13.3 Physical Properties of Alcohols, Phenols, and Ethers In an alcohol-containing sanitizer, the amount of ethanol is typically 60% (v/v) but can be as high as 85% (v/v). Because alcohols are flammable, hand sanitizers are a fire hazard in the home. Hand sanitizers that contain ethanol are used to kill bacteria on the hands. Learning Goal Describe the classification of alcohols; describe the boiling points and solubility of alcohols, phenols, and ethers.
Classification of Alcohols Alcohols are classified • by the number of alkyl groups attached to the carbon bonded to the hydroxyl. • as primary (1°), secondary (2°), or tertiary (3°).
Study Check Classify each alcohol as primary, secondary, or tertiary. A. B. CH3—CH2—CH2—OH C.
Solution Classify each alcohol as primary, secondary, or tertiary. A. secondary B. CH3—CH2—CH2—OHprimary C. tertiary
Boiling Points Because there is a large electronegativity difference between the oxygen and hydrogen atoms in the — OH group, • the oxygen has a partially negative charge. • the hydrogen has a partially positive charge. • hydrogen bonds form between the oxygen of one alcohol and hydrogen in the — OH group of another alcohol. Hydrogen bonds form between alcohol molecules but not between ether molecules. Small alcohol and ether molecules are soluble in water because they form hydrogen bonds.
Boiling Points • Hydrogen bonds cannot form between ether molecules because there are not any polar — OH groups. • Alcohols with similar mass have higher boiling points than do ethers because alcohols require higher temperatures (more energy) to break their hydrogen bonds. • The boiling points of ethers are similar to those of alkanes because neither can form hydrogen bonds.
Solubility: Alcohols and Ethers Alcohols • contain polar — OH groups and form hydrogen bonds with other alcohol molecules and with water. • that have one to three carbons are soluble in water. The solubility of alcohols in water decreases with increasing number of carbons.
Solubility: Alcohols and Ethers Ethers • can form hydrogen bonds with water. • form fewer hydrogen bonds than alcohols with water. • are only slightly soluble in water when they have fewer than four carbon atoms. • are not soluble in water if they have five or more carbon atoms.
Solubility: Phenols Phenols, once used as antiseptics, • are slightly soluble in water. • have an — OH group that can form hydrogen bonds with water. • can react with water to produce phenoxide ions. In water, the — OH group of phenol ionizes slightly, which makes it a weak acid (Ka = 1 × 10−10). • + H2O + H3O+
Phenol and Antiseptics Antiseptics, substances applied to the skin to kill microorganisms that cause infection, • were once made of dilute solutions of phenol. • were once used to disinfect wounds to prevent post-surgical infections such as gangrene. • are now used in Lysol, used to disinfect surfaces, and contain the antiseptics 2-phenylphenol and 2-benzyl-4-chlorophenol.
Chemistry Link to Health: Hand Sanitizers Hand sanitizers containing ethanol as their active ingredient • kill most bacteria and viruses that spread colds and flu. • are approximately 60% (v/v) but can be as high as 85% (v/v). • are highly flammable and produce a transparent, blue flame. • may also contain triclosan, which can accumulate in the environment, promoting growth of antibiotic-resistant bacteria.
Study Check Indicate whether each of the following is soluble in water and explain why. A. CH3—CH2—CH2—CH2—CH2—CH2—OH B. CH3—CH2—OH
Solution Indicate whether each of the following is soluble in water and explain why. A. CH3—CH2—CH2—CH2—CH2—CH2—OH not soluble Alcohols with long carbon chains (nonpolar) are not soluble. B. CH3—CH2—OH soluble Short-chain alcohols form hydrogen bonds with water.