chapter14 lec

Chapter FourteenSome Compounds with

Oxygen, Sulfur, or a HalogenJames E. Mayhugh

Oklahoma City University2007 Prentice Hall, Inc.

Fundamentals of General, Organic, and Biological Chemistry

5th Edition

Prentice Hall © 2007 Chapter Fourteen 2

Outline

► 14.1 Alcohols, Phenols, and Ethers► 14.2 Some Common Alcohols► 14.3 Naming Alcohols► 14.4 Properties of Alcohols► 14.5 Reactions of Alcohols► 14.6 Phenols► 14.7 Acidity of Alcohols and Phenols► 14.8 Ethers► 14.9 Thiols and Disulfides► 14.10 Halogen-Containing Compounds


14.1 Alcohols, Phenols, and Ethers

An alcohol has an –OH bonded to an alkyl group; a phenol has an –OH bonded directly to an aromatic ring; and an ether has an O bonded to two organic groups.


► Ethyl alcohol, dimethyl ether, and propane have similar molecular weights, yet ethyl alcohol boils more than 100° higher than the other two.

► The high boiling points of ethyl alcohol and water are due to hydrogen bonding.

► Alkanes and ethers do not have hydroxyl groups and cannot form hydrogen bonds. As a result, they have lower boiling points. Ethers, in fact, resemble alkanes in many of their properties.


14.2 Some Common Alcohols► Simple alcohols are very common organic chemicals.

They are useful as solvents, antifreeze agents, and disinfectants, and they are involved in the metabolic processes of all living organisms.

► Methyl alcohol is commonly known as wood alcohol because it was once prepared by heating wood in the absence of air. Today it is made in large quantities by reaction of carbon monoxide with hydrogen.

► Methanol is used to make formaldehyde and methyl tert-butyl ether (MTBE), an octane booster added to gasoline. Methyl alcohol is colorless, miscible with water, and toxic to humans when ingested.


► Ethyl alcohol produced by fermentation is called grain alcohol; with methyl alcohol, camphor, or kerosene added it is called denatured alcohol. Industrially, most ethanol is made by hydration of ethylene. Absolute alcohol is 100% ethyl alcohol. Gasohol is a blend of ethyl alcohol and gasoline.

► Isopropyl alcohol, or rubbing alcohol, is used for rubdowns, as a solvent, as a sterilant for instruments, and as a skin cleanser before drawing blood or giving injections. Less toxic than methyl alcohol, isopropyl alcohol is more toxic than ethyl alcohol.


► Ethylene glycol, a diol, is: a toxic, colorless liquid, miscible with water and insoluble in nonpolar solvents. Its two major uses are as antifreeze and as a material for making polyester.

► The triol, glycerol or glycerin, is: a nontoxic, colorless liquid that is miscible with water. It is used as a sweetener, a moisturizer, in plastics manufacture, in antifreeze and shock-absorber fluids, and as a solvent.


14.3 Naming Alcohols

► Common names of many alcohols identify the alkyl group and then add the word “alcohol.” In the IUPAC system:

► STEP 1: Name the parent compound. Find the longest chain that has the hydroxyl substituent attached, and name the chain by replacing the -e ending of the corresponding alkane with -ol:


► STEP 2: Number the carbon atoms in the main chain. Begin at the end nearer the hydroxyl group, ignoring the location of other substituents:

► If the compound is a cyclic alcohol, add the -ol ending to the name of the parent cycloalkane. In a cyclic alcohol, begin with the carbon that bears the –OH group and proceed in a direction that gives the other substituents the lowest possible numbers.


STEP 3: Write the name, placing the number that locates the hydroxyl group immediately before the parent compound name. Number the positions of all other substituents, and list them alphabetically. Note that in a cyclic alcohol, it is not necessary to use the number “1” to specify the location of the –OH group.


► Dialcohols, or diols, are often called glycols.► Ethylene glycol is the simplest glycol; propylene

glycol is often used as a solvent for medicines that need to be inhaled or rubbed onto the skin.

