Prof. F O Shode CHEM 241/ 11. Applied Organic Chemistry for Chemical Engineers. Shode F O 1

Transcription

1 Prof. F O Shode CHEM 241/ 11 Applied Organic Chemistry for Chemical Engineers Shode F O 1

2 General Introduction Shode F O 2

3 Course Information Course materials T/Bk, Notes, etc Appointment of Class Rep: Practicals: Two groups (A & B) on Thursdays Tests Dates: Friday 11 th March/29 th April 2011 Worksheets Home study (see Course Outline & Contents plus Supplementary Notes to be provided during the course). Lecture Periods: Tuesday (4 th & 5 th ); Friday (7th ) Shode F O 3

4 CHEM 241/ SCHEDULE OF PRACTICALS DATE GROUP PRAC 10/02/11 A Locker Checking 17/02/11 A Prac 1 24/02/11 B Prac 1 3/03/11 A Prac 2A (cancelled) 10/03/11 B Prac 2A 17/03/11 A Prac 2A 24/03/11 B Prac2B/Prac3 31/03/11 A Prac 2B/Prac 3 7/04/11 B Prac 4 14/04/11 A Prac 4 MID-TERM BREAK NO PRAC NO PRAC [21/04/11 2/05/11] 5/05/11 B Prac 5 12/05/11 A Prac 5 Shode F O 4

5 Course Outline Unit 1: Fundamental aspects of organic chemistry - Revision (Chapters 1 & 2). Unit 2: The chemistry of aromatic compounds: Benzene & substituted Benzene (Chapter 14). Unit 3: Chemistry of carbonyl compounds (I& II) (Chapters 16 & 17). Unit 4: Oxidation/Reduction reactions (Chapter 19). Unit 5: Structure elucidation using combined spectroscopic methods MS, IR, UV/Vis & NMR (Chapters 12 & 13) Unit 6: Synthetic Polymers (Chapter 28) Shode F O 5

6 ANY QUESTIONS OR COMMENTS? Shode F O 6

7 What is Chemistry? Chemistry is the study of matter (any substance that occupies space and has mass). The business of chemistry transforms the natural raw materials of the earth, sea and air into products that we use everyday. It creates products that brings major societal benefits to quality of life, health, productivity, convenience and safety. The value chain of the business of chemistry is shown below: Shode F O 7

8 The Value Chain of the Business of Chemistry Chemistry Discovery & Innovation Better Products Social & Economic Benefits from Better Products Improved Quality of Life, Safety & Well- Being Peace of Mind, Security & Enjoyment of Life Shode F O 8

9 Thus, the business of chemistry involves problem solving companies providing solutions to improve the world. It is a science and technology, knowledge-based industry that is key to a sustainable world economy and improved health and nutrition. Shode F O 9

10 The Outline of Chemical Industry Mining Inorganic Raw Materials Organic Raw Materials Oil & Gas Production Heat Air Water Chemical Processing Chemical Building Blocks Shode F O 10

11 Chemical Building Blocks Heat Air Water Chemical Processing Chemical Intermediates & Finished Products Other Manufacturers Consumers Exports Shode F O 11

12 Chemistry combines organic and inorganic materials from the earth, with heat, air, and water to make products useful in modern civilization. Organic chemicals begin with raw materials containing hydrocarbons such as oil, natural gas, and coal. Inorganic chemicals do not contain carbon but are made from ores taken from the earth, such as salt. Shode F O 12

13 Why do we study organic chemistry? What is organic chemistry? Simply, organic chemistry is the chemistry of CARBON and its compounds (except carbonates & its oxides) Several millions of carbon compounds are known. Many organic compounds (and materials made from them) play important roles in our lives. In fact, life without organic compounds is not possible. Shode F O 13

14 Assignment #1 3/Organic-Chemistry.html Shode F O 14

15 "I JUST WANT TO SAY ONE WORD TO YOU PLASTICS." SIGNIFYING THAT PLASTICS WERE THE WAVE OF THE FUTURE, THESE WORDS WERE UTTERED TO DUSTIN HOFFMAN'S CHARACTER IN THE 1967 FILM THE GRADUATE. (The Kobal Collection. Reproduced by permission.) Shode F O 15

16 CHEM 241 Unit 1 Revision of Some fundamental Concepts: [Bruice] Chapters 1 & 2 Shode F O 16

17 Chapter 1: Electronic Structure & Bonding Section Concept Page 1.1 The Structure of an atom Electronic Configuration Ionic & Covalent bonds How a structure of a compound is represented Atomic Orbitals Molecular Orbital Theory (MOT) Shode F O 17

