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t76 Alcohols,and Ethers t2 Halocarbons, CHAPTER form the strong bases called hydroxides, reactiue metals react uigorously with alcohols to form strongbasescalledakoxtdes: 2H-OH+ 2Na - + 2Na+ + H2 2H-OHydroxide + 2Na .----- 2R-O- 2R-OH + 2Na+ + H2 Alkoxide Becauseof their weak acidic character, aqueous solutions of alcohols are essentiallyneutral. Phenols are much stronger acids than alcohols, but they are still veryweak acids. Phenols produce slightly acidic solutions. I2.8 EXERCISE PRACTICE for the reaction of sodium with each of the following: Write the equation (b) phenol. (a) methanol 12.7Ethers AIMS: Tonome ond draw stracturesof ethers.To illustratethe synthesisof on etherfrom a holocorbonond on olkoxide ion. Focus Ethers are disubstituted derivatives of water. Ethers are cornpoundsin which both hydrogensof water are replacedby car' The R bon chains or rings. The general formula for ethers is R-O-R. stands for any alkyl or aryl group. 6 HH Watermolecule o RR Ethermolecule The alkyl or aryl groups joined by the ether linkage are named in alphabetical order and are followed by the word,ether For example: .r.-o<o cH3cH2-o-cH3 Ethylmethyl ether Methylphenyl ether Ethylmethyl ether and methylphenyl ether are asymmetrical ethers becausethe R groups attached to the oxygen are different.When both R groups are the sarne,the ether is symmetrical. Syrnmetrical ethers are named by using the prefix di-.For example: cH3cH2-o-cH2cH3 O"O Diethyl ether Diphenyl ether (phenyl ether) I2.7 Ethers ,77 Many modern anestheticscontain halogen and ether functional groups,as describedinA CloserLook Halocarbonand EtherAnesthetics. Halocarbon and EtherAnesthetics Enflurane is a stable liquid that is somewhat less volatile than halothane. Enflurane provides rapid anesthesia and rapid recovery for the patient. Although enflurane is broken down in the liver to produce fluoride ions, elevatedfluoride levels in the blood are not considereda problem. Isoflurane has physical, pharmacologic, and clinical properties that are similar to those of halothane and enflurane. This anesthetic is a more potent muscle relaxant than halothane, and induction of anesthesiais relativelyrapid. General anesthesiais usually induced with the administration of an intravenous anesthetic, regardless of the inhalant anesthetic subsequently used for anesthesiamaintenance. The most commonly used induction agentis the barbiturate thiopental, also known as Pentothal (see Sec. 15.10).In many instances,low concentrations of halothane, enflurane, or isoflurane are used in conjunction with nitrous oxide (N2O). Anesthetics have alleviated a great deal of pain and suffering during surgery.Zo cal anesthetics make one part of the body insensitive to pain but leave the patient conscious. Generalanesthetics act on the brain to produce unconsciousnessand insensitivity to pain. Many general anesthetics are halocarbons or ethers or contain both kinds of functional groups in their molecular structures. Diethyl ether (CzH5-O-C2H5), the first general anesthetic, was introduced into surgery in 1846byWilliam Morton, a Boston dentist (see figure). InIB47, chloroform (CHCI3)was introduced as a general anesthetic.Both diethyl ether and chloroform can cause undesirable side effects. Today, neither compound is used as an anestheticin the WesternHemisphere. lVhy are compounds such as diethyl ether and chloroform generalanesthetics?The potency of an anestheticis related to its solubility in fatty tissue. One theory for the action of generalanesthetics is that they dissolve in the fatlike membranes of nerve cells of the brain (neurons).This changes the properties of the membranes. As a consequence, the activity of the neurons is depressed,leading to anesthesia. The fat-solubility theory carries over into modern anesthetics.Today'sanestheticsinclude relatively nonpolar fluorine-containing organic compounds such as halothane (Fluothane, CF3CHBTCI). Enflurane (Ethrane, Efrane, CHFCICF2-O-CHF2) and isoflurane (Forane, CF3CHCI-O-CHF2) are also used. All these compounds are inhalant anesthetics.Thesecompounds are nonflammable and relativelysafe, and the patient recoversrapidly from their effects. Halothane is nonexplosive.The start of anesthesia is rapid, but slower than for anesthetics of greater solubility in membranes such as enflurane Thefirstuseof etheras an anestheticin 1846is