Alcohols and Ethers

<body> <p align="center"><font size="6"><strong>Alcohols and Ethers</strong></font></p> <div align="center"><center><table border="1" width="500"> <tr> <td align="center" width="100"><a href="#alcohols">Naming Alcohols</a></td> <td align="center" width="100"><a href="#test">Testing Blood Alcohol Levels</a></td> <td align="center" width="100"><a href="#hydro">Solubilities of Alcohols </a></td> <td align="center" width="100"><a href="#primary">Primary, Secondary, and Tertiary Alcohols</a></td> <td align="center" width="100"><a href="#phenols">Phenols</a></td> </tr> <tr> <td align="center" width="100"><a href="#boil">Boiling Points of Alcohols</a></td> <td align="center" width="100"><a href="#acid">Alcohols as Acids and Bases</a></td> <td align="center" width="100"><a href="#prepare">Preparation of Alcohols</a></td> <td align="center" width="100"><a href="#ethers">Ethers</a></td> <td align="center" width="100"><a href="#vs">Alcohols versus Ethers</a></td> </tr> </table> </center></div><p align="center"><a name="alcohols"><em><strong>Naming Alcohols</strong></em></a></p> <p><strong>Alcohols</strong> contain an<img src="graphics/em.gif" alt="--" width="22" height="9">OH group attached to a saturated carbon. The common names for alcohols are based on the name of the alkyl group.</p> <div align="center"><center><table border="0"> <tr> <td>CH<sub>3</sub>OH</td> <td> </td> <td> </td> <td><em>Methyl alcohol </em></td> </tr> <tr> <td>CH<sub>3</sub>CH<sub>2</sub>OH </td> <td> </td> <td> </td> <td><em>Ethyl alcohol</em> </td> </tr> <tr> <td>CH<sub>3</sub>CHOHCH<sub>3</sub></td> <td> </td> <td> </td> <td><em>Isopropyl alcohol</em> </td> </tr> </table> </center></div><p>The systematic nomenclature for alcohols adds the ending <em>-ol</em> to the name of the parent alkane and uses a number to identify the carbon that carries the <img src="graphics/em.gif" alt="--" width="22" height="9">OH group. The systematic name for isopropyl alcohol, for example, is 2-propanol. </p> <div align="center"><center><table border="0"> <tr> <td>CH<sub>3</sub>OH</td> <td> </td> <td> </td> <td><em>Methanol </em></td> </tr> <tr> <td>CH<sub>3</sub>CH<sub>2</sub>OH</td> <td> </td> <td> </td> <td><em>Ethanol</em> <a name="prob6"></a></td> </tr> <tr> <td>CH<sub>3</sub>CHOHCH<sub>3</sub> </td> <td> </td> <td> </td> <td><em>2-Propanol</em></td> </tr> </table> </center></div><p> </p> <div align="center"><center><table border="5" cellpadding="10" width="100%" bordercolor="#B87333"> <tr> <td><em><strong>Practice Problem 6:</strong></em><p>More than 50 organic compounds have been isolated from the oil that gives rise to the characteristic odor of a rose. One of the most abundant of these compounds is known by the common name <em>citronellol</em>. Use the systematic nomenclature to name this alcohol, which has the following structure. </p> <p align="center"><img src="graphics/21.gif" width="121" height="152"></p> <p align="left"><a href="prob6.html"><em><strong>Click here to check your answer to practice problem 6</strong></em></a></p> </td> </tr> </table> </center></div><p>Methanol, or methyl alcohol, is also known as <em>wood alcohol</em> because it was originally made by heating wood until a liquid distilled. Methanol is highly toxic, and many people have become blind or died from drinking it. Ethanol, or ethyl alcohol, is the alcohol associated with "alcoholic" beverages. It has been made for at least 6000 years by adding yeast to solutions that are rich in either sugars or starches. The yeast cells obtain energy from enzyme-catalyzed reactions that convert sugar or starch to ethanol and CO<sub>2</sub>. </p> <p align="center">C<sub>6</sub>H<sub>12</sub>O<sub>6</sub>(<em>aq</em>) <img src="graphics/arrowr.gif" alt="---->" width="68" height="12">2 CH<sub>3</sub>CH<sub>2</sub>OH(<em>aq</em>) + 2 CO<sub>2</sub>(<em>g</em>) </p> <p>When the alcohol reaches a concentration of 10 to 12% by volume, the yeast cells die. Brandy, rum, gin, and the various whiskeys that have a higher concentration of alcohol are prepared