Chemeketa Community College Alcohols, Ethers, Phenols, and Thiols Chapter 22 Larry Emme Chemeketa Community College

Functional Groups

The various classes of compounds are identified by the presence of certain characteristic groups called functional groups. Through the chemical reactions of functional groups, it is possible to create or synthesize new substances.

Classification of Alcohols

Alcohols are classified by the number of R groups (i. e Alcohols are classified by the number of R groups (i.e. carbon atoms) attached to the hydroxyl carbon as shown here. 6 6

Tests for Alcohols

Lucas Test Addition of ZnCl2 in concentrated HCl forms a “turbid” solution. Order of reactivity is 3o > 2o >> 1o.

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Polyhydroxy alcohols and polyols are general terms for alcohols that have more than one –OH group per molecule. Polyhydroxy compounds are very important molecules in living cells, as they include the carbohydrate class of biochemicals.

Structural Representations of Alcohols An alcohol such as 2-butanol can be written in a single-line formula by enclosing the –OH group in parentheses and placing it after the carbon to which it is bonded. =

Application to Biochemistry Blood sugar (glucose) contains five alcohol groups. Using the structure of glucose shown here, label each group as 1°, 2°, or 3°. O=CHCH(OH)CH(OH)CH(OH)CH(OH)CH2OH

Application to Biochemistry

Naming Alcohols

IUPAC Rules for Naming Alcohols Select the longest continuous chain of carbon atoms containing the –OH group. Number the carbon atoms in this chain so that the one bearing the -OH group has the lowest possible number.

IUPAC Rules for Naming Alcohols 3. Form the parent alcohol name by replacing the final –e of the corresponding alkane by –ol. When isomers are possible, locate the position of the –OH group by placing the number (hyphenated) of the carbon atom to which the –OH is bonded immediately before the parent alcohol name. 4. Name each alkyl side chain (or other group), and designate its position by number.

Name CH3CH2CH2CH2OH 1-butanol

Nomenclature of Alcohols

Physical Properties of Alcohols

Physical Properties of Alcohols The physical properties of alcohols are related to those of both water and alkane hydrocarbons. An alcohol molecule is made up of a waterlike hydroxyl group joined to a hydrocarbonlike alkyl group.

Boiling Points of Alcohols Alcohols have relatively high boiling points. The boiling points of the normal alcohols increase in a regular fashion with increasing number of carbon atoms. Branched-chain alcohols have lower boiling points than corresponding straight-chain alcohols.

Alcohols containing up to three carbon atoms are infinitely soluble in water. The –OH group on the alcohol molecule is responsible for both the water solubility and relatively high boiling points of the low-molar-mass alcohols.

Hydrogen Bonding in Alcohols

Glucose is one of the most important carbohydrates in biochemistry Glucose is one of the most important carbohydrates in biochemistry. It has six carbons and five alcohol groups (molar mass = 180.2 g). How would you predict the water solubility of glucose to differ from that of 1-hexanol?

Effect of Hydroxyl Groups on Solubility Note the difference in solubility of hexanol (only one –OH group) and glucose ( five –OH groups). CH3CH2CH2CH2CH2CH2OH 1-hexanol (solubility = 0.6g/100g H2O) D-glucose (solubility = 95g/100g H2O) 28 28

Effect of Branching on Boiling Point A branched-chain alcohol will have a lower boiling point than the corresponding straight-chain alcohol. For example 2-butanol is branched and has a b.p. of 91.5 C versus 118 C for 1-butanol. CH3CH2CH2CH2OH 1-butanol 29 29

Chemical Properties of Alcohols

Chemical Properties of Alcohols Acidic and Basic Properties Oxidation Dehydration Esterification (Chapter 24)

Basic Properties If an alcohol is mixed with a strong acid, it will accept a proton (act as a Brønsted-Lowry base) to form a protonated alcohol or oxonium ion.

Acidic Properties Alcohols can also act as Brønsted-Lowry acids. The resulting anion in the alcohol reaction is known as an alkoxide ion (RO-).

