Unit 5 Organic Functional Groups

Unit 5 Organic Functional Groups
Alcohols, ethers esters carboxilic acids, amines

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. 4

Figure 20.7: Benzene C6H6. 5

Two Lewis structures for the benzene ring.
6

Shorthand notation for benzene rings.
7

Some common mono-substituted benzene molecules
Toluene, sometimes you see this on marker pens ”contains no toluene” Has the condensed structural formula C6H5CH3 8

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 9

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

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

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.

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

4,4-dimethyl-2-pentanethiol
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 "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 chain 2. 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 group 4. Use a number to give location of alkoxy group

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

Naming Examples

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

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

Reactions of Alcohols Alcohols undergo combustion with O2 to produce CO2 and H2O. 2CH3OH + 3O CO H2O + Heat Dehydration removes H- and -OH from adjacent carbon atoms by heating with an acid catalyst. H OH | | H+, heat H—C—C—H H—C=C—H + H2O | | | | H H H H alcohol alkene

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 O2  2CO H2O Heat CH3-O-CH O2  2CO H2O 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

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+

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—CH 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.

Oxidation of Primary Alcohols
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 Secondary 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—CH CH3—C—CH3 + H2O | H 2-Propanol Propanone (Isopropyl alcohol) (Dimethylketone; Acetone)

Oxidation of Tertiary Alcohols
Tertiary alcohols are resistant to oxidation. [O] Tertiary alcohols no reaction OH | [O] CH3—C—CH3 no product | CH no H on the C-OH to oxidize 2-Methyl-2-propanol

Ethanol CH3CH2OH Ethanol: Acts as a depressant.
Kills or disables more people than any other drug. Is metabolized at a rate of mg/dL per hour by a social drinker. Is metabolized at a rate of 30 mg/dL per hour by an alcoholic.

Oxidation of Alcohol in the Body
Enzymes in the liver oxidize ethanol. The aldehyde produced impairs coordination. A blood alcohol level over 0.4% can be fatal O || CH3CH2OH CH3CH CO2 + H2O Ethyl alcohol acetaldehyde

Oxidation of alcohols in liver

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)

Alcohol Contents in Common Products
% Ethanol Product 50% Whiskey, rum, brandy 40% Flavoring extracts 15-25% Listerine, Nyquil, Scope 12% Wine, Dristan, Cepacol 3-9% Beer, Lavoris

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

Isopropyl is produced by addition of water to propylene (1-propene)

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.

Ethers and Epoxides; and Sulfides
Based on McMurry, Organic Chemistry, Chapter 18, 6th edition, (c) 2003

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 64

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 65

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 halides Are 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—CH CH3—O—CH3 + H2O Two Methanol Dimethyl ether

18.2 Synthesis of Ethers Diethyl ether prepared industrially by sulfuric acid–catalyzed dehydration of ethanol – also with other primary alcohols 70

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 71

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 72

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 73

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) 74

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 75

Claisen Rearrangement Mechanism
Concerted pericyclic 6-electron, 6-membered ring transition state Mechanism consistent with 14C labeling 76

Cyclic Ethers: Epoxides
Cyclic ethers behave like acyclic ethers, except if ring is 3-membered Dioxane and tetrahydrofuran are used as solvents 77

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 78

Preparation of Epoxides Using a Peroxyacid
Treat an alkene with a peroxyacid 79

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 80

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) 81

Halohydrins from Epoxides
Anhydrous HF, HBr, HCl, or HI combines with an epoxide Gives trans product 82

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) 83

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 84

Addition of Grignards to Ethylene Oxide
Adds –CH2CH2OH to the Grignard reagent’s hydrocarbon chain Acyclic and other larger ring ethers do not react 85

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 86

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 87

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 88

Aldehydes and Ketones

Carbonyl Group Carbon atom joined to oxygen by a double bond.
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

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
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 butanone 3-pentanone (ethyl methyl ketone) (diethyl ketone)

O CH2=CH-C-CH3 3-buten-2-one 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
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

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

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

Carboxylic acids:

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.

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)

The following molecules have a similar structure to carboxylic acids, and will be encountered in this unit and the next.

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 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.

