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Superbase
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<h2 id="definitions">Definitions</h2> <p>Generically <a href="/facts/International_Union_of_Pure_and_Applied_Chemistry/2AV6myCK">IUPAC</a> defines a superbase as a "compound having a very high <a href="/facts/Base_(chemistry)/M9wA7qeM">basicity</a>, such as <a href="/facts/Lithium_diisopropylamide/5rcW8ERX">lithium diisopropylamide</a>."<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> Superbases are often defined in two broad categories, <a href="/facts/Organic_chemistry/djxhxaNg">organic</a> and <a href="/facts/Organometallic_chemistry/bhqFz2P0">organometallic</a>. </p><p>Organic superbases are charge-neutral compounds with basicities greater than that of <a href="/facts/Proton_sponge/Mkyd00uB">proton sponge</a> (pKBH+ = 18.6 in MeCN)."<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> In a related definition: any species with a higher absolute <a href="/facts/Proton_affinity/ypQdxqNR">proton affinity</a> (APA = 245.3 kcal/mol) and intrinsic gas phase basicity (GB = 239 kcal/mol) than proton sponge.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> Common superbases of this variety feature <a href="/facts/Amidine/dhB1LGfz">amidine</a>, <a href="/facts/Guanidine/lGzDoPuJ">guanidine</a>, and <a href="/facts/Phosphazene/IR0jFetb">phosphazene</a> functional groups. Strong superbases can be designed by utilizing various approaches<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a><a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a><a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> to stabilize the conjugate acid, up to the theoretical limits of basicity.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p><p>Organometallic superbases, sometimes called Lochmann–Schlosser superbases, result from the combination of <a href="/facts/Alkali_metal/IkWbCLk2">alkali metal</a> <a href="/facts/Alkoxide/RqG0rm1v">alkoxides</a> and <a href="/facts/Organolithium_reagent/xgYnjhP3">organolithium</a> reagents.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> Caubère defines superbases as "bases resulting from a mixing of two (or more) bases leading to new basic species possessing inherent new properties. The term <i>superbase</i> does not mean a base is thermodynamically and/or kinetically stronger than another, instead it means that a basic reagent is created by combining the characteristics of several different bases."<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> </p> <h3>Organic superbases</h3> <p>Organic superbases are mostly charge-neutral, <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a> containing species, where nitrogen act as a proton acceptor. These include the phosphazenes, <a href="/facts/Organophosphine/kNgIF93U">phosphanes</a>, amidines, and guanidines. Other organic compounds that meet the physicochemical or structural definitions of 'superbase' include proton <a href="/facts/Chelation/4G79sXBB">chelators</a> like the aromatic proton sponges and the <a href="/facts/Bispidine/yAQpuR4R">bispidines</a>.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a><a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> <a href="/facts/Polycyclic_compound/9mq2JNFq">Multicyclic</a> <a href="/facts/Polyamine/VntSgncL">polyamines</a>, like <a href="/facts/DABCO/wxkhFvru">DABCO</a> might also be loosely included in this category.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> <a href="/facts/Phosphine/aYysn5TS">Phosphanes</a> and carbodiphosphoranes are also strong organosuperbases<i>.<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a><a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a><a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a><a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a></i> </p><p>Despite enormous proton affinity, many organosuperbases can exhibit low <a href="/facts/Nucleophile/xYccoaJQ">nucleophilicity</a>. </p><p>Superbases are used in <a href="/facts/Organocatalysis/oR5c1RDJ">organocatalysis</a>.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a><a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> </p> <h3>Organometallic</h3> <p>Organometallic compounds of <a href="/facts/Electropositive/H7Vq7Uah">electropositive</a> metals are superbases, but they are generally strong nucleophiles. Examples include <a href="/facts/Organolithium/xgYnjhP3">organolithium</a> and organomagnesium (<a href="/facts/Grignard_reagent/0vkLtPo1">Grignard reagent</a>) compounds. Another type of organometallic superbase has a reactive metal exchanged for a hydrogen on a <a href="/facts/Heteroatom/QzxXyfCT">heteroatom</a>, such as <a href="/facts/Oxygen/acyn6o8r">oxygen</a> (unstabilized <a href="/facts/Alkoxide/RqG0rm1v">alkoxides</a>) or nitrogen (metal <a href="/facts/Azanide/5rnJAKEp">amides</a> such as <a href="/facts/Lithium_diisopropylamide/5rcW8ERX">lithium diisopropylamide</a>).<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> </p><p>The <a href="/facts/Schlosser_base/fmxh41PL">Schlosser base</a> (or Lochmann-Schlosser base), the combination of <a href="/facts/N-butyllithium/v4Rz4Dc1"><i>n</i>-butyllithium</a> and <a href="/facts/Potassium_tert-butoxide/oywBqEER">potassium <i>tert</i>-butoxide</a>, is commonly cited as a superbase. <i>n</i>-Butyllithium and potassium <i>tert</i>-butoxide form a mixed aggregate of greater reactivity than either component reagent.<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a> </p> <h3>Inorganic</h3> <p>Inorganic superbases are typically <a href="/facts/Salt_(chemistry)/lsSKwGpn">salt</a>-like compounds with small, highly charged anions, e.g. <a href="/facts/Lithium_hydride/uWCl2pST">lithium hydride</a>, <a href="/facts/Potassium_hydride/NEp3Vbd7">potassium hydride</a>, and <a href="/facts/Sodium_hydride/Pnsh2T64">sodium hydride</a>. Such species are insoluble, but the surfaces of these materials are highly reactive and <a href="/facts/Slurries/erSTjthc">slurries</a> are useful in synthesis. <a href="/facts/Caesium_monoxide/uBCmopGC">Caesium oxide</a> is probably the strongest base according to quantum-chemical calculations.<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Superacid/dg82EcNa">Superacid</a></li> <li><a href="/facts/Phosphazene/IR0jFetb">Phosphazene</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Puleo, Thomas R.; Sujansky, Stephen J.; Wright, Shawn E.; Bandar, Jeffrey S. (2021). "Organic Superbases in Recent Synthetic Methodology Research". Chemistry – A European Journal. 27 (13): 4216–4229. doi:10.1002/chem.202003580. PMID 32841442. S2CID 221326865. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Pozharskii, Alexander F.; Ozeryanskii, Valery A. (2012). "Proton Sponges and Hydrogen Transfer Phenomena". Mendeleev Communications. 22 (3): 117–124. doi:10.1016/j.mencom.2012.05.001. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"BBC - h2g2 - History of Chemistry - Acids and Bases". Retrieved 2009-08-30. <a href="https://www.bbc.co.uk/dna/h2g2/alabaster/A708257" target="_blank">https://www.bbc.co.uk/dna/h2g2/alabaster/A708257</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Superbases for Organic Synthesis Ed. Ishikawa, T., John Wiley and Sons, Ltd.: West Sussex, UK. 2009. <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "superacid". doi:10.1351/goldbook.S06135 <a href="/wiki/International_Union_of_Pure_and_Applied_Chemistry" target="_blank">/wiki/International_Union_of_Pure_and_Applied_Chemistry</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Puleo, Thomas R.; Sujansky, Stephen J.; Wright, Shawn E.; Bandar, Jeffrey S. (2021). "Organic Superbases in Recent Synthetic Methodology Research". Chemistry – A European Journal. 27 (13): 4216–4229. doi:10.1002/chem.202003580. PMID 32841442. 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