DAMIETTA UNIVERSITY CHEM-103: BASIC ORGANIC CHEMISTRY LECTURE

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1 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

2 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

3 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

4 Pyridinium Chlorochromate (PCC) Chapter 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

5 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

6 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 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

7 Reduction with LiAlH 4 Chapter 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

8 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 Catalytic Hydrogenation Chapter

9 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

10 Homework: Which of the following compounds will give a positive iodoform test? 19 Homework 20 10

11 Homework 21 Organic Chemistry, 7 th Edition L. G. Wade, Jr. Ketones and Aldehydes 2010, Prentice Hall 22 11

12 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

13 Examples O O 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 methyl-2-butanone 4-hydroxy-3-methyl-2-butanone 1 O C H C H 3 C H 2 C H C H 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 methyl-4-oxopentanal 25 Write the IUPAC name of the following compounds 26 13

14 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

15 Carbonyl Structure Carbon is sp 2 hybridized. C O bond is shorter, stronger, and more polar than C C bond in alkenes. Chapter 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

16 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 Preparation of ketones R and R 1 may be alkyl or aryl 32 16

17 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 Nucleophilic Addition A strong nucleophile attacks the carbonyl carbon, forming an alkoxide ion that is then protonated. Aldehydes are more reactive than ketones. Chapter Reactions of aldehydes and ketones (1) Clemmensen reduction (2) Wolff-Kishner reduction 36 18

19 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 Other Condensations with Amines Chapter

20 Homework: Complete the following equations Chapter 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

21 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 Acetals as Protecting Groups Aldehydes are more reactive than ketones. Chapter

22 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 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

23 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 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

24 Homework: choose the correct answer (4) What are the major alkenes formed in the following reaction? (a) (b) (c) (d) Chapter 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

25 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 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

26 Homework: choose the correct answer (8) What is the product of the following reaction? (a) (b) (c) (d) Chapter 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

27 The Wittig Reaction PPh 3 : triphenylphosphine The Wittig reaction converts the carbonyl group into a new C C double bond. Chapter 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

28 Solved Problem Show how you would use a Wittig reaction to synthesize 1-phenyl-1,3- butadiene. Chapter 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