17.0 Introduction

Objectives

After completing this lesson, you should be able to

1. describe the structural differences among alcohols, phenols and enols.
2. write equations describing the industrial preparation of the two simplest alcohols: methanol and ethanol.

Key Terms

• alcohol
• enol
• phenol

Study Notes

The author of the textbook correctly points out the toxicity of methanol, and describes the adverse effects that can result from its consumption. These effects have not been exaggerated; you may recall reading about the deaths of three residents of Peerless Lake, Alberta, in March of 1986, brought about by drinking photocopier fluid which contained methanol (or methyl hydrate as it is often called in press reports). In April 1986,more than 20 people died and many more were blinded through drinking Italian wines to which methanol had been deliberately added. In 2000,more than 100 people died in El Salvador after black marketeers sold discarded liquor bottles that had been refilled with a methanol mixture. Almost everyone is aware that the alcohol present in alcoholic beverages is ethanol (also called ethyl alcohol or grain alcohol). However, many people do not realize that in its pure state, or in solutions of high concentration, this substance is poisonous. In the laboratory one may find containers labelled “absolute ethanol,” “95% ethanol” and “denatured ethanol.” The acquisition of ethanol by laboratories, and its subsequent disposal, is carefully monitored by provincial authorities. On no account should one consider drinking laboratory ethanol, even after it has been diluted to a concentration equivalent to that found in beer. Denatured alcohol is ethanol to which appropriate quantities of poisonous or nauseating substances (such as methanol) have been added. A third commonly encountered alcohol, isopropyl alcohol (“rubbing alcohol” or 2-propanol), is also toxic. It has the ability to kill germs and has a temporary lubricating effect during the rubbing process. Unlike methanol, 2-propanol is not absorbed through the skin; therefore it poses less of a health hazard.

The use of alcohols as fuels is well established. In 2010, the federal government joined several of the provinces in requiring that all gasoline must include an average of five per cent ethanol. Some gasoline producers, notably Husky/Mohawk, average ten per cent ethanol content in their products. Some especially modified vehicles can use fuel that consists of 85 per cent ethanol (E85). In December 1985, using ethanol as a fuel, a two-seater, single-engine aircraftmade a 20-minute demonstration flight in Sao Paulo, Brazil. In 1993, and ethanol-powered, two-seater aerobatic aircraft performed every day of the week-long Paris Airshow. However, ethanol causes deterioration in aircraft engines, and the mandatory use of ethanol in gasoline has posed problems for some aircraft owners. Research into technological “fixes” that would enable aircraft to use ethanol fuel is ongoing, notably at Baylor University, Waco, Texas. A phenol is an organic compound in which a hydroxyl group is directly bonded to one of the carbon atoms of an aromatic ring. Until the late nineteenth century, a person undergoing surgery had to face the fact that he or she might suffer the consequences of what we now know to be bacterial infection, contracted during the course of the operation. The physicians of the time did not know that bacteria existed, and had no way to counter the problems that bacteria caused. In 1867, Joseph Lister, who had learned of the existence of bacteria as a result of research done by Louis Pasteur, began using solutions of phenol to clean wounds and surgical instruments. The phenol solution was an effective antiseptic, killing bacteria, and as a result, a patient’s chances of surviving surgery improved greatly. Phenol itself was rather strong for these purposes—it burns healthy tissue—and substitutes were eventually found. One such substitute, used today in throat lozenges and mouthwashes, is 4-n-hexylresorcinol.

Contributors

Dr. Dietmar Kennepohl FCIC (Professor of Chemistry, Athabasca University)