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Alcohols, Aldehydes, and Ketones

Alcohols, Aldehydes, and Ketones

INTERCHAPTER P , , and

When an is present, the Tollen’s test produces a mirror on the inside of a test tube or flask, as shown here. The oxidation-reduction reaction that takes place is described by the equation O O

+ – – R C H(aq)+ 2 [Ag(NH3)2] (aq)+ 3 OH (aq) R C O (aq)+ 2 Ag(s) + 4 NH3(aq) + 2 H2O(l ) aldehyde silver- carboxylic metallic complex acid silver

In the reaction the aldehyde , R-CHO, is oxidized to a functional group, R‑COOH (which is deprotonated in the basic ), while the silver ions in the silver-ammonia complex are reduced to form metallic silver. The mirror forms because a thin film of metallic silver is deposited on the inside surface of the flask and adheres to the glass. This reaction was used in Victorian times to produce mirrors on glass.

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We shall continue our introduction to organic chem- CH3CHCH3 istry in this Interchapter. Up to now, we have learned CH OH CH H OH OH only about . We studied saturated 3 3 2 hydrocarbons in Interchapter F, unsaturated hydro- 2-propanol in Interchapter G, and aromatic hydrocar- (methyl ) (ethyl alcohol) ( or isopropanol) bons in Interchapter H. When we studied unsaturated hydrocarbons, we referred to the –carbon These alcohols have both common names (given here double bond as a functional group. The chemical in parentheses) and IUPAC (or systematic) names. properties of unsaturated hydrocarbons are a result The common names are formed by naming the of how the double bond reacts with reagents. In this group to which the –OH is attached and adding the Interchapter we shall learn about alcohols, aldehydes, word alcohol. The IUPAC name is formed by replac- and ketones. Alcohols have –OH as their functional ing the -e from the end of the name of the lon- H gest chain of carbon atoms containing the –OH group group, aldehydes have C O, and the functional with the suffix -ol. Thus, we have methanol, ethanol, and propanol. If the –OH group can be attached at group of ketones is C O. The simplest member of more than one position, then its position is denoted each class is by a number, as in H H H C 3 2 1 3 CH CHCH H C OH C O C O 3 3 3 2 1 H H3C CH CH CH OH H 3 2 2 OH methanol methanal propanone 1-propanol 2-propanol (methyl alcohol) () Title ()General - 4th ed 2-propanol is also called isopropyl alcohol or iso- Author McQuarrie/Gallogy propanol. An of 70% by volume of Title General Chemistry - 4th ed Artist George Kelvin P-1. Alcohols Are Organic Compounds 2‑propanol is sold as , the substance Author McQuarrie/Gallogy Figure # ethanol That Contain an –OH Group commonly used to cleanTitle theGeneral skin before Chemist administerry - 4th ed- Artist George Kelvin Date 07/30/10 ing an injection. FiguThere # classmethanol of organic compounds calledCheck alcohols if revision is charAppr- oved Author McQuarrie/Gallogy acterized by an –OH group attached to a Date 07/30/10 Artist George Kelvin Checkchain. if re vision ImportantAppr commonoved alcohols (Figure P.1) are Title General Chemistry - 4th edTitle General Chemistry - 4th ed Figure # 2-propanol

Author McQuarrie/Gallogy Author McQuarrie/Gallogy Date 08/09/10 Check if revision Approved Artist George Kelvin Artist George Kelvin

Figure # methanol Figure # ethanol

Date 08/09/10 Date 08/09/10 Approved Check if revision Check if revision Approved

methanol ethanol

methanol ethanol 2-propanol CH OH CH CH OH 3 3 2 CH3CHCH3 OH Figure P.1 Space-filling and ball-and-stick models of common alcohols: methanol, ethanol, and 2-propanol. P2 GENERAL CHEMISTRY, FOURTH EDItION | McQuarrie, Rock, and Gallogly

