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ALCOHOLS, PHENOLS, AND ETHERS Chapter 13: 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 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. 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. Example: Example: CH3 OH CH3 | | | CH3—CH2—CH—CH—CH—CH3 6 5 4 3 2 1 2,4-dimethyl-3-hexanol OH | CH3—CH2—CH2—CH—CH2—CH3 6 5 4 3 2 1 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-hexanol 3 NAMING PHENOLS 4 CLASSIFICATION OF ALCOHOLS • Substituted phenols are usually named as derivatives of the parent compound phenol. Examples: 5 6 1 PHYSICAL PROPERTIES OF ALCOHOLS PHYSICAL PROPERTIES OF ALCOHOLS, cont. • 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 PHYSICAL PROPERTIES OF ALCOHOLS, cont. 8 PHYSICAL PROPERTIES OF ALCOHOLS, cont. • The –OH group can hydrogen bond between alcohol molecules leading to relatively high boiling points. • Hydrogen bonding in pure ethanol: 9 PHYSICAL PROPERTIES OF ALCOHOLS, cont. 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. ALCOHOL REACTIONS, cont. • Oxidation – the removal of hydrogen atoms. • Under slightly different conditions (140°C), a dehydration reaction can occur between two alcohol molecules to produce an ether. • Alcohol oxidations with an oxidizing (O) agent, such as K2Cr2O7 and KMnO4: • Primary alcohols → aldehyde → carboxylic acid • Secondary alcohols → ketone • Tertiary alcohols → no reaction 13 ALCOHOL REACTIONS, cont. 14 IMPORTANT ALCOHOLS • Primary alcohol oxidation • Methanol (wood alcohol): CH3OH • Production: •Useful as a solvent and industrial starting material • Secondary alcohol oxidation • Highly toxic, if taken internally causes blindness and/or death 15 IMPORTANT ALCOHOLS, cont. 16 IMPORTANT ALCOHOLS, cont. • Ethanol (ethyl alcohol, grain alcohol): CH3CH2OH • 2-propanol (isopropyl alcohol) is the main component of rubbing alcohol • Produced commercially from ethylene and through biological (yeast) fermentation of carbohydrates • Useful as a solvent, industrial starting material, fuel ( (gasohol), h l) and d ffound d iin alcoholic l h li b 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. PHENOLS • Antifreezes 1,2-ethanediol (ethylene glycol) • Phenol behaves as a weak acid in water 1,2-propanediol (propylene glycol) and can react with bases to form salt. 19 USES OF PHENOLS: 20 USES OF PHENOLS: • In a dilute solution, phenol is used as a disinfectant. • Phenol derivatives used as antioxidants in food: • Phenol derivatives used as disinfectants: 21 22 • Hydrogen bonding of dimethyl ether: (a) with water and (b) no hydrogen bonding in the pure state: PROPERTIES OF ETHERS • Much less polar than alcohols • More soluble in water than alkanes, but less soluble than alcohols • Low boiling and melting points because of the inability to h d hydrogen b bond db between t molecules l l • inert and do not react with most reagents (like alkanes) • highly flammable (like alkanes) 23 24 4 THIOLS: THE –SH (SULFHYDRYL) GROUP THIOL REACTIONS • Most distinguishing characteristic is their strong and offensive odor • 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 THIOL REACTIONS, cont. 26 POLYFUNCTIONAL COMPOUNDS • Oxidation reactions can be reversed with a reducing agent (H): • Compounds with two or more functional groups • Functional groups determine chemical properties of compounds. Example: 27 28 5