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 a-Methylpropionic acid (or, using the IUPAC system, 2-Methylpropanoic acid)

C—C—C—C—C=O δ γ β α used in common names

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 —COOH IUPAC methylbutanoic acid Common -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:

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)

RCO2H RCO2- covalent ionic water 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:

Acidity of carboxylic acids
When carboxylic acids are placed in water, they undergo de-protonation as discussed earlier When carboxylic acids are placed in water, they undergo de-protonation as discussed in Ch-10: Remember from Ch-10: HA + H2O D A- + H3O+

Acidity of carboxylic acids

Carboxylic acid salts When carboxylic acids are reacted with strong bases, they are converted to salts as follows:

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:

Carboxylic acids, syntheses:
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

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 CH CH3 CH3CHCH2-OH KMnO4  CH3CHCOOH isobutyl alcohol isobutyric acid 2-methyl-1-propanol` methylpropanoic acid

oxidation of arenes: note: aromatic acids only!

carbonation of Grignard reagent:
R-X RMgX RCO2MgX RCOOH Increases the carbon chain by one carbon. Mg CO2 H+ CH3CH2CH2-Br CH3CH2CH2MgBr CH3CH2CH2COOH n-propyl bromide butyric acid Mg CO H+

Hydrolysis of a nitrile:
H2O, H+ R-CN R-CO2H heat H2O, OH- R-CN R-CO H+  R-CO2H R-X NaCN  R-CN H+, H2O, heat  RCOOH 1o alkyl halide Adds one more carbon to the chain. R-X must be 1o or CH3!

carboxylic acids, reactions:
as acids conversion into functional derivatives a)  acid chlorides b)  esters c)  amides reduction alpha-halogenation EAS

as acids: with active metals RCO2H Na  RCO2-Na H2(g) with bases RCO2H NaOH  RCO2-Na H2O relative acid strength? CH4 < NH3 < HCCH < ROH < HOH < H2CO3 < RCO2H < HF quantitative HA H2O  H3O A ionization in water Ka = [H3O+] [A-] / [HA]

Conversion into functional derivatives:
 acid chlorides

 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

 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

Reduction: RCO2H LiAlH4; then H+  RCH2OH 1o alcohol Carboxylic acids resist catalytic reduction under normal conditions. RCOOH H2, Ni  NR

Alpha-halogenation: (Hell-Volhard-Zelinsky reaction)
RCH2COOH X2, P  RCHCOOH HX X α-haloacid X2 = Cl2, Br2

5. EAS: (-COOH is deactivating and meta- directing)

carboxylic acids, reactions:
as acids conversion into functional derivatives a)  acid chlorides b)  esters c)  amides reduction alpha-halogenation EAS

Esters

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.

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 162

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:
3-bromobutanoic acid 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:

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:

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.

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. Methyl thiobutanoate

Esterification O Reaction of a carboxylic acid and alcohol
Acid catalyst O  H+ CH3 — C—OH + HO—CH2CH3  CH3 — C—O—CH2CH H2O

Hydrolysis O Esters react with water and acid catalyst
Split into carboxylic acid and alcohol O  H+ H — C—O—CH2CH H2O  H — C—OH + HO—CH2CH3

Saponification Esters react with a bases
Produce the salt of the carboxylic acid and alcohol O  CH3C—OCH2CH NaOH CH3C—O– Na HOCH2CH3 salt of carboxylic acid

Organic bases derived from ammonia
Amines 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)
: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”

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 

Types of reactions 1. preparation of amines:
Ammonia reacts with alkyl halide to give an amine NH3 + CH3Cl CH2-NH3 +Cl

RNH HCl  RNH Cl- water water insoluble soluble RNH OH-  RNH H2O water water soluble insoluble

Types of reactions 2. Reduction of Nitrogen compound
Ar-NO H2,Ni  Ar-NH2

Reduction of nitro compounds:

Amines, syntheses: Reduction of nitro compounds Ar-NO H2,Ni  Ar-NH2 Ammonolysis of 1o or methyl halides R-X + NH3  R-NH2 Reductive amination R2C=O NH3, H2, Ni  R2CHNH2 Reduction of nitriles R-CN H2, Ni  RCH2NH2 Hofmann degradation of amides RCONH KOBr  RNH2

Ammonolysis of 1o or methyl halides.

3. Reductive amination: Avoids E2

Reductive amination via the imine.

Reduction of nitriles R-CN H2, catalyst  R-CH2NH2 1o amine R-X NaCN  R-CN  RCH2NH2 primary amine with one additional carbon (R must be 1o or methyl)

5. Hofmann degradation of amides

Amines, syntheses: Reduction of nitro compounds 1o Ar Ar-NO H2,Ni  Ar-NH2 Ammonolysis of 1o or methyl halides R-X = 1o,CH3 R-X + NH3  R-NH2 Reductive amination avoids E2 R2C=O NH3, H2, Ni  R2CHNH2 Reduction of nitriles carbon R-CN H2, Ni  RCH2NH2 Hofmann degradation of amides - 1 carbon RCONH KOBr  RNH2

Unit 5 Organic Functional Groups

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Unit 5 Organic Functional Groups

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