Methanol is sometimes called wood alcohol relatively small. The low-molecular-mass alcohols form because it can be produced by heating wood in the bonds and mix completely (i.e., are miscible) absence of . Over three million metric tons of with in all proportions. As the hydrocarbon por- methanol are produced annually in the United States tion becomes larger, however, the of alcohols by the reaction described by in water decreases and eventually approaches the low catalyst solubility of the comparable hydrocarbon. In addition, CO(g) + 2 H (g)→ CH OH(l ) 2 high P, high T 3 the low-molecular-mass alcohols have much higher boiling points than their comparable hydrocarbons. Methanol is highly toxic and can cause blindness For example, ethane (molecular mass 30) has a boil- and death if taken internally. During Prohibition in ing point of −88.6°C, while the of metha- the United States, many people died or became seri- nol (molecular mass 32) is 64.6°C. The relatively high ously ill from drinking methanol, either because they boiling points of the low-molecular-mass alcohols are were not aware of the difference between methanol due to extensive hydrogen bonding in the liquid . and ethanol or because the alcohol they purchased The –OH group on the relatively unreactive hydro- contained methanol as a major impurity. carbon chain accounts for the reactive properties of Ethanol is an ingredient in all fermented bev- alcohols. We say that the –OH group is a functional erages. Various and the starch in potatoes, group, just as the double bond in serves as a grains, and similar substances can be used to produce functional group in that case. Alcohols undergo reac- ethanol by fermentation, a process in which yeast is tions analogous to those of water. For example, alco- used to convert to ethanol. Although ethanol hols react with alkali to form and may be best known as an ingredient in alcoholic bev- liberate hydrogen: erages, it is an important industrial chemical as well. Today most contain a certain percentage of 2 CH3OH(l ) + 2 Na(s) → 2 NaOCH3(alc) + H2(g) ethanol, and special multifuel vehicles exist that can sodium methoxide run entirely on ethanol (see Interchapter L). It is sometimes convenient to view alcohols as deriv- Alkoxides are strong Lewis bases, that is, electron- atives of water, in which one of the hydrogen atoms pair donors (see Section 20-1). is replaced by an alkyl group. This approach is most Table P.1 lists the boiling points and the solubili- useful when the hydrocarbon portion of the alcohol is ties in water of a number of alcohols. Note how the

Table P.1 Boiling points and in water of several pairs of hydrocarbons and alcohols of similar molecular masses

Molecular Boiling Solubility in water/g Name Formula mass point/°C per 100 g H2O at 25°C

ethane CH3CH3 30.069 −88.6 insoluble

methanol CH3OH 32.042 64.6 soluble in all proportions

CH3CH2CH3 44.096 −42.1 insoluble

ethanol CH3CH2OH 46.068 78.29 soluble in all proportions

CH3CH2CH2CH3 58.122 −0.5 insoluble

1‑propanol CH3CH2CH2OH 60.095 97.2 soluble in all proportions

pentane CH3CH2CH2CH2CH3 72.149 36.06 insoluble

1- CH3CH2CH2CH2OH 74.121 117.73 7.4

hexane CH3CH2CH2CH2CH2CH3 86.175 68.73 insoluble

1-pentanol CH3CH2CH2CH2CH2OH 88.148 137.98 2.20

heptane CH3CH2CH2CH2CH2CH2CH3 100.202 98.4 insoluble

1-hexanol CH3CH2CH2CH2CH2CH2OH 102.174 157.6 0.60

University Science Books, ©2011. All rights reserved. www.uscibooks.com P. alcohols, aldehydes, and ketones P3 solubility decreases as the relative size of the alkyl portion of the molecule increases. Also, note that for pairs of hydrocarbons and alcohols of compara- ble molecular mass, the alcohols have considerably higher boiling points. Alcohols can be converted to alkenes by acid-cata- lyzed dehydration. For example,

1-propanol HH H H H2SO4 H CC OH(l ) C C(g) + H O (l ) 200°C 2 H H H H

Many of the reactions that alcohols undergo depend on the number of carbon atoms that are bonded to the carbon atom bearing the –OH group. For this reason we define primary, secondary, and tertiary alcohols. A has one carbon atom bonded to the carbon atom bearing the –OH group; 2-propanol a secondary alcohol has two such carbon atoms; and a tertiary alcohol has three: H

H3CCC H3

CH3 CH2 CH2 OH OH 1-propanol 2-propanol a primary alcohol a secondary alcohol

CH3

H3CCC H3 OH 2-methyl-2-propanol 2-methyl-2-propanol a tertiary alcohol

Table P.2 lists some other structural formulas of alco- hols, their IUPAC names, and respective classes, just for practice. The t- in the common name t-butyl alco- hol (Table P.2) stands for tertiary. It is possible to have more than one –OH group in an alcohol. Two examples are

OH ethane-1,2- ( glycol)

