Chapter 4 Alcohols Phenols and Ethers

Chapter 4Alcohols, Phenols

and Ethers

General, Organic, and Biological Chemistry, Fifth EditionH. Stephen Stoker

Brroks/Cole Cengage Learning. Permission required for reproduction or display.

Prepared by:GIZEL R. SANTIAGO

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Chapter 3 Topics• Bonding Characteristics of Oxygen Atoms in Organic

Compounds• Structural Characteristics of Alcohols• Nomenclature for Alcohols• Isomerism for Alcohols• Important Commonly Encountered Alcohols • Physical Properties of Alcohols • Preparation of Alcohols • Classification of Alcohols • Chemical Reactions of Alcohols • Polymeric Alcohols

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Chapter 3 Topics

• Structural Characteristics of Phenols• Nomenclature for Phenols • Physical and Chemical Properties of Phenols • Occurrence of and Uses for Phenols • Structural Characteristics of Ethers • Nomenclature for Ethers • Isomerism for Ethers • Physical and Chemical Properties of Ethers 4• Cyclic Ethers • Sulfur Analogs of Alcohols • Sulfur Analogs of Ethers

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Bonding Characteristics of Oxygen Atoms in Organic CompoundsNormal bonding behavior for oxygen atoms in such functional groups is the formation of two covalent bonds. Oxygen is a member of Group VIA of the periodic table and thus possesses six valence electrons. To complete its octet by electron sharing, an oxygen atom can form either two single bonds or a double bond.

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Bonding Characteristics of Oxygen Atoms in Organic Compounds

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Thus, in organic chemistry, carbon forms four bonds, hydrogen forms one bond, and oxygen forms two bonds.

Bonding Characteristics of Oxygen Atoms in Organic Compounds

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A hydrocarbon derivatives containing a single oxygen atom with the generalized formula:

R-OH

Structural Characteristics of Alcohols

An alcohol is an organic compound in which an —OH group is bonded to a saturated carbon atom. A saturated carbon atom is a carbon atom that is bonded to four other atoms.

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Structural Characteristics of Alcohols

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Structural Characteristics of AlcoholsThe —OH group, the functional group that is characteristic of an alcohol, is called a hydroxyl group. A hydroxyl group is the —OH functional group. Examples of structural formulas for alcohols include

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Structural Characteristics of AlcoholsAlcohols may be viewed structurally as being alkyl derivatives of water in which a hydrogen atom has been replaced by an alkyl group.

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Structural Characteristics of AlcoholsAlcohols may also be viewed structurally as hydroxyl derivatives of alkanes in which a hydrogen atom has been replaced by a hydroxyl group.

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Nomenclature for Alcohols

Common names exist for alcohols with simple (generally C1 through C4) alkyl groups. To assign a common name:

Rule 1: Name all of the carbon atoms of the molecule as a single alkyl group.

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Rule 2: Add the word alcohol, separating the words with a space.

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Nomenclature for AlcoholsIUPAC rules for naming alcohols that contain a single hydroxyl group follow. Rule 1: Name the longest carbon chain to which the hydroxyl group is attached. The chain name is obtained by dropping the final -e from the alkane name and adding the suffix -ol.

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Nomenclature for AlcoholsRule 2: Number the chain starting at the end nearest the hydroxyl group, and use the appropriate number to indicate the position of the —OH group. (In numbering of the longest carbon chain, the hydroxyl group has priority over double and triple bonds, as well as over alkyl, cycloalkyl, and halogen substituents.)

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Rule 3: Name and locate any other substituents present. Rule 4: In alcohols where the —OH group is attached to a carbon atom in a ring, the hydroxyl group is assumed to be on carbon 1.

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Alcohols with More Than One Hydroxyl Group Polyhydroxy alcohols—alcohols that possess more than one hydroxyl group—can be named with only a slight modification of the preceding IUPAC rules. An alcohol in which two hydroxyl groups are present is named as a diol, one containing three hydroxyl groups is named as a triol, and so on. In these names for diols, triols, and so forth, the final -e of the parent alkane name is retained for pronunciation reasons.

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Alcohols with More Than One Hydroxyl Group

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Alcohols with More Than One Hydroxyl Group The first two of the preceding compounds have the common names ethylene glycol and propylene glycol. These two alcohols are synthesized, respectively, from the alkenes ethylene and propylene; hence the common names.