by distilling the alcohol produced by this fermentation reaction. Ethanol isn't as toxic as methanol, but it is still dangerous. Most people are intoxicated at blood alcohol levels of about 0.1 gram per 100 mL. An increase in the level of alcohol in the blood to between 0.4 and 0.6 g/100 mL can lead to coma or death. </p> <p align="center"><a href="#top"><img src="graphics/button.gif" alt="return to top" border="0" width="226" height="36"></a></p> <p align="center"><a name="test"><em><strong>Testing Blood Alcohol Levels</strong></em></a></p> <p>The method of choice for determining whether an individual is DUI<img src="graphics/em.gif" alt="--" width="22" height="9">driving under the influence<img src="graphics/em.gif" alt="--" width="22" height="9"> or DWI <img src="graphics/em.gif" alt="--" width="22" height="9">driving while intoxicated <img src="graphics/em.gif" alt="--" width="22" height="9"> is the Breathalyzer, for which a patent was issued to R. F. Borkenstein in 1958. The chemistry behind the Breathalyzer is based on the reaction between alcohol in the breath and the chromate or dichromate ion. </p> <p align="center">3 CH<sub>3</sub>CH<sub>2</sub>OH(<em>g</em>) + 2 Cr<sub>2</sub>O<sub>7</sub><sup>2-</sup>(<em>aq</em>) + 16 H<sup>+</sup>(<em>aq</em>) <img src="graphics/arrowr.gif" alt="---->" width="68" height="12">3 CH<sub>3</sub>CO<sub>2</sub>H(<em>aq</em>) + 4 Cr<sup>3+</sup>(<em>aq</em>) + 11 H<sub>2</sub>O(<em>l</em>)</p> <p>The instrument contains two ampules that hold small samples of potassium dichromate dissolved in sulfuric acid. One of these ampules is used a reference. The other is opened and the breath sample to be analyzed is added to this ampule. If alcohol is present in the breath, it reduces the yellow-orange Cr<sub>2</sub>O<sub>7</sub><sup>2-</sup> ion to the green Cr<sup>3+</sup> ion. The extent to which the color balance between the two ampules is disturbed is a direct measure of the amount of alcohol in the breath sample. Measurements of the alcohol on the breath are then converted into estimates of the concentration of the alcohol in the blood by assuming that 2100 mL of air exhaled from the lungs contains the same amount of alcohol as 1 mL of blood. </p> <p>Measurements taken with the Breathalyzer are reported in units of percent blood-alcohol concentration (BAC). In most states, a BAC of 0.10% is sufficient for a DUI or DWI conviction. (This corresponds to a blood-alcohol concentration of 0.10 grams of alcohol per 100 mL of blood.) </p> <p>Ethanol is oxidized to CO<sub>2</sub> and H<sub>2</sub>O by the alcohol dehydrogenase enzymes in the body. This reaction gives off 30 kilojoules per gram, which makes ethanol a better source of energy than carbohydrates (17 kJ/g), and almost as good a source of energy as fat (38 kJ/g). An ounce of 80-proof liquor can provide as much as 3% of the average daily caloric intake, and drinking alcohol can contribute to obesity. Many alcoholics are malnourished, however, because of the absence of vitamins in the calories they obtain from alcoholic beverages. </p> <p align="center"><a href="#top"><img src="graphics/button.gif" alt="return to top" border="0" width="226" height="36"></a></p> <p align="center"><a name="hydro"><em><strong>Solubilities of Alcohols</strong></em></a></p> <p>As a general rule, polar or ionic substances dissolve in polar solvents; nonpolar substances dissolve in nonpolar solvents. As a result, hydrocarbons don't dissolve in water. They are often said to be immiscible (literally, "not mixable") in water. Alcohols, as might be expected, have properties between the extremes of hydrocarbons and water. When the hydrocarbon chain is short, the alcohol is soluble in water. There is no limit on the amount of methanol (CH<sub>3</sub>OH) and ethanol (CH<sub>3</sub>CH<sub>2</sub>OH), for example, that can dissolve in a given quantity of water. As the hydrocarbon chain becomes longer, the alcohol becomes less soluble in water, as shown in the table below. One end of the alcohol molecules has so much nonpolar