Presentation on theme: "Chapter 5 Alcohols Thiols Ethers. Chapter 102 Structure of Water and Methanol Oxygen is sp 3 hybridized and tetrahedral. The H—O—H angle in water is 104.5°."— Presentation transcript:
Chapter 5 Alcohols Thiols Ethers
Chapter 102 Structure of Water and Methanol Oxygen is sp 3 hybridized and tetrahedral. The H—O—H angle in water is 104.5°. The C—O—H angle in methyl alcohol is 108.9°.
Chapter 103 Classification of Alcohols Primary: carbon with —OH is bonded to one other carbon. Secondary: carbon with —OH is bonded to two other carbons. Tertiary: carbon with —OH is bonded to three other carbons. Aromatic (phenol): —OH is bonded to a benzene ring.
Chapter 108 IUPAC Nomenclature Find the longest carbon chain containing the carbon with the —OH group. Drop the -e from the alkane name, add -ol. Number the chain giving the —OH group the lowest number possible. Number and name all substituents and write them in alphabetical order.
Chapter 1010 Alkenols (Enols) Hydroxyl group takes precedence. Assign the carbon with the —OH the lowest number. End the name in –ol, but also specify that there is a double bond by using the ending –ene before -ol 4-penten-2-ol pent-4-ene-2-ol CH 2 CHCH 2 CHCH 3 OH
Chapter 1012 Hydroxy Substituent When —OH is part of a higher priority class of compound, it is named as hydroxy. 4-hydroxybutanoic acid also known as -hydroxybutyric acid (GHB) CH 2 CH 2 CH 2 COOH OH carboxylic acid
Chapter 1013 Common Names Alcohol can be named as alkyl alcohol. Useful only for small alkyl groups. isobutyl alcohol sec-butyl alcohol CH 3 CH CH 3 CH 2 OH CH 3 CH OH CH 2 CH 3
Chapter 1014 Naming Diols Two numbers are needed to locate the two —OH groups. Use -diol as suffix instead of -ol. hexane-1,6- diol
Chapter 1015 Glycols 1, 2-diols (vicinal diols) are called glycols. Common names for glycols use the name of the alkene from which they were made. ethane-1,2- diol ethylene glycol propane-1,2- diol propylene glycol
Chapter 1016 Phenol Nomenclature —OH group is assumed to be on carbon 1. For common names of disubstituted phenols, use ortho- for 1,2; meta- for 1,3; and para- for 1,4. Methyl phenols are cresols. 3-chlorophenol (meta-chlorophenol) 4-methylphenol (para-cresol)
Chapter 1017 Give the systematic (IUPAC) name for the following alcohol. The longest chain contains six carbon atoms, but it does not contain the carbon bonded to the hydroxyl group. The longest chain containing the carbon bonded to the —OH group is the one outlined by the green box, containing five carbon atoms. This chain is numbered from right to left in order to give the hydroxyl-bearing carbon atom the lowest possible number. The correct name for this compound is 3-(iodomethyl)-2-isopropylpentan-1-ol. Solved Problem 1 Solution
Chapter 1018 Physical Properties Alcohols have high boiling points due to hydrogen bonding between molecules. Small alcohols are miscible in water, but solubility decreases as the size of the alkyl group increases.
Chapter 1019 Boiling Points of alcohols Alcohols have higher boiling points than ethers and alkanes because alcohols can form hydrogen bonds. The stronger interaction between alcohol molecules will require more energy to break them resulting in a higher boiling point.
Chapter 1020 Solubility in Water Small alcohols are miscible in water, but solubility decreases as the size of the alkyl group increases.
Chapter 1021 Methanol “Wood alcohol” Industrial production from synthesis gas Common industrial solvent Toxic Dose: 100 mL methanol Used as fuel at Indianapolis 500 – Fire can be extinguished with water – High octane rating – Low emissions – Lower energy content – Invisible flame
Chapter 1022 Ethanol Fermentation of sugar and starches in grains 12–15% alcohol, then yeast cells die Distillation produces “hard” liquors Azeotrope: 95% ethanol, constant boiling Denatured alcohol used as solvent Gasahol: 10% ethanol in gasoline Toxic dose: 200 mL
Chapter 1023 Acidity of Alcohols pK a range: 15.5–18.0 (water: 15.7) Acidity decreases as the number of carbons increase. Halogens and other electron withdrawing groups increase the acidity. Phenol is 100 million times more acidic than cyclohexanol!