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Isomerism for Alcohols Constitutional isomerism is possible for alcohols containing three or more carbon atoms. As with alkenes, both skeletal isomers and positional isomers are possible. For monohydroxy saturated alcohols, there are two C3 isomers, four C4 isomers, and eight C5 isomers. The three pentanols are positional isomers as are the four methylbutanols.

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Isomerism for Alcohols

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Important Commonly Encountered Alcohols

Commonly encountered alcohols are methyl, ethyl, and isopropyl alcohols (all monohydroxy alcohols), ethylene glycol and propylene glycol (both diols), and glycerol (a triol).

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Important Commonly Encountered Alcohols Methyl Alcohol (Methanol) Methyl alcohol, with one carbon atom and one —OH group, is the simplest alcohol. This colorless liquid is a good fuel for internal combustion engines. Since 1965 all racing cars at the Indianapolis Speedway have been fueled with methyl alcohol.

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Important Commonly Encountered Alcohols (Methyl alcohol fires are easier to put out than gasoline fi res because water mixes with and dilutes methyl alcohol.) Methyl alcohol also has excellent solvent properties, and it is the solvent of choice for paints, shellacs, and varnishes.

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Methyl alcohol is sometimes called wood alcohol, terminology that draws attention to an early method for its preparation—the heating of wood to a high temperature in the absence of air. Today, nearly all methyl alcohol is produced via the reaction between H2 and CO.

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Important Commonly Encountered Alcohols Drinking methyl alcohol is very dangerous. Within the human body, methyl alcohol is oxidized by the liver enzyme alcohol dehydrogenase to the toxic metabolites formaldehyde and formic acid.

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Important Commonly Encountered Alcohols Formaldehyde can cause blindness (temporary or permanent). Formic acid causes acidosis. Ingesting as little as 1 oz (30 mL) of methyl alcohol can cause optic nerve damage.

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Ethyl Alcohol (Ethanol) Ethyl alcohol, the two-carbon monohydroxy alcohol, is the alcohol present in alcoholic beverages and is commonly referred to simply as alcohol or drinking alcohol. Like methyl alcohol, ethyl alcohol is oxidized in the human body by the liver enzyme alcohol dehydrogenase.

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Important Commonly Encountered Alcohols Acetaldehyde, the first oxidation product, is largely responsible for the symptoms of hangover. The odors of both acetaldehyde and acetic acid are detected on the breath of someone who has consumed a large amount of alcohol. Ethyl alcohol oxidation products are less toxic than those of methyl alcohol.

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Important Commonly Encountered Alcohols Long-term excessive use of ethyl alcohol may cause undesirable effects such as cirrhosis of the liver, loss of memory, and strong physiological addiction. Links have also been established between certain birth defects and the ingestion of ethyl alcohol by women during pregnancy (fetal alcohol syndrome).

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Important Commonly Encountered Alcohols Ethyl alcohol can be produced by yeast fermentation of sugars found in plant extracts. The synthesis of ethyl alcohol from grains such as corn, rice, and barley, is the reason why ethyl alcohol is often called grain alcohol.

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Fermentation is the process by which ethyl alcohol for alcoholic beverages is produced. The maximum concentration of ethyl alcohol obtainable by fermentation is about 18% (v/v), because yeast enzymes cannot function in stronger alcohol solutions. Alcoholic beverages with a higher concentration of alcohol than this are prepared by either distillation or fortification with alcohol obtained by the distillation of another fermentation product.

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Important Commonly Encountered Alcohols Denatured alcohol is ethyl alcohol that has been rendered unfit to drink by the addition of small amounts of toxic substances (denaturing agents). Almost all of the ethyl alcohol used for industrial purposes is denatured alcohol. Most ethyl alcohol used in industry is prepared from ethene via a hydration reaction

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Important Commonly Encountered Alcohols The reaction produces a product that is 95% alcohol and 5% water. In applications where water does interfere with its use, the mixture is treated with a dehydrating agent to produce 100% ethyl alcohol. Such alcohol, with all traces of water removed, is called absolute alcohol.

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Important Commonly Encountered Alcohols Isopropyl Alcohol (2-Propanol) Isopropyl alcohol is one of two three-carbon monohydroxy alcohols; the other is propyl alcohol. A 70% isopropyl alcohol–30% water solution is marketed as rubbing alcohol. Isopropyl alcohol’s rapid evaporation rate creates a dramatic cooling effect when it is applied to the skin, hence its use for alcohol rubs to combat high body temperature. It also finds use in cosmetics formulations such as after-shave lotion and hand lotions.

