unit 5 organic functional groups alcohols, ethers esters carboxilic acids, amines
TRANSCRIPT
Unit 5
Organic Functional Groups
Alcohols, ethers esters carboxilic acids, amines
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3
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You need to recognize the benzene structure in structural formulas
This is the general layout with a perfect hexagon. In this particular diagram you do not see the double bonds.
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Figure 20.7: Benzene C6H6.
6
Two Lewis structures for the benzene ring.
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Shorthand notation for benzene rings.
8
Some common mono-substituted benzene molecules
Toluene, sometimes you see this on marker pens ”contains no toluene”
Has the condensed structural
formula C6H5CH3
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– IUPAC Substitutive Nomenclature• An IUPAC name may have up to 4 features:
locants, prefixes, parent compound and suffixes
• Numbering generally starts from the end of the chain which is closest to the group named in the suffix
Alcohols, Phenols and Thiols
• “Alcohols have a general formula R-OH
• Phenols have a hdroxyl group attached directly to an aromatic ring
• Thiols and thiophenols are similar to alcohols and phenols, except the oxygen is replaced by sulfur
Structures of Alcohols, Phenols, Thiols and Ethers
• Alcohols, phenols, thiols and ethers consist of a hydrocarbon singly bonded to an oxygen or a sulfur
• Alcohols have an -OH group attached to an alkane, phenols have an -OH group attached to a benzene, thiols have an -SH group attached to an alkane and ethers have an O bonded to two C’s
OH
SH
OH
O
Alchol Phenol
Thiol Ether
Naming Alcohols• Parent name ends in -ol• Find longest chain containing the C to which the OH
group is attached• Number C’s starting at end nearest OH group• Locate and number substituents and give full name
- use a number to indicate position of OH group- cyclic alcohols have cyclo- before the parent name; numbering begins at the OH group, going in direction that gives substituents lowest possible numbers- use a prefix (di-, tri-) to indicate multiple OH groups in a compound
Nomenclature
Ethanol(Ethyl alcohol)
1-Propanol(Propyl alcohol)
2-Propanol(Isopropyl alcohol)
1-Butanol(Butyl alcohol)
OH
OH
OHOH
2-Butanol(sec-Butyl alcohol)
2-Methyl-1-propanol(Isobutyl alcohol)
2-Methyl-2-propanol(tert-Butyl alcohol)
OH
Cyclohexanol(Cyclohexyl alcohol)
OHOH
OH
Unsaturated alcohols
• 2 endings are needed: one for the double or triple bond and one for the hydroxyl group.
• The –ol suffix comes last and takes precidence in numbering.
•
Nomenclature Unsaturated alcohols
• CH2=CHCH2OH Cyclohexanol
• 2-propen-1-ol
• phyenylmethanol
Classification of Alcohols
• Alcohols can be classified as methyl, primary, secondary or tertiary
• Classification is based on the number of alkyl groups attached to the carbon to which the OH group is attached
• If OH is attached to a 1 C, it’s a 1 alcohol, etc.
C OH
H
H
H
C OH
H
H3C
H
C OH
CH3
H3C
H
C OH
CH3
H3C
CH3
Methyl Primary Secondary Tertiary
Naming Phenols• Phenol is the common name for an OH group
attached to a benzene, and is accepted by IUPAC• Are usually named as derivatives of the parent
compound• Compounds with additional substituents are
named as substituted phenols• Ortho, meta and para are used when there is only
one other substituent• If there are two or more additional substituents,
each must be numbered, beginning at the OH and going in direction that gives substituents lowest numbers (or alphabetical if same in both directions)
Nomenclature of Phenols
• Phenol p-chlorophenol
• 2,4,6-tribromophenol
Many phenols have pleasant odors, and some are bioactive- Euganol (from cloves) is a topical anesthetic- Thymol (from thyme) is an antiseptic
• The hydroxyl group is named as a substituent when it occurs in the same molecule with carboxylic acid, aldehyde or ketone.
• M-hydroxy benzoic acid
• P-hydroxybenzaldehyde
Naming Thiols• Parent name ends in -thiol• Find longest chain containing the C to which the SH
group is attached• Number C’s starting at end nearest SH group• Parent name is alkane name of carbon portion of
longest chain, followed by thiol• Locate and number substituents and give full name
- use a number to indicate position of SH group- cyclic thiols have cyclo- before the parent name; numbering begins at the SH group, going in direction that gives substituents lowest possible numbers- use a prefix (di-, tri-) to indicate multiple SH groups in a compound
Naming Thiols
• CH3–SH
• methanethiol
• 4,4-dimethyl-2-pentanethiol
•
Thiols - Nomenclature
• Common names for simple thiols are derived by naming the alkyl group bonded to -SH and adding the word "mercaptanmercaptan"
CH3CH2SH
CH3CH3CHCH2SH
Ethanethiol(Ethyl mercaptan)
2-Methyl-1-propanethiol(Isobutyl mercaptan)
Naming Ethers• Simple ethers are named by their common names• For common names: name each alkyl group
attached to the oxygen followed by ether• For complex ethers IUPAC names are used• For IUPAC names:
1. Name as an alkane, with larger alkyl group being the parent chain2. The smaller alkyl group and the O are named together as an alkoxy group (replace -yl with -oxy)3. Number chain starting at end nearest alkoxy group4. Use a number to give location of alkoxy group
OCH3CH3CH2OCH2CH3
Cyclohexyl methyl ether(Methoxycyclohexane)
Diethyl ether
Naming Cyclic Ethers
• Cyclic ethers are generally named by their common names (we will not study the IUPAC names)
• A cyclic ether containing two carbons is called ethylene oxide (generally known as epoxides)
• A cyclic ether containing 4 carbons (with 2 double bonds) is called a furan
• A cyclic ether containing 5 carbons (with 2 double bonds) is called a pyran
• A cyclic ether containing 4 carbons and 2 oxygens is called a dioxane
O
O
furan
O O
O
1,4-dioxane
O
O
ethylene oxide tetrahydrofuran pyran tetrahydropyran
Naming Examples
OH
SH
OHOH
CH3
OH
BrBrO
O
O
O
2-propanol 2-ethyl-4-methylcyclopentanol propanethiol ortho-methylphenol
2,4-dibromophenol diethyl ether furan 1,4-dioxane
Physical Properties of Alcohols, Phenols, Thiols and Ethers • All of these types of compounds have a bent geometry
around the O or the S, and are polar compounds
• Alcohols and phenols contain a very polarized O-H bond, and they can H-bond with themselves and with other alcohols or water
- Small alcohols (4 or less C’s) are soluble in water
While larger larger alcohols become insoluble
- Phenol is soluble in water (even with 6 C’s) because it partially ionizes in water (it’s a weak acid)
- Alcohols and phenols have relatively high boiling points
• Thiols are much less polar than alcohols because the electronegativity of S is the same as that of C (2.5), much less than that of O (3.5), so C-S and S-H bonds are not polar- thiols do not H-bond and have relatively low boiling points
• Ethers do not H-bond with themselves, so have boiling points similar to hydrocarbons-ethers are only slightly soluble in water and are highly flammable
Physical Properties– bp increases as MW increases– solubility in water decreases as MW increases
CH3CH2CH2OH
CH3CH2CH2CH3
CH3OHCH3CH3CH3CH2OH
CH3CH2CH3
CH3CH2CH2CH2OH
CH3CH2CH2CH2CH3
Structural Formula NameMolecularWeight
bp(°C)
Solubilityin Water
methanol 32 65 infiniteethane 30 -89 insoluble
ethanol 46 78 infinite
propane 44 -42 insoluble
1-propanol 60 97 infinite
butane 58 0 insoluble
8 g/100 g117741-butanol
pentane 72 36 insoluble
Boiling Points of Alcohols
• Alcohols contain a strongly electronegative O in the OH groups.
