DOCSLIB.ORG

Chapter 17 Aromatic Reactions

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Chapter 17 Aromatic Reactions Chapter 17 Reactions of Aromatic Compounds Electrophilic Aromatic Substitution Electrophile substitutes for a hydrogen on the benzene ring. Chapter 17: Aromatics 2-Reactions Slide 17-2 1 Mechanism Step 1: Attack on the electrophile forms the sigma complex. Step 2: Loss of a proton gives the substitution product. => Chapter 17: Aromatics 2-Reactions Slide 17-3 Bromination of Benzene • Requires a stronger electrophile than Br2. • Use a strong Lewis acid catalyst, FeBr3. Br Br + - FeBr3 Br Br FeBr3 H H H H H H + - Br _ Br Br FeBr3 + + FeBr4 H H H H H H Br + HBr => Chapter 17: Aromatics 2-Reactions Slide 17-4 2 Comparison with Alkenes • Cyclohexene adds Br2, ΔH = -121 kJ • Addition to benzene is endothermic, not normally seen. • Substitution of Br for H retains aromaticity, ΔH = -45 kJ. • Formation of sigma complex is rate-limiting. => Chapter 17: Aromatics 2-Reactions Slide 17-5 Energy Diagram for Bromination => Chapter 17: Aromatics 2-Reactions Slide 17-6 3 Chlorination and Iodination • Chlorination is similar to bromination. Use AlCl3 as the Lewis acid catalyst. • Iodination requires an acidic oxidizing agent, like nitric acid, which oxidizes the iodine to an iodonium ion. + + H + HNO3 + 1/2 I2 I + NO2 + H2O => Chapter 17: Aromatics 2-Reactions Slide 17-7 Nitration of Benzene Use sulfuric acid with nitric acid to form the nitronium ion electrophile. + NO2 then forms a sigma complex with benzene, loses H+ to form nitrobenzene. Chapter 17: Aromatics 2-Reactions Slide 17-8 4 Sulfonation Sulfur trioxide, SO3, in fuming sulfuric acid is the electrophile. _ O O O O S S + S + S + _ _ O O O O O O O O Chapter 17: Aromatics 2-Reactions Slide 17-9 Desulfonation • All steps are reversible, so sulfonic acid group can be removed by heating in dilute sulfuric acid. • This process is used to place deuterium in place of hydrogen on benzene ring. H D H H large excess D D D2SO4/D2O H H D D H D Benzene-d 6 Chapter 17: Aromatics 2-Reactions Slide 17-10 5 Nitration of Toluene • Toluene reacts 25 times faster than benzene. The methyl group is an activating group. • The product mix contains mostly ortho and para substituted molecules. => Chapter 17: Aromatics 2-Reactions Slide 17-11 Sigma Complex Intermediate is more stable if nitration occurs at the ortho or para position. => Chapter 17: Aromatics 2-Reactions Slide 17-12 6 Energy Diagram => Chapter 17: Aromatics 2-Reactions Slide 17-13 Activating, O-, P- Directing Substituents • Alkyl groups stabilize the sigma complex by induction, donating electron density through the sigma bond. • Substituents with a lone pair of electrons stabilize the sigma complex by resonance. + OCH3 OCH3 + NO NO2 2 => H H Chapter 17: Aromatics 2-Reactions Slide 17-14 7 Substitution on Anisole => Chapter 17: Aromatics 2-Reactions Slide 17-15 The Amino Group Aniline, like anisole, reacts with bromine water (without a catalyst) to yield the tribromide. Sodium bicarbonate is added to neutralize the HBr that’s also formed. => Chapter 17: Aromatics 2-Reactions Slide 17-16 8 Summary of Activators => Chapter 17: Aromatics 2-Reactions Slide 17-17 Deactivating Meta- Directing Substituents • Electrophilic substitution reactions for