character it is said to be <strong>hydrophobic </strong>(literally, "water-hating"). The other end contains an -OH group that can form hydrogen bonds to neighboring water molecules and is therefore said to be <strong>hydrophilic</strong> (literally, "water-loving"). As the hydrocarbon chain becomes longer, the hydrophobic character of the molecule increases, and the solubility of the alcohol in water gradually decreases until it becomes essentially insoluble in water. </p> <p align="center"><em>Solubilities of Alcohols in Water </em></p> <div align="center"><center><table border="0"> <tr> <td><em>Formula </em></td> <td> </td> <td><em>Name</em></td> <td> </td> <td><em>Solubility in <br> Water (g/100 g)</em> </td> </tr> <tr> <td>CH<sub>3</sub>OH </td> <td> </td> <td>methanol</td> <td> </td> <td>infinitely soluble </td> </tr> <tr> <td>CH<sub>3</sub>CH<sub>2</sub>OH</td> <td> </td> <td>ethanol</td> <td> </td> <td>infinitely soluble </td> </tr> <tr> <td>CH<sub>3</sub>(CH<sub>2</sub>)<sub>2</sub>OH</td> <td> </td> <td>propanol</td> <td> </td> <td>infinitely soluble </td> </tr> <tr> <td>CH<sub>3</sub>(CH<sub>2</sub>)<sub>3</sub>OH</td> <td> </td> <td>butanol </td> <td> </td> <td>9 </td> </tr> <tr> <td>CH<sub>3</sub>(CH<sub>2</sub>)<sub>4</sub>OH </td> <td> </td> <td>pentanol </td> <td> </td> <td>2.7 </td> </tr> <tr> <td>CH<sub>3</sub>(CH<sub>2</sub>)<sub>5</sub>OH</td> <td> </td> <td>hexanol </td> <td> </td> <td>0.6</td> </tr> <tr> <td>CH<sub>3</sub>(CH<sub>2</sub>)<sub>6</sub>OH</td> <td> </td> <td>heptanol</td> <td> </td> <td>0.18 </td> </tr> <tr> <td>CH<sub>3</sub>(CH<sub>2</sub>)<sub>7</sub>OH</td> <td> </td> <td>octanol</td> <td> </td> <td>0.054 </td> </tr> <tr> <td>CH<sub>3</sub>(CH<sub>2</sub>)<sub>9</sub>OH</td> <td> </td> <td>decanol</td> <td> </td> <td>insoluble in water </td> </tr> </table> </center></div><p align="center"><a href="#top"><img src="graphics/button.gif" alt="return to top" border="0" width="226" height="36"></a></p> <p align="center"><a name="primary"><em><strong>Primary, Secondary, and Tertiary Alcohols</strong></em></a></p> <p>Alcohols are classified as either <em>primary</em> (1), <em>secondary</em> (2), or <em>tertiary</em> (3) on the basis of their structures. </p> <p align="center"><img src="graphics/22.gif" width="299" height="88"> </p> <p>Ethanol is a primary alcohol because there is only one alkyl group attached to the carbon that carries the <img src="graphics/em.gif" alt="--" width="22" height="9">OH substituent. The structure of a primary alcohol can be abbreviated as RCH<sub>2</sub>OH, where R stands for an alkyl group. The isopropyl alcohol found in rubbing alcohol is a secondary alcohol, which has two alkyl groups on the carbon atom with the <img src="graphics/em.gif" alt="--" width="22" height="9">OH substituent (R<sub>2</sub>CHOH). An example of a tertiary alcohol (R<sub>3</sub>COH) is <em>tert</em>-butyl (or <em>t</em>-butyl) alcohol or 2-methyl-2-propanol. </p> <p align="center"><a href="#top"><img src="graphics/button.gif" alt="return to top" border="0" width="226" height="36"></a></p> <p align="center"><a name="phenols"><em><strong>Phenols</strong></em></a></p> <p>Another class of alcohols are the <em>phenols</em>, in which an <img src="graphics/em.gif" alt="--" width="22" height="9">OH group is attached to an aromatic ring, as shown in the figure below. Phenols are potent disinfectants. When antiseptic techniques were first introduced in the 1860s by Joseph Lister, it was phenol (or carbolic acid, as it was then known) that was used. Phenol derivatives, such as <em>o</em>-phenylphenol, are still used in commercial disinfectants such as Lysol. </p> <p align="center"><img src="graphics/23.gif" alt="structure" width="298" height="113"> </p> <p align="center"><a href="#top"><img src="graphics/button.gif" alt="return to top" border="0" width="226" height="36"></a></p> <p align="center"><a name="boil"><em><strong>Boiling Points of Alcohols</strong></em></a></p> <p align="left">Water has an unusually high boiling point because of the hydrogen bonds