Chapter 12 Organic Compounds with Oxygen and Sulfur

Chapter 12 Organic Compounds with Oxygen and Sulfur 12. 2 Properties of Alcohols, Ethers, and Thiols Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 1

Boiling Points of Alcohols • contain polar OH groups. • form hydrogen bonds with other alcohol molecules. • have higher boiling points than alkanes and ethers of similar mass. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 2

Boiling Points of Ethers • do not have a polar group. • have an O atom, but there is no H attached. • cannot form hydrogen bonds between ether molecules. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 3

Solubility of Alcohols and Ethers in Water Alcohols and ethers • are more soluble in water than alkanes because the oxygen atom can hydrogen bond with water. • with 1 -4 C atoms are soluble, but not with 5 or more C atoms. 4

Comparing Solubility and Boiling Points Compound Molar Mass Boiling Point (°C) Soluble in Water? Alkane CH 3─CH 2─CH 3 44 -42 No Ether CH 3─O─CH 3 46 -23 Yes Alcohol CH 3─CH 2─OH 46 78 Yes 5

Reactivity of Alkanes vs. Alcohols Hydrocarbon + O 2 carbon dioxide + water + heat energy D Ex. CH 4 + 2 O 2 CO 2 + 2 H 2 O D Heat released is 802 k. J/mol of methane Effect of partially oxidizing a hydrocarbon, let’s look at the combustion reaction of CH 3 OH (methanol), in which 1 H has been replaced by an –OH group. 2 CH 3 OH + 3 O 2 2 CO 2 + 4 H 2 O D Heat released is 640 k. J/mol of methanol (1. 5 moles of O 2 required to with 1 mole of CH 3 OH!) 6

These reactions illustrates two important principles. 1 st, the more reduced a molecule, the more energy is released during oxidation on a molar basis. Methane is fully reduced and gives off more energy during combustion than methanol. 2 nd, the number of oxygen molecules required to react with a fuel molecule can give an estimate of how much energy is available. More highly reduced molecules require more oxygen during combustion and produces more energy. 7

Reduction of hydrocarbons vs. their oxidation OH CH 3 OH Partially Oxidized 8

Solubility of Phenol • is soluble in water. • has a hydroxyl group that ionizes slightly (weak acid). • is corrosive and irritating to skin. + H 2 O + H 3 O + 9