DAMIETTA UNIVERSITY CHEM-103: BASIC ORGANIC CHEMISTRY LECTURE 6 Dr Ali El-Agamey 1 Oxidation States Easy for inorganic salts: CrO 4 2- reduced to Cr 2 O 3. KMnO 4 reduced to MnO 2. Oxidation: Gain of O, O 2, or X 2 ; loss of H 2. Reduction: Gain of H 2 (or H - ); loss of O or O 2 ; and loss of X 2. The gain or loss of H +, - OH, H 2 O, HX, etc. is neither an oxidation nor a reduction. Chapter 11 2 1
Oxidation States of Carbons Chapter 11 3 Oxidation of 2 Alcohols Oxidation of 2 alcohol gives a ketone. Oxidizing agent is Na 2 Cr 2 O 7 /H 2 SO 4 (orange color). Active reagent probably is H 2 CrO 4 (chromic acid). Color is changed from orange to greenish-blue chromium (III). Chapter 11 4 2
Oxidation of 1 Alcohols to Carboxylic Acids Chromic acid reagent (or KMnO 4 ) oxidizes primary alcohols to carboxylic acids. The oxidizing agent is too strong to stop at the aldehyde. Chapter 11 5 Pyridinium Chlorochromate (PCC) PCC is a complex of chromium trioxide, pyridine, and HCl. Oxidizes primary alcohols to aldehydes. Oxidizes secondary alcohols to ketones. Chapter 11 6 3
Pyridinium Chlorochromate (PCC) Chapter 11 7 3 Alcohols Cannot Be Oxidized Carbon does not have hydrogen, so oxidation is difficult and involves the breakage of a C C bond. Chromic acid test is for primary and secondary alcohols because tertiary alcohols do not react. Chapter 11 8 4
Examples Chapter 11 9 Reduction of Carbonyl Reduction of aldehyde yields 1º alcohol. Reduction of ketone yields 2º alcohol. Reagents: Sodium borohydride, NaBH 4 Lithium aluminum hydride, LiAlH 4 Raney nickel Chapter 10 10 5
Sodium Borohydride NaBH 4 is a source of hydrides (H - ) Only reacts with carbonyl of aldehyde or ketone, not with carbonyls of esters or carboxylic acids. Chapter 10 11 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 10 12 6
Reduction with LiAlH 4 Chapter 10 13 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 10 14 7
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 (NaBH 4 and LiAlH 4 ) are more selective so they are used more frequently for carbonyl reductions. Chapter 10 15 Catalytic Hydrogenation Chapter 10 16 8
Reagent used: Haloform reaction Sodium hypohalite Potassium hypohalite 17 Mechanism: Haloform reaction Oxidation Halogenation Cleavage Iodoform (Yellow ppt) Haloform reaction can convert an alcohol to a carboxylic acid with one less carbon atom. 18 9
Homework: Which of the following compounds will give a positive iodoform test? 19 Homework 20 10
Homework 21 Organic Chemistry, 7 th Edition L. G. Wade, Jr. Ketones and Aldehydes 2010, Prentice Hall 22 11
Nomenclature of aldehydes and ketones IUPAC nomenclature (1) Ketones: Parent name is alkanone Choose the longest continuous chain containing the carbonyl group. In cyclic ketones the carbonyl carbon atom is assigned the number 1. (2) Aldehydes: Parent name is alkanal An aldehyde carbon is at the end of a chain, so it is number 1. For cycloalkanes with aldehyde substituent, the suffix - 23 carbaldehyde is used. Nomenclature of aldehydes and ketones IUPAC nomenclature Functional group Name as substituent Aldehydes Formyl Ketones Oxo Alcohols Hydroxy Amines Amino Ethers Alkoxy Halides Halo 24 12
Examples O O 1 3 4 1 3 4 C H 3 C C H C H 3 C H 3 C C H C H 2 O H 2 2 C H C H 3 3 3-methyl-2-butanone 4-hydroxy-3-methyl-2-butanone 1 O C H 3 5 2 C H 3 C H 2 C H C H 2 3 3-methylpentanal O C H 1 3 B r 3-bromocyclohexanone O C H 3 O C H 3 C C H C H 2 C H 4 3 1 3-methyl-4-oxopentanal 25 Write the IUPAC name of the following compounds 26 13
Homework: Write the IUPAC name of the following compounds 27 Organic Chemistry, 7 th Edition L. G. Wade, Jr. Ketones and Aldehydes 2010, Prentice Hall 28 14
Carbonyl Structure Carbon is sp 2 hybridized. C O bond is shorter, stronger, and more polar than C C bond in alkenes. Chapter 18 29 Boiling Points Ketones and aldehydes are more polar, so they have a higher boiling point than comparable alkanes or ethers. They cannot hydrogen-bond to each other, so their boiling point is lower than comparable alcohol. Chapter 18 30 15
