Topic 4Alcohols, Phenols and Ethers

Alcohols, phenols and ethers contain an oxygen joined by single bonds: to a hydrogen and to an sp³ carbon (alcohols) or an aromatic carbon (phenols), or to two carbons (ethers). Their properties and reactivity are explained by the polarity of the C–O and O–H bonds and by the lone pairs of the oxygen. The topic ends with their sulfur analogues: thiols and sulfides.

Alcohols

CH₃OH	CH₃CH₂OH	(CH₃)₂CHOH	OHCH₂CH₂OH	OHCH₂CH(OH)CH₂OH

Methanol	Ethanol	Isopropanol	Ethylene glycol	Glycerin
It is called wood alcohol because it can be obtained by wood dry distillation. It is used as a solvent for paints and as a fuel. It is HIGHLY POISONOUS and produces blindness when swallowed or breathed, even in low amounts. A 30 mL dose is lethal. Metabolically, it is transformed into formaldehyde and formic acid, which prevent oxygen transport in the blood.	It is obtained by fermentation of carbohydrates (sugars and starch) that is self-inhibited when alcohol content reaches ca. 15%. In order to raise the alcohol content of beverages, it is necessary to perform a distillation but the azeotropic 95:5 alcohol:water mixture cannot be surpassed. Pure alcohol consumption is avoided by the addition of denaturing substances. Ethanol is VERY POISONOUS and kills a person when its blood level is above 0.4% . It is metabolized in the liver at a rate of 10 mL/h. Nevertheless, it is used as an antidote against methanol or ethylene glycol poisoning.	It mixes with water and most organic solvents in all ratios. It is used as antifreeze, solvent, cleaner, dehydrating agent, extracting agent, synthesis intermediate and antiseptic. It is highly TOXIC by oral ingestion or inhalation.	It was called glycol because Wurtz, who discovered it in 1855, noticed a certain sweet taste. It is used as solvent, antifreeze, hydraulic fluid, reaction intermediate in the synthesis of explosives, plasticizers, resins, fibers and artificial waxes. It is TOXIC by ingestion.	It was discovered by Scheele in 1779. Its name also comes from its sweet taste. It is a very viscous substance, soluble in water and NON-TOXIC. The alkaline hydrolysis of triglycerides (fats) produces glycerine and soaps. The triple nitrate of glycerine is a powerful explosive.

Nomenclature

The OH group is hydrophilic and the carbon chain hydrophobic: methanol is very soluble in water and poorly soluble in hexane; a long-chain alcohol, the opposite

Physical and Bond Properties

Acid dissociation of an alcohol and its amphoteric character

Acid-Base Properties

Preparation

In the alcohol, the electron-deficient carbon is not attacked by nucleophiles because hydroxide is a very bad leaving group; the OH hydrogen is weakly acidic

Reactivity

Phenols

C₆H₅OH

Phenol

Phenol, formerly named carbolic acid, was discovered by Runge in 1834 in coal tar. It melts at 43ºC, boils at 183ºC and has a not too pleasant, characteristic smell. It is very soluble in water and in the majority of organic solvents. It is caustic and very poisonous. Just 1 g can kill an average person. Phenol can poison by skin absorption. Its uncontrolled release as industrial waste can make a large damage to aquifers. It kills the aquatic fauna at a concentration as low as 1 ppm. In the presence of chlorine (used in water treatment) phenol can be transformed into chlorophenol of a foul taste. However, phenol can be easily and naturally removed from the environment by pond rushes or reeds, very common aquatic plants.

Nomenclature

Acid-base equilibrium of phenol and resonance forms of the phenoxide ion, with the negative charge delocalized over the ring

Acid-Base Properties

Industrial methods for phenol production: alkaline fusion of benzenesulfonic acid, hydrolysis of chlorobenzene and hydroperoxidation of cumene

Preparation

Reactivity

Ethers

Ethers are in general species of low reactivity and many of them are thus used as solvents. Nevertheless some of them bear quite attractive structures and spectacular properties. They are the crown ethers, discovered by Pedersen in 1967.

12-Crown-4 ether and the Li⁺, Na⁺ and K⁺ ions

15-Crown-5 ether and the Li⁺, Na⁺ and K⁺ ions

18-Crown-6 ether and the Li⁺, Na⁺ and K⁺ ions

The discovery of crown ethers and the study of their properties opened up the horizon to what has been called Supramolecular Chemistry and earned Pedersen and two other researchers, Lehn and Cram, the 1987 Nobel Prize in Chemistry.

Charles J. Pedersen (1904-1989): American chemist of Norwegian origin, linked to the research department of Du Pont where he made important discoveries related to ethyllead, hydrocarbon stabilization and, in the 60's, crown-ether chemistry. The latter research earned him the 1987 Nobel Prize in Chemistry together with D.J. Cram and J.-M. Lehn.

Jean-Marie Lehn (1939-): French chemist, professor of the Louis Pasteur University at Strasbourg, carries out important research in the field of Organic Synthesis, especially related to the preparation and behavior of cyclic molecules ("hollow molecules") with structures similar to those of the active sites of enzymes. He shared with Cram and Pedersen the 1987 Nobel Prize in Chemistry.

Portrait of Donald J. Cram holding a molecular model

D.J. Cram (1919-2001): American chemist, professor of the University of California at Los Angeles. He widened Pedersen's work on crown-ethers and prepared 3D molecular architectures mimicking the way natural molecules work. He shared with Pedersen and Lehn the Nobel Prize of Chemistry in 1987.