• Thus, hydrogen bonds form between alcohol molecules.
• Hydrogen bonds contribute to higher boiling points for alcohols compared to alkanes and ethers of similar mass.
Boiling Points of Ethers
• Ethers have an O atom, but there is no H attached.
• Thus, hydrogen bonds cannot form between ether molecules.
Acidity and Basicity of Alcohols and Phenols• Alcohols and phenols, like water, can act as either weak acids or weak
bases (although phenol is more acidic) ( hydroxyl group can act as a proton donor)
• Phenols are more acidic because the anion that forms upon loss of the proton is stabilized by resonance
O
H+HCl O
H
H
+ Cl
O
H+ NH3
O + NH4
O
H
+ H2O
O
+ H3O
O O O O
• Alcohols undergo combustion with O2 to produce CO2 and H2O.
2CH3OH + 3O2 2CO2 + 4H2O + Heat
• Dehydration removes H- and -OH from adjacent carbon atoms by heating with an acid catalyst. H OH
| | H+, heatH—C—C—H H—C=C—H + H2O
| | | | H H H H
alcohol alkene
Reactions of Alcohols
Combustion Reactions of Alcohols and Ethers• Both alcohols and ethers can burn with oxygen to
produce water, carbon dioxide and heat (just like hydrocarbons)
• However, ethers are much more flammable than alcohols and care should be taken when working with ethers in the laboratory (just a spark from static electricity can set off ether fumes)
Examples:
CH3CH2OH + 3O2 2CO2 + 3H2O + Heat
CH3-O-CH3 + 3O2 2CO2 + 3H2O + Heat
Dehydration of Alcohols to Form Alkenes• An alcohol can lose a water molecule to form an alkene using an acid
catalyst such as H2SO4 and heat (an “elimination reaction”)• This is the reverse of the addition of H2O to an alkene• Dehydration is favored by using heat (endothermic reaction) and a
solvent other than water (lower concentration of H2O)• When more than one alkene can be formed, Zaitsev’s rule states that
the more substituted alkene will be the major product• Order of reactivity = 3 > 2 > (1 > methyl)
- In fact this reaction only works with 3 and 2 alcohols
+
Heat
H3O+
+
Heat
H3O+
CH3
+ H2O
+ H2O
OH
H
OH
H
CH3
Mechanism of Acid-Catalyzed Dehydration of an Alcohol• First, the acid catalyst protonates the alcohol• Next, H2O is eliminated to form a carbocation• Finally, a proton is removed to form an alkene + H3O+
OH
+
H
OH
HO
H H
+H
O
H
OH H
+H
O
H
H
+H
O
H H
O
H
H
+
• The important things to remember about alcohol dehydration are that:
• 1. they all begin by protonation of a hydroxyl group
• 2. the ease of alcohol dehydration is:
• 3>2>1 ( tertiary to primary)
Reaction of alcohols with hydrogen halides
• Alcohols react with hydrogen halides (HCl, HBr, HI) to give alkyl halides
• (CH3)3COH + H-Cl ----- (CH3)3C-Cl + H-OH
• t-butyl alcohol t-butyl chloride
Formation of Ethers
• Ethers form when dehydration takes place at low temperature.
H+
CH3—OH + HO—CH3 CH3—O—CH3 + H2O
Two Methanol Dimethyl ether
Oxidation and Reduction
• In organic chemistry, oxidation is a loss of hydrogen atoms or a gain of oxygen.
• In an oxidation, there is an increase in the number of C-O bonds.
• Reduction is a gain of hydrogen or a loss of oxygen. The number of C-O bonds decreases.
• In the oxidation [O] of a primary alcohol, one H is lost from the –OH and another H from the carbon bonded to the OH.
[O] Primary alcohol Aldehyde
OH O | [O] ||
CH3—C—H CH3—C—H + H2O |
H Ethanol Ethanal (ethyl alcohol) (acetaldehyde)
Oxidation of Primary Alcohols
• The oxidation of a secondary alcohol removes one H from –OH and another H from the carbon bonded to the –OH.
[O] Secondary alcohol Ketone OH O
| [O] || CH3—C—CH3 CH3—C—CH3 + H2O |
H 2-Propanol Propanone (Isopropyl alcohol) (Dimethylketone; Acetone)
Oxidation of Secondary Alcohols
• Tertiary alcohols are resistant to oxidation.[O]
Tertiary alcohols no reaction OH | [O] CH3—C—CH3 no product | CH3 no H on the C-OH to oxidize 2-Methyl-2-propanol
Oxidation of Tertiary Alcohols
Ethanol: Acts as a depressant. Kills or disables more
people than any other drug. Is metabolized at a rate of
12-15 mg/dL per hour by a social drinker.