Solubility of Ketones and Aldehydes Good solvent for alcohols. Lone pair of electrons on oxygen of carbonyl can accept a hydrogen bond from O H or N H. Acetone and acetaldehyde are miscible in water. Chapter 18 31 Preparation of ketones R and R 1 may be alkyl or aryl 32 16
Preparation of ketones 33 Preparation of ketones A Grignard or organolithium reagent can attack the carbon of the nitrile. The imine is then hydrolyzed to form a ketone. Chapter 18 34 17
Nucleophilic Addition A strong nucleophile attacks the carbonyl carbon, forming an alkoxide ion that is then protonated. Aldehydes are more reactive than ketones. Chapter 18 35 Reactions of aldehydes and ketones (1) Clemmensen reduction (2) Wolff-Kishner reduction 36 18
Formation of Imines Ammonia or a primary amine reacts with a ketone or an aldehyde to form an imine. Imines are nitrogen analogues of ketones and aldehydes with a C N bond in place of the carbonyl group. Optimum ph is around 4.5 Chapter 18 37 Other Condensations with Amines Chapter 18 38 19
Homework: Complete the following equations Chapter 18 39 Formation of Acetals Acetals can easily be converted into carbonyl compounds and alcohol in the presence of dilute acid (H 3 O + ) (remember reaction is reversible) however, they are stable in the presence of base. Chapter 18 40 20
Cyclic Acetals Addition of a diol produces a cyclic acetal. The reaction is reversible. This reaction is used in synthesis to protect carbonyls from reaction. Chapter 18 41 Acetals as Protecting Groups Aldehydes are more reactive than ketones. Chapter 18 42 21
Reaction and Deprotection The acetal will not react with NaBH 4, so only the ketone will get reduced. Hydrolysis conditions will protonate the alcohol and remove the acetal to restore the aldehyde. Chapter 18 43 Homework: choose the correct answer (1) What is the IUPAC name for the following compound? (a) 1,3-pentamethylpropane (b) 1,1,3,3-tetramethylbutane (c) 2,4,4-trimethylpentane (d) 2,2,4-trimethylpentane Chapter 18 44 22
Homework: choose the correct answer (2) When a double bond is formed between two atoms, one of the bonds is a sigma bond and the other is a pi bond. The pi bond is created by the overlap of... (a) sp 2 hybrid orbitals (b) sp 3 hybrid orbitals (c) p orbitals (d) s orbitals Chapter 18 45 Homework: choose the correct answer (3) For the following two pairs of molecules, identify which partner will have the higher boiling point. (a) Pair 1: A; Pair 2: C (b) Pair 1: B; Pair 2: D (c) Pair 1: A; Pair 2: D (d) Pair 1: B; Pair 2: C 46 23
Homework: choose the correct answer (4) What are the major alkenes formed in the following reaction? (a) (b) (c) (d) Chapter 18 47 Homework: choose the correct answer (5) Which product is obtained upon the reaction of (Z)-2-hexene with HBr? (a) 2,3-Dibromohexane (b) 2-Bromohexane (c) 3-Bromohexane (d) 2-Bromohexane and 3-bromohexane Chapter 18 48 24
Homework: choose the correct answer (6) Which of the following compounds gives 3- methyl-2-butanol upon reduction with LiAlH 4? (a) a (b) b (c) c (d) d Chapter 18 49 Homework: choose the correct answer (7) Which of the following sets of reaction conditions will give the product indicated? (a) (CH 3 O) 2 Ag, heat (b) CH 3 OH, HO -, separate water (c) 1) CH 3 ONa, 2) MeI (d) CH 3 OH, H +, separate water Chapter 18 50 25
Homework: choose the correct answer (8) What is the product of the following reaction? (a) (b) (c) (d) Chapter 18 51 Homework: choose the correct answer (9) When benzaldehyde reacts with HCN and catalytic amounts of NaCN in ethanol, the product is (a) (b) (c) (d) Chapter 18 52 26
The Wittig Reaction PPh 3 : triphenylphosphine The Wittig reaction converts the carbonyl group into a new C C double bond. Chapter 18 53 The Wittig Reaction In 1979, the Nobel Prize was awarded to Georg Wittig and to H.C. Brown in recognition of their remarkable contributions to synthetic organic chemistry. 1 Chapter 18 54 27
Solved Problem Show how you would use a Wittig reaction to synthesize 1-phenyl-1,3- butadiene. Chapter 18 55 Homework Show how you would synthesize the following compound using Wittig reaction. 1 Show how you would synthesize the following compound from starting materials containing no more than six carbon atoms. (a) (b) Chapter 18 56 28