{"id":23562,"date":"2021-04-07T12:07:43","date_gmt":"2021-04-07T11:07:43","guid":{"rendered":"https:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=23562"},"modified":"2021-04-07T12:07:43","modified_gmt":"2021-04-07T11:07:43","slug":"dimethyl-ketal-hydrolysis-catalysed-by-hydroxide-and-hydronium-ions","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23562","title":{"rendered":"Dimethyl ketal hydrolysis catalysed by hydroxide and hydronium ions"},"content":{"rendered":"<div class=\"kcite-section\" kcite-section-id=\"23562\">\n<p>In the <a href=\"https:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=23522\">preceding post<\/a>, I looked at a computed mechanism for the hydrolysis of a ketal by water. Of course, pure water consists of three potential catalysts, water itself or [H<sub>2<\/sub>O], and the products of autoionisation, [OH<sup>&#8211;<\/sup>] and\u00a0[H<sub>3<\/sub>O<sup>+<\/sup>]. The latter are in much smaller concentration, equivalent to a penalty of ~11.9 kcal\/mol on any free energy barrier. Here I take a look at these ion-catalysed routes to see if that penalty can be overcome.<\/p>\n<p>The calculations can be found at FAIR\u00a0DOI: <a href=\"https:\/\/doi.org\/10.14469\/hpc\/8071\">10.14469\/hpc\/8071<\/a>. The hydroxyl anion route is shown below, and has a computed free energy barrier of 34.1 kcal\/mol. Only the first TS is shown here, since already we know that the barrier must be at least that high regardless of subsequent steps. This means that hydroxide anion catalysis must be insignificant.<\/p>\n<p><a href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketal-ionic-OH.svg\"><img decoding=\"async\" class=\"aligncenter size-large wp-image-23577\" src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketal-ionic-OH.svg\" alt=\"\" width=\"400\" \/><\/a><\/p>\n<p><a href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketal-hydroxyide_ener.svg\"><img decoding=\"async\" class=\"aligncenter size-large wp-image-23565\" src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketal-hydroxyide_ener.svg\" alt=\"\" width=\"450\" \/><\/a><\/p>\n<p><a href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketyl-hydroxyl.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-large wp-image-23567\" src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketyl-hydroxyl.gif\" alt=\"\" width=\"450\" height=\"254\" \/><\/a><\/p>\n<p>Next, the acid catalysed route, which is a two-stage path.<a href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketal-ionic-H.svg\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter  wp-image-23580\" src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketal-ionic-H.svg\" alt=\"\" width=\"403\" height=\"156\" \/><\/a><\/p>\n<p><a href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketalhydronium_ener.svg\"><img decoding=\"async\" class=\"aligncenter size-large wp-image-23564\" src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketalhydronium_ener.svg\" alt=\"\" width=\"450\" \/><\/a><\/p>\n<p>Firstly one methoxy group is protonated from the hydronium cation and the C-O bond cleaves (IRC 14 to 8). In the second stage, a water molecule abstracts the C-H hydrogen, regenerating the hydronium cation (IRC 2 to -2), during which process the transition state occurs to form an enol. This transition state has a free energy barrier of 16.2 kcal\/mol. Both the second TS (13.4 kcal\/mol) which reverses this to form a hemiacetal and TS3, which eliminates the second methanol to form a ketone (-3.5 kcal\/mol) are lower in energy.<\/p>\n<p><a href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketyl-hydronium.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-large wp-image-23566\" src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketyl-hydronium.gif\" alt=\"\" width=\"450\" height=\"254\" \/><\/a><\/p>\n<p>So we conclude that the hydronium cation catalysed route is easily accessible at ambient temperatures. Adding ~11.9 kcal\/mol to account for the [H<sub>3<\/sub>O<sup>+<\/sup>]<sup>-7<\/sup> concentration of this ion in water gives a &#8220;pure water&#8221; barrier of ~28 kcal\/mol, which corresponds to a rather slow but viable hydrolysis (ie ~days half life) at ambient temperatures. Armed with this information, we can now start to address the hydrolysis of a bio-active ketal-based herbicide in water.<\/p>\n<!-- kcite active, but no citations found -->\n<\/div> <!-- kcite-section 23562 -->","protected":false},"excerpt":{"rendered":"<p>In the preceding post, I looked at a computed mechanism for the hydrolysis of a ketal by water. Of course, pure water consists of three potential catalysts, water itself or [H2O], and the products of autoionisation, [OH&#8211;] and\u00a0[H3O+]. The latter are in much smaller concentration, equivalent to a penalty of ~11.9 kcal\/mol on any free [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"activitypub_content_warning":"","activitypub_content_visibility":"","activitypub_max_image_attachments":5,"activitypub_interaction_policy_quote":"anyone","activitypub_status":"","footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[1086],"tags":[],"ppma_author":[2661],"class_list":["post-23562","post","type-post","status-publish","format-standard","hentry","category-reaction-mechanism-2"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.4 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Dimethyl ketal hydrolysis catalysed by hydroxide and hydronium ions - Henry Rzepa&#039;s Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23562\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Dimethyl ketal hydrolysis catalysed by hydroxide and hydronium ions - Henry Rzepa&#039;s Blog\" \/>\n<meta property=\"og:description\" content=\"In the preceding post, I looked at a computed mechanism for the hydrolysis of a ketal by water. Of course, pure water consists of three potential catalysts, water itself or [H2O], and the products of autoionisation, [OH&#8211;] and\u00a0[H3O+]. The latter are in much smaller concentration, equivalent to a penalty of ~11.9 kcal\/mol on any free [&hellip;]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23562\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa&#039;s Blog\" \/>\n<meta property=\"article:published_time\" content=\"2021-04-07T11:07:43+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketal-ionic-OH.svg\" \/>\n<meta name=\"author\" content=\"Henry Rzepa\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Henry Rzepa\" \/>\n\t<meta name=\"twitter:label2\" content=\"Estimated reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"2 minutes\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"Dimethyl ketal hydrolysis catalysed by hydroxide and hydronium ions - Henry Rzepa&#039;s Blog","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23562","og_locale":"en_GB","og_type":"article","og_title":"Dimethyl ketal hydrolysis catalysed by hydroxide and hydronium ions - Henry Rzepa&#039;s Blog","og_description":"In the preceding post, I looked at a computed mechanism for the hydrolysis of a ketal by