Is metabolized at a rate of 30 mg/dL per hour by an alcoholic.
Ethanol CH3CH2OH
Enzymes in the liver oxidize ethanol. The aldehyde produced impairs coordination. A blood alcohol level over 0.4% can be fatal.
O ||
CH3CH2OH CH3CH 2CO2 + H2OEthyl alcohol acetaldehyde
Oxidation of Alcohol in the Body
Oxidation of alcohols in liver
CH3CH2OH CH3C
O
HCH3C
O
OH
CO2 + H2O
ethyl alcoholethanol
acetaldehydeethanal
acetic acidethanoic acid
alcoholdehydrogenase
CH3OH HCO
H
alcoholdehydrogenase
metyl alcoholmethanol
formaldehydemethanal
reacts with proteins causing denaturationgreat toxicity to humansnot toxic to horses and rats
HCO
OH
formic acidmethanoic acid
acetaldehydedehydrogenase
Effect of Alcohol on the Body
Breathalyzer test
• K2Cr2O7 (potassium dichromate)• This orange colored solution is used in the
Breathalyzer test (test for blood alcohol level)
• Potassium dichromate changes color when it is reduced by alcohol
• K2Cr2O7 oxidizes the alcohol
Breathalyzer reaction
orange-red green
8H++Cr2O72-+3C2H5OH→2Cr3++3C2H4O+7H2O
dichromate ethyl chromium (III) acetaldehyde
ion alcohol ion
(from K2Cr2O7)
H3C C H
H
OH[O]
H3C C
O
H
+ H2O
ethylalcohol
acetaldehyde
% Ethanol Product
50% Whiskey, rum, brandy
40% Flavoring extracts
15-25% Listerine, Nyquil, Scope
12% Wine, Dristan, Cepacol
3-9% Beer, Lavoris
Alcohol Contents in Common Products
The proof of an alcohol
• The proof of an alcoholic beverage is merely twice the percentage of alcohol by volume.
• The term has its origin in an old seventeenth-century English method for testing whiskey.
• Dealers were often tempted to increase profits by adding water to booze.
• A qualitative method for testing the whiskey was to pour some of it on gunpowder and ignite it.
• If the gunpowder ignited after the alcohol had burned away, this was considered “proof” that the whiskey did not contain too much water.
Preparation of alcohols
• Ethanol is made by hydration of ethylene (ethene) in the presence of acid catalyst
C C
H
H
H
H
+ HOH[H+]
C C H
OH
HH
H
H
Isopropyl
• is produced by addition of water to propylene (1-propene)
H3CHC CH2 + HOH
[H+]H3C
HC CH3
OH
(Markovnikov's rule)
CH3CH2CH2OHpropyl alcohol is never formed
Methanol
• is made commercially from carbon monoxide and hydrogen
• CO + 2H2 → CH3OH
Oxidation of Thiols.
• Mild oxidizing agents remove two hydrogen atoms from two thiol molecules.
• The remaining pieces of thiols combine to form a new molecule, disulfide, with a covalent bond between two sulfur atoms.
• R – S – H H – S – R+I2 → RS – SR+2HI
• 2 RSH + H2O2 → RS – SR + 2 H2O
The chemistry of the “permanent” waving of hair.
• Hair is protein, and it is held in shape by disulfide linkages between adjacent protein chains.
• The first step involves the use of lotion containing a reducing agent such as thioglycolic acid, HS – CH2 – COOH.
• The wave lotion ruptures the disulfide linkages of the hair protein.• The hair is then set on curles or rollers and is treated with a mild
oxidizing agent such as hydrogen peroxide (H2O2).• Disulfide linkages are formed in new positions to give new shape to
the hair.• Exactly the same chemical process can be used to straighten naturally
curly hair.• The change in hair style depends only on how one arranges the hair
after the disulfide bonds have been reduced and before the reoxidation takes place.
Based on McMurry, Organic Chemistry, Chapter 18, 6th edition, (c) 2003
Ethers and Epoxides; and Sulfides
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Ethers and Their Relatives
An ether has two organic groups (alkyl, aryl, or vinyl) bonded to the same oxygen atom, R–O–R
Diethyl ether is used industrially as a solvent Tetrahydrofuran (THF) is a solvent that is a cyclic
ether Thiols (R–S–H) and sulfides (R–S–R) are sulfur (for
oxygen) analogs of alcohols and ethers
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18.1 Names and Properties of Ethers Simple ethers are named by identifying the two organic substituents and adding the
word ether If other functional groups are present, the ether part is considered an alkoxy substituent R–O–R ~ tetrahedral bond angle (112° in dimethyl ether) Oxygen is sp3-hybridized Oxygen atom gives ethers a slight dipole moment
Physical Properties of ethers
They have a lower boiling point than alcohols They cannot form hydrogen bonds with one
another. Ethers are less dense than water Alcohols and ethers are usually mutually
soluble. Ethers are relatively inert compounds, making
ethers excellent solvents in organic reactions.
Grignard Reagent
One example of the solvating power of ethers is in the preparation of Grignard reagents.
These reagents are useful in organic synthesis
Was discovered in 1912 by Victor Grignard These reagents are alkyl – or arylmagnesium
halidesAre organometallic compounds because they contain a carbon-metal bond
Grignard Reagent
Grignard found that when magnesium turnings are stirred with ether solution of an alkyl or aryl haide, an exothermic reaction occurs
R-X + Mg dry ether R-MgX
gringard reagent
Gringard reagents usually react if the alkyl or aryl group is negatively charged ( carbanion) and the magnesium is positively charged
Formation of Ethers by dehydration of alcohols
Ethers form when dehydration takes place at low temperature.