HO CH2 CH2 OH HO CH2 CH CH2 OH ethane-1,2-diol propane-1,2,3-triol () ( or glycerin)

Ethylene glycol can be obtained by a controlled oxi- dation of ethylene,

oxidation propane-1,2,3-triol H2C CH2 HO CH2 CH2 OH (glycerol or glycerine) P4 GENERAL CHEMISTRY, FOURTH EDItION | McQuarrie, Rock, and Gallogly

Table P.2 The structural formulas, corresponding IUPAC names, and classes of some alcohols

Structural formula IUPAC name Class

CH3 tertiary H C C CH CH 2-methyl-2-butanol 3 2 3 alcohol OH

CH CH CH CH 3 2 CH 2 3 3-pentanol secondary OH alcohol

CH3

H C C OH 2-methyl-2-propanol tertiary 3 (t-butyl alcohol) alcohol

CH3

and glycerol is obtained from the of fats. The annual production of ethylene glycol in the United States exceeds two million metric tons. The Figure P.2 Alfred Bernhard Nobel (1833–1896) was low (–11.5°C) and high boiling point born in Stockholm, Sweden. At an early age, his father (198°C) of ethylene glycol along with its complete moved his family to St. Petersburg, Russia, where he set with water make it an excellent antifreeze up a successful business manufacturing naval mines, (Chapter 16). Glycerol, a colorless, odorless, syrupy armaments, and other devices. Alfred was fluent liquid, has a wide range of uses, from medical, phar- in several languages and in his youth wanted to become a poet and a dramatist, but his father insisted that he maceutical, and cosmetic preparations to dynamite, study chemistry. His early education in chemistry was in which is a mixture of nitroglycerin (below) and an St. Petersburg, although he later carried out research in inert absorbent. Dynamite was developed and pat- several private laboratories in Europe and the United ented in 1867 by the Swedish chemist and engineer States. He returned to Sweden with his father in 1863 when Alfred Nobel (Figure P.2), who later instituted the his family’s business went bankrupt after the Crimean War. Nobel Prize foundation. Nobel turned his attention to making safer , and in 1867 he developed dynamite, which is nitroglycerin incorporated into an absorbent. Nobel earned a large fortune from his explosives business. He was also very O involved in social and peace-related issues and held views

+ that were considered quite radical during his time. Upon N his death, he willed much of his considerable fortune to O O– institute a foundation to award prizes for contributions to –O O CH O O– the fields of physics, chemistry, physiology and medicine, N+ C C N+ literature, and peace. These awards have become one of H2 H2 the world’s most prestigious prizes and are now known as O O the Nobel Prize. Although he had several loves in his life, 1,2,3-trinitroxypropane he never married, but in 1905 the Nobel Peace Prize was (nitroglycerin) awarded to Bertha von Suttner, his one-time secretary and a lifelong friend.

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P-2. Aldehydes and Ketones Contain a in cigarette smoke. About five million metric tons Carbon–Oxygen Double Bond of formaldehyde are manufactured annually in the United States. Most of this goes into the production Primary alcohols can be oxidized to produce alde- of various plastic materials. A solution of formalde- hydes. Aldehydes are compounds that have the gen- hyde in water, called formalin, preserves biological eral formula RCHO, specimens. However, this use is being phased out R in a number of countries because formaldehyde is a C O carcinogen. H is a colorless, flammable liquid with a pungent, fruity . It is used in the manufacture where R is a hydrogen atom or an alkyl group. The of perfumes, flavors, plastics, synthetic rubbers, dyes, –CHO functional group, called the aldehyde group, and a variety of other organic chemicals. is characteristic of aldehydes. The two simplest alde- A commonly used for the oxi- hydes are dation of primary alcohols to produce aldehydes is H H3C dichromate, K Cr O (s), dissolved in an C O C O 2 2 7 aqueous acidic solution: H H methanal ethanal (formaldehyde) (acetaldehyde) H H 2– These two aldehydes are generally referred to by their Cr2O7 (aq) CH3CH2 C OH (aq) + CH3CH2 C O(aq) common names. H (aq) Formaldehyde is a gas with an offensive and char- H acteristic odor. It is one of the irritants in smog and 1-propanol propanal

