><\/li><li><a href=\"https:\/\/www.masterorganicchemistry.com\/2023\/11\/06\/bond-rotation-how-to-draw\/\" class=\"\"><span>How To Draw A Bond Rotation<\/span><\/a><\/li><\/ul><\/div>\n<p><strong><a id=\"noteone\"><\/a>Note 1.\u00a0<\/strong>Lithium can be used in place of sodium (Na). Also, solvents such as tetrahydrofuran (THF) can be used, so long as there is a source of protons &#8211;\u00a0<em>t<\/em>-BuOH is a popular choice (<span style=\"color: #993366;\"><em>similar to the Birch Reduction &#8211; <a style=\"color: #993366;\" href=\"https:\/\/www.masterorganicchemistry.com\/2019\/10\/17\/birch-reduction\/\">see this article<\/a><\/em><\/span>).\u00a0 The reaction is generally highly selective for reducing alkynes, but alkenes can be reduced if higher temperatures are employed.<\/p>\n<p>For a pretty comprehensive study of different conditions for carrying out this reaction, see <a href=\"https:\/\/pubs.acs.org\/doi\/abs\/10.1021\/jo00920a002\">this article<\/a> (House &#8211; JOC 1974 p. 747)<\/p>\n<p><strong><a id=\"notetwo\"><\/a>Note 2. <\/strong>Terminal alkynes are not very good substrates for these reductions. In one example, attempted reduction of a terminal alkyne resulted in a 31% yield, along with a considerable amount of recovered starting material. Can you figure out why? [Quiz 1]<\/p>\n<p><strong><a id=\"notethree\"><\/a>Note 3.<\/strong>\u00a0 In the mechanism above, the vinyl radical is drawn <em>trans<\/em>. It&#8217;s been found that vinyl radicals can quite readily interconvert between their\u00a0<em>cis<\/em> and\u00a0<em>trans<\/em> forms, with a relatively low barrier to inversion (about 3 kcal\/mol).\u00a0<em><span style=\"color: #993366;\">Just for reference, this is roughly the energy barrier between staggered and eclipsed forms of ethane. So it&#8217;s extremely low, in other words!\u00a0<\/span><\/em><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35904\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2024\/01\/F1-vinyl-radical-interconversion-of-cis-and-trans-vinyl-radicals.gif\" alt=\"vinyl radical interconversion of cis and trans vinyl radicals\" width=\"640\" height=\"273\" \/><\/a><\/p>\n<p>In contrast, vinyl anions are very stable. Once formed, they don&#8217;t generally lose their configurational geometry (27 kcal\/mol). Incredibly, they can be heated in diethyl ether for an hour without losing their configuration.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35905\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2024\/01\/F2-vinyl-anions-are-configurationally-stable-do-not-invert-even-in-boiling-ether-after-one-hour.gif\" alt=\"-vinyl anions are configurationally stable - do not invert even in boiling ether after one hour\" width=\"640\" height=\"218\" \/><\/a><\/p>\n<p><strong><a id=\"notefour\"><\/a>Note 4. <\/strong>The stereoselectivity for this reaction can be quite high (&gt;95:5). Several studies have been made on the origins of the high stereoselectivity\u00a0 [<a href=\"#reffour\">Ref<\/a>].<\/p>\n<p>An early study proposed that the high\u00a0<em>trans<\/em> selectivity was due to formation of a di-anion, which preferentially gave the\u00a0<em>trans<\/em> product due to electrostatic lone-pair repulsion. It would be nice if this were true, since it is so intuitively simple. Alas, experiments and calculations indicate that dianions are generally too unstable to be formed under the reaction conditions, except in some special cases<span style=\"color: #993366;\"><em> (e.g. diarylacetylenes).