H+
CH3—OH + HO—CH3 CH3—O—CH3 + H2O
Two Methanol Dimethyl ether
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18.2 Synthesis of Ethers
Diethyl ether prepared industrially by sulfuric acid–catalyzed dehydration of ethanol – also with other primary alcohols
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The Williamson Ether Synthesis
Reaction forming an ether from an organohalide and an alcohol
Best method for the preparation of ethers Alkoxides prepared by reaction of an alcohol with a
strong base such as sodium hydride, NaH
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Silver Oxide-Catalyzed Ether Formation Reaction of alcohols with Ag2O directly with alkyl
halide forms ether in one step Glucose reacts with excess iodomethane in the
presence of Ag2O to generate a pentaether in 85%
yield
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Alkoxymercuration of Alkenes
React alkene with an alcohol and mercuric acetate or trifluoroacetate
Demercuration with NaBH4 yields an ether
Overall Markovnikov addition of alcohol to alkene
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Reactions of Ethers: Acidic Cleavage Ethers are generally unreactive Strong acid will cleave an ether at elevated
temperature HI, HBr produce an alkyl halide from less hindered
component by SN2 (tertiary ethers undergo SN1)
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18.4 Reactions of Ethers: Claisen Rearrangement Specific to allyl aryl ethers, ArOCH2CH=CH2
Heating to 200–250°C leads to an o-allylphenol Result is alkylation of the phenol in an ortho position
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Claisen Rearrangement Mechanism
Concerted pericyclic 6-electron, 6-membered ring transition state
Mechanism consistent with 14C labeling
77
Cyclic Ethers: Epoxides
Cyclic ethers behave like acyclic ethers, except if ring is 3-membered
Dioxane and tetrahydrofuran are used as solvents
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Epoxides (Oxiranes) Cyclic ethers with a three-membered ring containing one oxygen atom
also called oxiranes Three membered ring ether is called an oxirane (root “ir” from “tri” for 3-
membered; prefix “ox” for oxygen; “ane” for saturated) Also called epoxides Ethylene oxide (oxirane; 1,2-epoxyethane) is industrially important as an
intermediate Prepared by reaction of ethylene with oxygen at 300 °C and silver oxide
catalyst
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Preparation of Epoxides Using a Peroxyacid Treat an alkene with a peroxyacid
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Epoxides from Halohydrins
Addition of HO-X to an alkene gives a halohydrin Treatment of a halohydrin with base gives an epoxide Intramolecular Williamson ether synthesis
81
18.6 Reactions of Epoxides: Ring-Opening Water adds to epoxides with dilute acid at room
temperature Product is a 1,2-diol (on adjacent C’s: vicinal) Mechanism: acid protonates oxygen and water adds
to opposite side (trans addition)
82
Halohydrins from Epoxides
Anhydrous HF, HBr, HCl, or HI combines with an epoxide
Gives trans product
83
Regiochemistry of Acid-Catalyzed Opening of Epoxides Nucleophile preferably adds to less hindered site if
primary and secondary C’s Also at tertiary because of carbocation character
(See Figure 18.2)
84
Base-Catalyzed Epoxide Opening Strain of the three-membered ring is relieved on ring-
opening Hydroxide cleaves epoxides at elevated
temperatures to give trans 1,2-diols
85
Addition of Grignards to Ethylene Oxide Adds –CH2CH2OH to the Grignard reagent’s
hydrocarbon chain Acyclic and other larger ring ethers do not react
86
18.7 Crown Ethers
Large rings consisting repeating (-OCH2CH2-) or similar units Named as x-crown-y
x is the total number of atoms in the ring y is the number of oxygen atoms 18-crown-6 ether: 18-membered ring containing 6 oxygen
atoms Central cavity is electronegative and attracts cations
87
Sulfides
Sulfides (RSR), are sulfur analogs of ethers Named by rules used for ethers, with sulfide in
place of ether for simple compounds and alkylthio in place of alkoxy
88
Sulfides
Thiolates (RS) are formed by the reaction of a thiol with a base
Thiolates react with primary or secondary alkyl halide to give sulfides (RSR’)
Thiolates are excellent nucleophiles and react with many electrophiles
Aldehydes and Ketones
Carbonyl Group
• Carbon atom joined to oxygen by a double bond.
• Characteristic of:
• Ketones
• Aldehydes
Aldehydes
• Comes from alcohol dehydrogenation
• Obtained by removing of a hydrogen from an alcohol
• The –CH=O group is called a formyl group
Aldehydes
• Both common and IUPAC names frequently used
• Common names from acids from which aldehydes can be converted
Aldehydes
• IUPAC
• Longest chain with aldehyde
• Drop “e” and add “-al”
• Aldehyde takes precedence over all other groups so far
• Examples
Common Aldehyde names
• Formaldehyde Ethanal (acetaldehyde)
• Propanal (propionaldehyde) Butanal (n-butyraldehyde)
Aldehyde group has priority over double bonds or hydroxyl group
• Cyclopentanecarbaldehyde Benzaldehyde
• salicylaldehyde
CHO
benzaldehyde
CHO
CH3
o-tolualdehyde
HC
H
O
formaldehyde
CH2CH=O
phenylacetaldehyde
• Aldehydes are commonly detected by means of the Wagner Test ( which is composed of 2 grams of iodine and 6 grams of KI dissolved in 100 ml of water)
• Positive results produce a brown or reddish brown precipitant
Ketones
• Naming:– Drop “e”, add “-one”– Many common names– Simplest is 3 carbons
• C. name: acetone• IUPAC: propanone
Ketones
• Carbonyl carbon gets lowest number
• See examples…
• Acetone 2-butanone 3-pentanone• (ethyl methyl ketone) (diethyl ketone)