Chapter 1024 Table of K a Values
Chapter 1025 Formation of Alkoxide Ions Ethanol reacts with sodium metal to form sodium ethoxide (NaOCH 2 CH 3 ), a strong base commonly used for elimination reactions. More hindered alcohols like 2-propanol or tert-butanol react faster with potassium than with sodium.
Chapter 1026 Formation of Phenoxide Ion The aromatic alcohol phenol is more acidic than aliphatic alcohols due to the ability of aromatic rings to delocalize the negative charge of the oxygen within the carbons of the ring.
Chapter 1027 Charge Delocalization on the Phenoxide Ion The negative charge of the oxygen can be delocalized over four atoms of the phenoxide ion. There are three other resonance structures that can localize the charge in three different carbons of the ring. The true structure is a hybrid between the four resonance forms.
Chapter 1028 Synthesis of Alcohols (Review) Alcohols can be synthesized by nucleophilic substitution of alkyl halide. Hydration of alkenes also produce alcohols:
Chapter 1029 Synthesis of Vicinal Diols Vicinal diols can be synthesized by two different methods: Syn hydroxylation of alkenes – Cold, dilute, basic potassium permanganate
Chapter 1031 Sodium Borohydride NaBH 4 is a source of hydrides (H - ) Hydride attacks the carbonyl carbon, forming an alkoxide ion. Then the alkoxide ion is protonated by dilute acid. Only reacts with carbonyl of aldehyde or ketone, not with carbonyls of esters or carboxylic acids.
Chapter 1032 Lithium Aluminum Hydride LiAlH 4 is source of hydrides (H - ) Stronger reducing agent than sodium borohydride, but dangerous to work with. Reduces ketones and aldehydes into the corresponding alcohol. Converts esters and carboxylic acids to 1º alcohols.
Chapter 1033 Reduction with LiAlH 4 The LiAlH 4 (or LAH) will add two hydrides to the ester to form the primary alkyl halide. The mechanism is similar to the attack of Grignards on esters.
Chapter 1034 Reducing Agents NaBH 4 can reduce aldehydes and ketones but not esters and carboxylic acids. LiAlH 4 is a stronger reducing agent and will reduce all carbonyls.
Chapter 1035 Catalytic Hydrogenation Raney nickel is a hydrogen rich nickel powder that is more reactive than Pd or Pt catalysts. This reaction is not commonly used because it will also reduce double and triple bonds that may be present in the molecule. Hydride reagents are more selective so they are used more frequently for carbonyl reductions.
Chapter 1036 Thiols (Mercaptans) Sulfur analogues of alcohols are called thiols. The —SH group is called a mercapto group. Named by adding the suffix -thiol to the alkane name. They are commonly made by a substitution. Primary alkyl halides work better.
Chapter 1037 Synthesis of Thiols The thiolate will attack the carbon displacing the halide. This is a substitution reaction methyl halides will react faster than primary alkyl halides. To prevent dialylation use a large excess of sodium hydrosulfide with the alkyl halide.
Chapter 1138 Alcohol Reactions Dehydration to alkene Oxidation to aldehyde, ketone Substitution to form alkyl halide Reduction to alkane Esterification Williamson synthesis of ether
Chapter 1139 Summary Table
Chapter 1140 Oxidation States Easy for inorganic salts (reduced, organic oxidized) – CrO 4 2- reduced to Cr 2 O 3 – KMnO 4 reduced to MnO 2 Oxidation: loss of H 2, gain of O, O 2, or X 2 Reduction: gain of H 2 or H -, loss of O, O 2, or X 2 Neither: gain or loss of H +, H 2 O, HX
Chapter 1141 Oxidation States Easy for inorganic salts (reduced, organic oxidized) – CrO 4 2- reduced to Cr 2 O 3 – KMnO 4 reduced to MnO 2 Oxidation: loss of H 2, gain of O, O 2, or X 2 Reduction: gain of H 2 or H -, loss of O, O 2, or X 2 Neither: gain or loss of H +, H 2 O, HX
Chapter º, 2º, 3º Carbons
Chapter 1143 Oxidation of 2° Alcohols 2° alcohol becomes a ketone Reagent is Na 2 Cr 2 O 7 /H 2 SO 4 = H 2 CrO 4 Active reagent probably H 2 CrO 4 Color change: orange to greenish-blue =>
Chapter 1144 Oxidation of 1° Alcohols 1° alcohol to aldehyde to carboxylic acid Difficult to stop at aldehyde Use pyridinium chlorochromate (PCC) to limit the oxidation. PCC can also be used to oxidize 2° alcohols to ketones.