► Numbering starts from the end closer to an –OH group, and the -diol name ending is used.


► Alcohols are classified as primary, secondary, or tertiary according to the number of carbon substituents bonded to the hydroxyl-bearing carbon.

► Alcohols with one substituent are said to be primary, those with two substituents are secondary, and those with three substituents are tertiary.


14.4 Properties of Alcohols► Alcohols are much more polar than hydrocarbons.

Hydrogen bonding also occurs and has a strong influence on alcohol properties.

► Straight-chain alcohols with up to 12 C’s are liquids, and each boils at a considerably higher temperature than the related alkane.

► Alcohols with a small organic part resemble water. Methanol and ethanol are miscible with water and they can dissolve small amounts of many salts.

► Alcohols with a large organic part are more like alkanes. 1-Heptanol is nearly insoluble in water and can’t dissolve salts but does dissolve alkanes.


Alcohols with 2 or more –OH groups can form more than one hydrogen bond. They are higher boiling and more water soluble than similar alcohols with one –OH group.


14.5 Reactions of Alcohols

► Alcohols undergo loss of water (dehydration) on treatment with a strong acid catalyst.

► The –OH group is lost from a C, and an –H is lost from an adjacent C to yield an alkene product:


► When more than one alkene can result from dehydration of an alcohol, a mixture of products is usually formed.

► A good rule of thumb is that the major product has the greater number of alkyl groups attached to the double-bond carbons.


► Primary and secondary alcohols are converted into carbonyl-containing compounds on treatment with an oxidizing agent. A carbonyl group is a functional group that has a C=O. The symbol [O] will indicate a generalized oxidizing agent.

► An organic oxidation is one that increases the number of C-O bonds and/or decreases the number of C-H bonds.


Primary alcohols are converted either into aldehydes if carefully controlled conditions are used, or into carboxylic acids if an excess of oxidant is used.


Secondary alcohols are converted into ketones on treatment with oxidizing agents.


Tertiary alcohols do not normally react with oxidizing agents because they do not have a hydrogen on the carbon atom to which the –OH group is bonded.


14.6 Phenols► Phenol is the name both of a specific compound,

hydroxybenzene, and of a family of compounds. ► Phenols are usually named with the ending -phenol

rather than -benzene even though their structures include a benzene ring.


► Phenol is a medical antiseptic first used by Joseph Lister in 1867. Lister showed that the occurrence of postoperative infection dramatically decreased when phenol was used to cleanse the operating room and the patient’s skin.

► The medical use of phenol is now restricted because it can cause burns and is toxic. Only solutions with <1.5% phenol or lozenges with <50 mg of phenol are now allowed in nonprescription drugs. Many mouthwashes and throat lozenges contain alkyl-substituted phenols such as thymol as active ingredients for pain relief.

► Alkyl-phenols such as the cresols are common as disinfectants in hospitals. Antiseptics safely kill microorganisms on living tissue, disinfectants should only be used on inanimate objects.


14.7 Acidity of Alcohols and PhenolsAlcohols and phenols are weakly acidic. They dissociate slightly in water and establish equilibria between neutral and anionic forms:


► Methanol and ethanol are about as acidic as water, with Ka 10-15. Their aqueous solutions are neutral.

► An alkoxide ion, or anion of an alcohol, is as strong a base as hydroxide ion.

► Phenols are considerably more acidic than water. Phenol itself has Ka = 1.010-10. Phenols react with dilute aqueous sodium hydroxide to give an anion.


14.8 Ethers

Ethers, compounds with two organic groups bonded to the same O atom, are named by identifying the two organic groups and adding the word ether.


Compounds that contain the oxygen atom in a ring are classified as cyclic ethers and are often given common names.


► An –OR group is referred to as an alkoxy group; -OCH3 is a methoxy group, -OCH2CH3 is an ethoxy group, and so on.

► These names are used when the ether functional group is present in a compound that also has other functional groups.


