Hydroxyl Group

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B. Physical Properties of Alcohols

N One striking property of alcohols is their relatively high boiling points.

N The simplest alcohol, methanol, boils at 65C.

N Alcohols containing up to three carbon atoms are infinitely soluble in water. With oneexception (2-methyl-2-propanol), alcohols with four or more carbon atoms have limited

solubility in water.

C. Chemical Properties of Alcohols

N An alcohol contains the hydroxyl functional group (-OH).

N Chemists have chosen the term functional group to indicate that this group brings a

function to an organic molecule.

N The -OH group interacts with water so that when a molecule adds a hydroxyl group, its

solubility in water increases.

N In general, the functions of a hydroxyl group help determine the properties of an

alcohol.

D. COMMON ALCOHOLS

1. Methanol

When wood is heated to a high temperature in an atmosphere lacking oxygen, methano(wood alcohol) and other products are formed and driven off.

The process is called destructive distillation, and until about 1925, nearly all methanol was

obtained in this way.

The most economical nonpetroleum source of carbon monoxide for making methanol iscoal.

In addition to coal, burnable materials such as wood, agricultural wastes, and sewagesludge also are potential sources of methanol.

Methanol is a volatile (bp 65C), highly flammable liquid.

Methanol is very poisonous:

o A few teaspoons of methanol taken internally can cause blindness; a

few tablespoons full can cause death.

o However, it is not the methanol that is the true toxin. (Methanol is a

mild intoxicant, less potent than ethanol.)

o Instead, the true toxin is methanoic acid (formic acid).

o The liver tries to eliminate methanol by first oxidizing Oxidation is

quickly accomplished, but the product, methanoic acid, is more difficult tometabolize.

o The blood concentration of this acid increases; metabolic acidosis

occurs and central energy metabolism is inhibiteddeath may follow.

o Luckily, it takes at least several hours for these toxic effects to first

appear, and victims can be taken to the hospital, where effective antidotes

are available.


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2. Ethanol

o The earliest and most widely known alcohol.

o It has been known by a variety of other names, such as ethyl alcohol, alcohol, grain

alcohol, and spirits.

o Huge quantities of this substance are prepared by fermentation.

o Starch and sugar are the raw materials.

o Starch is first converted to sugar by enzyme- or acid catalyzed hydrolysis. The conversion

of simple sugars to ethanol is accomplished by yeast:

o Pure ethanol (100%) is highly hygroscopic. It takes up water rapidly, to a stable

concentration of 95.6% ethanol.

o For legal use in beverages, ethanol is made by fermentation, but a large part of the

alcohol for industrial uses is made by the acid-catalyzed addition of water to ethylene

o Ethanol acts physiologically as a food, as a drug, and as a poison.

o It is a food in the limited sense that the body is able to metabolize it to carbon dioxide

and water with the production of energy.

o As a drug, ethanol is often mistakenly thought to be a stimulant, but it is in fact a

depressant.

o In moderate quantities, ethanol causes drowsiness and depresses brain functions,

impairing activities requiring skill and judgment (such as automobile driving).

o In larger quantities, ethanol causes nausea, vomiting, impaired perception, and

incoordination. If a very large amount is consumed, unconsciousness and ultimately deathmay occur.

3. 2-Propanol (Isopropanol, Isopropyl Alcohol)

o Made from propene derived from petroleum.

o Isopropyl alcohol is used

(1) to manufacture other chemicals (especially acetone)(2) as an industrial solvent

(3) as the principal ingredient in rubbing-alcohol formulations.

o 2-Propanol is not a potable alcohol, and merely breathing large quantities of the vapor

may cause dizziness, headache, nausea, vomiting, mental depression, and coma.

o It is metabolized by the liver. Being a secondary alcohol, it is quickly oxidized to a ketone

but is not oxidized further to a carboxylic acid:

4. Ethylene Glycol (1,2-Ethanediol)

o Ethylene glycol is the simplest alcohol, containing two OH groups.