nitrobenzene are 100,000 times slower than for benzene. • The product mix contains mostly the meta isomer, only small amounts of the ortho and para isomers. • Meta-directors deactivate all positions on the ring, but the meta position is less deactivated. => Chapter 17: Aromatics 2-Reactions Slide 17-18 9 Ortho Substitution on Nitrobenzene => Chapter 17: Aromatics 2-Reactions Slide 17-19 Para Substitution on Nitrobenzene => Chapter 17: Aromatics 2-Reactions Slide 17-20 10 Meta Substitution on Nitrobenzene => Chapter 17: Aromatics 2-Reactions Slide 17-21 Energy Diagram => Chapter 17: Aromatics 2-Reactions Slide 17-22 11 Structure of Meta-Directing Deactivators • The atom attached to the aromatic ring will have a partial positive charge. • Electron density is withdrawn inductively along the sigma bond, so the ring is less electron-rich than benzene. => Chapter 17: Aromatics 2-Reactions Slide 17-23 Summary of Deactivators => Chapter 17: Aromatics 2-Reactions Slide 17-24 12 More Deactivators => Chapter 17: Aromatics 2-Reactions Slide 17-25 Halobenzenes • Halogens are deactivating toward electrophilic substitution, but are ortho, para-directing! • Since halogens are very electronegative, they withdraw electron density from the ring inductively along the sigma bond. • But halogens have lone pairs of electrons that can stabilize the sigma complex by resonance. => Chapter 17: Aromatics 2-Reactions Slide 17-26 13 Sigma Complex for Bromobenzene Ortho and para attacks produce a bromonium ion and other resonance structures. No bromonium ion possible with meta attack. => Chapter 17: Aromatics 2-Reactions Slide 17-27 Energy Diagram => Chapter 17: Aromatics 2-Reactions Slide 17-28 14 Summary of Directing Effects => Chapter 17: Aromatics 2-Reactions Slide 17-29 Multiple Substituents The most strongly activating substituent will determine the position of the next substitution. May have mixtures. OCH3 OCH3 OCH3 SO H SO 3 3 + H2SO4 O2N O2N O2N SO3H => Chapter 17: Aromatics 2-Reactions Slide 17-30 15 Friedel-Crafts Alkylation • Synthesis of alkyl benzenes from alkyl halides and a Lewis acid, usually AlCl3. • Reactions of alkyl halide with Lewis acid produces a carbocation which is the electrophile. • Other sources of carbocations: alkenes + HF, or alcohols + BF3. => Chapter 17: Aromatics 2-Reactions Slide 17-31 Examples of Carbocation Formation Cl CH3 + _ C Cl AlCl CH3 CH CH3 + AlCl3 3 H3C H _ F HF + H2C CH CH3 H3C CH CH3 + BF3 OH H O BF + _ 3 + H3C CH CH3 H3C CH CH3 H3C CH CH3 HOBF3 => Chapter 17: Aromatics 2-Reactions Slide 17-32 16 Formation of Alkyl Benzene CH3 H +C H CH(CH3)2 + CH3 H F - CH H F B OH 3 HF CH + + CH(CH ) F F 3 2 CH B OH 3 F H => Chapter 17: Aromatics 2-Reactions Slide 17-33 Limitations of Friedel-Crafts • Reaction fails if benzene has a substituent that is more deactivating than halogen. • Carbocations rearrange. Reaction of benzene with n-propyl chloride and AlCl3 produces isopropylbenzene. • The alkylbenzene product is more reactive than benzene, so polyalkylation occurs. => Chapter 17: Aromatics 2-Reactions Slide 17-34 17 Friedel-Crafts Acylation • Acyl chloride is used in place of alkyl chloride. • The acylium ion intermediate is resonance stabilized and does not rearrange like a carbocation. • The product is a phenyl ketone that is less reactive