Aldehydes are readily oxidized to carboxylic acids (see Interchapter R), so it is necessary to stop the oxidation of a primary alcohol at the aldehyde stage in order to prevent the aldehyde from being oxidized further to the carboxylic acid. One way to do this is to remove the aldehyde as soon as it is formed by distilling it from the reaction mixture. Reactions such as these methanal can be used to measure alcohol content (see sidebox, (formaldehyde) page P6). Aldehydes do not hydrogen-bond and con- sequently have lower boiling points than the corre- sponding primary alcohols. The systematic nomenclature for aldehydes uses the longest chain of consecutive carbon atoms con- taining the –CHO group as the parent compound. The systematic name of an aldehyde is formed by dropping the terminal ‑e and adding ‑al to the name of the corresponding alkane. For example, the IUPAC

name for formaldehyde, CH2O(g), is methanal and ethanal that for acetaldehyde, CH3CHO(l ), is ethanal. (acetaldehyde) Table P.3 lists the structural formulas and the IUPAC names of some aldehydes for practice. P6 GENERAL CHEMISTRY, FOURTH EDItION | McQuarrie, Rock, and Gallogly

Table P.3 The structural formulas and the corresponding IUPAC names of some aldehydes Many law enforcement agencies use a device called a breathalyzer in the field to estimate the ethanol IUPAC name content of the blood of someone who is suspected of being intoxicated while driving. Breathalyzers O function by analyzing the extent to which the propanal oxidation of ethanol produces either acetaldehyde CH3CH2 C H or acetic acid. One type of breathalyzer uses a – mixture. When O alcohol from the breath is exhaled into the butanal CH3CH2CH2 C H mixture, the ethanol is oxidized by the potassium

dichromate, K2Cr2O7(acid). The K2Cr2O7(acid), which is reddish-, is reduced to Cr3+(aq), O which is green. The greater the concentration of pentanal CH3CH2CH2CH2 C H alcohol vapor in the breath, the more green the solution becomes. The color can be quantified spectroscopically and is directly related to the CH 3 O concentration of ethanol vapor in the breath. This 3-methylbutanal CH3 CH CH2 C H concentration in turn can be related to the concen- tration of ethanol in the blood because, as blood passes through the pulmonary arteries, an equi- CH 3 O librium is established between the ethanol in the blood and the ethanol in the lungs. CH3 CH CH CH2 C H 3,4-dimethylpentanal

CH3

CH2CH3 O 3-methylpentanal CH3 CH CH2 C H

Secondary alcohols can be oxidized according to

R′ oxidation R′ ROC H C O R H

2-propanol The resulting compound in this reaction is called a (isopropanol) . The general formula of a ketone is R(CO)R′ where R and R′ are alkyl groups and the C=O group is called a . Propanone, commonly

called acetone, (CH3)2CO(l ), is the simplest ketone and can be prepared from the oxidation of 2‑propa- nol (isopropanol):

H 2– H3C Cr2O7 (aq) H3CCC H3 (aq) C O (aq) H+(aq) H3C OH propanone (acetone) 2-propanol propanone (isopropanol) (acetone)

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Acetone is a colorless, volatile liquid with a sweet odor. Tertiary alcohols are resistant to oxidation. The Over two million metric tons of acetone are produced carbon atom bearing the –OH group is already annually in the United States. It is used extensively bonded to three other carbon atoms and so cannot as a because it dissolves many organic com- form a double bond with an oxygen atom to produce pounds yet is completely miscible with water. It dis- a ketone: solves fats, oils, , rubber, lacquers, varnishes, rubber cements, and coatings ranging from nail pol- CH3 Cr O2– (aq) ish to enamel . 2 7 H3COC H(aq) + no oxidation The IUPAC nomenclature for ketones uses the H (aq) longest chain of consecutive carbon atoms contain- CH3 ing the carbonyl group as the parent compound. The tertiary alcohol: 2-methyl-2-propanol ketone is named by dropping the terminal -e and add- ing -one to the name of the corresponding alkane, with a preceding numeral to indicate on which car- TERMS YOU SHOULD KNOW bon atom in the chain the carbonyl group is located (if necessary). For example, the IUPAC name of alcohol P1 functional group P2 CH3 C CH2CH2CH2CH3 P2 O primary alcohol P3 secondary alcohol P3 is 2-hexanone and that of tertiary alcohol P3 aldehyde P5 CH CH C CH CH CH 3 2 2 2 3 aldehyde group P5 O ketone P6 carbonyl group P6 is 3-hexanone. Table P.4 lists the structural formulas and names of some ketones for practice. QUESTIONS