water. Of course, pure water consists of three potential catalysts, water itself or [H2O], and the products of autoionisation, [OH&#8211;] and\u00a0[H3O+]. The latter are in much smaller concentration, equivalent to a penalty of ~11.9 kcal\/mol on any free [&hellip;]","og_url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23562","og_site_name":"Henry Rzepa&#039;s Blog","article_published_time":"2021-04-07T11:07:43+00:00","og_image":[{"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketal-ionic-OH.svg","type":"","width":"","height":""}],"author":"Henry Rzepa","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Henry Rzepa","Estimated reading time":"2 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23562#article","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23562"},"author":{"name":"Henry Rzepa","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"headline":"Dimethyl ketal hydrolysis catalysed by hydroxide and hydronium ions","datePublished":"2021-04-07T11:07:43+00:00","mainEntityOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23562"},"wordCount":317,"commentCount":0,"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23562#primaryimage"},"thumbnailUrl":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/04\/ketal-ionic-OH.svg","articleSection":["reaction mechanism"],"inLanguage":"en-GB","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23562#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23562","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23562","name":"Dimethyl ketal hydrolysis catalysed by hydroxide and hydronium ions - 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Water hydrolysis will degrade them, a typical residency time being in the order of a few days. I noted in passing a dioxepin-based\u2026","rel":"","context":"In &quot;reaction mechanism&quot;","block_context":{"text":"reaction mechanism","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1086"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/03\/R-1024x699.jpg?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":8246,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8246","url_meta":{"origin":23562,"position":1},"title":"Thalidomide. The role of water in the mechanism of its aqueous racemisation.","author":"Henry Rzepa","date":"November 10, 2012","format":false,"excerpt":"Thalidomide is a chiral molecule, which was sold in the 1960s as a sedative in its (S,R)-racemic form. The tragedy was that the (S)-isomer was tetragenic, and only the (R) enantiomer acts as a sedative. What was not appreciated at the time is that interconversion of the (S)- and (R)\u2026","rel":"","context":"In &quot;Interesting chemistry&quot;","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/11\/thal1.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":10015,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=10015","url_meta":{"origin":23562,"position":2},"title":"A sideways look at the mechanism of ester hydrolysis.","author":"Henry Rzepa","date":"March 29, 2013","format":false,"excerpt":"The mechanism of ester hydrolysis is a staple of examination questions in organic chemistry. To get a good grade, one might have to reproduce something like the below. Here, I subject that answer to a reality check. In this scheme, HA is a general acid, R=Me, and the net result\u2026","rel":"","context":"In \"ALSO\"","block_context":{"text":"ALSO","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=also"},"img":{"alt_text":"acyl-ester","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/03\/acyl-ester.gif?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":10184,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=10184","url_meta":{"origin":23562,"position":3},"title":"Intermediates in oxime formation from hydroxylamine and propanone: now you see them, now you don&#8217;t.","author":"Henry Rzepa","date":"April 14, 2013","format":false,"excerpt":"A recent theme here has been to subject to scrutiny well-known mechanisms supposedly involving intermediates. These transients can often involve the creation\/annihilation of charge separation resulting from \u00a0proton transfers, something that a cyclic mechanism can avoid. Here I revisit the formation of an oxime from hydroxylamine and propanone, but with\u2026","rel":"","context":"In &quot;Interesting chemistry&quot;","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"N-pre","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/04\/N-pre.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":15415,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=15415","url_meta":{"origin":23562,"position":4},"title":"I\u2019ve started so I\u2019ll finish. The ionisation mechanism and kinetic isotope effects for 1,3-dimethylindolin-2 one","author":"Henry Rzepa","date":"January 7, 2016","format":false,"excerpt":"This is the third and final study deriving from my Ph.D.. The first two topics dealt with the mechanism of heteroaromatic electrophilic attack using either a diazonium cation or a proton as electrophile, followed by either proton abstraction or carbon dioxide loss from the resulting Wheland intermediate. This final study\u2026","rel":"","context":"In &quot;Historical&quot;","block_context":{"text":"Historical","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=565"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":20464,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=20464","url_meta":{"origin":23562,"position":5},"title":"The Graham reaction: Deciding upon a reasonable mechanism and curly arrow representation.","author":"Henry Rzepa","date":"February 18, 2019","format":false,"excerpt":"Students learning organic chemistry are often asked in examinations and tutorials to devise the mechanisms (as represented by curly arrows) for the core corpus of important reactions, with the purpose of learning skills that allow them to go on to improvise mechanisms for new reactions. A common question asked by\u2026","rel":"","context":"In &quot;Curly arrows&quot;","block_context":{"text":"Curly arrows","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=2327"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"jetpack_likes_enabled":false,"authors":[{"term_id":2661,"user_id":1,"is_guest":0,"slug":"admin","display_name":"Henry Rzepa","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","0":null,"1":"","2":"","3":"","4":"","5":"","6":"","7":"","8":""}],"_links":{"self":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/23562","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=23562"}],"version-history":[{"count":14,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/23562\/revisions"}],"predecessor-version":[{"id":23586,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/23562\/revisions\/23586"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=23562"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=23562"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=23562"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=23562"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}