depictedin this painting. and isoflurane. t78 Alcohols, and Ethers l2 Halocarbons, CHAPTER Just as alcohols can be prepared by using hydroxide ions to displace halogenfrom a halocarbon,etherscan be preparedby using alkoxideions' For example: CH. ------ CH3CH2-O-CH3 + CH3CH2O EthVlmethVl Sodium ethoxide Iodomethane + i:it;;;r The ether linkage is often found in rings. Rings that contain elements other than carbon are called heterocyclic rings or heterocycles.Here are some common oxygen-containing heterocycles: na \o/ Furan \n/ P1'ran Tetrahydrofuran \o/ Tetrahydropyran The fundamental ring structures of furan and pgan are found in many natural sugars.Compounds containing an oxygenatom in a three-membered ring are called epoxides.Epoxyethaneis the simplest example. Ho \616/ ,/\ H H H Epoxyethane (ethylene oxide) Other epoxidesare used to make cements and adhesives.Withthe exception of the epoxides,the ether linkage is very resistantto chemical modification. Sincethey arethree-memberedrings,epoxiderings arehighly strained. Therefore,epoxidesare much more reactive than other ethers' For example, ro rHECnsrlx Potnr:A mistakenconviction Folr.ow-up You may recall from the Case in Point that a mother was accused in 1989 of murdering her oldest son by ethylene glycol poisoning. She was convlcted and sentenced to life in prison. The case might have ended there, except for a quirk of fate and the efforts of Dr. William S1yand Dr, James Shoemaker of the St. Louis University School of Medicine. The quirk of fate was that while the accused mother was in custody ln 1990, she gave birth to a second son, who soon began to exhibit the same symptoms as his late older brother. It was impossible that she had polsoned her youngest son. The St. Louis University scientlsts, who had foilowed the case on television, rec- ognized that a rare inherited disease, methylmalonic acidemia, has symptoms very similar to those of ethylene glycol poisoning. Contrary to findings reported in.previous blood tests, new tests undertaken by Dr. Shoemaker revealed no evidence of ethylene glycol in the blood of either child. Dr. Piero Rinaldo of the Yale University School of Medicine verifled from blood samples that bolh sons had been born with methylmalonic acidemia. In September 1991, the mother's conviction was reversed and all charges were dismissed. Thanks to science and caring scientists, she has resumed her Lifewith her husband and -^-^i-i-- rurrt4[lttrv ^^n JUrl. 12.8Physical Properties ,79 the epoxide ring of epoxyethaneis easily opened. In aqueous solution containing a trace of strong acid, the product is ethylene glycol: A ," "..c_c Hl t" OH + Ll-(lH + HCI ll OH H-C-C_H tt HH Although very useful as antifreeze,ethylene glycol is toxic and can be fatal if ingested, a fact that led to the accusation of murder described in the Casein Point early in this chapter. 12.8Physicolproperties AIM: To relate differencesin boiling point ond solubility to the molecular structuresof hydrocarbons,holocorbons, alcohols,and ethers. The physical properties of organic molecules depend on their molecular structure. Thus far we have seen the aliphatic and aromatic hydrocarbons,halocarbons, alcohols, and ethers. Except for an occasional comment, not much has been said about their physical properties. This is not an oversight. Discussion of the physical properties of all four classesof compounds at one time will help us understand why the properties are what they are. Boillngpoints Hydrocarbons and halocarbons of low molar mass tend to be gasesor lowboiling liquids. Hydrocarbon molecules such as the alkanes are nonpolar. The electron pair in a carbon-hydrogenor carbon-carbon bond is about equally shared by the nuclei of the elements involved. The carbon-halogen bond is only slightly polar. You,may recall from Section 8.1 that attractions between molecules, because of hydrogen bonding, require that the molecules contain hydrogen attached to very electronegativeatoms such as oxygen.There is no hydrogen bonding in hydrocarbons and halocarbons. Consequently, the forces that hold hydrocarbon or halocarbon molecules together in the liquid state are very weak. Table 11.1 shows that all alkanes containing fewer than five carbons are gasesat room temperature. Boiling points of closely related organic compounds usually increaseas molar mass increases.The data in Table 12.4show this principle. Remember that a pure liquid boils when enough heat energy has been supplied to let molecules in the liquid escape.The sum of weak forces holding heary nonpolar molecules together in a liquid is greater than the sum of weak forces holding light nonpolar molecules together. Like water, alcohols are capable of intermolecular hydrogen bonding. Alcohols therefore boil at higher temperaturcs than alkanes and halocarbons containing comparablenumbers of atoms (Table12.5). Ethers usually have lower boiling points than alcohols of comparable molar mass, but they have higher boiling points than comparable hydrocarbons and halocarbons. 