OCH2=CH-C-CH3
3-buten-2-one 2-methylcyclopentanone
Cyclohexanone acetophenone (methyl phenyl ketone)
• Benzophenone dicyclopropyl ketone
• (diphenyl ketone)
Common Carbonyl Compounds
• Formaldehyde (simplest aldehyde)– Manufactured from methanol– Used in many polymers
• Acetaldehyde– Prepared from ethyl alcohol– Formed in the detoxification of alcohol in the liver
• Acetone (simplest ketone)– Formed in the human body as a by-product of lipid
metabolism– Excreted in the urine
• Hormones– Steroid hormones– Progesterone/Testosterone
Physical Properties of Aldehydes and Ketones
• Carbon-oxygen double bond is very polar– Affects boiling points– More than ethers (C-O bonds)– Less than alcohols (C-OH bonds)
• Odors– Low aldehydes very pungent– High aldehydes pleasant odors (perfumes)
• Solubility – Similar to alcohols and ethers– Soluble up to about 4 carbons– Insoluble after that
Quinones
• Unique class of carbonyl compounds
• Are cyclic conjugated diketones
• Simplest ex is 1,4 benzoquinone
• Example vitamin k
Alizarin
• Alizarin: orange red quinone used to dye red coats of British army during American revolution
Preparations of Aldehydes and ketones
• ALDEHYDE
• 1. oxidation• 2. reduction• 3. hydration
• KETONE
• 1. oxidation• 2. reduction• 3. hydrolysis
Preparation of Aldehydes
• Oxidation – Leads to carboxylic acid unless care is taken– 1° alcohols
Preparation of Ketones
• Oxidation of a 2° alcohol
• Utilizes chromium compounds and sulfuric acid
Chemical Properties of Aldehydes and Ketones
• Both under-go combustion reactions
• Oxidation– Aldehydes can be oxidized, ketones can’t
• Tollen’s reagent• Benedict’s reagent• Fehling’s reagent
Chemical Properties of Aldehydes and Ketones
• Reduction – Variety of agents can reduce aldehydes and
ketones to alcohols
– NaBH4 and H2 commonly used
Chemical Properties of Aldehydes and Ketones
• Hydration– Formaldehyde dissolves readily in water– Acetaldehyde somewhat also
• Form hydrates
Chemical Properties of Aldehydes and Ketones
• Addition of Alcohols to Carbonyl Groups– Hemiacetal
• Aldehyde + alcohol
– Hemiketal • Ketone + alcohol
– Not very stable– Differs from
1 mol to 2 mol
Chemical Properties of Aldehydes and Ketones
• Hemiacetals + HCl = acetal (caused by presence of excess alcohol)
• Hemiketal + HCl = ketal
Keto-Enol Tautomerism
• Aldehydes and ketones may exist as an equilibrium mixture of 2 forms, called the keto form and the enol form.
• The two forms differ in the locaiton of the protons and a double bond
• This type f structural isomerism is called a tautomerism.
• The two forms of the aldehyde or ketone are called tautomers. ( structural isomers)
• Most simple aldehydes and ketones exist mainly in the keto form.
Keto-Enol Tautomerism
• H O OH
• -C-C- C=C
• Keto form Enol form
•
Structure of carboxylic acids and their derivatives
• The functional group present in a carboxylic acid is a combination of a carbonyl group and a hydroxyl group; however, the resulting carboxyl group ( -COOH) possesses properties that are unlike those present in aldehydes/ketones and alcohols.
carbonyl group hydroxyl group carboxyl group
C O H
O
O HC
O
Structure of carboxylic acids and their derivatives
• Carboxylic acids have the following general formula:
• Some simple carboxylic acids:
• Since carbon can have only four bonds, there are no cyclic carboxylic acids (i.e. the carboxyl group cannot form part of a carbon ring)
CR O H
O
formic acidIUPAC: methanoic acid
acetic acidIUPAC: ethanoic acid IUPAC: benzoic acid
O H
O
CCH 3 O H
O
CH O H
O
C
Structure of carboxylic acids and their derivatives
• The following molecules have a similar structure to carboxylic acids, and will be encountered in this unit and the next.
carboxylic acid acid chloride acid anhydride amideester
Ch-16 Ch-16 Ch-16 Ch-16 Ch-17
OR'C
O
R C N H 2
O
RR
O
OC
O
RC Cl
O
RC O H
O
R
Carboxyl Group
Carboxylic acids contain the carboxyl group on carbon 1.
O
CH3 — C—OH = CH3—COOH
carboxyl group
IUPAC nomenclature for carboxylic acids
• For monocarboxylic acids (one –COOH group):
– Select the longest, continuous carbon chain that involves the carboxyl group. This is the parent chain and the –COOH carbon is designated as C-1.
– Name the parent chain by dropping the “e” from the corresponding alkane name and changing to “oic acid”
– Indicate the identity and location of substituents on the parent chain at the front of the carboxylic acid’s name
Butanoic acid
2-Methylpropanoic acid3,3-Dibromobutanoic acid
3,5-Dichlorobenzoic acid
C H 3
C H 3
C H
O
C
OH
Cl
Cl
O H
O
Br
Br
C H 3 O H
O
CC H 2CC H 3 C H 2 O H
O
CC H 2
Benzoic acid
IUPAC nomenclature for carboxylic acids
• Dicarboxylic acids:– For these compounds, both ends of a chain will
end with a –COOH group. The parent chain is the one that involves both –COOH groups.
– The parent chain is named as an alkane and the term “dioic acid” is added afterwards to indicate the diacid structure.
(Succinic acid) Bromosuccinic acid)
Butanedioic acid Bromobutanedioic acid
Br O
O H
O
OH
O
O H
O
OH
Common names for carboxylic acids
Common names for dicarboxylic acids
Common names for carboxylic acids
• For common-name carboxylic acids and diacids, substituents are often numbered using a Greek system:
• So the following molecule could be called -Methylpropionic acid (or, using the IUPAC system, 2-Methylpropanoic acid)
12345carbon number
Greek letter
C O H
O
C H 2C H 2C H 2C H 3
CH
CH 3
C O H
O
CH 3
5 4 3 2 1C—C—C—C—C=Oδ γ β α used in common names
CH3CH2CH2CHCOOH
BrCH3CHCH2COOH
CH3
bromovaleric acid -methylbutyric acid
isovaleric acid
COOH
COOH COOH COOH
CH3
CH3CH3
benzoic acid
o-toluic acid m-toluic acid p-toluic acid
Special names!