\u00a0<\/em><\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-35968\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/2013\/05\/F3-evidence-for-di-anion-in-reduction-of-alkynes-to-alkenes.gif\" alt=\"evidence for di-anion in reduction of alkynes to alkenes\" width=\"640\" height=\"241\" \/><\/a><\/p>\n<p>The origin of the high\u00a0<em>trans<\/em> selectivity has not been definitively established.<\/p>\n<p>General consensus is that initial reduction of the alkyne preferentially forms a <em>trans<\/em> radical anion <span style=\"color: #800080;\"><em>(exactly <strong>how<\/strong> favored this is, and to what extent it undergoes inversion to a cis radical anion,\u00a0 still needs to be studied more)<\/em><\/span>. After protonation, a vinyl radical is formed. It&#8217;s known that vinyl radicals have a low barrier to inversion (3 kcal\/mol) so a big factor is the rate of the second reduction step relative to the rate of inversion of the vinyl radical. There can&#8217;t be complete equilibration between the <em>cis<\/em> and <em>trans<\/em> vinyl radicals, because they&#8217;ve each been made independently in the presence of Na, and the equilibrium ratio\u00a0 of\u00a0 <em>trans:cis\u00a0<\/em> isomers after reduction is only about 80:20. [<a href=\"#reffive\">Ref<\/a>] So the high selectivity (&gt;95% in some conditions) must mean that reduction is fast, relative to equilibration, and must indicate some strong initial preference for formation of the <em>trans<\/em> radical anion. <span style=\"color: #800080;\"><em>\u00a0(indeed, if fewer equivalents of sodium are added, or if the temperature of the reaction is raised, the high selectivities erode back to about 80:20).\u00a0<\/em><\/span><\/p>\n<p>&nbsp;<\/p>\n<hr \/>\n<h2><strong><a id=\"quiz\"><\/a>Quiz Yourself!<\/strong><\/h2>\n<p><br \/>\n<img loading=\"lazy\" decoding=\"async\" class=\"wp-image-36214 aligncenter\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/0702-Front-Image-Only.png\" alt=\"\" width=\"600\" height=\"450\" \/><\/a><\/p>\n<p style=\"text-align: center;\"><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a MOC member<\/strong><\/a> to see the clickable quiz with answers on the back.<\/p>\n<p><br \/>\n<br \/>\n<img loading=\"lazy\" decoding=\"async\" class=\"wp-image-36214 aligncenter\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/3347-Front-Image-Only.png\" alt=\"\" width=\"600\" height=\"450\" \/><\/a><\/p>\n<p style=\"text-align: center;\"><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a MOC member<\/strong><\/a> to see the clickable quiz with answers on the back.<\/p>\n<p><br \/>\n<br \/>\n<img loading=\"lazy\" decoding=\"async\" class=\"wp-image-36214 aligncenter\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/0691-Front-Image-Only.png\" alt=\"\" width=\"600\" height=\"450\" \/><\/a><\/p>\n<p style=\"text-align: center;\"><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a MOC member<\/strong><\/a> to see the clickable quiz with answers on the back.<\/p>\n<p><br \/>\n<br \/>\n<img loading=\"lazy\" decoding=\"async\" class=\"wp-image-36214 aligncenter\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/1656-Front-Image-Only.png\" alt=\"\" width=\"600\" height=\"450\" \/><\/a><\/p>\n<p style=\"text-align: center;\"><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a MOC member<\/strong><\/a> to see the clickable quiz with answers on the back.<\/p>\n<p><br \/>\n<br \/>\n<img loading=\"lazy\" decoding=\"async\" class=\"wp-image-36214 aligncenter\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/2664-Front-Image-Only.png\" alt=\"\" width=\"600\" height=\"450\" \/><\/a><\/p>\n<p style=\"text-align: center;\"><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a MOC member<\/strong><\/a> to see the clickable quiz with answers on the back.