Anhydrous

<h2 id="solids">Solids</h2>
<p>Many salts and solids can be dried using heat, or under vacuum. <a href="/facts/Desiccator/7IEu9GnF">Desiccators</a> can also be used to store reagents in dry conditions.
</p><p>Common <a href="/facts/Desiccant/wD2YIcPc">desiccants</a> include <a href="/facts/Phosphorus_pentoxide/GKTSUNqS">phosphorus pentoxide</a> and <a href="/facts/Silica_gel/qrNxnft5">silica gel</a>. Chemists may also require dry glassware for sensitive reactions. This can be achieved by drying glassware in an oven, by flame, or under vacuum.
</p><p>Dry solids can be produced by <a href="/facts/Freeze-drying/aURqwbrQ">freeze-drying</a>, which is also known as lyophilization.
</p>
<h2 id="liquids-or-solvents">Liquids or solvents</h2>
<p>In many cases, the presence of water can prevent a reaction from happening, or cause undesirable products to form. To prevent this, anhydrous solvents must be used when performing certain reactions. Examples of reactions requiring the use of anhydrous solvents are the <a href="/facts/Grignard_reaction/DfhXQ6SG">Grignard reaction</a> and the <a href="/facts/Wurtz_reaction/teXQemUj">Wurtz reaction</a>.
</p><p>Solvents have typically been dried using distillation or by reaction with reactive metals or <a href="/facts/Metal_hydride/v2rlBGMg">metal hydrides</a>. These methods can be dangerous and are a common cause of lab fires. More modern techniques include the use of <a href="/facts/Molecular_sieve/Lzle8J7k">molecular sieves</a> or a column purification system. Molecular sieves are far more effective than most common methods for drying solvents and are safer and require no special equipment for handling.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> Column solvent purification devices (generally referred to as Grubb's columns) recently became available, reducing the hazards (water reactive substances, heat) from the classical dehydrating methods.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a><a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p><p>Anhydrous solvents are commercially available from chemical suppliers, and are packaged in sealed containers to maintain dryness.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> Typically anhydrous solvents will contain approximately 10 ppm of water and will increase in wetness if they are not properly stored.
</p><p>Organic solutions can be dried using a range of <a href="/facts/Desiccant/wD2YIcPc">drying agents</a>. Typically following a workup the organic extract is dried using <a href="/facts/Magnesium_sulfate/o3GwKEoQ">magnesium sulfate</a> or a similar drying agent to remove most remaining water.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a>
</p><p>Anhydrous acetic acid is known as <a href="/facts/Glacial_acetic_acid/uyBKA2Pd">glacial acetic acid</a>.
</p>
<h2 id="gases">Gases</h2>
<p>Several substances that exist as gases at <a href="/facts/Standard_conditions_of_temperature_and_pressure/JhJv9KFJ">standard conditions of temperature and pressure</a> are commonly used as concentrated <a href="/facts/Aqueous_solution/eRNr3MH2">aqueous solutions</a>. To clarify that it is the gaseous form that is being referred to, the term <i>anhydrous</i> is prefixed to the name of the substance:
</p>
<ul><li>Gaseous <a href="/facts/Ammonia/MtLtJFtz">ammonia</a> is generally referred to as <i>anhydrous</i> ammonia, to distinguish it from its solution in water, household <a href="/facts/Ammonia_solution/pRg1m03X">ammonia solution</a>, also known as ammonium hydroxide.</li>
<li>Gaseous <a href="/facts/Hydrogen_chloride/7Wzkhomd">hydrogen chloride</a> is generally referred to as <i>anhydrous</i>, to distinguish it from its solution in water, <a href="/facts/Hydrochloric_acid/HqItJlUT">hydrochloric acid</a>.</li></ul>
<p>Reactions which produce water can be kept dry using a <a href="/facts/Dean%25E2%2580%2593Stark_apparatus/cARLn6f4">Dean–Stark apparatus</a>.
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Air-free_technique/pEW9wY6e">Air-free technique</a> – laboratory technique for handling chemicals while excluding airPages displaying wikidata descriptions as a fallback</li>
<li><a href="/facts/Acidic_oxide/2h1jor4I">Acidic oxide</a> – Type of oxide, a.k.a. acid anhydride</li>
<li><a href="/facts/Base_anhydride/NpRH4jCx">Base anhydride</a> – Oxide of a chemical element from alkali- or alkaline earth metals</li>
<li><a href="/facts/Hydrate/dev82l69">Hydrate</a> – Substance containing water or its constituent elements</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Williams, D. Bradley G.; Lawton, Michelle (2010-12-17). "Drying of Organic Solvents: Quantitative Evaluation of the Efficiency of Several Desiccants". The Journal of Organic Chemistry. 75 (24): 8351–8354. doi:10.1021/jo101589h. ISSN 0022-3263. PMID 20945830. <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>"Guidelines for solvent purification at UC Davis". Archived from the original on September 4, 2006. <a href="https://web.archive.org/web/20060904103225/http://fire.ucdavis.edu/main/ucdfdinfobull22.htm" target="_blank">https://web.archive.org/web/20060904103225/http://fire.ucdavis.edu/main/ucdfdinfobull22.htm</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>"Drying Solvents". <a href="https://chem.libretexts.org/Ancillary_Materials/Demos%2C_Techniques%2C_and_Experiments/General_Lab_Techniques/Drying_Solvents" target="_blank">https://chem.libretexts.org/Ancillary_Materials/Demos%2C_Techniques%2C_and_Experiments/General_Lab_Techniques/Drying_Solvents</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>"New Aldrich Sure/Seal® packaging for Anhydrous Solvents and Air-Sensitive Reagents". Sigma-Aldrich. Retrieved 2018-03-26. <a href="https://www.sigmaaldrich.com/chemistry/solvents/sureseal.html" target="_blank">https://www.sigmaaldrich.com/chemistry/solvents/sureseal.html</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>"Drying agents". www.chem.ucla.edu. Retrieved 2018-03-26. <a href="http://www.chem.ucla.edu/~bacher/Specialtopics/Drying%20Agents.html" target="_blank">http://www.chem.ucla.edu/~bacher/Specialtopics/Drying%20Agents.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
</ol>

Anhydrous open-in-new

Anhydrous