Naming Carboxylic Acids
Formula IUPAC Common alkan -oic acid prefix – ic acid
HCOOH methanoic acid formic acid
CH3COOH ethanoic acid acetic acid
CH3CH2COOH propanoic acid propionic acid
CH3CH2CH2COOH butanoic acid butyric acid
Naming Rules
• Identify longest chain• (IUPAC) Number carboxyl carbon as 1• (Common) Assign , , to carbon atoms
adjacent to carboxyl carbon
CH3
|
CH3 — CH—CH2 —COOHIUPAC 3-methylbutanoic acidCommon -methylbutryic acid
Polyfunctional carboxylic acids
• Carboxylic acids that contain other functional groups besides the –COOH group are called polyfunctional carboxylic acids. Some examples are shown below:
an unsaturated acid a hydroxy acid a keto acid
C
O
C C C O H
O
CC C
O H
C O H
O
C
O
CCC O H
Properties
• Carboxylic acids are weak acids
CH3COOH + H2O CH3COO– + H3O+
• Neutralized by a base
CH3COOH + NaOH CH3COO– Na+ + H2O
Physical properties:
polar, no hydrogen bonding
mp/bp are relatively moderate for covalent substances
water insoluble
(except: four-carbons or less)
C O sp2 120o
C O C O
RCO2H RCO2-
covalent ionicwater insoluble water soluble
Carboxylic acids are insoluble in water, but soluble in 5% NaOH.
Preparation of carboxylic acids
• We saw in earlier that carboxylic acids can be prepared from aldehydes (which can be prepared from primary alcohols):
• Aromatic carboxylic acids can be made by oxidizing alkyl-substituted aromatic molecules:
1o alcohol
[O] [O]
aldehyde carboxylic acid
HO
O
CRH
O
CRHOR
K2Cr2O7
H2SO4
2CO2 3H2O
O H
O
CC H 3C H 2C H 2
+ +
Acidity of carboxylic acids
• When carboxylic acids are placed in water, they undergo de-protonation as discussed in Ch-10:
H2O - H3O+
carboxylate ion hydroniumcarboxylic acid
O
O
CRHO
O
CR + +
Remember from Ch-10:HA + H2O A- + H3O+
• When carboxylic acids are placed in water, they undergo de-protonation as discussed earlier
Acidity of carboxylic acids
oxalic acidIUPAC: Ethanedioic acid
oxalate ionIUPAC: Ethanedioate ion
2H2O -
H2O -
-
H3O+
2H3O+
acetate ionIUPAC: Ethanoate ion
acetic acidIUPAC: Ethanoic acid
O
O
C
O
C OOH
O
C
O
C O H
O
O
CCH 3O H
O
CCH 3
+
+
+
+
Carboxylic acid salts
• When carboxylic acids are reacted with strong bases, they are converted to salts as follows:
Na+
Na+
base
base sodium acetateIUPAC: Sodium ethanoate
salt
water
water
NaOH
NaOH
-
-
H2O
H2O
acetic acidIUPAC: Ethanoic acid
carboxylic acid
CH 3
O
C O H CH 3
O
C O
O
O
CRHO
O
CR
+
+
+
+
Carboxylic acid salts
• Salts of carboxylic acids are much more water-soluble than the acids themselves. Also, they can be converted back to the acid form by reacting them with a strong acid:
strong acid
Na+
sodium acetateIUPAC: Sodium ethanoate
-
salt
HCl NaCl
acetic acidIUPAC: Ethanoic acid
O
O
CCH 3 CH 3
O
C O H ++
Carboxylic acids, syntheses:
1. oxidation of primary alcohols
RCH2OH + K2Cr2O7
RCOOH
2. oxidation of arenes
ArR + KMnO4, heat ArCOOH
3. carbonation of Grignard reagents
RMgX + CO2 RCO2MgX + H+ RCOOH
4. hydrolysis of nitriles (alkyl cyanide)
RCN + H2O, H+, heat RCOOH
1. oxidation of 1o alcohols: most common oxidizing agents are potassium permanganate, chromic acid anhydride, nitric acid
CH3CH2CH2CH2-OH + CrO3 CH3CH2CH2CO2H n-butyl alcohol butyric acid 1-butanol butanoic acid
CH3 CH3
CH3CHCH2-OH + KMnO4 CH3CHCOOH isobutyl alcohol isobutyric acid2-methyl-1-propanol` 2-methylpropanoic acid
2. oxidation of arenes:
CH3
CH3
H3C
CH2CH3
KMnO4, heat
KMnO4, heat
KMnO4, heat
COOH
COOH
HOOC
COOH
toluene benzoic acid
p-xylene terephthalic acid
ethylbenzene benzoic acid
+ CO2
note: aromatic acids only!
3. carbonation of Grignard reagent:
R-X RMgX RCO2MgX RCOOH
Increases the carbon chain by one carbon.
Mg CO2 H+
CH3CH2CH2-Br CH3CH2CH2MgBr CH3CH2CH2COOHn-propyl bromide butyric acid
Mg CO2 H+
C
O
O
RMgX + R CO
O-+ +MgX
H+
R CO
OH
CH3
Br
Mg
CH3
MgBr
CO2 H+
CH3
COOH
p-toluic acid
CH3
Br2, hvCH2Br
MgCH2MgBr
CO2
H+
CH2 COOH
phenylacetic acid
4. Hydrolysis of a nitrile:
H2O, H+
R-CN R-CO2H heat
H2O, OH-
R-CN R-CO2- + H+ R-CO2H
heat
R-X + NaCN R-CN + H+, H2O, heat RCOOH1o alkyl halide
Adds one more carbon to the chain.R-X must be 1o or CH3!
CH3
Br2, hvCH2Br
NaCN
CH2 CN
H2O, H+, heat
CH2 COOH
CH3CH2CH2CH2CH2CH2-BrKCN
CH3CH2CH2CH2CH2CH2-CN
H2O, H+, heat
CH3CH2CH2CH2CH2CH2-COOH
1-bromohexane
heptanoic acid
toluene
phenylacetic acid
CO2H
CH2OH
CH3
Br
C N
MgBr
KMnO4, heat
KMnO4
MgCO2; then H+
H2O, H+, heat
carboxylic acids, reactions:
1. as acids
2. conversion into functional derivatives
a) acid chlorides
b) esters
c) amides
3. reduction
4. alpha-halogenation
5. EAS
as acids:
a) with active metals
RCO2H + Na RCO2-Na+ + H2(g)
b) with bases
RCO2H + NaOH RCO2-Na+ + H2O
c) relative acid strength?