<\/p>\n<p><br \/>\n<br \/>\n<img loading=\"lazy\" decoding=\"async\" class=\"wp-image-36214 aligncenter\" src=\"https:\/\/www.masterorganicchemistry.com\/wp-content\/uploads\/quiz-previews\/2665-Front-Image-Only.png\" alt=\"\" width=\"600\" height=\"450\" \/><\/a><\/p>\n<p style=\"text-align: center;\"><a href=\"https:\/\/www.masterorganicchemistry.com\/moc-membership\/\"><strong>Become a MOC member<\/strong><\/a> to see the clickable quiz with answers on the back.<\/p>\n<p><\/p>\n<hr \/>\n<h2><strong><a id=\"references\"><\/a>(Advanced) References and Further Reading<\/strong><\/h2>\n<ol>\n<li><strong>Reduction of Organic Compounds by Lithium in Low Molecular Weight Amines. 11. Stereochemistry. Chemical Reduction of an Isolated Nonterminal Double Bond<\/strong><br \/>\nROBERT A. BENKESER, GESE SCHROLI, AND DALE &amp; I. SALVE<br \/>\n<i>J. Am. Chem. Soc. <\/i><strong>1955<\/strong>, 77, 12, 3378-3379<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/abs\/10.1021\/ja01617a066\">10.1002\/ja01617a066<\/a><br \/>\nLithium and low-molecular weight amines (methylamine, ethylamine, isopropylamine) can also be used for dissolving metal reduction of alkynes. The advantage is that these reagents are easier to handle over sodium\/ammonia.<\/li>\n<li><strong>The Preparation of Higher cis and trans Olefins<\/strong><br \/>\nKenneth N. Campbell and Lawrence T. Eby<br \/>\n<em>Journal of the American Chemical Society<\/em> <strong>1941<\/strong> 63 (1), 216-219<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/ja01846a050\">10.1021\/ja01846a050<\/a><br \/>\nOne of the first reports on the reduction of alkynes to trans alkenes with sodium and liquid NH3. Reductions of 5-decyne, 4-octyne, 3-octyne, and 3-hexyne proceed in good (&gt;80%) yields.<\/li>\n<li><strong>Reactions involving electron transfer. V. Reduction on nonconjugated acetylenes<br \/>\n<\/strong>Herbert O. House and Edith F. Kinloch<strong><br \/>\n<\/strong><em>The Journal of Organic Chemistry<\/em> <strong>1974<\/strong> <em>39<\/em> (6), 747-755<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/pubs.acs.org\/doi\/abs\/10.1021\/jo00920a002\">10.1021\/jo00920a002<\/a><br \/>\nStudy of the product distribution of metal reduction of internal and terminal alkynes using Na in HMPA-THF.<\/li>\n<li><strong><a id=\"reffour\"><\/a>Dissolving Metal Reduction of Acetylenes:\u2009 A Computational Study<br \/>\n<\/strong>Robert Damrauer<strong><br \/>\n<\/strong><em>The Journal of Organic Chemistry<\/em> <strong>2006<\/strong> <em>71<\/em> (24), 9165-9171<strong><br \/>\nDOI: <\/strong><a href=\"https:\/\/pubs.acs.org\/doi\/abs\/10.1021\/jo061583j\">10.1021\/jo061583j<\/a><br \/>\nThis is a computational investigation using DFT (density functional theory) which studies the stability of proposed intermediates in the dissolving metal reduction of acetylene, both in the gas phase and with explicit ammonia solvation.<br \/>\n<em><span style=\"color: #000000;\">&#8220;Findings include the probable bent nature of the radical anion species in ammonia, the likelihood that the trans stereochemistry of the reduction is determined at the vinyl anion stage, and the elimination of a dianion as a possible species that determines the stereochemical result.