© 2013 Pearson Education, Inc. Outline 14.1 Alcohols, Phenols, and Ethers 14.2 Some Common Alcohols...

© 2013 Pearson Education, Inc.

Outline

14.1 Alcohols, Phenols, and Ethers14.2 Some Common Alcohols14.3 Naming Alcohols14.4 Properties of Alcohols14.5 Reactions of Alcohols14.6 Phenols14.7 Acidity of Alcohols and Phenols14.8 Ethers14.9 Thiols and Disulfides14.10 Halogen-Containing Compounds


Goals

1. What are the distinguishing features of alcohols, phenols, ethers, thiols, and alkyl halides? Be able to describe the structures and uses of compounds with these functional groups.

2. How are alcohols, phenols, ethers, thiols, and alkyl halides named? Be able to give systematic names for the simple members of these families and write their structures, given the names.

3. What are the general properties of alcohols, phenols, and ethers? Be able to describe such properties as polarity, hydrogen bonding, and water solubility.

4. Why are alcohols and phenols weak acids?

Be able to explain why alcohols and phenols are acids

5. What are the main chemical reactions of alcohols and thiols?

Be able to describe and predict the products of the dehydration of alcohols and of the oxidation of alcohols and thiols.


14.1 Alcohols, Phenols, and Ethers

• Alcohol is a compound that has an —OH group bonded to a saturated, alkane-like carbon atom.

• Phenol is a compound that has an —OH group bonded directly to an aromatic, benzene-like ring.

• Ether is a compound that has an oxygen atom bonded to two organic groups, R—O—R.


14.1 Alcohols, Phenols, and Ethers

• The structural similarity between alcohols and water also leads to similarities in physical properties.

• The high boiling point of water is due to hydrogen bonding. Hydrogen bonds also form between alcohol (or phenol) molecules.

• Alkanes and ethers cannot form hydrogen bonds.


14.2 Some Common Alcohols

• METHYL ALCOHOL, CH3OH, is known as wood alcohol because it was prepared by heating wood in the absence of air. Today it is made by reaction of carbon monoxide with hydrogen.

• Methanol is used industrially as a solvent, and as a starting material for preparing formaldehyde.

• Methyl alcohol is colorless, miscible with water, and toxic. It causes blindness in low doses (about 15 mL for an adult) and death in larger amounts (100–250 mL).



• ETHYL ALCOHOL, CH3CH2OH, is sometimes known as grain alcohol and is the alcohol present in alcoholic beverages.

• During fermentation, starches and sugars are converted to simple sugars and then to ethanol by yeast enzymes.

• Fermentation can produce concentrations up to 14% ethanol, but higher concentrations can be produced by distillation or addition of a distilled product.

• Nonbeverage alcohol is often denatured by addition of an unpleasant tasting and toxic substance.

• Industrially, ethyl alcohol is made by hydration of ethylene. Distillation yields 95% ethanol, and dehydration gives 100% or absolute ethanol.

• In some states, a blend of ethanol and gasoline is commercially available.



• ISOPROPYL ALCOHOL, (CH3)2CHOH, is often called rubbing alcohol.

• It is used for rubdowns and in astringents, as a solvent, a sterilant, and as a skin cleanser.

• Though less toxic than methyl alcohol, it is much more toxic than ethanol.

• ETHYLENE GLYCOL, (HOCH2CH2OH), is a diol.

• It is a colorless liquid, miscible with water, and insoluble in non-polar solvents.

• It is used as an engine antifreeze and coolant; it is also used as a starting material for the manufacture of polyester.

• It is highly toxic and has a slightly sweet taste. As a result, it is being phased out in favor of propylene glycol (CH3CH(OH)CH2OH), which is tasteless and non-toxic.



• GLYCEROL (HOCH2CH(OH)CH2OH), is a triol also called glycerin.

• It is a colorless liquid that is miscible with water.

• It is not toxic, and has a sweet taste that makes it useful for use in foods. It is also used as a moisturizer, in plastics manufacture, in antifreeze and shock absorbers, and as a solvent.

• Because of extensive hydrogen bonding, it is an extremely viscous fluid.

• Glycerol also provides the structural backbone of animal fats and vegetable oils.


14.3 Naming Alcohols• STEP 1: Name the parent compound. Find the longest

chain that has the hydroxyl substituent attached, and name the chain by replacing the -e ending of the corresponding alkane with -ol.

• STEP 2: Number the carbon atoms in the main chain. Begin at the end nearer the hydroxyl group, ignoring the location of other substituents: In a cyclic alcohol, begin with the carbon that bears the —OH group and proceed in a direction that gives the other substituents the lowest possible numbers.