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Important Commonly Encountered Alcohols Isopropyl alcohol has a bitter taste. Its toxicity is twice that of ethyl alcohol, but it causes few fatalities because it often induces vomiting and thus doesn’t stay down long enough to be fatal. In the body it is oxidized to acetone.Large amounts (about 150 mL) of ingested isopropyl alcohol can be fatal; death occurs from paralysis of the central nervous system.

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Ethylene Glycol (1,2-Ethanediol) and Propylene Glycol (1,2-Propanediol) Ethylene glycol and propylene glycol are the two simplest alcohols possessing two —OH groups. Besides being diols, they are also classified as glycols. A glycol is a diol in which the two —OH groups are on adjacent carbon atoms.

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Both of these glycols are colorless, odorless, high-boiling liquids that are completely miscible with water. Their major uses are as the main ingredient in automobile “year-round” antifreeze and airplane “de-icers” and as a starting material for the manufacture of polyester fibers.

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Ethylene glycol is extremely toxic when ingested. In the body, liver enzymes oxidize it to oxalic acid. Oxalic acid, as a calcium salt, crystallizes in the kidneys, which leads to renal problems.

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Propylene glycol, on the other hand, is essentially nontoxic and has been used as a solvent for drugs. Like ethylene glycol, it is oxidized by liver enzymes; however, pyruvic acid, its oxidation product, is a compound normally found in the human body, being an intermediate in carbohydrate metabolism.

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Important Commonly Encountered Alcohols Glycerol (1,2,3-Propanetriol) Glycerol, which is often also called glycerin, is a clear, thick liquid that has the consistency of honey. Its molecular structure involves three —OH groups on three different carbon atoms.

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Important Commonly Encountered Alcohols Glycerol is normally present in the human body because it is a product of fat metabolism. It is present, in combined form, in all animal fats and vegetable oils. In some Arctic species, glycerol functions as a “biological antifreeze”.

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Important Commonly Encountered Alcohols Because glycerol has a great affinity for water vapor (moisture), it is often added to pharmaceutical preparations such as skin lotions and soap. Florists sometimes use glycerol on cut flowers to help retain water and maintain freshness. Its lubricative properties also make it useful in shaving creams and in applications such as glycerol suppositories for rectal administration of medicines. It is used in candies and icings as a retardant for preventing sugar crystallization.

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Physical Properties of Alcohols Alcohol molecules have both polar and nonpolar character. The hydroxyl groups present are polar, and the alkyl (R) group present is nonpolar.The physical properties of an alcohol depend on whether the polar or the nonpolar portion of its structure “dominates.” Factors that determine this include the length of the nonpolar carbon chain present and the number of polar hydroxyl groups present.

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Physical Properties of Alcohols

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Physical Properties of Alcohols Boiling Points and Water Solubilities The boiling point for 1-alcohols, unbranched-chain alcohols with an —OH group on an end carbon, increases as the length of the carbon chain increases. This trend results from increasing London forces with increasing carbon chain length. Alcohols with more than one hydroxyl group present have significantly higher boiling points (bp) than their monohydroxy counterparts.

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Physical Properties of Alcohols Boiling Points and Water Solubilities

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Physical Properties of Alcohols Boiling Points and Water Solubilities The boiling-point trend is related to increased hydrogen bonding between alcohol molecules.

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Physical Properties of Alcohols Boiling Points and Water Solubilities Small monohydroxy alcohols are soluble in water in all proportions. As carbon chain length increases beyond three carbons, solubility in water rapidly decreases because of the increasingly nonpolar character of the alcohol. Alcohols with two —OH groups present are more soluble in water than their counterparts with only one —OH group. Increased hydrogen bonding is responsible for this. Diols containing as many as seven carbon atoms show appreciable solubility in water.

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Physical Properties of Alcohols Alcohols and Hydrogen Bonding A comparison of the properties of alcohols with their alkane counterparts:1.Alcohols have higher boiling points than

alkanes of similar molecular mass. 2.Alcohols have much higher solubility in

water than alkanes of similar molecular mass.