&#8221;<\/span><\/em><\/li>\n<li><strong><a id=\"reffive\"><\/a>Configuration of vinyl radicals. The generation and trapping of each member of a configurationally isomeric pair of vinyl radicals<br \/>\n<\/strong>G. Dann. Sargent and M. Warren. Browne<br \/>\n<em>Journal of the American Chemical Society<\/em> <strong>1967<\/strong> 89 (11), 2788-2790<br \/>\n<strong>DOI:<\/strong> <a href=\"https:\/\/pubs.acs.org\/doi\/abs\/10.1021\/ja00987a082\">10.1021\/ja00987a082<\/a><br \/>\nSome classic experiments here. The authors prepare pure E- and Z- 3-bromo-3-hexene, and subject them to one-electron reduction with lithium naphthalenide to make the vinyl radical, which is quickly trapped in solution. This lets them calculate the inversion barrier for vinyl radicals (about 3 kcal\/mol). The (Z) vinyl radical rapidly equilibrates to give majority <em>trans<\/em> alkene. Once formed, pure (E) vinyl radical gives about 85:15 <em>trans: cis\u00a0<\/em>alkenes. This is lower selectivity than what is typically seen in Na\/NH3 reductions, so inversion of a vinyl radical would therefore seem unimportant in the mechanism for reduction of alkynes.<\/li>\n<li><strong>Reduction of alkyl- and arylacetylenes by an electrochemical method<br \/>\n<\/strong>Robert A. Benkeser and Cline A. Tincher<br \/>\n<em>The Journal of Organic Chemistry<\/em> 1968 33 (7), 2727-2730<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/jo01271a024\">10.1021\/jo01271a024<\/a><\/li>\n<li><strong>Reduction of Organic Compounds by Lithium in Low Molecular Weight Amines. II. Stereochemistry. Chemical Reduction of an Isolated Non-terminal Double Bond<br \/>\n<\/strong>Robert A. Benkeser, Gene Schroll, and Dale M. Sauve<br \/>\n<em>Journal of the American Chemical Society<\/em> <strong>1955<\/strong> 77 (12), 3378-3379<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/ja01617a066\">10.1021\/ja01617a066<\/a><br \/>\nReplacing liquid ammonia as solvent with other amines results in even more powerful reducing conditions.<\/li>\n<li><strong>Toxic Fluorine Compounds. XVIII.1 The Synthesis of the Toxic Principle of Dichapetalum toxicarium (18-Fluoro-cis-9-octadecenoic Acid) and Related \u03c9-Fluoro Unsaturated Acids2,3<\/strong><br \/>\nR. E. A. Dear and F. L. M. Pattison<br \/>\n<em>Journal of the American Chemical Society<\/em> <strong>1963<\/strong> 85 (5), 622-626<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/ja00888a032\">10.1021\/ja00888a032<\/a><br \/>\nThis paper contains a reduction with Na\/NH3.<\/li>\n<li><strong>Many-Membered Carbon Rings. VI. Unsaturated Nine-membered Cyclic Hydrocarbons<\/strong><br \/>\nA. T. Blomquist, Liang Huang Liu, and James C. Bohrer<br \/>\n<em>Journal of the American Chemical Society<\/em> <strong>1952<\/strong> 74 (14), 3643-3647<br \/>\n<strong>DOI<\/strong>: <a href=\"https:\/\/pubs.acs.org\/doi\/pdf\/10.1021\/ja01134a052\">10.1021\/ja01134a052<\/a><br \/>\nThis article has an example of the reduction of cyclononyne to give\u00a0<em>trans<\/em>-cyclononene.<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"<p>Partial Reduction of Alkynes to trans-Alkenes (olefins) With Sodium in Ammonia (Na\/NH3) Alkynes can be hydrogenated to alkanes with Pd\/C and excess H2, or partially <\/p>\n","protected":false},"author":1,"featured_media":35941,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1419],"tags":[921,922,524,920,808,923],"post_folder":[],"class_list":["post-7268","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-alkyne-reactions","tag-alkyne-reduction","tag-cis-alkene","tag-lindlar","tag-nanh3","tag-sodium","tag-trans-alkene"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Partial Reduction of Alkynes With Na\/NH3 To Give Trans Alkenes<\/title>\n<meta name=\"description\" content=\"Partial reduction of alkynes to trans alkenes can be achieved with sodium in ammonia Na\/NH3 (not NaNH2\/NH3!)\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" 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