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o Like most other relatively cheap, low-molar-mass alcohols, it is commercially derived from

petroleum.

o This alcohol is commonly referred to as ethylene glycol in commercial products.

5. Glycerol (1,2,3-Propanetriol)

o Also known as glycerine or 1,2,3-propanetriol, is an important trihydroxy alcohol.

o Glycerol is a syrupy liquid with a sweet, warm taste.

o It is about six-tenths as sweet as cane sugar.

o It is obtained as a by-product of the processing of animal and vegetable fats to make soap

and other products and is also synthesized commercially from propene.

o The major uses of glycerol are

(1) as a raw material in the manufacture of polymers and explosives(2) as an emollient in cosmetics(3) as a humectant in tobacco products

(4) as a sweetener.

o Consequently, glycerol is a hygroscopic substance; that is, it has the ability to take up

water vapor from the air. It is therefore used as a skin moisturizer in cosmetic

preparations.

o Glycerol is also used as an additive in tobacco products; by taking up moisture from the

air, it prevents the tobacco from becoming excessively dry and crumbly.

B. Properties of Phenols

N In the pure state, phenol is a slightly pink crystalline solid with a melting point of about 41C

and a characteristic odor.

N Phenol is highly poisonous. The ingestion of even small amounts of it may cause nausea,vomiting, circulatory collapse, and death from respiratory failure.

N Phenol is a weak acid; it is more acidic than alcohols and water, but less acidic than aceticand carbonic acids. The pH values are as follows: 0.1 Macetic acid, 2.87; water, 7.0; 0.1 M

phenol, 5.5.

N In general, the phenols are toxic to microorganisms. They are widely used as antisepticsand disinfectants.

N

Phenol was the first compound to be used extensively as an operating room disinfectantJoseph Lister (18271912) first used phenol for this purpose in 1867. The antiseptic powerof phenols is increased by substituting alkyl groups (up to six carbons) in the benzene ring.

C. Production of Phenol

N Phenol is obtained from coal tar.

N In addition, several commercial methods are used to produce phenol synthetically. The mosteconomical of these methods starts with benzene and propene, which react to formcumene.


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N Cumene is then oxidized by air to cumene hydroperoxide, which is treated with dilute sulfuricacid to obtain phenol and acetone.

III. Ethers

N Ethers have the general formula ROR-. The groups R and R can be derived from

saturated, unsaturated, or aromatic hydrocarbons, and for a given ether, R and R may bealike or different.

N Individual ethers, like alcohols, may be known by several names. The ether having theformula CH3CH2-O-CH2CH3 and formerly widely used as an anesthetic is called diethylether, ethyl ether, ethoxyethane, or simply ether.

N Common names of ethers are formed from the names of the groups attached to the

oxygen atom, followed by the word ether

N To name ethers by the IUPAC System, we need to learn the name of another group, the

alkoxy group (RO -).

N An alkoxy group consists of an alkyl or aryl group and an oxygen atom.

N It is named by dropping the -ylof the alkyl name and adding the suffix -oxy.

A. Preparation of Ethers

N Ethers can be synthesized by intermolecular dehydration of alcohols.

N Ethers are also formed by reacting alkyl halides with sodium alkoxides or sodium

phenoxides (Williamson synthesis).

IV. Thiols

N Sulfur and oxygen are found next to each other in the same family on the periodic table.

N This proximity indicates some similarity in the formulas of their compounds.

NOrganic compounds that contain the SH group are analogs of alcohols. The SH-containing

compounds are known as thiols, or mercaptans.

N Thiols are named by the same system as alcohols, except that the suffix -thiolis used in placeofol.

N Thiols have a higher molar mass than corresponding alcohols but boil at lower temperatures

NUnlike alcohols, thiols have foul odors and do not hydrogen-bond.

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Hydroxyl Group