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Physical Properties of Alcohols Alcohols and Hydrogen Bonding The differences in physical properties between alcohols and alkanes are related to hydrogen bonding. Because of their hydroxyl group(s), alcohols can participate in hydrogen bonding, whereas alkanes cannot. Hydrogen bonding between alcohol molecules is similar to that which occurs between water molecules.

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Physical Properties of Alcohols Alcohols and Hydrogen Bonding Extra energy is needed to overcome alcohol–alcohol hydrogen bonds before alcohol molecules can enter the vapor phase. Hence alcohol boiling points are higher than those for the corresponding alkanes (where no hydrogen bonds are present).

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Physical Properties of Alcohols Alcohols and Hydrogen Bonding Extra energy is needed to overcome alcohol–alcohol hydrogen bonds before alcohol molecules can enter the vapor phase. Hence alcohol boiling points are higher than those for the corresponding alkanes (where no hydrogen bonds are present). As the alcohol chain length increases, alcohols become more alkane-like (nonpolar), and solubility decreases.

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Preparation of Alcohols A general method for preparing alcohols—the hydration of alkenes. Alkenes react with water (an unsymmetrical addition agent) in the presence of sulfuric acid (the catalyst) to form an alcohol. Markovnikov’s rule is used to determine the predominant alcohol product.

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Preparation of Alcohols Another method of synthesizing alcohols involves the addition of H2 to a carbon– oxygen double bond (a carbonyl group). A carbonyl group behaves very much like a carbon–carbon double bond when it reacts with H2 under the proper conditions. As a result of H2 addition, the oxygen of the carbonyl group is converted to an —OH group.

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Preparation of Alcohols

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Preparation of Alcohols Alcohols are classified as primary (10), secondary (20), or tertiary (30) depending on the number of carbon atoms bonded to the carbon atom that bears the hydroxyl group.

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A primary alcohol is an alcohol in which the hydroxyl-bearing carbon atom is bonded to only one other carbon atom. A secondary alcohol is an alcohol in which the hydroxylbearing carbon atom is bonded to two other carbon atoms. A tertiary alcohol is an alcohol in which the hydroxyl-bearing carbon atom is bonded to three other carbon atoms.

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Increasing the number of R groups around the carbon atom bearing the OH group decreases the extent of hydrogen bonding. This effect, called stearic hindrance, becomes particularly important when the R groups are large. Thus, 10 alcohols are best able to hydrogen-bond and 30 alcohols are least able to hydrogen-bond.

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Chemical Reactions of Alcohols Combustion Hydrocarbons of all types undergo combustion in air to produce carbon dioxide and water. Alcohols are also flammable; as with hydrocarbons, the combustion products are carbon dioxide and water. Methyl alcohol is the fuel of choice for racing cars. Oxygenated gasoline, which is used in winter in many areas of the United States because it burns “cleaner,” contains ethyl alcohol as one of the “oxygenates.”

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Chemical Reactions of Alcohols

Intermolecular Alcohol DehydrationAt a lower temperature (1400C) than that required for alkene formation (1800C), an intermolecular rather than an intramolecular alcohol dehydration process can occur to produce an ether—a compound with the general structure R—O—R.

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A condensation reaction is a chemical reaction in which two molecules combine to form a larger one while liberating a small molecule, usually water. Two alcohol molecules combine to give an ether and water.

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Chemical Reactions of Alcohols OxidationOrganic redox reactions use the following set of operational rules instead of oxidation numbers. 1. An organic oxidation is an oxidation that increases the

number of C—O bonds and/ or decreases the number of C—H bonds.

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

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Chemical Reactions of Alcohols Some alcohols readily undergo oxidation with mild oxidizing agents; others are resistant to oxidation with these same oxidizing agents. Primary and secondary alcohols, but not tertiary alcohols, readily undergo oxidation in the presence of mild oxidizing agents to produce compounds that contain a carbon–oxygen double bond (aldehydes, ketones, and carboxylic acids).

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Chemical Reactions of Alcohols A number of different oxidizing agents can be used for the oxidation, including potassium permanganate (KMnO4), potassium dichromate (K2Cr2O7), and chromic acid (H2CrO4).

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The net effect of the action of a mild oxidizing agent on a primary or secondary alcohol is the removal of two hydrogen atoms from the alcohol. One hydrogen comes from the —OH group, the other from the carbon atom to which the —OH group is attached. This H removal generates a carbon–oxygen double bond.