than benzene. => Chapter 17: Aromatics 2-Reactions Slide 17-35 Mechanism of Acylation O O O HCl C R _ C R + C + Cl AlCl3 H AlCl3 R + H => Chapter 17: Aromatics 2-Reactions Slide 17-36 18 Clemmensen Reduction Acylbenzenes can be converted to alkylbenzenes by treatment with aqueous HCl and amalgamated zinc. Works for non- aromatic ketones as well; rearrangements can occur. O O 1) C CH2CH3 CH2CH2CH3 AlCl3 Zn(Hg) + CH3CH2C Cl 2) H2O aq. HCl => Chapter 17: Aromatics 2-Reactions Slide 17-37 Wolff-Kishner Reduction Acylbenzenes can be also converted to alkylbenzenes by treatment with aqueous NH2NH2 and hydroxide (mechanism next chapter). Works for non-aromatic ketones as well. O H H NH2NH2 KOH aq. ethylene glycol Chapter 17: Aromatics 2-Reactions Slide 17-38 19 Gatterman-Koch Formylation • Formyl chloride is unstable. Use a high pressure mixture of CO, HCl, and catalyst. • Product is benzaldehyde. O + _ AlCl3/CuCl CO + HCl H C Cl H C O AlCl4 O O C + C H + + HCl H Chapter 17: Aromatics 2-Reactions Slide 17-39 Nucleophilic Aromatic Substitution • A nucleophile replaces a leaving group on the aromatic ring. • Electron-withdrawing substituents activate the ring for nucleophilic substitution. => Chapter 17: Aromatics 2-Reactions Slide 17-40 20 Examples of Nucleophilic Substitution => Chapter 17: Aromatics 2-Reactions Slide 17-41 Addition-Elimination Mechanism => Chapter 17: Aromatics 2-Reactions Slide 17-42 21 Benzyne Mechanism • Reactant is halobenzene with no electron-withdrawing groups on the ring. • Use a very strong base like NaNH2. => Chapter 17: Aromatics 2-Reactions Slide 17-43 Benzyne Intermediate => Chapter 17: Aromatics 2-Reactions Slide 17-44 22 Chlorination of Benzene • Addition to the benzene ring may occur with high heat and pressure (or light). • The first Cl2 addition is difficult, but the next 2 moles add rapidly. • The product, benzene hexachloride, is an insecticide. => Chapter 17: Aromatics 2-Reactions Slide 17-45 Catalytic Hydrogenation • Elevated heat and pressure is required. • Possible catalysts: Pt, Pd, Ni, Ru, Rh. • Reduction cannot be stopped at an intermediate stage. CH3 CH3 3H2, 1000 psi Ru, 100°C => CH3 CH3 Chapter 17: Aromatics 2-Reactions Slide 17-46 23 Birch Reduction: Regiospecific • A carbon bearing an e--withdrawing group is reduced. O O C _ C O OH Na, NH3 H CH3CH2OH • A carbon bearing an e--releasing group is not reduced. OCH OCH3 3 Li, NH3 (CH3)3COH, THF => Chapter 17: Aromatics 2-Reactions Slide 17-47 Birch Mechanism => Chapter 17: Aromatics 2-Reactions Slide 17-48 24 Side-Chain Oxidation Alkylbenzenes are oxidized to benzoic acid by hot KMnO4 or Na2Cr2O7/H2SO4. _ CH(CH3)2 COO KMnO , OH- 4 _ H2O, heat COO CH CH2 Chapter 17: Aromatics 2-Reactions Slide 17-49 Side-Chain Halogenation • Benzylic position is the most reactive. • Chlorination is not as selective as bromination, results in mixtures. • Br2 reacts only at the benzylic position. Br CH CH CH 2 2 3 CHCH2CH3 Br2, h! Chapter 17: Aromatics 2-Reactions Slide 17-50 25 SN1 Reactions • Benzylic carbocations are resonance-stabilized, easily formed. • Benzyl halides (even primary!) undergo SN1 reactions. CH3CH2OH, heat CH2Br CH2OCH2CH3 => Chapter 17: Aromatics 2-Reactions Slide 17-51 SN2 Reactions • Benzylic halides are 100 times more reactive than primary halides via SN2.