18 Covalent Bonds: Theories, Types, & Theories: Properties Valence-Bond Theory (VBT): Sharing of valence electrons by two atoms to form single bond, double bond, and triple bond. Molecular Orbital Theory (MOT): Covalent bonds are formed by overlapping of atomic orbitals leading to sigma (σ) bond, and pi (π) bonds. VSEPR (valence-shell electron-pair repulsion)model: combines VBT, MOT, and the minimisation of electron repulsion Shode F O 18

19 Hybridization [Bruice: pg 29-35] This concept means that some atoms, prior to form bonds, mix their atomic orbitals to form new equal energy hybrid orbitals with stereochemical consequences. There are three common types of hybridization in Organic Molecules namely: sp 3 hybridization sp 2 hybridization sp hybridization. Shode F O 19

20 Covalent Bond Type (VBT) Single Bond ( ) Double Bond ( ) Triple Bond ( ) Molecular Orbitals(MOT) σ(bonding) and σ* (anti-bonding) σ(bonding) + π(bonding) and σ*(antibonding) + π* (anti-bonding) σ(bonding) + 2 x π(bonding) + 2 x π* (anti-bonding) + σ* (anti-bonding) Shode F O 20

21 Continuum of Bond Types Electronegativity differences Shode F O 21

22 Understanding bond polarity is critical to understanding how organic reactions occur: RULE - electron-rich atoms/molecules are attracted to electron-deficient atoms/molecules Shode F O 22

23 Bond Properties: Revise Bond length Bond angle Bond energies Bond rotation Shode F O 23

24 Simple Molecular Structures Space-filling MODELS Shode F O 24

25 Representation of Molecular Structures Electron-Dot formula (Lewis structures) Valence-Bond formula (Kekulé structures) Condensed formula Bond-Line formula Shode F O 25

26 Assignment 1 1. Problem #20 (Bruice, p28) 2. What is the hybridization of each of the carbon and oxygen atoms in the following compounds? HO OH O O H 3 C N O CH 3 N HO OH O N N vitamin C CH 3 caffeine Shode F O 26

27 Chemistry of Aromatic Compounds: Benzene & Substituted Benzene UNIT 2 Shode F O 27

28 Introduction BENZENE[CAS Number: ] It is a high volume chemical with production exceeding 1 million pounds annually in the U.S. Shode F O 28

29 The History of Benzene Benzene was discovered in 1825 by the English scientist Michael Faraday, who isolated it from oil gas and gave it the name bicarburet of hydrogen. In 1833, the German chemist Eilhard Mitscherlich produced it via the distillation of benzoic acid (from gum benzoin) and lime. Mitscherlich gave the compound the name benzin. Molecular structure deduced in 1834 by Mitcherlich In 1845, the English chemist Charles Mansfield, working under August Wilhelm von Hofmann, isolated benzene from coal tar. Four years later, Mansfield began the first industrial-scale production of benzene, based on the coal-tar method. Shode F O 29

30 Introduction: Which industries use Benzene Laboratory Chemicals Pesticide Mfg (Herbicides) Pesticide Mfg (Insecticides) Pharmaceuticals Mfg Printing Pulp and Paper Manufacture How is it used? Solvents - Dilution Solvents - Herbicide Manufacture Solvents - Insecticide Manufacture Solvents - Pharmaceuticals Solvents for Equipment Cleaning Solvents for de-inking paper Wood Stains and Varnishes Vanish Solvents Shode F O 30

31 Chemistry of benzene Physical properties: It is a colourless liquid, bp 80 o C (mp 5 o C). It is highly toxic! It has a sweetsmelling aroma (a fragrant liquid). Shode F O 31

32 Structure of Benzene Molecular Formula: C 6 H 6 It is highly unsaturated. [Compare alkanes, alkenes, & alkynes]. It does not react like alkenes & alkynes. [No addition reaction products] In 1858, August Kekulé proposed a cyclic structure for benzene based on a supernatural revelation: Shode F O 32

33 Structure of Benzene Cont d H H H H H H This will imply simply alternating C-C and C=C bonds (1.47Å & 1.34Å) Shode F O 33

34 The Grandfathers of benzene chemistry Shode F O 34

35 The Kekulé Model August Kekule proposed a rapid oscillation (I & II) between the 3 C=C and the 3 alternating C-C of hexagonal benzene (C 6 H 6 ). Shode F O 35