between the H<sub>2</sub>O molecules. Alcohols can form similar hydrogen bonds, as shown in the figure below. </p> <p align="center"><img src="graphics/24.gif" alt="image" width="145" height="59"> </p> <p>As a result, alcohols have boiling points that are much higher than alkanes with similar molecular weights. The boiling point of ethanol, for example, is 78.5ºC, whereas propane, with about the same molecular weight, boils at -42.1ºC. </p> <p align="center"><a href="#top"><img src="graphics/button.gif" alt="return to top" border="0" width="226" height="36"></a></p> <p align="center"><a name="acid"><em><strong>Alcohols as Acids and Bases</strong></em></a></p> <p>Alcohols are Bronsted acids in aqueous solution. </p> <p align="center">CH<sub>3</sub>CH<sub>2</sub>OH(<em>aq</em>) + H<sub>2</sub>O(<em>l</em>) <img src="graphics/arrowr.gif" alt="----->" width="68" height="12">H<sub>3</sub>O<sup>+</sup>(<em>aq</em>) + CH<sub>3</sub>CH<sub>2</sub>O<sup>-</sup>(<em>aq</em>) </p> <p>Alcohols therefore react with sodium metal to produce sodium salts of the corresponding conjugate base.</p> <p align="center">2 Na(<em>s</em>) + 2 CH<sub>3</sub>OH(<em>l</em>) <img src="graphics/arrowr.gif" alt="----->" width="68" height="12">2 Na<sup>+</sup>(<em>alc</em>) + 2 CH<sub>3</sub>O<sup>-</sup>(<em>alc</em>) + H<sub>2</sub>(<em>g</em>) </p> <p>The conjugate base of an alcohol is known as an <strong>alkoxide</strong>. </p> <div align="center"><center><table border="0"> <tr> <td>[Na<sup>+</sup>][CH<sub>3</sub>O<sup>-</sup>]</td> <td> </td> <td> </td> <td>[Na<sup>+</sup>][CH<sub>3</sub>CH<sub>2</sub>O<sup>-</sup>] </td> </tr> <tr> <td>sodium methoxide </td> <td> </td> <td> </td> <td>sodium ethoxide</td> </tr> </table> </center></div><p align="center"><a href="#top"><img src="graphics/button.gif" alt="return to top" border="0" width="226" height="36"></a></p> <p align="center"><a name="prepare"><em><strong>Preparation of Alcohols</strong></em></a></p> <p>Alcohols can be prepared by adding water to an alkene in the presence of a strong acid such as concentrated sulfuric acid. This reaction involves adding an H<sub>2</sub>O molecule across a C=C double bond. Because these reactions follow <a href="1organic/reaction.html#mark">Markovnikov's rule</a>, the product of the reaction is often a highly substituted 2 or 3 alcohol. </p> <p align="center"><img src="graphics/25.gif" width="327" height="45"> </p> <p>Less substituted 1 alcohols can be prepared by substitution reactions that occur when a primary alkyl halide is allowed to react with the OH<sup>-</sup> ion. </p> <p align="center">CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>Br + OH<sup>-</sup> <img src="graphics/arrowr.gif" alt="----->" width="68" height="12"> CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>OH + Br <sup>-</sup> </p> <p align="center"><a href="#top"><img src="graphics/button.gif" alt="return to top" border="0" width="226" height="36"></a></p> <p align="center"><a name="ethers"><em><strong>Ethers</strong></em></a></p> <p>Alcohols (ROH) can be thought of as derivatives of water in which one of the hydrogen atoms has been replaced by an alkyl group. If both of the hydrogen atoms are replaced by alkyl groups, we get an <strong>ether</strong> (ROR). These compounds are named by adding the word <em>ether</em> to the names of the alkyl groups. </p> <div align="center"><center><table border="0"> <tr> <td>CH<sub>3</sub>CH<sub>2</sub>OCH<sub>2</sub>CH<sub>3</sub></td> <td> </td> <td> </td> <td> </td> <td><em>diethyl ether </em></td> </tr> </table> </center></div><p>Diethyl ether, often known by the generic name "ether," was once used extensively as an anesthetic. Because mixtures of diethyl ether and air explode in the presence of a spark, ether has been replaced by safer anesthetics. </p> <p align="center"><a href="#top"><img src="graphics/button.gif" alt="return to top" border="0" width="226" height="36"></a></p> <p align="center"><a name="vs"><em><strong>Alcohols versus Ethers</strong></em></a></p> <p>There are important differences