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12.3 Alcohols ,67 rigid, like plastic milk containers. Polypropylene is prepared by polymerization of propene. CH" f"' t- -+ ICH:CH, +CH-CH|+* Propene {propylene) Pollpropylene Polypropylene makes a stiffer polymer than polyethylene, and it is used extensivelyin utensils and containers. Polystyreneis preparedby the po\rmerization of styrene (vinyl benzene): <-\ ttl >.' rCH2:CH * Styrene (vinyl benzene) Figure12.5 polymersplayan imporSynthetic tantrolein ourdailylives. -FCHz-CH+" Polysty'rene Polystyreneis a poor heat conductor when produced as a foam. It is used to insulate homes and in the manufacture of molded items such as coffee cups and coolers. Polyisopreneis the polyrner that constitutes natural rubber. It is used in the manufacture of boots, tires, and rubber tubing. The polyisoprene molecule contains cls double bonds: +c{, ,rCHr:6611:CH2 I CHs ------- C:C H"c/ Isoprene /,cH2+" tu, Polyisoprene Figure 12.3shows a small selection of the wide variety of articles made from polyrners. 12.5Alcohols AIMS: Tonome ond drow structuresof olcohols,glycols,ond phenols.Toidentify on olcoholos being primory secondoryor teftiory. Toidentify fhe usesof some commonolcohols. Focus Alcohols are organic derivatives of water. Alcohols are compounds in which one hydrogen of the water molecule is replacedby a hydrocarbon chain or ring. Thefunctional group - OH in alcohok is called a hydro:ry function or hydroryl Soup. In organic chemistry, the symbol R is often used to represent any carbon chains or carbon rings. Therefore,the generalformula of an alcohol can be written as ROH. o HH Watermolecule "/ o9 / / ,-" hvdroxyl group RH Alcoholmolecule 568 CHAPTER12 Halocarbons, Alcohols,and Ethers Chemists often arrange aliphatic alcohols into structural categories according to the number of R groups attached to the carbontl-ntis bonded to the hydroxyl group. The R groups in a molecule may be the same or may be different. Only one R group and two hydrogens are attached to the C-OH of a primary (abbreviated l') alcohol. Two R groups and one hydrogen are attached to the C-OH of a secondary (2") alcohol. A tertiary (3") alcohol has three R groups and no hydrogens attached to the C-OH. H I R-C I OH R I R-C-OH R-C-OH H R | 2.5 EXAri[PLE I I I H Primary (f ') alcohol R (2")alcohol Secondary Tertiary (3') alcohol Determining'whetfter an,'alcoholis primary secondatyioilertiary ' ,, , - ,,,:.' ,..,. Identiff each of the following compounds as a primary, secondary or tertiary alcohol. CHq cH3cH2cH2oH I CH3CHCH2OH CH. t- CH3-C-CH2OH I CHs sotuTtoN The alcohols in this example have increasingly complex hydrocarbon chains. However, it is the number of alkyl groups bonded to the carbon in C-OH that determines whether an alcohol is primary, secondary or tertiary: A primary alcohol has one R group and two hydrogens attached, a secondary alcohol has two R groups and one hydrogen attached, and a tertiary alcohol has three R groups and no hydrogens attached. In each ofthe examples,the carbon bonded to the hydroxyl group has only one R group and two hydrogens attached. Therefore, each of these alcohols is a primary alcohol. Naming alcohols To name straight-chain and substituted alcohols by the IUPAC system, we drop the -eending of the name of the parent alkane and add the ending -ol. The parent alkane is the longest continuous chain of carbons that includes the carbon attached to the hydroxyl group. In numbering the longest continuous chain, we give the position of the hydroxyl group the lowest possible number. Alcohols containing two, three, and four -OH substituents are named diols, triols, and tetrols, respectively. Common names of aliphatic alcohols are written in the same way as those for the halocarbons. The altcylgroup-methyl, for example-is named and followed by the word alcohol, as in methyl alcohol. Compounds with more than one -OH sub- 12.5 Alcohols 569 stituent are called glycok. Here are some simple irliphatic alcohols along with their IUPAC and common niunes: cH3-oH CH3-CHr-OH CH3-CH2-CH2-OH CH3-CH-CH3 OH Methanol (methyl alcohol) 1-Propanol (propyl alcohol) Ethanol (ethyl alcohol) CH" t- cH3-c-cHs ?". GH3-CH2-CH-CH3 OH 2-Propanol (isopropyl alcohol) CI{3-CH-CH2-OH OH 2-Methyl-2-propanol (tert-butyl alcohol) 2-Butanol (sec-butyl alcohol) 2-Methyl-1-propanol (isobutyl alcohol) OH /) \-j Cyclohexanol (cycloheryl alcohol) Hr9-9H, CH3-CH-CH2 lttl OH OH OH OH l,2-Ethanediol l,2-Propanediol (ethylene glycol) (tlre common narlrehas arr -ene ending but the molecule contains no double bond) PRACTICE EXERCISE I2.5 Name the following alcohols. (a) CH,CH,CI{2CH,OH (b) CH, cI{3cHoH oH cH2-cH-cH2 tll OH OH OH 1,2,3-Propanetriol (glycerol) (c) CHsCHzfHCH2oH CHt ?". (e)CrLfoH CH3 ':. PRACTICE EXERCISE 12.6 ,: Classify each of the alcohols in Practice Exercise 12.5 as primary, ::r: secondary, or tertiary. Uses of alcohols Many aliphatic alcohols are used in the laboratory, in the health sciences, and in industry. Isopropyl alcohol, a colorless, nearly odorless liquid (bp 82 'C), is the rubbing alcohol used for massages.It is also used as a base for perfumes, creams,lotions, and other cosmetics.Ethylene glycol (bp 197 .C) is the principal ingredient of antifreeze.Its advantagesover other high-boiling liquids are its