36 Flaws in Kekulé s Model Why does benzene possess 150 kj/mol less energy than predicted? Shode F O 36

37 2. Addition versus Substitution: Compounds with C=C (alkenes) typically undergo addition reactions such as bromination. Shown below are reactions of ethene/bromine and benzene/bromine: Shode F O 37

38 3. X-Ray studies revealed the following bond lengths: 0.153nm for typical C-C, 0.134nm for typical C=C, and 0.139nm for the 6 carbon- carbon bonds in benzene. Why does benzene possess 6 bonds intermediate between C=C and C-C? Shode F O 38

39 Resonance Theory Resonance To help explain molecules like benzene, Linus Pauling proposed resonance theory in 1931 (Pauling also gave us hybrid orbitals, electronegativity, and valence bond theory). As a result of Pauling's resonance, benzene is viewed as a hybrid of III& IV and represented by V. Shode F O 39

40 Shode F O 40

41 The six carbons are arranged in a hexagon with one hydrogen atom attached to each carbon. The 12 atoms of benzene are planar with carbon in the sp2 hybrid state and 120 bond angles. Because the six bond lengths are equivalent, Kekule's rapid equilibrium must be ruled out. To describe benzene we need to use contributingstructures III & IV or one structure with a circle in the middle (V). Structures III &IV do not exist! Whatever benzene might be, it displays characteristics of its contributing structures. For an analogy, consider crossing a bloodhound with a greyhound: Although the offspring is unique, it displays characteristics (smell& speed) of its parents--it does not flip flop between a greyhound one instant and a bloodhound the next. Shode F O 41

42 Bloodhound Greyhound Shode F O 42

43 Why does benzene possess 150 kj/mol less energy than predicted? This missing energy, called resonance energy, is attributed to overlapof p- orbitals. Structures VI and VII show pi bonding for the contributing structures while VIII illustrates delocalizationof pi electrons over the 6 carbon atoms. Shode F O 43

44 Benzene can be represented as IX using molecular models with p-orbitals. The circle in the middle of V is an abbreviated way to represent the delocalization of the 6 pi electrons. Resonance energy is the difference in energies between III (or IV) and V(V has lower energy). Due to resonance, benzene is 150 kj/mol more stable than calculations would predict. Shode F O 44

45 Why does benzene resist addition and prefer substitution? If benzene were to undergo addition, resonance would be disrupted and this would render the structure less stable. Therefore benzene prefers to substitute (Br for H) and maintain resonance. Why does benzene possess 6 bonds intermediate between C=C and C-C? According to resonance, the bonds are not C-C or C=C but a hybrid of the two. X-ray studies confirm this with the intermediate bond lengths. Shode F O 45

46 Aromaticity: Reactions of Benzene For a compound to be aromatic, it must obey the following criteria: 1. The molecule must be cyclic. 2. The molecule must be planar. 3. It must contain (4n + 2) π electrons, called Huckel s rule.[n = 0,1,2,3, etc] Why? This results in an uninterrupted cyclic cloud of π electrons, a characteristic feature of aromatic compounds. π bonding results from the overlap of p orbitals. Shode F O 46

47 Why are the following molecules aromatic? N H O N Benzene Napthalene Pyridine Pyrrole Furan Shode F O 47

48 Benzene:planar, cyclic, 4n + 2 πe - s where n = 1 Naphthalene:cyclic, planar, 4n + 2πe - s where n = 2. Pyridine:cyclic, planar, 4n + 2πe - s (n = 1), lone pair on N is non-bonding. Pyrrole:cyclic, planar, 4n + 2πes - (n = 1), lone pair on N involved in p orbital overlap. Furan: cyclic, planar, 4n + 2πe - s (n = 1), one lone pair on O involved in p orbital overlap and the other is nonbonding. Shode F O 48

49 Why are the following molecules not aromatic? cyclobutadiene cycloheptatriene cyclopropenyl anion Cyclobutadiene: not 4n + 2 π e - s cycloheptatriene: has an sp 3 carbon atom, not planar cyclopropenyl anion: not 4n + 2 π e - s Shode F O 49

50 Exercises: Are the following compounds aromatic or non-aromatic? H C + H C:- Cyclopentadiene Cyclopentadienyl cation Cyclopentadienyl anion Shode F O 50

51 Reactivity considerations Why does the aromatic ring undergo electrophilic substitution reactions rather than electrophilic addition reactions? An electrophile (Y + ) is attracted to the π electrons. When it attaches itself, a carbocation intermediate results. H + Y + Y carbocation intermediate This carbocation intermediate can follow two routes. What are they? Shode F O 51