CH4 < NH3 < HCCH < ROH < HOH < H2CO3 < RCO2H < HF
d) quantitative
HA + H2O H3O+ + A- ionization in water
Ka = [H3O+] [A-] / [HA]
2. Conversion into functional derivatives:
)a acid chlorides
R COH
O SOCl2
or PCl3orPCl5
R CCl
O
CO2H + SOCl2 COCl
CH3CH2CH2 CO
OH
PCl3CH3CH2CH2 C
O
Cl
)b esters
“direct” esterification: H+
RCOOH + R´OH RCO2R´ + H2O
-reversible and often does not favor the ester
-use an excess of the alcohol or acid to shift equilibrium
-or remove the products to shift equilibrium to completion
“indirect” esterification:
RCOOH + PCl3 RCOCl + R´OH RCO2R´
-convert the acid into the acid chloride first; not reversible
C CO
O
CH3
+ H2O
SOCl2
CCH3OH
O
OH+ CH3OH
O
Cl
H+
)a amides
“indirect” only!
RCOOH + SOCl2 RCOCl + NH3 RCONH2
amide
Directly reacting ammonia with a carboxylic acid results in an ammonium salt:
RCOOH + NH3 RCOO-NH4+
acid base
OH
O
3-Methylbutanoic acid
PCl3
Cl
O NH3
NH2
O
CO
OH
PCl3C
O
ClC
O
NH2
NH3
NH3
amide
CO
O NH4
ammonium salt
1. Reduction:
RCO2H + LiAlH4; then H+ RCH2OH
1o alcohol
Carboxylic acids resist catalytic reduction under normal conditions.
RCOOH + H2, Ni NR
CH3CH2CH2CH2CH2CH2CH2COOH
Octanoic acid(Caprylic acid)
LiAlH4 H+
CH3CH2CH2CH2CH2CH2CH2CH2OH
1-Octanol
CH2 CO
OH
H2, PtNR
LiAlH4
H+
CH2CH2OH
4. Alpha-halogenation: (Hell-Volhard-Zelinsky reaction)
RCH2COOH + X2, P RCHCOOH + HX X α-haloacid X2 = Cl2, Br2
COOH
Br2,PNR (no alpha H)
CH3CH2CH2CH2COOH + Br2,P CH3CH2CH2CHCOOH
Brpentanoic acid2-bromopentanoic acid
5. EAS: (-COOH is deactivating and meta- directing)
CO2H
CO2H
NO2
CO2H
SO3H
CO2H
Br
NR
HNO3,H2SO4
H2SO4,SO3
Br2,Fe
CH3Cl,AlCl3
benzoic acid
carboxylic acids, reactions:
1. as acids
2. conversion into functional derivatives
a) acid chlorides
b) esters
c) amides
3. reduction
4. alpha-halogenation
5. EAS
Esters
In and ester, the H in the carboxyl group is replaced with an alkyl group
O
CH3 — C—O —CH3 = CH3—COO —CH3
ester group
Esters in Plants
Esters give flowers and fruits their pleasant fragances and flavors.
162
Naming esters
• The alcohol part of the name comes first and the carboxylic part second
• For example CH3COOCH3 is made from CH3COOH and CH3OH. i.e Ethanoic acid and methanol
• It’s name is Methyl ethanoate
Naming Esters
• Name the alkyl from the alcohol –O-• Name the acid with the C=O with –ate
acid alcohol
O
methyl
CH3 — C—O —CH3
Ethanoate methyl ethanoate (IUPAC)
(acetate) methyl acetate (common)
Some Esters and Their Names
Flavor/Odor
Raspberries
HCOOCH2CH3 ethyl methanoate
(IUPAC)
ethyl formate (common)
Pineapples
CH3CH2CH2 COOCH2CH3
ethyl butanoate (IUPAC)
ethyl butyrate (common)
esters
Give the IUPAC and common names of the following compound, which is responsible for the flavor and odor of pears.
O
CH3 — C—O —CH2CH2CH3
Solution
O propyl
CH3 — C—O —CH2CH2CH3
propyl ethanoate (IUPAC)
propyl acetate (common)
Draw the structure of the following compounds:
A. 3-bromobutanoic acid
B. Ethyl propionoate
Solution
A. 3-bromobutanoic acid
Br
|
CH3CHCH2COOH
B. Ethyl propionoate O
CH3 CH2 COCH2CH3 CH3CH2COOCH2CH3
Chemical reactions of esters
• Ester hydrolysis: the hydrolysis of an ester is accomplished by reacting water with the ester in the presence of an acid catalyst (this is the reverse reaction of esterification).
• An example:
carboxylic acidalcoholester
H+
H2OO HR
O
COHR
O
CO R'R' +
H+
H2O
Methyl propanoate Methanol Propanoic acid
O
C H 3C H 2COHO HC H 3C H 3
O
C H 3CH 2CO +
Chemical reactions of esters
• Ester saponification: another hydrolysis reaction, but this time, under basic conditions. Rather than a carboxylic acid, the acid salt is produced here.
• Example:
-Na+
carboxylic acid saltalcoholester
NaOH
H2OO
O
CO HRR
O
CO R'R' +
2-Propyl propanoate 2-Propanol Sodium propanoate
-Na+NaOH
H2OC H 3C H 2O H
C H 3
C H
C H 3
C H 3
C H 3
C H C H 3C H 2 O
O
C
O
CO +
Sulfur analogs of esters
• Earlier we saw sulfur analogs of alcohols, ethers, aldehydes, and ketones. Esters also have known sulfur analogs, thioesters:
• Thioesters are made by condensation reactions involving carboxylic acids and thiols.
S RC
O
CH 3C O H
O
CH 3 SH R+
Sulfur analogs of esters
• Thioesters, like esters, have relatively low boiling points (compared to alcohols and carboxylic acids) and may be found in foods as flavorings.
• Acetyl coenzyme A, a thioester, is important in metabolic cycles that provide our bodies with energy.