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Primary and secondary alcohols, the two types of oxidizable alcohols, yield different products upon oxidation. A 10 alcohol produces an aldehyde that is often then further oxidized to a carboxylic acid, and a 20 alcohol produces a ketone.

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Chemical Reactions of Alcohols Primary alcohol oxidation

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Chemical Reactions of Alcohols Secondary alcohol oxidation

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Chemical Reactions of Alcohols Tertiary alcohols do not undergo oxidation with mild oxidizing agents. This is because they do not have hydrogen on the —OH-bearing carbon atom.

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Chemical Reactions of Alcohols Halogenation Alcohols undergo halogenation reactions in which a halogen atom is substituted for the hydroxyl group, producing an alkyl halide. Alkyl halide production in this manner is superior to alkyl halide production through halogenation of an alkane because mixtures of products are not obtained. A single product is produced in which the halogen atom is found only where the —OH group was originally located.

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Several different halogen-containing reactants, including phosphorus trihalides (PX3; X is Cl or Br), are useful in producing alkyl halides from alcohols.

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Polymeric Alcohols It is possible to synthesize polymeric alcohols with structures similar to those of substituted polyethylenes. One of the simplest such compounds is poly(vinyl alcohol) (PVA).

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Polymeric Alcohols Poly(vinyl alcohol) is a tough, whitish polymer that can be formed into strong films, tubes, and fi bers that are highly resistant to hydrocarbon solvents. Unlike most organic polymers, PVA is water-soluble. Water-soluble fi lms and sheetings are important PVA products. PVA has oxygen-barrier properties under dry conditions that are superior to those of any other polymer. PVA can be rendered insoluble in water, if needed, by use of chemical agents that cross-link individual polymer strands.

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Structural Characteristics of PhenolsA phenol is an organic compound in which an —OH group is attached to a carbon atom that is part of an aromatic carbon ring system.

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Structural Characteristics of PhenolsThe general formula for phenols is Ar–OH, where Ar represents an aryl group. An aryl group is an aromatic carbon ring system from which one hydrogen atom has been removed. A hydroxyl group is thus the functional group for both phenols and alcohols.

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Structural Characteristics of Phenols

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Nomenclature for PhenolsPhenol is also the IUPAC-approved name for the simplest member of the phenol family of compounds.

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Nomenclature for PhenolsPhenol is also the IUPAC-approved name for the simplest member of the phenol family of compounds.

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Nomenclature for Phenols

The name phenol is derived from a combination of the terms phenyl and alcohol.

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Nomenclature for PhenolsThe IUPAC rules for naming phenols are simply extensions of the rules used to name benzene derivatives with hydrocarbon or halogen substituents. The parent name is phenol. Ring numbering always begins with the hydroxyl group and proceeds in the direction that gives the lower number to the next carbon atom bearing a substituent. The numerical position of the hydroxyl group is not specified in the name because it is 1 by definition.

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Nomenclature for Phenols

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Nomenclature for PhenolsMethyl and hydroxy derivatives of phenol have IUPAC-accepted common names. Methylphenols are called cresols. The name cresol applies to all three isomeric methylphenols.

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Nomenclature for PhenolsFor hydroxyphenols, each of the three isomers has a different common name.

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Physical and Chemical PhenolsPhenols are generally low-melting solids or oily liquids at room temperature. Most of them are only slightly soluble in water. Many phenols have antiseptic and disinfectant properties. The simplest phenol, phenol itself, is a colorless solid with a medicinal odor. Its melting point is 410C, and it is more soluble in water than are most other phenols.

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Physical and Chemical PhenolsThe similarities and differences between these two reaction chemistries are as follows: 1. Both alcohols and phenols are

flammable. 2. Dehydration is a reaction of alcohols but

not of phenols; phenols cannot be dehydrated.

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Physical and Chemical Phenols3. Both 10 and 20 alcohols are oxidized by mild oxidizing agents. Tertiary (30) alcohols and phenols do not react with the oxidizing agents that cause 10 and 20 alcohol oxidation. Phenols can be oxidized by stronger oxidizing agents. 4. Both alcohols and phenols undergo halogenation in which the hydroxyl group is replaced by a halogen atom in a substitution reaction.