Load more

Recommended publications
  • Nomenclature of Carboxylic Acid Derivatives Acid Halide Substituents
    Gentilucci, Carboxylic Acid Derivatives Nomenclature of Carboxylic Acid Derivatives Gentilucci, Carboxylic Acid Derivatives Acid halides 1. Alkane + the suffix -oyl followed by the halogen. 2. Select the longest continuous carbon chain, containing the acyl group. 3. Number the carbon chain, beginning at the end nearest to the acyl group. 4. Number the substituents and write the name, listing substituents alphabetically. Acid halide substituents attached to rings are named using the suffix - carbonyl. 1 Gentilucci, Carboxylic Acid Derivatives Anhydrides 1. Symmetrical: replace the ending "acid" with "anhydride ". 2. Asymmetrical: select the longest continuous carbon chain, containing the carboxylic acid group, and derive the parent name by replacing the -e ending with -oic anhydride . 3. Number the carbon chain, beginning at the end nearest to the acyl group. 4. Number the substituents and write the name, listing substituents alphabetically. Gentilucci, Carboxylic Acid Derivatives Amides are named by replacing the ending -oic acid with -amide . 1. Select the longest continuous carbon chain, containing the acyl group, and derive the parent name by replacing the -e ending with -amide . 2. Number the carbon chain, beginning at the end nearest to the acyl group. 3. Number the substituents and write the name, listing substituents alphabetically. 4. If the nitrogen atom is further substituted, the substituents are preceded by N- to indicate that they are attached to the nitrogen. Acid halide substituents attached to rings are named using the suffix - carboxamide. 2 Gentilucci, Carboxylic Acid Derivatives Carboxylate esters 1. Select the longest continuous carbon chain containing the acyl group, and derive the parent name by replacing the -e ending with –oate .
    [Show full text]
  • Carbonyl Compounds
    Carbonyl Compounds What are Carbonyl Compounds? Carbonyl compounds are compounds that contain the C=O (carbonyl) group. Preparation of Aldehydes: 1. Preparation from Acid Chloride (Rosenmund Reduction): This reaction was named after Karl Wilhelm Rosenmund, who first reported it in 1918. The reaction is a hydrogenation process in which an acyl chloride is selectively reduced to an aldehyde. The reaction, a hydrogenolysis, is catalysed by palladium on barium sulfate, which is sometimes called the Rosenmund catalyst. 2. Preparation from Nitriles: This reaction involves the preparation of aldehydes (R-CHO) from nitriles (R- CN) using SnCl2 and HCl and quenching the resulting iminium salt ([R- + − CH=NH2] Cl ) with water (H2O). During the synthesis, ammonium chloride is also produced. The reaction is known as Stephen Aldehyde synthesis. Dr. Sumi Ganguly Page 1 3. Preparation from Grignard Reagent: When Grignard Reagent is reacted with HCN followed by hydrolysis aldehyde is produced. Preparation of Ketones: 1. Preparation from Acid Chloride (Friedel-Crafts Acylation): Acid chlorides when reacted with benzene in presence of anhydrous AlCl3, aromatic ketone are produced. However, only aromatic ketones can be prepared by following this method. In order to prepare both aromatic and aliphatic ketones acid chlorides is reacted with lithium dialkylcuprate (Gilman Reagnt). Dr. Sumi Ganguly Page 2 The lithium dialkyl cuprate is produced by the reaction of two equivalents of the organolithium reagent with copper (I) iodide. Example: 3. Preparation from Nitriles and Grignard Reagents: When Grignard Reagent is reacted with RCN followed by hydrolysis aldehyde is produced. Dr. Sumi Ganguly Page 3 Physical Characteristic of Carbonyl Compounds: 1) The boiling point of carbonyl compounds is higher than the alkanes with similar Mr.
    [Show full text]
  • Indium Promoted-Convenient Method for Acylation of Alc이iols with Acyl Chlorides
    Communications to the Editor Bull. Korean Chem. Soc. 2003, Vol. 24, No. 2 155 Indium Promoted-Convenient Method for Acylation of Alc이iols with Acyl Chlorides Dae Hyan Cho, Joong Gon Kim,f and Doo Ok Jang* Department of Chemistry, Yonsei University, Wonju 220-710, Korea ‘Biotechnology Division, Hanwha Chemical R & D Center, Daejeon 305-345, Korea Received November 9, 2002 Key Words : Indium, Alcohol, Acylation, Acyl chloride Even though various reagents for coupling of alcohols tions for the acylation of alcohols with acyl chlorides in the with carboxylic acids and transesterification of esters have presence of indium. The results are summarized in Table 1. been developed,1 there is still a great demand for a process Reaction of 2 (1 equiv) with 1 (1 equiv) in the presence of by using acyl chlorides for the acylation of alcohols in the indium (1 equiv) in CH3CN at room temperature produced case of substrates having steric hindrance or low reactivity. the corresponding ester in only 21% yield and the starting The acylation of alcohols with acyl chlorides is commonly acyl chloride and alcohol were recovered. The optimal yield carried out in the presence of tertiary amines such as 4- of the ester was attained with 3 equiv of 1 or 2 in the presence (methylamino) pyridine or 4 -pyrrolidinopyridine.2 Many of 3 equiv of indium. The solvent effect of acylation of 2 methods for the acylation of alcohols with acyl chlorides with 1 in the presence of indium was studied. The reaction have been developed using a variety of reagents.3 Most proceeded efficiently in common organic solvents such as recently, benzoylation of alcohols with lithium perchlorate DMF, Et2。，THF or CHzCh whereas non-polar solvents hase been reported.4 However, these methods have their own such as n-hexane or benzene gave poor yields of the ester.