• STEP 3: Write the name, placing the number that locates the hydroxyl group immediately before the compound name. Number all other substituents, and list them alphabetically. In a cyclic alcohol, do not use the number 1 to specify the location of the —OH group.


14.3 Naming Alcohols


14.3 Naming Alcohols• Dialcohols, or diols,

contain two hydroxy groups in the same molecule. The IUPAC names of these alcohols are formed by attaching the ending diol to the alkane name.

• The names will contain two numbers indicating the carbons bonded to the two —OH groups, with the numbering starting at the end closest to one of the —OH groups.


14.3 Naming Alcohols• Diols with two —OH groups on adjacent carbons are

often referred to by the common name glycols. • This is preferably reserved for two compounds, ethylene

glycol and propylene glycol. • Alcohols are classified as primary, secondary, or tertiary

according to the number of carbon substituents bonded to the hydroxyl-bearing carbon.

• This classification is useful as many of the reactions of alcohols are a function of their substitution.


14.4 Properties of Alcohols

• Alcohols are polar because of the electronegative oxygen atom.

• Hydrogen bonding occurs and has a strong influence on alcohol properties.

• Straight-chain alcohols with up to 12 carbons are liquid.

• Methanol and ethanol are miscible with water and can dissolve small amounts of ionic compounds. Both are also miscible with many organic solvents


14.4 Properties of Alcohols

• All alcohols are composed of a “water-loving” or hydrophilic part and a “water-fearing” or hydrophobic part.

• Alcohols with a larger hydrophobic part, are more like alkanes and less like water.

• Alcohols with two or more —OH groups can form more than one hydrogen bond. They are therefore higher boiling and more water-soluble than similar alcohols with one —OH group.


14.5 Reactions of Alcohols

• DEHYDRATION: Alcohols undergo loss of water on treatment with a strong acid.

• The reaction is driven to completion by heating.• The —OH group is lost from one carbon, and an

—H is lost from an adjacent carbon to yield an alkene.



• When more than one alkene can result, a mixture of products is formed.

• The major product has the greater number of alkyl groups directly attached to the double-bond carbons.



Mastering Reactions: How Eliminations Occur• When an alcohol is treated with a strong acid, the oxygen atom of

the alcohol protonates in an equilibrium process.• This converts the —OH group into a water molecule.• The water molecule leaves, and a carbocation remains.• The favorability of this reaction is a function of the stability of the

carbocation. 3° alcohols undergo this process more readily than 2° alcohols, and 1° alcohols undergo the process very slowly.

• Water acting as a Lewis base, can remove an adjacent hydrogen, forming the alkene.

• Heating selectively drives off the alkene due to its lower boiling point.

• Zaitsev’s Rule states that the more substituted alkene will be favored. This is the result of the equilibrium process that is operating: the less stable form is more likely to revert to the carbocation.



• OXIDATION occurs when primary and secondary alcohols are converted into carbonyl-containing compounds by an oxidizing agent.

• A carbonyl group is a carbon attached to an oxygen by a double bond.

• Any oxidizing agent can be used.

• In organic chemistry, a more general definition of oxidation and reduction is used.

– An organic oxidation is one that increases the number of C—O bonds and/or decreases the number of C—H bonds.

– An organic reduction is one that decreases the number of C—O bonds and/or increases the number of C—H bonds.



• Two hydrogen atoms are removed during the reaction; one from the —OH group, and one from the carbon attached to the —OH group.

• Primary alcohols are converted into aldehydes under controlled conditions, or carboxylic acids, if an excess of oxidant is used.



• Secondary alcohols (R2CHOH) are converted into ketones (R2C=O) on treatment with oxidizing agents.

• Tertiary alcohols do not normally react with oxidizing agents because they do not have a hydrogen on the carbon atom to which the —OH group is bonded.


14.5 Reactions of AlcoholsEthyl Alcohol as a Drug and a Poison

• Ethyl alcohol is a central nervous system (CNS) depressant. Its direct effects resemble the response to anesthetics.

• Ethyl alcohol is absorbed in the stomach and small intestine, then rapidly distributed to all body fluids and organs.

– In the pituitary gland, alcohol inhibits the production of a hormone that regulates urine flow, causing increased urine production and dehydration.

– In the stomach, ethyl alcohol stimulates production of acid. – Throughout the body, it causes blood vessels to dilate.

• Ethyl alcohol is metabolized in the liver in a two-step process: oxidation of the alcohol to acetaldehyde, followed by oxidation of the aldehyde to acetic acid. When continuously present, alcohol and acetaldehyde are toxic. The liver usually suffers the worst damage because it is the major site of alcohol metabolism.