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Physical and Chemical PhenolsAcidity of Phenols One of the most important properties of phenols is their acidity. Unlike alcohols, phenols are weak acids in solution. As acids, phenols have Ka values of about 10-10. Such Ka values are lower than those of most weak inorganic acids (10-5 to 10-10). The acid ionization reaction for phenol itself is

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Physical and Chemical PhenolsAcidity of Phenols The negative ion produced from the ionization is called the phenoxide ion. When phenol itself is reacted with sodium hydroxide (a base), the salt sodium phenoxide is produced.

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Occurrence of and Uses for PhenolsDilute (2%) solutions of phenol have long been used as antiseptics. Concentrated phenol solutions, however, can cause severe skin burns. Today, phenol has been largely replaced by more effective phenol derivatives such as 4-hexylresorcinol. The compound 4-hexylresorcinol is an ingredient in many mouthwashes and throat lozenges.

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Occurrence of and Uses for Phenols

The phenol derivatives o-phenylphenol and 2-benzyl-4-chlorophenol are the active ingredients in Lysol, a disinfectant for walls, floors, and furniture in homes and hospitals.

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Occurrence of and Uses for PhenolsA number of phenols possess antioxidant activity. An antioxidant is a substance that protects other substances from being oxidized by being oxidized itself in preference to the other substances. An antioxidant has a greater affinity for a particular oxidizing agent than do the substances the antioxidant is “protecting”; the antioxidant, therefore, reacts with the oxidizing agent first.

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Many foods sensitive to air are protected from oxidation through the use of phenolic antioxidants. Two commercial phenolic antioxidant food additives are BHA (butylated hydroxy anisole) and BHT (butylated hydroxy toluene).

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Occurrence of and Uses for PhenolsA naturally occurring phenolic antioxidant that is important in the functioning of the human body is vitamin E.

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Occurrence of and Uses for PhenolsA number of phenols found in plants are used as flavoring agents and/or antibacterials. Included among these phenols are

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Occurrence of and Uses for PhenolsCertain phenols exert profound physiological effects. For example, the irritating constituents of poison ivy and poison oak are derivatives of catechol. These skin irritants have 15-carbon alkyl side chains with varying degrees of unsaturation (zero to three double bonds).

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Structural Characteristics of EthersAn ether is an organic compound in which an oxygen atom is bonded to two carbon atoms by single bonds. In an ether, the carbon atoms that are attached to the oxygen atom can be part of alkyl, cycloalkyl, or aryl groups.

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Structural Characteristics of EthersAll ethers contain a C—O—C unit, which is the ether functional group.

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Structural Characteristics of Ethers

Generalized formulas for ethers, which depend on the types of groups attached to the oxygen atom (alkyl or aryl), include R—O—R, R—O—R’ (where R’ is an alkyl group different from R), R—O—Ar, and Ar—O—Ar.

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An ether can be visualized as a derivative of water in which both hydrogen atoms have been replaced by hydrocarbon groups. Note that unlike alcohols and phenols, ethers do not possess a hydroxyl (—OH) group.

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Nomenclature for Ethers

Common names are almost always used for ethers whose alkyl groups contain four or fewer carbon atoms. There are two rules, one for unsymmetrical ethers (two different alkyl/ aryl groups) and one for symmetrical ethers (both alkyl/aryl groups the same).

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Rule 1: For unsymmetrical ethers, name both hydrocarbon groups bonded to the oxygen atom in alphabetical order and add the word ether, separating the words with a space. Such ether names have three separate words within them.

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Nomenclature for EthersRule 2: For symmetrical ethers, name the alkyl group, add the prefix di-, and then add the word ether, separating the words with a space. Such ether names have two separate words within them.

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Nomenclature for EthersEthers with more complex alkyl/aryl groups are named using the IUPAC system. In this system, ethers are named as substituted hydrocarbons. The smaller hydrocarbon attachment and the oxygen atom are called an alkoxy group, and this group is considered a substituent on the larger hydrocarbon group. An alkoxy group is an —OR group, an alkyl (or aryl) group attached to an oxygen atom.

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Nomenclature for EthersThe general symbol for an alkoxy group is —O—R (or —OR). The rules for naming an ether using the IUPAC system are

Rule 1: Select the longest carbon chain and use its name as the base name.

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Nomenclature for EthersRule 2: Change the -yl ending of the other hydrocarbon group to -oxy to obtain the alkoxy group name; methyl becomes methoxy, ethyl becomes ethoxy, etc. Rule 3: Place the alkoxy name, with a locator number, in front of the base chain name.