580 l2 Halocarbons, Alcohols,and Ethers CHAPTER Compared Table12.4MolarMassesand BoilingPointsof the Chloromethanes with Thoseof Methane Molecular structure Molar mass(g) Name methane chloromethane (methyl chloride) dichloromethane (methylene chloride) trichloromethane (chloroform) tetrachloromethane (carbon tetrachloride) CHn cH3cl cH2cl2 cHC13 CCL 16 50.5 Boiling point("C) - 161 -24 85.0 40 129.5 61 154.0 74 Alkyl andAryl Chlorides TableI2.5 BoilingPointsof Alcoholsand €omparable Boiling point("C) Alcohol CH3OH CH3CH2OH CH3CH2CH2OH o"" o"" Solubility Hydrophobic hudor(Greek): water phobos(Greek): fear 65 7B 97 t62 t82 Alkylchloride CH3CI CH3CH2CI CH3CH2CH2CI O" G" Boiling point("C) -64 13 47 143 t32 in water The hydrocarbon parts of chains and rings of organic molecules are hydrophobic ("water-hating")-repelled by water Oil and water dont mix. If we mix two nonpolar liquids, however, they form a solution. A good rule of thumb is that "like dissolveslike." With the principle that "like dissolves like" in mind, how would we expect alcohols to behave with respect to their solubilities in water? Since alcohols are derivatives of water, we might expect them to have similar properties. And to a point, this is correct. Alcohols of up to four carbons are soluble in water in all proportions. The solubility of alcohols with four or more carbons in the chain is usually much less.For example, the solubility of l-butanol is only 7.9 gll00 mL of water.The reasonis that alcoholsconsist of two parts: the carbon chain and the hydroxyl group. These parts are in opposition to each other. The carbon chain is nonpolar and hydrophobic, but the hydroxyl group forms hydrogen bonds with water. Groupssuch 12.9SulfurCompounds I8l Hydrophilic hudor (Greek): water philos (Greek): loving as -OH that interact strongly with water, usually W hydrogen bonding, are called hydrophilic ("water-Iouing") gtoups. Alcohols with short carbon chains are soluble in water. Those with longer carbon chains will not dissolve. And some alcohols whose carbon chains are not too long are only slightly soluble. Ethers are more soluble in water than hydrocarbons and halocarbons but less soluble than alcohols of approximately the same molar mass.The reason is that the oxygens in ethers are hydrogen-bond acceptors, but ethers have no hydroxyl hydrogens to donate in hydrogen bonding. This lower solubility compared with alcohols is overcome in molecules with more than one ether linkage. Dioxane, a cyclic compound with two ether linkages, is soluble in water in all proportions; diethyl ether, with the same number of carbons but only one ether linkage, is not. O: :O CH3CH2.-O-CH2CH3 Dioxane (soluble in water in all proportions) Diethyl ether (solubility in water: B 9/100 mL) PRACTICE EXERCISE I2.9 Name and classitrbyfunctional groups the following compounds, and identi{i the one that is most polar. (a) CHsOCHg (c) CH3CHTOH &) CH3CHzCI (d) cH3cH2cH3 PRACTICE EXERCISE I2.I O Arrange the compounds in Practice Exercise12.9in order of increasing polarity then comment on their relative boiling points and water solubilities. 12.9Sulfurcompounds AIM: Toidentify nome, structures, ond usesof somecommon thiols, thioethers,ond disulfides. Just as alcohols and ethers are organic derivatives of water, thioalcohols and thioethers are organic derivatives of hydrogen sulfide, H2S. Thiols and thioethers are sulfur analogues of alcohols and ethers. Thioalcohols and thioethers Thioalcohols, compounds wi,th the general formula R-S-fi, are also calledthiols. Thiols are also calledtnercaptans-a name coined becauseof their readyability to "captttrre"or react with the element mercury.The odor of 582 Alcoholt and Ethers CHAPTER l2 Halocarbons, the fluid that skunks eject to protect themselvesfrom predators comes partiallv from two thiols. H"c '\ Thiol theian {Greek): sulfur The odor frorn a skunk can be removedfrom a contaminated object by treatment with a solution of the follollring composition: 1 quart 3YoIJ2A2,I /4 cup baking soda,and I teaspconliquid soap. After treatment, the object should be rinsed with tap water. H C:C. ,/\ ,/ H 9H. | CH3-CHCH2CHz-SH CH2-SH 3-Methyl- I -butanethiol rrans-2-Butenethiol Sulfur compounds are well knornm among chemists as the most foul smelling of all organic compounds. Sometimes,however, even an odor can be put to good use. Natural gasis odorless,but the gas piped to a gasrange has a characteristic smell. The gas company has added a trace of methanethiol or ethanethiol to the natural gas so that leaks can be detected. cH3-sH cH3cH2-sH Methanethiol fmethyl mercaptan) Ethanethiol (ethyl mercaptan) In very low concentrations,the odors of some thiols and sulfides are even desirablein cooking. The pungent smell of onions comes from propanethiol. CH3CH2CH2-SH Propanethiol (propyl mercaptan) Thioethers, compounds with the generalformula R-S-R, are also called sulfides.The characteristic aroma and flavor of garlic comes from divinyl sulfide. \,/\./ C : C ---,,/ H-S-H -..- C:C Divinyl sulfide Disulfrdes Sulfur atoms can form relatively stable bonds with other sulfur atoms. The sulfur-sulfur bond is not as stable as the carbon-carbon bond, and sulfur does not form long chains. But disulfides, organic compounds of the general are found in many proteins, especially structural formula R-S-S-R, those of hair, hooves,and nails (seeSec. 18.6).A third compound in the defensefluid of skunks is a disulfide: Htc\ C:C Hl ./H ta"r-r-r-cHs 12.10 Polyfunctional Compounds 585 Disulfides are prepared by the mild oxidation of thiols. Thiols permitted to stand in air spontaneously oxidize to disulfides: 2CH3S-H i.' Methanethiol Crt S-SCH. Methyl disr'lfids Once formed, disulfides can be further oxidized to sulfonic acids bv hydrogen peroxide: CH3S-SCH3 Methyl disulfide Hz{)2, 2C1I3SO3H Methyl sulfonic acid Disulfides are easily reduced to thiols. Although many reducing agents are suitable, hydrogen works well: CH3S-SCI{3 -En' ZCU.-SH Methyl disulflde Methanethiol I2.l 0 Polyfunctionolcompounds AIM: Torecognizethe functionolgroups of a given polyfunctionol molecule. Focus Many organic molecules contain more than one functional group. exA fig'i ';=-':'':;' So far our introduciion to functionatgroup chemistry has been focused on molecules with only one kind of functional group. Polyfunctional organic compounds contain two or more functional groups. Tetrahydrocannabinol is an example of a polyfunctional molecule, as shor,rrnin the following example. idtiigi4t+,Ett*i,t,":'';,:';,:;'t:,', : : ' , , ' , ' ; ; ; , , , " " , , ' ,""',,'', " , , , " 1 1 - IdentiSrthe functionalgroupsin the tetrahydrocannabinol molecule. c}{2cH2cH2cH2cH3 CH. Tetrahydrocannabinol SOLUTION Inspect the molecule to find the functional groups, such as multiple carbon-carbon bonds, hydroxyl groups, ether linkages, and so forth. The ta4 Alcohols,and Ethers l2 Halocarbons, CHAPTER tetrahydrocannabinol molecule contains three functional groups: a cyclic ether linkage, a phenolic hydroxyl group, and a carbon-carbon double bond. These functional groups are in color in the following structure. CH2CH2CH2CHzCH3 CHe Tetrahydrocannabinol is the active ingredient of the Cannabis satiua (marijuana) plant. The effects of marijuana use on health and society are still being debated. One interesting finding is that smoking marijuana reduces the pressure of the optic fluid and may therefore be helpful in relieving the symptoms of glaucoma, a serious eye disease. Another polyfunctional compound is hexachlorophene, which is both an aromatic halocarbon and aphenol: HO CI \--J ."r\ /-\ / cr,Tct CI Hexachlorophene Hexachlorophene is an antiseptic. Until recently, it was an important ingredient in germicides and soaps used in hospitals. Its use was curbed, however,when it was found that the babies of female hospital workers who frequently washed their hands with hexachlorophene soap had a higher incidence of birth defects than babies born to women in the general population. I2.I I PRACTICE EXERCISE The structure that follows is a urushiol, a family of compounds that are the irritants in poison ivy. It is a polyfunctional compound with the following structure. How many funciional groups can you identify? HO OH (CHz)zCH:CHzCH : CH(CH2) CH3