SCH3 CH2 CH 3CH2C
OMethyl thiobutanoate
CoASCCH 3
O
Esterification
• Reaction of a carboxylic acid and alcohol• Acid catalyst
O H+
CH3 — C—OH + HO—CH2CH3
O
CH3 — C—O—CH2CH3 + H2O
Hydrolysis
• Esters react with water and acid catalyst• Split into carboxylic acid and alcohol
O H+
H — C—O—CH2CH3 + H2O
O
H — C—OH + HO—CH2CH3
Saponification
• Esters react with a bases • Produce the salt of the carboxylic acid and
alcohol O
CH3C—OCH2CH3 + NaOH
O CH3C—O– Na+ + HOCH2CH3
salt of carboxylic acid
Organic bases derived from ammonia
• Primary, secondary or tertiary depending on whether 1, 2, or 3 organic groups are attached to the nitrogen.
H-N-H R-N-H R-N-R R-N-R
H H H R ammonia primary secondary tertiary
Amines(organic ammonia) :NH3
:NH2R or RNH2 1o amine (R may be Ar)
:NHR2 or R2NH 2o amine
:NR3 or R3N 3o amine
NR4+ 4o ammonium salt
amines are classified by the class of the nitrogen, primary amines have one carbon bonded to N, secondary amines have two carbons attached directly to the N, etc.
Nomenclature.
Common aliphatic amines are named as “alkylamines”
CH3NH2
methylamine1o
(CH3)2NH
dimethylamine 2o
(CH3)3N
trimethylamine 3o
CH3CH2NHCH3
ethylmethylamine 2o
CH3CH2CHCH3
NH2
sec-butylamine 1o
CH3CCH3
CH3
NH2
tert-butylamine
1o
NH2
cyclohexylamine 1o
Complex amines are named by prefixing"amino"-" ( or N-methylamino, N,N-dimethylamino-, etc.) to the parent chain:
CH3CH2CHCH2CH2CH3
NH2
3-aminohexane
CH3NHCH2CH2OH
2-(N-methylamino)ethanol
CH2NH2
benzylamine
NH2 NH2NH2 NH2
CH3
CH3
CH3aniline o-toluidine m-toluidine
p-toluidine
NCH3H3C
N,N-dimethylaniline
HN
diphenylamine
Amines, physical properties:
Nitrogen is sp3 hybridized, amines are polar
and can hydrogen bond.
mp/bp are relatively high for covalent substances
amines are basic and will turn litmus blue
insoluble in water (except for four-carbons or less)
soluble in 5% HCl
“fishy” smell
N
Types of reactions
• 1. preparation of amines:• Ammonia reacts with alkyl halide to give an amine
• NH3 + CH3Cl -------- CH2-NH3 +Cl
RNH2 + HCl RNH3+ + Cl-
water waterinsoluble soluble
RNH3+ + OH- RNH2 + H2O
water watersoluble insoluble
Types of reactions
2. Reduction of Nitrogen compound
Ar-NO2 + H2,Ni Ar-NH2
Reduction of nitro compounds:
NO2
metal + acid; then OH-
or H2 + Ni, Pt, or Pd
NH2
R NO2 R NH2
Chiefly for primary aromatic amines.
$$$
Amines, syntheses:
1. Reduction of nitro compounds
Ar-NO2 + H2,Ni Ar-NH2
2. Ammonolysis of 1o or methyl halides
R-X + NH3 R-NH2
3. Reductive amination
R2C=O + NH3, H2, Ni R2CHNH2
4. Reduction of nitriles
R-CN + 2 H2, Ni RCH2NH2
5. Hofmann degradation of amides
RCONH2 + KOBr RNH2
2. Ammonolysis of 1o or methyl halides.
R-XNH3 RNH2
R-XR2NH
R-XR3N
R-X
R4N+X-
1o 2o 3o
4o salt
R-X must be 1o or CH3
CH3CH2CH2CH2BrNH3
CH3CH2CH2CH2NH2
n-butylamine
CH3CH2CH2NH2CH3Cl
CH3CH2CH2NHCH3
n-propylamine methyl-n-propylamine
NH2
2 CH3CH2BrN
Et
Et
aniline N,N-diethylaniline
H2C NH2
benzylamine
(xs) CH3I H2C N
CH3
CH3
CH3 Ibenzyltrimethylammonium iodide
Ammonolysis of alkyl halides is an SN2 reaction. Thealkyl halide must be primary or methyl. If the alkyl halideis secondary or tertiary, then an E2 reaction will take placeand the product will be an alkene!
Br
+ NH3
NH2
2o RX
3. Reductive amination:
OH2, Ni
or NaBH3CNCH NH2+ NH3
OH2, Ni
or NaBH3CNCH NHR+ RNH2
OH2, Ni
or NaBH3CNCH NR2+ R2NH
1o amine
3o amine
2o amine
Avoids E2
C
O
NH3
C
OH
NH2
C
NH
- H2O
H2, Ni
C
H
NH2
imine
H2,Ni
Reductive amination via the imine.
H3CC
O
CH3
acetone
NH3, H2/NiCH3CHCH3
NH2
isopropylamine
CCH2CH3
O
propiophenone
+ CH3CH2NH2NaBH3CN
CHCH2CH3
NH
CH2CH3
1-(N-ethylamino)-1-phenylpropane
O
cyclohexanone
NH3, H2/Ni NH2
cyclohexylamine
4. Reduction of nitriles
R-CN + 2 H2, catalyst R-CH2NH2
1o amine
R-X + NaCN R-CN RCH2NH2
primary amine with one additional carbon (R must be 1o or methyl)
CH2BrNaCN
CH2C N2 H2, Ni
CH2CH2NH2
benzyl bromide 1-amino-2-phenylethane
5. Hofmann degradation of amides
R CNH2
O KOBrR-NH2
Removes one carbon!
2,2-dimethylpropanamide
OBrCH3C
CH3
CH3
NH2
tert-butylamine
CH3C
CH3
CH3
CO
NH2
Amines, syntheses:
1. Reduction of nitro compounds 1o Ar
Ar-NO2 + H2,Ni Ar-NH2
2. Ammonolysis of 1o or methyl halides R-X = 1o,CH3
R-X + NH3 R-NH2
3. Reductive amination avoids E2
R2C=O + NH3, H2, Ni R2CHNH2
4. Reduction of nitriles + 1 carbon
R-CN + 2 H2, Ni RCH2NH2
5. Hofmann degradation of amides - 1 carbon
RCONH2 + KOBr RNH2