► Ethers are polar but do not form hydrogen bonds to one another. Simple ethers are higher boiling than comparable alkanes but lower boiling than alcohols.

► Dimethyl ether is soluble and diethyl ether is partially soluble in water.

► Ethers with large organic groups are insoluble in water. Ethers are alkane-like and do not react with most acids, bases, or other reagents.

► The simple ethers are highly flammable. On standing in air, many ethers form explosive peroxides, compounds that contain an O-O bond.

► Diethyl ether acts quickly and effectively as an anesthetic, but it has a long recovery time and induces nausea so it has now been replaced by safer anesthetics such as enflurane and isoflurane.


14.9 Thiols and Disulfides

Thiols, or mercaptans, are sulfur analogs of alcohols. Skunk scent is caused by the two thiols shown below center and right. The systematic name of a thiol is formed by adding -thiol to the parent name.


► Thiols (R-SH) react with mild oxidizing agents to yield a disulfide (R-S-S-R).

► The reverse reaction (R-S-S-R 2R-SH) occurs when a disulfide is treated with a reducing agent.

► Hair protein is rich in S-S and –SH groups. When hair is “permed,” some disulfide bonds are broken and new ones are formed, giving hair a different shape.


14.10 Halogen-Containing Compounds

Alkyl halides, R-X, have an alkyl group, R, bonded to a halogen, X. Their common names consist of the name of the alkyl group followed by the halogen name with an -ide ending. Systematic names consider the halogen atom as a substituent on a parent alkane.


► Halogenated organic compounds have a variety of medical and industrial uses:

-Anesthetics-Solvents, propellants, degreasing agents-Fire extinguishers-Herbicides, fungicides, insecticides

► Despite the enormous benefits of halogenated organic compounds, their use has been restricted, and sometimes banned altogether because:

-They persist in the environment and are not broken down rapidly. -They accumulate in some animals to harmful levels.-They can damage the ozone layer.


► Halogen-containing organic compounds are important in marine organisms; few are significant in human biochemistry. One exception is thyroxine, an iodine-containing hormone secreted by the thyroid gland.

► A deficiency of iodine in the diet leads to a low thyroxine level, which causes a swelling of the thyroid gland called goiter. To ensure adequate iodine in the diet KI is sometimes added to table salt.


Chapter Summary► An alcohol has an –OH group bonded to a saturated,

alkane-like carbon atom; a phenol has an –OH group bonded directly to an aromatic ring; and an ether has an oxygen atom bonded to two organic groups.

► Phenols are notable for their use as disinfectants and antiseptics; ethers are used primarily as solvents.

► Thiols are sulfur analogs of alcohols, with unpleasant odors. Thiols are found in proteins.

► Alkyl halides contain a halogen atom bonded to an alkyl group. Halogenated compounds are widely used in industry as solvents and in agriculture as herbicides, fungicides, and insecticides.


Chapter Summary Cont.► Alcohols are named using the -ol ending, and

phenols are named using the -phenol ending. Ethers are named by identifying the two organic groups attached to oxygen, followed by the word ether. Thiols use the name ending -thiol, and alkyl halides are named as halo-substituted alkanes.

► Both alcohols and phenols are like water in their ability to form hydrogen bonds. As the size of the organic part increases, alcohols become less soluble in water. Ethers do not hydrogen-bond and are more alkane-like in their properties.


Chapter Summary Cont.► Alcohols and phenols are weak acids that can donate H+

to a strong base. Alcohols and water have similar acidity; phenols are more acidic than water.

► Alcohols dehydrate to yield alkenes when treated with a strong acid, and they undergo oxidation to yield compounds that contain a carbonyl group. Primary alcohols are oxidized to yield either aldehydes or carboxylic acids, secondary alcohols are oxidized to yield ketones and tertiary alcohols are not oxidized.

► Thiols react with mild oxidizing agents to yield disulfides (RSSR), a reaction of importance in protein chemistry. Disulfides can be reduced back to thiols.


End of Chapter 14

chapter14 lec

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