• Alcohol concentration can be measured in expired air by the color change that occurs when the yellow-orange potassium dichromate is reduced to blue-green chromium(III). The color change can be interpreted by instruments to give an accurate measure of alcohol concentration in the blood.


14.6 Phenols

• The word phenol is the name both of a specific compound (hydroxybenzene, C6H5OH), as well as a family of compounds.

• Phenol itself, formerly called carbolic acid, is a medical antiseptic that also numbs the skin.– It was first used by Joseph Lister, who showed that

the instance of post-operative infection dramatically decreased when phenol was used to cleanse the operating room and the patient’s skin.

• The presence of an alkyl group lowers the absorption through skin, rendering alkyl-substituted phenols less toxic than phenol.


14.6 Phenols

• Some other alkyl-substituted phenols such as the cresols (methylphenols) are common as disinfectants.

• Phenols are usually named with the ending phenol rather than -benzene.


14.6 Phenols

• The properties of phenols are influenced by the electronegative oxygen and hydrogen bonding.

• Most phenols are somewhat water-soluble and have higher melting and boiling points than similar alkylbenzenes.

• They are less soluble in water than alcohols.

• Many biomolecules contain a hydroxyl-substituted benzene ring.


14.7 Acidity of Alcohols and Phenols

• Alcohols and phenols are very weakly acidic because of the positively-polarized —OH hydrogen.

• They dissociate slightly in solution and establish equilibria between neutral and anionic forms.



• Methanol and ethanol dissociate so little in water that their aqueous solutions are neutral (pH 7).

• An alkoxide ion, or anion of an alcohol, is as strong a base as a hydroxide ion.

• An alkoxide ion is produced by reaction of an alkali metal with an alcohol.



• Phenols are about 10,000 times more acidic than water.

• A phenoxide ion is produced by reaction of a phenol with dilute aqueous sodium hydroxide.



Phenols as Antioxidants

• Butylated hydroxytoluene and butylated hydroxyanisole, or their abbreviations BHT and BHA, are probably familiar.

• Foods that contain unsaturated fats—those having carbon–carbon double bonds—become rancid when oxygen from the air reacts with their double bonds.

• BHT and BHA prevent oxidation by donating a hydrogen atom from their —OH group to the free radical as soon as it forms.

• The BHA or BHT is converted into a stable and unreactive free radical, which causes no damage. Vitamin E, a natural antioxidant within the body, acts similarly .

• Free radicals are suspected of playing a role in both cancer and aging of living tissue.



Phenols as Antioxidants


14.8 Ethers

• Ethers are named by identifying the two organic groups and adding the word ether.

• Cyclic ethers are often referred to by their common names.


14.8 Ethers

• An —OR group is referred to as an alkoxy group.

• Ethers do not form hydrogen bonds to one another.• They are higher boiling than alkanes but lower boiling

than alcohols. • The oxygen atom in ethers can hydrogen-bond with

water, causing dimethyl ether to be water-soluble and diethyl ether to be partially miscible with water.

• Ethers make good solvents for reactions where a polar solvent is needed but no —OH groups can be present.


14.8 Ethers

• Ethers are alkane-like in many properties and do not react with acids or bases.

• Simple ethers are highly flammable. • On standing in air, many ethers form explosive

peroxides, compounds that contain an O—O bond. Ethers must be handled with care and stored in the absence of oxygen.

• Diethyl ether was a mainstay of the operating room until the 1940s. It acts quickly and is very effective, but has a long recovery time and often induces nausea.


14.8 Ethers

• Ethers are found throughout the plant and animal kingdoms. Some are present in plant oils and are used in perfumes; others have a variety of biological roles.


14.9 Thiols and Disulfides

• Many oxygen-containing compounds have sulfur analogs.

• Thiols, also called mercaptans, are sulfur analogs of alcohols.

• The systematic name of a thiol is formed by adding -thiol to the parent hydrocarbon name.



• The most outstanding characteristic of thiols is their appalling odor.

• Skunk scent and the odor when garlic and onions are being sliced are thiols.

• Natural gas is odorless, but methanethiol is added to make leak detection easy.

• Thiols react with mild oxidizing agents to yield disulfides. Two thiols join in this reaction, the hydrogen from each is lost, and a bond forms between the sulfurs.

• The reverse occurs when a disulfide is treated with a reducing agent.



Inhaled Anesthetics • William Morton’s demonstration in 1846 of ether-induced anesthesia is one

of the most important medical breakthroughs of all time.