solubility in water and a freezing point of -IT.4"C.If T70 Alcohols,and Ethers t2 Halocarbons, CHAPTER water is added to ethylene glycol, the mixture freezesat an even lower temperature-a 50To (vlv) aqueous solution of ethylene glycol freezes at -36 'C. Glycerolis a viscous,sweet-tasting,water-solubleliquid. It is used as a lubricant in suppositories and as a moistening agent in cosmetics, foods, and drugs.Glycerolis also an important component of fats and oils. Ethanol (bp 78.5 'C) is the most important alcohol. Also called grain alcohol, much ethanol is produced byyeast fermentation of sugar.Archaeological evidenceindicates that cave dwellers had produced alcoholic beveragesby using fermentation. Since those early times, people have pursued and perfected that art. Virtually every grain, fruit, or vegetablehas been fermented: corn, wheat, r1r€,rice, grapes,tomatoes,dandelions,elderberries, cherries,potatoes, and even cactus pulp. The proofof an alcoholic beverage is twice the alcohol content. For example, 100 proof spirits contain 50% ethanol. Ethanol itself is tastelessand odorless.The differencesin taste among alcoholic beveragesare the result of other products formed during the fermentation process.Among these products are the fusel oils, which include propyl, isopropyl, and other straight- and branched-chain aliphatic alcohols.Fusel oils are often toxic and are one causeof the hangover effects of excessivedrinking. Most ethanol is produced by the fermentation of corn starch and cane sugar.Ethanol is an alternative fuel for use in automobiles. It is mixed with gasolineto form gasohol.At a concentrationof 10%ethanol,gasoholcan be used in a standardautomobile engine. Ethanol is a hypnotic or sleep-inducingdrug. Its abuseis a seriouspublic health problem. Someexpertsestimatethat one in nine adultAmericans have a drinking problem of some kind. There is no evidencethat moderate drinking is harmful. Ethanol for industrial use is often denatured. Denatured alcohol ls ethanol that contains an added substanceto make it toxic. Methanol, sometimes called wood alcoholbecausebefore 1925it was preparedby the distillation of wood, is often the denaturant.The inability to remember the difference between grain alcohol and wood alcohol has spelled tragedy for many people.Wood alcohol is extremelytoxic: l0 mL has been reported to causepermanent blindness-and as little as 30 mL, death. Someundenatured ethanol is used in laboratories under careful supervision. Pure ethanol is labeled absolutealcohol.A preparation containing 5Towater is also available.Nobody should ever attempt to drink laboratory alcohol. Phenols Phenols are compounds in which a hydroxyl group is attached directly to an aromatic ring. Many phenolic compounds are found in nature. Shown below are phenol, the parent compound, and some natural and qmthetic derivatives. c(cH3)3 ;-*4t* I ll cHi\'/ CHa BHT Th1.rnol 'cH. 1 2 . 5A l c o h o l s ,71 Phenol was formerly used as an antiseptic in hospitals (seeA closer Look: Phenolic Antiseptics and Disinfectants).A synthetic derivative of phenol, burylated hydroxy toluene (BHT), is widely used as a food preservative. BHT is often put in food wrappers rather than in the food itself to keep it from imparting a rather antisepticflavor to the product. PhenolicAntisepticsand Disinfectants Phenol, also called carbolic acid,wasfirst used as a medical antiseptic in 1867by Ioseph Lister. He demonstrated that the incidence of infections after surgical procedures was dramatically reduced when solutions of phenol were used to clean the surgical instruments, the operating room, and the patient's skin. Today'suse of phenol for medicinal purposesis more limited. \il/hen phenol is absorbedthrough the skin, ingested,or inhaled, it is toxic. It also can causeseverechemical burns. However,it is available as an antiseptic in aqueousor alcoholic solutions that contain a maximum of 1.5Vophenol. Phenol is an ingredient in a variety of throat lozengesthat can contain up to 50 mg phenol per lozenge.It is a useful topical drug for treating sore throats because it numbs the inflamed area. A number of derivativesof the parent phenol are used today as antiseptics. Many mouthwashesand throat lozengesinclude alkyl-substituted phenols as their uciive ingredients for pain relief (seefigure). The compound 4-hexylresorcinol has a superior antibacterial action to that of phenol. It is also much less toxic. Therefore,it is an ingredient of choice in mouthwashes and throat lozenges. around the home. Disinfectants are formulated for use on inanimate objects, not living tissues. Phenol's germicidal properties result because these chemicals have the ability to disrupt the microorganisms'cell wall permeabiliry. The naturally occurring phenol eugenol is found in clovesand is used in dentistry to relieve toothaches. Methyl salicylate, another phenol derivative commonly known as oil of wintergreen, is a flavoring agent and is used in liniments to relieve sore muscles.Another derivative of phenol, thymol, is used as an antiseptic in mouthwashpreparations. OH cH2cH2cH2cH2CH2CH3 4-hexylresorcinoi Phenols and methyl phenols {cresols) are commonly used as disinfectants in hospitals and Phenoland its derivativesare the activeingredientsin many of the preparationsused for oral hygiene.