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Nomenclature for EthersThe simplest aromatic ether involves a methoxy group attached to a benzene ring. This ether goes by the common name anisole.

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The ether MTBE (methyl tert-butyl ether) has been a widely used gasoline additive since the early 1980s.

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As an additive, MTBE not only raises octane levels but also functions as a clean-burning “oxygenate” in EPA-mandated reformulated gasolines used to improve air quality in polluted areas. The amount of MTBE used in gasoline is now decreasing in response to a growing problem: contamination of water supplies by small amounts of MTBE from leaking gasoline tanks and from spills.

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Nomenclature for EthersMTBE in the water supplies is not a health-and safety issue at this time, but its presence does affect taste and odor in contaminated supplies.

Compounds with ether functional groups occur in a variety of plants. The phenolic flavoring agents eugenol, isoeugenol, and vanillin are also ethers; each has a methoxy substituent on the ring.

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Isomerism for EthersEthers contain two carbon chains (two alkyl groups), unlike the one carbon chain found in alcohols. Constitutional isomerism possibilities in ethers depend on (1) the partitioning of carbon atoms between the two

alkyl groups and (2) isomerism possibilities for the individual alkyl groups

present. Isomerism is not possible for a C2 ether (two methyl groups) or a C3 ether (a methyl and an ethyl group).

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Isomerism for EthersFor C4 ethers, isomerism arises not only from carbon atom partitioning between the alkyl groups (C1—C3 and C2—C2) but also from isomerism within a C3 group (propyl and isopropyl). There are three C4 ether constitutional isomers.For C5 ethers, carbon partitioning possibilities are C2—C3 and C1—C4. For C4 groups there are four isomeric variations: butyl, isobutyl, sec-butyl, and tert-butyl.

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Isomerism for Ethers

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Isomerism for EthersFunctional Group Isomerism

Ethers and alcohols with the same number of carbon atoms and the same degree of saturation have the same molecular formula. The simplest manifestation of this phenomenon involves dimethyl ether, the C2 ether, and ethyl alcohol, the C2 alcohol. Both have the molecular formula C2H6O.

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Isomerism for EthersFunctional Group IsomerismFunctional group isomers are constitutional isomers that contain different functional groups. When three carbon atoms are present the ether–alcohol functional group isomerism possibilities are

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Physical and Chemical Properties of EthersThe boiling points of ethers are similar to those of alkanes of comparable molecular mass and are much lower than those of alcohols of comparable molecular mass.

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Physical and Chemical Properties of Ethers

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Ethers, in general, are more soluble in water than are alkanes of similar molecular mass because ether molecules are able to form hydrogen bonds with water. Ethers have water solubilities similar to those of alcohols of the same molecular mass.

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Physical and Chemical Properties of EthersDiethyl ether and butyl alcohol have the same solubility in water. Because ethers can also hydrogen-bond to alcohols, alcohols and ethers tend to be mutually soluble. Nonpolar substances tend to be more soluble in ethers than in alcohols because ethers have no hydrogen-bonding network that has to be broken up for solubility to occur.

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Physical and Chemical Properties of EthersTwo chemical properties of ethers are especially important. 1. Ethers are flammable. Special care must be exercised in laboratories where ethers are used. Diethyl ether, whose boiling point of 350C is only a few degrees above room temperature, is a particular fl ash-fire hazard.

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Physical and Chemical Properties of EthersTwo chemical properties of ethers are especially important. 2. Ethers react slowly with oxygen from the air to form unstable hydroperoxides and peroxides.

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Such compounds, when concentrated, represent an explosion hazard and must be removed before stored ethers are used. Like alkanes, ethers are unreactive toward acids, bases, and oxidizing agents. Like alkanes, they do undergo combustion and halogenation reactions.

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Physical and Chemical Properties of EthersThe general chemical unreactivity of ethers, coupled with the fact that most organic compounds are ether-soluble, makes ethers excellent solvents in which to carry out organic reactions. Their relatively low boiling points simplify their separation from the reaction products.

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The intermolecular dehydration of a primary alcohol will produce an ether.

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Cyclic EthersCyclic ethers contain ether functional groups as part of a ring system. Some examples of such cyclic ethers, along with their common names, follow.