    [Show full text]
  • Nitrobenzene
    This report contains the collective views of an international group of experts and does not necessarily represent the decisions or the stated policy of the United Nations Environment Programme, the International Labour Organization or the World Health Organization. Environmental Health Criteria 230 NITROBENZENE First draft prepared by L. Davies, Office of Chemical Safety, Therapeutic Goods Administration, Australian Department of Health and Ageing, Canberra, Australia Plese note that the pagination and layout of this web verson are not identical to those of the (to be) printed document Published under the joint sponsorship of the United Nations Environment Programme, the International Labour Organization and the World Health Organization, and produced within the framework of the Inter-Organization Programme for the Sound Management of Chemicals. World Health Organization Geneva, 2003 The International Programme on Chemical Safety (IPCS), established in 1980, is a joint venture of the United Nations Environment Programme (UNEP), the International Labour Organization (ILO) and the World Health Organization (WHO). The overall objectives of the IPCS are to establish the scientific basis for assessment of the risk to human health and the environment from exposure to chemicals, through international peer review processes, as a prerequisite for the promotion of chemical safety, and to provide technical assistance in strengthening national capacities for the sound management of chemicals. The Inter-Organization Programme for the Sound Management of Chemicals (IOMC) was established in 1995 by UNEP, ILO, the Food and Agriculture Organization of the United Nations, WHO, the United Nations Industrial Development Organization, the United Nations Institute for Training and Research and the Organisation for Economic Co-operation and Development (Participating Organizations), following recommendations made by the 1992 UN Conference on Environment and Development to strengthen cooperation and increase coordination in the field of chemical safety.
    [Show full text]
  • Part I. the Total Synthesis Of
    AN ABSTRACT OF THE THESIS OF Lester Percy Joseph Burton forthe degree of Doctor of Philosophy in Chemistry presentedon March 20, 1981. Title: Part 1 - The Total Synthesis of (±)-Cinnamodialand Related Drimane Sesquiterpenes Part 2 - Photochemical Activation ofthe Carboxyl Group Via NAcy1-2-thionothiazolidines Abstract approved: Redacted for privacy DT. James D. White Part I A total synthesis of the insect antifeedant(±)-cinnamodial ( ) and of the related drimanesesquiterpenes (±)-isodrimenin (67) and (±)-fragrolide (72)are described from the diene diester 49. Hydro- boration of 49 provided the C-6oxygenation and the trans ring junction in the form of alcohol 61. To confirm the stereoselectivity of the hydroboration, 61 was convertedto both (t)-isodrimenin (67) and (±)-fragrolide (72) in 3 steps. A diisobutylaluminum hydride reduction of 61 followed by a pyridiniumchlorochromate oxidation and treatment with lead tetraacetate yielded the dihydrodiacetoxyfuran102. The base induced elimination of acetic acid preceded theepoxidation and provided 106 which contains the desired hydroxy dialdehydefunctionality of cinnamodial in a protected form. The epoxide 106 was opened with methanol to yield the acetal 112. Reduction, hydrolysis and acetylation of 112 yielded (t)- cinnamodial in 19% overall yield. Part II - Various N- acyl- 2- thionothiazolidineswere prepared and photo- lysed in the presence of ethanol to provide the corresponding ethyl esters. The photochemical activation of the carboxyl function via these derivatives appears, for practical purposes, to be restricted tocases where a-keto hydrogen abstraction and subsequent ketene formation is favored by acyl substitution. Part 1 The Total Synthesis of (±)-Cinnamodial and Related Drimane Sesquiterpenes. Part 2 Photochemical Activation of the Carboxyl Group via N-Acy1-2-thionothiazolidines.
