Chapter 13: Alcohols, Phenols, and Ethers ALCOHOLS, PHENOLS, AND ETHERS Hydroxy group the OH functional group An alcohol has an OH group attached to an aliphatic carbon. General formula: R-OH A phenol has an OH group on a benzene ring. An ether has the functional group: General formula: R-O-R 1 2 NAMING ALCOHOLS Step 1: Name the longest chain to which the OH group is attached. Use the hydrocarbon name of the chain, drop the final e, and replace it with ol. Step 2: Number the longest chain to give the lowest number to the carbon with the attached OH. Step 3: Locate the OH position. OH CH 3 CH 2 CH 2 CH CH 2 CH 3 6 5 4 3 2 1 3-hexanol Step 4: Locate and name any other groups attached to the longest chain. Step 5: Combine the name and location of other groups, the location of the OH, and the longest chain into the final name. CH 3 OH CH 3 CH 3 CH 2 CH CH CH CH 3 6 5 4 3 2 1 2,4-dimethyl-3-hexanol Note: Alcohols containing two OH groups are diols, three OH groups are triols. The IUPAC names for these compounds have endings of diol and triol rather than ol. 3 4 NAMING PHENOLS Substituted phenols are usually named as derivatives of the parent compound phenol. CLASSIFICATION OF ALCOHOLS Examples: 5 6 1
PHYSICAL PROPERTIES OF ALCOHOLS The OH group is polar and capable of hydrogen bonding. This makes low molecular weight alcohols highly soluble in water. Hydrogen bonding in a water-methanol solution: Larger alkanes have greater hydrophobic regions and are less soluble or insoluble in water. Water interacts only with the OH group of 1-heptanol: 7 8 The OH group can hydrogen bond between alcohol molecules leading to relatively high boiling points. Hydrogen bonding in pure ethanol: 9 10 ALCOHOL REACTIONS The removal of water (dehydration) from an alcohol at 180 C is an elimination reaction that produces an alkene. 11 12 2
ALCOHOL REACTIONS, cont. Under slightly different conditions (140 C), a dehydration reaction can occur between two alcohol molecules to produce an ether. ALCOHOL REACTIONS, cont. Oxidation the removal of hydrogen atoms. Alcohol oxidations with an oxidizing (O) agent, such as K 2 Cr 2 O 7 and KMnO 4 : Primary alcohols aldehyde carboxylic acid Secondary alcohols ketone Tertiary alcohols no reaction 13 14 ALCOHOL REACTIONS, cont. Primary alcohol oxidation IMPORTANT ALCOHOLS Methanol (wood alcohol): CH 3 OH Production: Secondary alcohol oxidation Useful as a solvent and industrial starting material Highly toxic, if taken internally causes blindness and/or death 15 16 IMPORTANT ALCOHOLS, cont. Ethanol (ethyl alcohol, grain alcohol): CH 3 CH 2 OH Produced commercially from ethylene and through biological (yeast) fermentation of carbohydrates IMPORTANT ALCOHOLS, cont. 2-propanol (isopropyl alcohol) is the main component of rubbing alcohol Useful as a solvent, industrial starting material, fuel (gasohol), and dfound din alcoholic li beverages. Moderately toxic 1,2,3-propanetriol (glycerol) is used as a food moistening agent (nontoxic) and for its soothing qualities (soaps) 17 18 3
IMPORTANT ALCOHOLS, cont. Antifreezes 1,2-ethanediol (ethylene glycol) PHENOLS Phenol behaves as a weak acid in water 1,2-propanediol (propylene glycol) and can react with bases to form salt. 19 20 USES OF PHENOLS: In a dilute solution, phenol is used as a disinfectant. USES OF PHENOLS: Phenol derivatives used as antioxidants in food: Phenol derivatives used as disinfectants: 21 22 PROPERTIES OF ETHERS Much less polar than alcohols Hydrogen bonding of dimethyl ether: (a) with water and (b) no hydrogen bonding in the pure state: More soluble in water than alkanes, but less soluble than alcohols Low boiling and melting points because of the inability to hd hydrogen bond dbt between molecules l inert and do not react with most reagents (like alkanes) highly flammable (like alkanes) 23 24 4
THIOLS: THE SH (SULFHYDRYL) GROUP Most distinguishing characteristic is their strong and offensive odor THIOL REACTIONS Oxidation forms disulfide (-S-S-) linkages, which are important structural features of some proteins: ethanethiol added to natural gas 1-propanethiol odor in garlic and onions trans-2-butene-1-thiol odor associated with skunks 25 26 THIOL REACTIONS, cont. Oxidation reactions can be reversed with a reducing agent (H): POLYFUNCTIONAL COMPOUNDS Compounds with two or more functional groups Functional groups determine chemical properties of compounds. 27 28 5