Reactivity of Alcohols with Na or K The order of reactivity of alcohols with sodium or potassium is: primary > secondary > tertiary. Reactivity decreases with increasing molar mass, since the –OH group becomes a relatively smaller, less significant part of the molecule.

Oxidation Oxidation is the loss of hydrogen or the gain of bonds to oxygen by the organic reactant. Carbon atoms exist in progressively higher stages of oxidation in different functional groups.

The –OH group gives an organic compound the capability of forming an aldehyde, ketone, or carboxylic acid.

Common Oxidizing Agents KMnO4 K2Cr2O7 O2

Dehydration Alcohols can be dehydrated with sulfuric acid to form alkenes.

Dehydration For many alcohols, there is more than one way to remove water. Therefore the double bond can be located in different positions. The major product in such cases is the alkene in which the C=C bond has the greatest number of alkyl substituents on it (or the least number of hydrogens).

Saytzeff’s Rule During intramolecular dehydration, if there is a choice of positions for the carbon-carbon double bond, the preferred location is the one that generally gives the more highly substituted alkene – that is, the alkene with the most alkyl groups attached to the double-bond carbons.

Esterification (Conversion of Alcohols to Ethers) An alcohol can react with a carboxylic acid to form an ester and water.

Utility of the Hydroxyl Functional Group

Common Alcohols

Three General Methods for Making Alcohols Hydrolysis of an ester. Alkaline hydrolysis of an alkyl halide (1° and 2° alcohols only). Catalytic reduction of aldehydes and ketones.

Hydrolysis of an Ester Hydrolysis is a reaction of water with another species in which the water molecule is split.

Alkaline hydrolysis of an alkyl halide (1° and 2° alcohols only). CH3CH2Cl + NaOH(aq)  CH2CH3OH + NaCl

Catalytic Reduction of Aldehydes and Ketones Produces primary and secondary alcohols. Chapter 23

Preparation of Methanol Methanol is a common industrial solvent prepared by the high-pressure catalytic hydrogenation of carbon monoxide. The most economical nonpetroleum source of carbon monoxide for making methanol is coal. 49 49

Uses of Methanol Conversion to formaldehyde (use in manufacture of polymers). Manufacture of other chemicals, especially various kinds of esters Denaturing ethyl alcohol Industrial solvent

Ethanol Large quantities of ethanol are prepared by fermentation. The conversion of simple sugars to ethanol is accomplished by yeast. Industrially, ethanol is made by acid-catalyzed addition of water to ethylene.

Uses of Ethanol An intermediate in the manufacture of other chemicals such as acetaldehyde, acetic acid, ethyl acetate, and diethyl ether. A solvent for many organic substances. A compounding ingredient for pharmaceuticals, perfumes, flavorings, etc. An essential ingredient in alcoholic beverages.

2-Propanol (Isopropyl Alcohol) 2-Propanol is made from propene.

Uses of 2-Propanol (Isopropyl Alcohol) To manufacture other chemicals (especially acetone). As an industrial solvent. As the principal ingredient in rubbing alcohol formulations.

Ethylene Glycol (1,2-Ethanediol) Industrial synthesis

Uses of Ethylene Glycol (1,2-Ethanediol) In the preparation of the synthetic polyester fiber Dacron and film Mylar As a major ingredient in “permanent-type” antifreeze cooling systems As a solvent in the paint and plastic industries In the formulations of printing ink and ink for ballpoint pens.

Glycerol (1,2,3-Propanetriol) Glycerol (also known as glycerine) is an important trihydroxyalcohol. It is obtained as a by-product of the processing of animal and vegetable fats to make soap and other products. It is synthesized commercially from propene.

Each directly related to the three –OH groups. Uses of Glycerol Each directly related to the three –OH groups. As a raw material in the manufacture of polymers and explosives (nitroglycerin). As an emollient in cosmetics. As a humectant in tobacco products. As a sweetener.

Phenols

Phenols The term phenol is used for the class of compounds that have a hydroxy group attached to an aromatic ring. The parent compound is also called phenol, C6H5OH.