    [Show full text]
  • Reactions of Benzene & Its Derivatives
    Organic Lecture Series ReactionsReactions ofof BenzeneBenzene && ItsIts DerivativesDerivatives Chapter 22 1 Organic Lecture Series Reactions of Benzene The most characteristic reaction of aromatic compounds is substitution at a ring carbon: Halogenation: FeCl3 H + Cl2 Cl + HCl Chlorobenzene Nitration: H2 SO4 HNO+ HNO3 2 + H2 O Nitrobenzene 2 Organic Lecture Series Reactions of Benzene Sulfonation: H 2 SO4 HSO+ SO3 3 H Benzenesulfonic acid Alkylation: AlX3 H + RX R + HX An alkylbenzene Acylation: O O AlX H + RCX 3 CR + HX An acylbenzene 3 Organic Lecture Series Carbon-Carbon Bond Formations: R RCl AlCl3 Arenes Alkylbenzenes 4 Organic Lecture Series Electrophilic Aromatic Substitution • Electrophilic aromatic substitution: a reaction in which a hydrogen atom of an aromatic ring is replaced by an electrophile H E + + + E + H • In this section: – several common types of electrophiles – how each is generated – the mechanism by which each replaces hydrogen 5 Organic Lecture Series EAS: General Mechanism • A general mechanism slow, rate + determining H Step 1: H + E+ E El e ctro - Resonance-stabilized phile cation intermediate + H fast Step 2: E + H+ E • Key question: What is the electrophile and how is it generated? 6 Organic Lecture Series + + 7 Organic Lecture Series Chlorination Step 1: formation of a chloronium ion Cl Cl + + - - Cl Cl+ Fe Cl Cl Cl Fe Cl Cl Fe Cl4 Cl Cl Chlorine Ferric chloride A molecular complex An ion pair (a Lewis (a Lewis with a positive charge containing a base) acid) on ch lorine ch loronium ion Step 2: attack of
    [Show full text]
  • Synthesis of 2, 4-Dinitrophenoxyacetic Acid, Pyridylglycine and 2- Methoxy-5-Nitrophenylglycine As Intermediates for Indigo Dyes
    IOSR Journal of Applied Chemistry (IOSR-JAC) e-ISSN: 2278-5736.Volume 9, Issue 2 Ver. II (Feb. 2016), PP 01-05 www.iosrjournals.org Synthesis of 2, 4-Dinitrophenoxyacetic Acid, Pyridylglycine and 2- Methoxy-5-Nitrophenylglycine as Intermediates for Indigo Dyes Nwokonkwo, D.C1, Nwokonkwo, H.C2, Okpara, N. E3 ,2,3 1Faculty of Science Industrial Chemistry Department Ebonyi State University Abakaliki, Nigeria Abstract : The preparation of indigo dye intermediates was carried out using 2, 4-dinitrophenol, 2- aminopyridine and 2-methoxy-5-nitroaniline as starting materials or reactants in the search for new indigo dye intermediates. Approximately 0.5 mole of 2, 4-dinitrophenol, 0.42 mole of 2- aminopyridine and 0.2 mole of 2- methoxy-5-nitroaniline, were treated separately with appropriate quantity of chloroacetic acid and sodium hydroxide pellets using nitrobenzene a high boiling liquid as solvent. The products that resulted: 2, 4- dinitrophenoxyacetic acid, pyridylglycine and 2-methoxy-5-nitrophenylglycine were purified using solvent extraction, activated carbon and column chromatography to reveal different amorphous powders in each case. Their structures were established by spectral analysis: ultraviolet spectroscopy (UV), infrared spectroscopy (IR), mass spectrometry (MS), proton nuclear magnetic resonance spectroscopy (1H-NMR) and carbon- 13 magnetic resonance spectroscopy (13C-NMR). Keywords: Analysis, Dye, Extraction, Intermediates, Precursors, Solvent I. Introduction The sources of organic raw materials for the synthetic dyes are mainly coal tar distillate from petroleum industry. These primary raw materials are benzene, toluene, o-, m- and p- xylenes naphthalenes anthracene etc [1]. A great variety of inorganic chemicals are also used as well. In some cases, laboratory preparation of the required compound may act as the sources of the raw material.