Chapter ° Alcohols Don’t Oxidize Cannot lose 2 H’s Basis for chromic acid test
Chapter 1146 Alcohol as a Nucleophile ROH is weak nucleophile RO - is strong nucleophile New O-C bond forms, O-H bond breaks.
Chapter 1147 Alcohol as an Electrophile OH - is not a good leaving group unless it is protonated, but most nucleophiles are strong bases which would remove H +. Convert to tosylate (good leaving group) to react with strong nucleophile (base). + + C-Nuc bond forms, C-O bond breaks
Chapter 1148 Reduction of Alcohols Dehydrate with conc. H 2 SO 4, then add H 2
Chapter 1149 Reaction with HBr -OH of alcohol is protonated -OH 2 + is good leaving group 3° and 2° alcohols react with Br - via S N 1 1° alcohols react via S N 2
Chapter 1150 Reaction with HCl Chloride is a weaker nucleophile than bromide. Add ZnCl 2, which bonds strongly with -OH, to promote the reaction. The chloride product is insoluble. Lucas test: ZnCl 2 in conc. HCl – 1° alcohols react slowly or not at all. – 2 alcohols react in 1-5 minutes. – 3 alcohols react in less than 1 minute.
Chapter 1151 Limitations of HX Reactions Poor yields of 1° and 2° chlorides May get alkene instead of alkyl halide
Chapter 1152 Reactions with Phosphorus Halides Good yields with 1° and 2° alcohols PCl 3 for alkyl chloride (but SOCl 2 better) PBr 3 for alkyl bromide
Chapter 1153 Dehydration Reactions Conc. H 2 SO 4 (or H 3 PO 4 ) produces alkene Carbocation intermediate Zaitsev product Bimolecular dehydration produces ether Low temp, 140°C and below, favors ether High temp, 180°C and above, favors alkene
Ethers O H H O H R O R R Hydrogen Oxide Aka Water AlcoholEther Ethers contain an sp 3 hybridized oxygen atom Ethers do not hydrogen bond between each other, but will hydrogen bond with water and alcohols. Ethers are polar and water soluble
Ether Nomenclature Common System Give alkyl names to the carbon groups (alkyl groups) bonded to the oxygen, followed by ether. Examples
Ether Nomenclature Common System Give alkyl names to the carbon groups (alkyl groups) bonded to the oxygen, followed by ether. Examples Dimethyl ether
Ether Nomenclature Common System Give alkyl names to the carbon groups (alkyl groups) bonded to the oxygen, followed by ether. Examples Dimethyl ether Ethylmethyl ether
Ether Nomenclature Common System Give alkyl names to the carbon groups (alkyl groups) bonded to the oxygen, followed by ether. Examples Dimethyl ether Ethylmethyl ether Isopropylmethyl ether
Ether Nomenclature Common System Give alkyl names to the carbon groups (alkyl groups) bonded to the oxygen, followed by ether. Examples Dimethyl ether Ethylmethyl ether Isopropylmethyl ether Sec-butylcyclopropyl ether
Ether Nomenclature IUPAC System Name the longest chain of carbons in the normal fashion. The oxygen containing group is named by giving the carbon portion the Latin root followed by oxy. Examples Methoxymethane
Ether Nomenclature IUPAC System Name the longest chain of carbons in the normal fashion. The oxygen containing group is named by giving the carbon portion the Latin root followed by oxy. Examples Methoxymethane Methoxyethane
Ether Nomenclature IUPAC System Name the longest chain of carbons in the normal fashion. The oxygen containing group is named by giving the carbon portion the Latin root followed by oxy. Examples Methoxymethane Methoxyethane 2-Methoxypropane
Ether Nomenclature IUPAC System Name the longest chain of carbons in the normal fashion. The oxygen containing group is named by giving the carbon portion the Latin root followed by oxy. Examples Methoxymethane Methoxyethane 2-Methoxypropane 2-Cyclopropoxybutane
Ether Formation Primary alcohols can dehydrate to ethers This reaction occurs at lower temperature than the competing dehydration to an alkene This method generally does not work with secondary or tertiary alcohols because elimination competes strongly The mechanism is an S N 2 reaction:
Williamson Ether Synthesis Good for unsymmetrical ethers