Naming Phenols Many phenols are named as derivatives of the parent compound, via the general methods for naming aromatic compounds.

Derivatives of Phenol Compounds of phenol are the active ingredients in the essential oils of nutmeg, thyme, cloves, and vanilla. 62

Common Phenols

Common Phenols/Alcohols

Common Phenols/Alcohols

Common Phenols

Herbicides produced by Phenols

Properties of Phenols

Properties of Phenols Colorless, crystalline solid, mp = 41 °C Highly poisonous More acidic than alcohols and water

Production of Phenol

Production of Phenol Phenol is obtained from coal tar. Several commercial methods are used to produce phenol synthetically.

Ethers

Ethers Ethers have the general formula below where both R groups can be the same or different. ROR′

Naming Simple Ethers Name each alkyl group in alphabetical order followed by the word ether as shown here. Use a prefix if both alkyl groups are the same. 76 76

Naming Ethers Using IUPAC Rules Name the longest continuous carbon chain corresponding to the parent alkane. 2. Change the –yl ending of the other hydrocarbon group to –oxy to obtain the alkoxy group name. 3. Combine the two names from Steps 1 and 2, giving the alkoxy name and its position on the longest carbon chain first, to form the ether name. For example… …would be named methoxyethane 77 77

Examples of Naming Alkoxy Groups 78 78

Examples of Naming Ethers 79 79

Structures and Properties of Ethers

Properties of Ethers Ethers are somewhat more polar than alkanes, but are much less polar than alcohols. Ethers – especially diethyl ether – are exceptionally good solvents for organic compounds.

Formation of Peroxides from Ethers Oxygen of the air slowly reacts with ethers to form unstable peroxides that are subject to explosive decomposition.

Preparation of Ethers

Preparation of Ethers by Intramolecular Dehydration Ethers can be prepared by splitting out water from two molecules of an primary alcohol. This type of reaction is known as a condensation reaction. 85 85

Williamson Synthesis of Ethers The alkyl halide, RX, may be a methyl or primary group, but not a secondary or tertiary alkyl group or an aryl group. The alkoxide, R’ONa, may be methyl, primary, secondary, tertiary, or an aryl group. RX + R’ONa  ROR’ + NaX Alkyl halide alkoxide ether

Thiols

are similar to alcohols contain a thiol (-SH) group Thiols or mercaptans contain sulfur are similar to alcohols contain a thiol (-SH) group often have strong odors found in cheese, onions, garlic, and oysters are used to detect gas leaks 88

Thiols are named in the IUPAC system by adding thiol to the alkane name of the longest carbon chain. (Methyl Mercaptan) 89

Properties of Thiols Foul odors. 2. Oxidation to disulfides: 2 RSH  R-S-S-R [O] thiol disulfide

Striped Skunk (Mephitis mephitis) Thiols E-2-buten-1-thiol 38-44% 3-methyl-1-butanethiol 18-26% 2-quinolinemethanethiol 3-12%

For pets that have been sprayed, bathe the animal in a mixture of 1 quart of 3% hydrogen peroxide (from drug store), 1/4 cup of baking soda (sodium bicarbonate) and a teaspoon of liquid detergent. After 5 minutes rinse the animal with water. Repeat if necessary. The mixture must be used after mixing and will not work if it is stored for any length of time. DO NOT STORE IN A CLOSED CONTAINER - it releases oxygen gas so it could break the container. This mixture may bleach the pet's hair.

Why tomato juice is believed to eliminate skunk odor Why tomato juice is believed to eliminate skunk odor. Bathing an animal in tomato juice seems to work because at high doses of skunk spray the human nose quits smelling the odor (olfactory fatigue). When this happens, the odor of tomato juice can easily be detected. A person suffering olfactory fatigue to skunk spray will swear that the skunk odor is gone and was neutralized by the tomato juice. Another person coming on the scene at this point will readily confirm that the skunk spray has not been neutralized by the tomato juice.

The End