    [Show full text]
  • Derivatives of Carboxylic Acids
    Acylation A4 1 DERIVATIVES OF CARBOXYLIC ACIDS ACYL (ACID) CHLORIDES - RCOCl ACID ANHYDRIDES - (RCO)2O named from corresponding acid named from corresponding acid remove -ic add -yl chloride remove acid add anhydride CH3COCl ethanoyl chloride (CH3CO)2O ethanoic anhydride C6H5COCl benzene carbonyl chloride δ− δ+ O δ− CH C O 3 δ− δ+ O δ+ CH3 C δ− CH3 C δ− Cl O bonding in acyl chlorides bonding in acid anhydrides Chemical Properties • colourless liquids which fume in moist air • acyl chlorides are more reactive than anhydrides • attacked at the positive carbon centre by nucleophiles • nucleophiles include water, alcohols, ammonia and amines • undergo addition-elimination reactions Uses of Acylation Industrially Manufacture of Cellulose acetate - making fibres Aspirin (acetyl salicylic acid) - analgaesic Ethanoic anhydride is more useful • cheaper • less corrosive • less vulnerable to hydrolysis • less dangerous reaction Laboratory Used to make carboxylic acid, esters, amines, N-substituted amines Ethanoyl chloride is used as it • is more reactive • gives a cleaner reaction Q.1 Investigate how aspirin is made industrially and in the laboratory. Why are the reagents and chemicals different? What properties of Aspirin make it such a useful drug? 2 A4 Acylation ADDITION ELIMINATION REACTIONS - OVERVIEW Mechanism • species attacked by nucleophiles at the positive carbon end of the C=O bond • the nucleophile adds to the molecule • either Cl or RCOO¯ is eliminated • a proton is removed General example - with water ACID CHLORIDES H Cl + Cl H O O
    [Show full text]
  • Reactions of Aromatic Compounds Just Like an Alkene, Benzene Has Clouds of  Electrons Above and Below Its Sigma Bond Framework
    Reactions of Aromatic Compounds Just like an alkene, benzene has clouds of electrons above and below its sigma bond framework. Although the electrons are in a stable aromatic system, they are still available for reaction with strong electrophiles. This generates a carbocation which is resonance stabilized (but not aromatic). This cation is called a sigma complex because the electrophile is joined to the benzene ring through a new sigma bond. The sigma complex (also called an arenium ion) is not aromatic since it contains an sp3 carbon (which disrupts the required loop of p orbitals). Ch17 Reactions of Aromatic Compounds (landscape).docx Page1 The loss of aromaticity required to form the sigma complex explains the highly endothermic nature of the first step. (That is why we require strong electrophiles for reaction). The sigma complex wishes to regain its aromaticity, and it may do so by either a reversal of the first step (i.e. regenerate the starting material) or by loss of the proton on the sp3 carbon (leading to a substitution product). When a reaction proceeds this way, it is electrophilic aromatic substitution. There are a wide variety of electrophiles that can be introduced into a benzene ring in this way, and so electrophilic aromatic substitution is a very important method for the synthesis of substituted aromatic compounds. Ch17 Reactions of Aromatic Compounds (landscape).docx Page2 Bromination of Benzene Bromination follows the same general mechanism for the electrophilic aromatic substitution (EAS). Bromine itself is not electrophilic enough to react with benzene. But the addition of a strong Lewis acid (electron pair acceptor), such as FeBr3, catalyses the reaction, and leads to the substitution product.
    [Show full text]
  • Investigation of Nitro-Organic Compounds in Diesel Engine Exhaust: DE-AC36-08-GO28308 Final Report, February 2007–April 2008 5B
    Subcontract Report Investigation of Nitro-Organic NREL/SR-540-45597 Compounds in Diesel Engine June 2010 Exhaust Final Report February 2007 – April 2008 John Dane and Kent J. Voorhees Colorado School of Mines Department of Chemistry and Geochemistry Golden, Colorado Subcontract Report Investigation of Nitro-Organic NREL/SR-540-45597 Compounds in Diesel Engine June 2010 Exhaust Final Report February 2007 – April 2008 John Dane and Kent J. Voorhees Colorado School of Mines Department of Chemistry and Geochemistry Golden, Colorado NREL Technical Monitor: Matthew Ratcliff Prepared under Subcontract No. NEV-7-77395-01 National Renewable Energy Laboratory 1617 Cole Boulevard, Golden, Colorado 80401-3393 303-275-3000 • www.nrel.gov NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Operated by the Alliance for Sustainable Energy, LLC Contract No. DE-AC36-08-GO28308 NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.