52 + Y + H Y Z - Z Y r carbocation intermediate a non-aromatic product of electrophilic addition H + Y + Y Z - Y a carbocation intermediate an aromatic product of electrophilic substitution The non-aromatic product is much less stable that the aromatic product. Benzene undergoes electrophilic substitution reactions that preserve aromatic stabilisation. Shode F O 52

53 The five most common electrophilic aromatic substitution reactions are: 1. Halogenation 2. Nitration 3. Sulphonation + Y + 4. Friedel-Crafts acylation 5. Friedel-Crafts alkylation H carbocation intermediate They take place by the same two step mechanism. Y Z - Y an aromatic product of electrophilic substitution They differ only in how the electrophile (Y + ) that is needed to start the reaction is generated. Shode F O 53

54 Halogenation of benzene bromination + Br 2 FeBr 3 Br chlorination + Cl 2 FeCl 3 bromobenzene Cl iodination I 2 HNO 3 2 I + chlorobenzene + I + I iodobenzene Shode F O 54

55 Mechanism for bromination Br Br + FeBr 3 Br Br FeBr 3 + Br Br FeBr 3 Lewis acid weakens Br-Br bond H Br + FeBr 4 - B Br + HB + Mechanism for chlorination (replace Br for Cl above) Mechanism for iodination I 2 oxidising agent 2 I e - + I + H I B I + HB + Shode F O 55

56 Nitration of benzene HNO 3 NO 2 H 2 SO 4 Mechanism H HO NO 2 + H OSO 3 H HO nitric acid nitrobenzene NO + 2 NO 2 + H 2 O nitronium ion + NO 2 + NO 2 H B NO 2 + HB + Shode F O 56

57 Sulphonation of Benzene SO 3 H + H 2 SO 4 + H 2 O O O O H O HO S OH + HO S OH HO S OH + - O S OH O O O O O SO 3 + H 2 O HO S + H 2 O O HO 3 S H B SO 3 H + SO 3 H + HB + Shode F O 57

58 Desulphonation SO 3 H H 3 O + / 100 o C + SO 3 + H + Mechanism SO 3 H + H + SO 3 H H + SO 3 H Shode F O 58

59 FRIEDEL-CRAFTS ACYLATION OF BENZENE R O C acyl group O O + R C Cl acyl chloride 1. AlCl 3 2. H 2 O R + HCl O + O R C O O C R 1. AlCl 3 2. H 2 O R + HCl acid anhydride Shode F O 59

60 Mechanism for Friedel Crafts Acylation O H 3 C C Cl AlCl 3 H 3 C C O H 3 C C O acylium ion + AlCl 4 - H B O C O CH 3 C + H 3 C C O CH 3 + HB + Shode F O 60

61 Friedel Crafts Alkylation + RCl AlCl 3 R + HCl Mechanism R = alkyl group CH 3 CH 2 Cl + AlCl 3 CH 3 CH AlCl CH 3 CH 2 + CH 2 CH 3 H B CH 2 CH 3 + HB + Shode F O 61

62 Stability of carbocations: Tertiary > Secondary > Primary + CH 3 CH 2 CH 2 CH 2 Cl CH 3 CH 2 CHCH 2 H 1-chlorobutane AlCl 3 0 o C 1,2 hydride shift CH 3 CH 2 CHCH 3 CH 3 + CH 3 CCH 2 Cl AlCl 3 2-phenylbutane rearranged alkyl subsituent 65% CH 3 CHCH 2 CH 3 CH 3 C + CH 3 CH 2 CH 3 1-phenylbutane unrearranged alkyl subsituent 35% + CH 2 CH 2 CH 2 CH 3 CH 3 CH 2 CCH 3 CH 3 CH 3 100% rearranged 0% unrearranged Reason: 1,2-methyl shift CH 3 CH 3 CH 3 C CH 2 CH 3 C CH 2 CH 3 CH 3 Shode F O 62

63 What can be done about this problem? Answer: Acylation followed by reduction. O + CH 3 CH 2 CH 2 CCl AlCl 3 CCH 2 CH 2 CH 3 O reduction CH 2 CH 2 CH 2 CH 3 Two methods of reduction: Clemmenson reduction: Zn(Hg), HCl, heat Wloff-Kishner reduction: H 2 NNH 2, OH -, heat Shode F O 63