between both the physical and chemical properties of alcohols and ethers. Consider diethyl ether and 1-butanol, for example, which are constitutional isomers with the formula C<sub>4</sub>H<sub>10</sub>O. </p> <div align="center"><center><table border="0"> <tr> <td>CH<sub>3</sub>CH<sub>2</sub>OCH<sub>2</sub>CH<sub>3</sub></td> <td> </td> <td> </td> <td> </td> <td>CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>OH </td> </tr> <tr> <td><em>BP</em> = 34.5ºC </td> <td> </td> <td> </td> <td> </td> <td><em>BP </em>= 117.2ºC </td> </tr> <tr> <td><em>d</em> = 0.7138 g/mL</td> <td> </td> <td> </td> <td> </td> <td><em>d</em> = 0.8098 g/mL </td> </tr> <tr> <td>insoluble in water </td> <td> </td> <td> </td> <td> </td> <td>soluble in water </td> </tr> </table> </center></div><p>The shapes of these molecules are remarkably similar, as shown in the figure below.</p> <p align="center"><img src="graphics/img39.gif" align="middle" width="344" height="33"> </p> <p>The fundamental difference between these compounds is the presence of <img src="graphics/em.gif" alt="--" width="22" height="9">OH groups in the alcohol that are missing in the ether. Because hydrogen bonds can't form between the molecules in the ether, the boiling point of this compound is more than 80ºC lower than the corresponding alcohol. Because there are no hydrogen bonds to organize the structure of the liquid, the ether is significantly less dense than the corresponding alcohol. </p> <p>Ethers can act as a hydrogen-bond acceptor, as shown in the figure below. But, they can't act as hydrogen-bond donors. As a result, ethers are less likely to be soluble in water than the alcohol with the same molecular weight. </p> <p align="center"><img src="graphics/img40.gif" align="middle" width="141" height="75"> </p> <p>The absence of an <img src="graphics/em.gif" alt="--" width="22" height="9">OH group in an ether also has important consequences for its chemical properties. Unlike alcohols, ethers are essentially inert to chemical reactions. They don't react with most oxidizing or reducing agents, and they are stable to most acids and bases, except at high temperatures. They are therefore frequently used as solvents for chemical reactions. </p> <p><a name="protic"></a>Compounds that are potential sources of an H<sup>+</sup> ion, or proton, are often described as being <strong>protic. </strong>Ethanol, for example, is a <em>protic</em> solvent. </p> <p align="center">CH<sub>3</sub>CH<sub>2</sub>OH(<em>aq</em>) + H<sub>2</sub>O(<em>l</em>) <img src="graphics/arrowr.gif" alt="----->" width="68" height="12">H<sub>3</sub>O<sup>+</sup>(<em>aq</em>) + CH<sub>3</sub>CH<sub>2</sub>O<sup>-</sup>(<em>aq</em>) </p> <p>Substances that can't act as a source of a proton are said to be <strong>aprotic</strong>. Because they don't contain an <img src="graphics/em.gif" alt="--" width="22" height="9">OH group, ethers are <em>aprotic</em> solvents. </p> <p>Ethers can be synthesized by splitting out a molecule of water between two alcohols in the presence of heat and concentrated sulfuric acid. </p> <div align="center"><center><table border="0"> <tr> <td> </td> <td> </td> <td align="center"><font size="2">H<sup>+</sup></font> </td> <td> </td> <td> </td> </tr> <tr> <td> </td> <td>2 CH<sub>3</sub>CH<sub>2</sub>OH </td> <td><img src="graphics/arrowr.gif" alt="----->" width="68" height="12"></td> <td>CH<sub>3</sub>CH<sub>2</sub>OCH<sub>2</sub>CH<sub>3</sub></td> <td> </td> </tr> </table> </center></div><p>They can also be formed by reacting a primary alkyl halide with an alkoxide ion. </p> <p align="center">CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>Br + CH<sub>3</sub>O<sup>-</sup> <img src="graphics/arrowr.gif" alt="----->" width="68" height="12">CH<sub>3</sub>CH<sub>2</sub>CH<sub>2</sub>OCH<sub>3</sub> + Br<sup>-</sup> </p> <p align="center"><a href="#top"><img src="graphics/button.gif" alt="return to top" border="0" width="226" height="36"></a></p> <hr> <p><img src="http://chemed.chem.purdue.edu/Count.cgi?df=toprev_org2_alcohols.dat"></p> </body>