    [Show full text]
  • N Goalby Chemrevise.Org 1 Reaction with Water
    Carboxylic acid derivatives: Acyl Chlorides and Acid Anhydrides Acyl Chlorides Acid Anhydrides Acid anhydrides have a similar reactivity to O Acyl chlorides are much O acyl chlorides and therefore bring about the CH3 C more reactive than same changes in functional groups. carboxylic acids CH3 C Cl O ethanoyl chloride The main difference is the by-products. CH3 C Acyl chlorides mostly give off HCl. Acid O anhydrides give off RCOOH ethanoic anhydride. Explaining reactivity Many of the reactions of the carboxylic acid derivatives follow the pattern below with an attack by an nucleophile. O O CH3 C + :X- CH3 C + :W- On a simplistic level, the stronger the electron attracting power of ‘W’, the W X more positive the carbon, and the more attractive the carbon is to Where –W: and :W- can be –Cl and Cl- (acyl chlorides) nucleophiles. - or -OCH3 and OCH3 (esters) The relative attractive powers of the –W: are - `or -NH2 and NH2 (amides) -Cl > -OH > -OCH3 > -NH2 Therefore in the case of hydrolysis reactions, acyl chlorides are highly reactive and will be hydrolysed by weak nucleophiles such as water. Amides and Esters contain only weak electron attracting W groups and need strong nucleophiles such as hydroxide ions in NaOH to hydrolyse. This difference in reactivity is caused by a combination of two factors 1. the electronegativity of the Cl’s, N’s and O’s causing electron density to be withdrawn from the carbon making the carbon more positive and more attractive to nucleophiles- This factor makes them more reactive. 2. delocalisation of the lone pairs on these atoms into the carbonyl system which reduces the reactivity.
    [Show full text]
  • 1-Bromo-2-Nitrobenzene Standard
    Page 1/9 Safety Data Sheet acc. to OSHA HCS Printing date 03/30/2019 Version Number 2 Reviewed on 03/30/2019 * 1 Identification · Product identifier · Trade name: 1-Bromo-2-nitrobenzene Standard (1X1 mL) · Part number: PPS-350-1 · Application of the substance / the mixture Reagents and Standards for Analytical Chemical Laboratory Use · Details of the supplier of the safety data sheet · Manufacturer/Supplier: Agilent Technologies, Inc. 5301 Stevens Creek Blvd. Santa Clara, CA 95051 USA · Information department: Telephone: 800-227-9770 e-mail: [email protected] · Emergency telephone number: CHEMTREC®: 1-800-424-9300 2 Hazard(s) identification · Classification of the substance or mixture GHS02 Flame Flam. Liq. 2 H225 Highly flammable liquid and vapor. GHS07 Eye Irrit. 2A H319 Causes serious eye irritation. STOT SE 3 H336 May cause drowsiness or dizziness. · Label elements · GHS label elements The product is classified and labeled according to the Globally Harmonized System (GHS). · Hazard pictograms GHS02 GHS07 · Signal word Danger · Hazard-determining components of labeling: acetone · Hazard statements Highly flammable liquid and vapor. Causes serious eye irritation. May cause drowsiness or dizziness. · Precautionary statements Keep away from heat/sparks/open flames/hot surfaces. - No smoking. Ground/bond container and receiving equipment. Use explosion-proof electrical/ventilating/lighting/equipment. Use only non-sparking tools. (Contd. on page 2) US 48.1.26 Page 2/9 Safety Data Sheet acc. to OSHA HCS Printing date 03/30/2019 Version Number 2 Reviewed on 03/30/2019 Trade name: 1-Bromo-2-nitrobenzene Standard (1X1 mL) (Contd. of page 1) Take precautionary measures against static discharge.
    [Show full text]