Table P.4 The structural formulas and the P-1. Assign IUPAC names to each of the following corresponding IUPAC names of some ketones alcohols: (common names are in parentheses) CH3 CH3CH OH Structural formula IUPAC name (a) (b) CH3CH2CCH2OH CH3 CH CH C CH 3 2 3 CH3 O (methyl ethyl ketone) CH3 Cl CH2CH CH2Cl (c) (d) CH3CH2C OH CH CH CH CH 3 2 2 C 3 2-pentanone OH H O (methyl propyl ketone) P-2. Write a structural formula for each of the follow- CH CH CH CH ing alcohols: 3 2 C 2 3 3-pentanone O (diethyl ketone) (a) 2,3-dimethyl-1-butanol (b) 5-methyl-3-hexanol CH 3 (c) 2-chloro-1-hexanol CH CH CH 3 C 3 3-methyl-2-butanone (d) 1,2-dichloro-3-pentanol O P8 GENERAL CHEMISTRY, FOURTH EDItION | McQuarrie, Rock, and Gallogly

P-3. Classify the following alcohols as primary, sec- P-8. Assign IUPAC names to the following ketones: ondary, or tertiary: CH3 C CH3 CH3CH2CH2 C CH2CH3 H (a) (b) O O (a) CH3CH2OH (b) H3CCC H3 CH3CH2 C CH3 CH3 C CH2CH3 OH (c) (d) O O CH3 CH3 P-9 (c) CH3CH2CH (d) CH3COH . Write Lewis formulas for (a) 2-methyl-3-pentanone OH CH3 (b) 3,3-dimethyl-2-hexanone CH3 OH (c) butanone (e) (f) CH3CCH2OH CH3CH2CHCH3 CH3 P-10. Determine which alcohol you would use to pro- duce each of the following aldehydes: P-4. Complete and balance the following equations: (a) ethanal (a) CH3CH2OH(l ) + Na(s) → (b) 2-methylpropanal (b) CH3CH2CH2OH(l ) + Na(s) → (c) 2,2-dimethylpropanal (c) CH3CHOHCH3(l ) + K(s) →

P-5. What are the products of P-11. Determine which alcohol you would use to pro- duce each of the following ketones: Cr O2–(aq) (a) CH CHOHCH CH (l) 2 7 → 3 2 3 H+(aq) (a) 3-pentanone

(b) CH3CH2OH(l) + NaH(s) → (b) 2-pentanone H SO (conc) (c) CH CH CH OH(l) 2 4 → (c) 3-hexanone 3 2 2 200°C

P-6. Assign IUPAC names to the following aldehydes: P-12. Why do we write propanone, rather than 2-propanone (dropping the number two), but not O CH3 O propanol, rather than 2-propanol? (a) (b) CH3CH2CH2CH CH3CHCH2CH P-13. Alkoxides react with alkyl halides to produce . For example,

CH3 O O + − + − Na CH3O + CH3Br → CH3OCH3 + Na Br (c) (d) CH3CHCHCH2CH CH3CH2CH CH3 The product here is called dimethyl . Ethers are compounds with the general formula ROR′, where R P-7. Write the structural formula for each of the fol- and R′ are alkyl groups. Devise a procedure to syn- lowing aldehydes: thesize starting with ethene (ethylene) (a) propanal and any inorganic substances. Diethyl ether was once (b) 2-methylpentanal used as an anesthetic. (c) 4-methylpentanal (d) 3,3-dimethylhexanal

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P-14. Methyl ketones such as propanone (acetone), a under basic conditions. After filtration, washing, and widely used solvent of commercial importance, can drying, the product was found to weigh be detected by the iodoform, CHI3(s), test, in which 15.6 g. Calculate the theoretical yield and the per- the ketone is reacted with hypoiodite in aqueous centage yield. base, according to P-15. Aldehydes can be reduced to primary alcohols – H3CCC H3 (aq) + 3 IO (aq) → by the strong , NaBH (s). Determine which aldehyde you would use O O 4 – to produce each of the following primary alcohols: H3CC (aq) +CHI3(s) + 2 OH (aq) O– yellow (a) 1-propanol (b) 2-methyl-1-propanol A 5.00-mL sample of acetone (d = 0.792 g∙mL−1 at 25°C) was allowed to react with excess hypoiodite (c) 2,2-dimethyl-1-butanol

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