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Cyclic Ethers

Ethylene oxide has few direct uses. Its importance is as a starting material for the production of ethylene glycol, a major component of automobile antifreeze. THF is a particularly useful solvent in that it dissolves many organic compounds and yet is miscible with water.

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Cyclic Ethers

Many cyclic structures that are polyhydroxy derivatives of the five-membered (furan) and six-membered (pyran) cyclic ether systems. These carbohydrate derivatives are called furanoses and pyranoses.Vitamin E and THC, the active ingredient in marijuana, have structures in which a cyclic ether component is present.

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Cyclic Ethers

Cyclic ethers are our first encounter with heterocyclic organic compounds. A heterocyclic organic compound is a cyclic organic compound in which one or more of the carbon atoms in the ring have been replaced with atoms of other elements. The hetero atom is usually oxygen or nitrogen.

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Cyclic EthersCyclic ethers—compounds in which the ether functional group is part of a ring system—exist. Cyclic alcohols—compounds in which the alcohol functional group is part of a ring system—do not exist. To incorporate an alcohol functional group into a ring system would require an oxygen atom with three bonds, and oxygen atoms form only two bonds.

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Cyclic Ethers

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Sulfur Analogs of Alcohols

Many organic compounds containing oxygen have sulfur analogs, in which a sulfur atom has replaced an oxygen atom. Sulfur is in the same group of the periodic table as oxygen, so the two elements have similar electron configurations.

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Thiols, the sulfur analogs of alcohols, contain —SH functional groups instead of —OH functional groups. The thiol functional group is called a sulfhydryl group. A sulfhydryl group is the —SH functional group. A thiol is an organic compound in which a sulfhydryl group is bonded to a saturated carbon atom. An older term used for thiols is mercaptans.

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Sulfur Analogs of AlcoholsNomenclature for Thiols Thiols are named in the same way as alcohols in the IUPAC system, except that the -ol becomes -thiol. The prefix thio- indicates the substitution of a sulfur atom for an oxygen atom in a compound.

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Sulfur Analogs of AlcoholsAs in the case of diols and triols, the -e at the end of the alkane name is also retained for thiols.Common names for thiols are based on use of the term mercaptan, the older name for thiols. The name of the alkyl group present (as a separate word) precedes the word mercaptan.

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Properties of Thiols Two important properties of thiols are lower boiling points than alcohols of similar size (because of lack of hydrogen bonding) and a strong, disagreeable odor. The familiar odor of natural gas results from the addition of a low concentration of methanethiol (CH3—SH) to the gas. The exceptionally low threshold of detection for this thiol enables consumers to smell a gas leak long before the gas, which is itself odorless, reaches dangerous levels. The scent of skunks is due primarily to two thiols.

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Properties of Thiols

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Properties of Thiols Thiols are easily oxidized but yield different products than their alcohol analogs. Thiols form disulfides. Each of two thiol groups loses a hydrogen atom, thus linking the two sulfur atoms together via a disulfide group, —S—S—.

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Properties of Thiols Reversal of this reaction, a reduction process, is also readily accomplished. Breaking of the disulfide bond regenerates two thiol molecules.

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Properties of Thiols These two “opposite reactions” are of biological importance in the area of protein chemistry. Disulfide bonds formed from the interaction of two —SH groups contribute in a major way to protein structure.

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Properties of Thiols

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Sulfur Analogs of Ethers

Sulfur analogs of ethers are known as thioethers (or sulfides). A thioether is an organic compound in which a sulfur atom is bonded to two carbon atoms by single bonds. The generalized formula for a thioether is R—S—R. Like thiols, thioethers (or sulfides) have strong characteristic odors.

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Sulfur Analogs of Ethers Thioethers are named in the same way as ethers, with sulfide used in place of ether in common names and alkylthio used in place of alkoxy in IUPAC names.

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Sulfur Analogs of Ethers Thiols and thioethers are functional group isomers in the same manner that alcohols and ethers are functional group isomers.

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Sulfur Analogs of Ethers 1-propanethiol and the thioether methylthioethane both have the molecular formula C3H8S.

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Sulfur Analogs of Ethers

End of Chapter 4Alcohols, Phenols

and Ethers

General, Organic, and Biological Chemistry, Fifth EditionH. Stephen Stoker

Brroks/Cole Cengage Learning. Permission required for reproduction or display.

Chapter 4 Alcohols Phenols and Ethers

Science

Transcript of Chapter 4 Alcohols Phenols and Ethers