• Hundreds of substances have subsequently been shown to act as inhaled anesthetics.

• Halothane, enflurane, isoflurane, and methoxyflurane are the most commonly used. All are potent at low doses, nontoxic, and nonflammable.

• Little is known about how inhaled anesthetics work in the body.

• The potency of anesthetics correlates well with their solubility in olive oil, leading scientists to believe that they dissolve in the membranes surrounding nerve cells.

• Depth of anesthesia is determined by the concentration of anesthetic agent that reaches the brain.

• Anesthetic potency is usually expressed as a minimum alveolar concentration (MAC), defined as the concentration of anesthetic in inhaled air that results in anesthesia in 50% of patients.

• Nitrous oxide, is the least potent of the common anesthetics and methoxyflurane is the most potent.



• Thiols are important because they occur in the amino acid cysteine, which is part of many proteins.

• The easy formation of bonds between cysteines helps shape large protein molecules.

• The proteins in hair are unusually rich in S—S and S—H groups.

Figure 14.2 Chemistry can curl your hair. A permanent wave results when disulfide bridges are formed between iSH groups in hair protein molecules.


14.10 Halogen-Containing Compounds• The simplest halogen-containing compounds are

alkyl halides, RX.

• Their common names consist of the name of the alkyl group followed by the halogen name with an -ide ending.

• The halogen atom is a substituent on a parent alkane.– The parent alkane is named in the usual way.

– The halo-substituent name is then given as a prefix, just as if it were an alkyl group.


14.10 Halogen-Containing Compounds• Halogenated compounds are also used widely in industry

as solvents and degreasing agents.• The use of halogenated herbicides and fungicides has

resulted in vastly increased crop yields in recent decades.

• The widespread application of chlorinated insecticides, such as DDT, is largely responsible for the progress made toward worldwide control of malaria and typhus.

• Despite their enormous benefits, chlorinated pesticides present problems because they persist in the environment, remaining in the fatty tissues of organisms and accumulating up the food chain.

• The use of many has been restricted, and others have been banned altogether.


Chapter Summary, Continued

1. What are the distinguishing features of alcohols, phenols, ethers, thiols, and alkyl halides?

• An alcohol has an —OH group (a hydroxyl group) bonded to a saturated, alkane-like carbon atom

• A phenol has an —OH group bonded directly to an aromatic ring. • An ether has an oxygen atom bonded to two organic groups. • Thiols are sulfur analogs of alcohols, R—SH • Alkyl halides contain a halogen atom bonded to an alkyl group

R—X.• The —OH group is present in many biochemically active molecules.• Phenols are notable for their use as disinfectants and antiseptics.• Ethers are used primarily as solvents.• Thiols are found in proteins. • Halogenated compounds are rare in human biochemistry, but are

widely used in industry as solvents and in agriculture as herbicides, fungicides, and insecticides.


Chapter Summary, Continued2. How are alcohols, phenols, ethers, thiols,

and alkyl halides named?

• Alcohols are named using the -ol ending, and phenols are named using the -phenol ending.

• Ethers are named by identifying the two organic groups attached to oxygen, followed by the word ether.

• Thiols use the name ending -thiol.

• Alkyl halides are named as halo-substituted alkanes.



3. What are the general properties of alcohols, phenols, and ethers?

• Both alcohols and phenols are like water in their ability to form hydrogen bonds.

• As the size of the organic part increases, alcohols become less soluble in water.

• Ethers do not hydrogen-bond and are more alkane-like in their properties.



4. Why are alcohols and phenols weak acids?

• Like water, alcohols and phenols are weak acids that can donate H+ from their group to a strong base.

• Alcohols are similar to water in acidity.

• Phenols are more acidic than water and will react with aqueous NaOH.



5. What are the main chemical reactions of alcohols and thiols?

• Alcohols undergo loss of water (dehydration) to yield alkenes when treated with a strong acid.

• They undergo oxidation to yield compounds that contain a carbonyl group (C=O).

• Primary alcohols are oxidized to yield either aldehydes (RCHO) or carboxylic acids (RCO2H).

• Secondary alcohols are oxidized to yield ketones (R2C=O).

• Tertiary alcohols are not oxidized.

• Thiols react with mild oxidizing agents to yield disulfides (RSSR), a reaction of importance in protein chemistry.

• Disulfides can be reduced back to thiols.

© 2013 Pearson Education, Inc. Outline 14.1 Alcohols, Phenols, and Ethers 14.2 Some Common Alcohols...

Documents

Transcript of © 2013 Pearson Education, Inc. Outline 14.1 Alcohols, Phenols, and Ethers 14.2 Some Common Alcohols...