Chapter 13 Alcohols, Phenols, and Ethers Spencer L. Seager Michael R. Slabaugh Jennifer P. Harris

ALCOHOLS, PHENOLS, & ETHERS A hydroxy group is 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’

ALCOHOL EXAMPLES

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: CH 3 —CH 2 —CH 2 —CH—CH 2 —CH OH | 3-hexanol

NAMING ALCOHOLS (continued) 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. Example: 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. CH 3 —CH 2 —CH—CH—CH—CH OH | 2,4-dimethyl-3-hexanol CH 3 | CH 3 |

NAMING PHENOLS Substituted phenols are usually named as derivatives of the parent compound phenol. Examples:

CLASSIFICATION OF ALCOHOLS

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:

PHYSICAL PROPERTIES OF ALCOHOLS (continued) Larger alkanes have greater hydrophobic regions and are less soluble or insoluble in water. Water interacts only with the –OH group of 1-heptanol:

PHYSICAL PROPERTIES OF ALCOHOLS (continued)

The –OH group can hydrogen bond between alcohol molecules leading to relatively high boiling points. Hydrogen bonding in pure ethanol:

PHYSICAL PROPERTIES OF ALCOHOLS (continued)

ALCOHOL REACTIONS The removal of water (dehydration) from an alcohol at 180°C is an elimination reaction that produces an alkene.

ALCOHOL DEHYDRATION TO ALKENE EXAMPLES

DEHYDRATION OF AN ALCOHOL Protonation of alcohol Formation of carbocation and water Formation of double bond and regeneration of catalyst

ALCOHOL REACTIONS (continued) Under slightly different conditions (140°C), a dehydration reaction can occur between two alcohol molecules to produce an ether. Just for your information – not on exam

ALCOHOL REACTIONS (continued) 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

ALCOHOL REACTIONS (continued) Primary alcohol oxidation Secondary alcohol oxidation

ALCOHOL REACTIONS (continued) Tertiary alcohol oxidation

ALCOHOL OXIDATION EXAMPLES (1) The tube on the left contains orange K 2 Cr 2 O 7 and is next to the colorless ethanol. (2) After mixing, the ethanol is oxidized, and chromium is reduced, forming a grayish green precipitate.

ALCOHOL REACTIONS (continued)

MULTISTEP REACTIONS 1 st step 2 nd step

IMPORTANT ALCOHOLS Methanol (wood alcohol): CH 3 OH Useful as a solvent and industrial starting material Highly toxic, if taken internally causes blindness and/or death Ethanol (ethyl alcohol, grain alcohol): CH 3 CH 2 OH Produced commercially from ethylene and through biological (yeast) fermentation of carbohydrates Useful as a solvent, industrial starting material, fuel (gasohol), and found in alcoholic beverages Moderately toxic

IMPORTANT ALCOHOLS (continued) 2-Propanol (isopropyl alcohol) is the main component of rubbing alcohol. 1,2,3-Propanetriol (glycerol) is used as a food moistening agent (nontoxic) and for its soothing qualities (soaps). Cholesterol is a waxy steroid found in cell membranes and transported in blood stream. High level can lead to heart disease. Antifreezes - 1,2-ethanediol (ethylene glycol) and 1,2-propanediol

EXAMPLES OF ALCOHOLS

PHENOLS Phenol behaves as a weak acid in water. Phenol can react with bases to form salt.

USES OF PHENOLS In a dilute solution, phenol is used as a disinfectant. Phenol derivatives used as disinfectants:

USES OF PHENOLS (continued) Phenol derivatives used as antioxidants in food:

NAMING ETHERS IUPAC name: Name the smaller of the two R groups as an alkoxy group attached to the parent chain by replacing the –yl ending of the R group with –oxy. Common name: Name the groups attached to the oxygen alphabetically and add the word ether. common: sec-butyl ethyl ether

CYCLIC ETHERS Heterocyclic rings contain atoms other than carbon in the ring.

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 hydrogen bond between molecules Inert and do not react with most reagents (like alkanes) Highly flammable (like alkanes)

PROPERTIES OF ETHERS (continued) Hydrogen bonding of dimethyl ether: (a) with water and (b) no hydrogen bonding in the pure state.

THIOLS: THE –SH (SULFHYDRYL) GROUP Most distinguishing characteristic is their strong and offensive odor ethanethiol – added to natural gas 1-propanethiol – odor in garlic and onions trans-2-butene-1-thiol – odor associated with skunks

THIOL REACTIONS Oxidation forms disulfide (-S-S-) linkages, which are important structural features of some proteins: Specific example:

THIOL REACTIONS (continued) Oxidation reactions can be reversed with a reducing agent (H):

THIOL REACTIONS (continued) Reacts with heavy metals (Pb 2+, Hg 2+ ) to form insoluble compounds, with adverse biological results: Heavy metal poisoning

POLYFUNCTIONAL COMPOUNDS Polyfunctional compounds are compounds with two or more functional groups. Functional groups determine chemical properties of compounds. Example:

POLYFUNCTIONAL COMPOUNDS (continued)