Arenes - Organic Chemistry I - Lecture Slides, Slides of Organic Chemistry

Download Arenes - Organic Chemistry I - Lecture Slides and more Slides Organic Chemistry in PDF only on Docsity! Arenes: compounds containing both aliphatic and aromatic parts. Alkylbenzenes Alkenylbenzenes Alkynylbenzenes Etc. Emphasis on the effect that one part has on the chemistry of the other half. Reactivity & orientation docsity.com Example: ethylbenzene EAS in the aromatic part -CH2CH3 activates and directs ortho- & para- CH2 CH3 CH2 CH3 CH2 CH3 CH2 CH3 CH CH3 Br2, Fe Br Br Br2, heat Br + HBr + Free radical halogenation in the side chain -C6H5 activates and directs benzyl docsity.com Use of phenyl C6H5- = “phenyl” CH2CH2 2-methyl-3-phenylheptane 1,2-diphenylethane do not confuse phenyl (C6H5-) with benzyl (C6H5CH2-) docsity.com Alkenylbenzenes, nomenclature: CH=CH2 styrene CH2CH=CH2 3-phenylpropene (allylbenzene) (Z)-1-phenyl-1-butene Special name Rest are named as substituted alkenes docsity.com Alkynylbenzenes, nomenclature: SS C)-cze# S phenylacetylene phenylethyne 5-phenyl-2-hexyne docsity.com Modification of side chain: Br + H2, Ni + Sn, HCl Br + Mg; then H2o ethylbenzene docsity.com Friedel-Crafts: Ar-H + R-X, AlCl3  Ar-R + HX Ar-H + R-OH, H+  Ar-R + H2O Ar-H + alkene, H+  Ar-R docsity.com CH3 CH3 C CH3 H3C CH3 + H3C C CH3 Br CH3 AlCl3 + CH3CH2-OH, H + CH2 CH3 + CH2=CHCH3, H + CH CH3 CH3 isopropylbenzene ethylbenzene p-tert-butyltoluene docsity.com polyalkylation CH3 CH3Br, AlCl3 + CH3 CH3 CH3 CH3 + CH3 CH3 H3C + The alkyl group activates the ring making the products more reactive that the reactants leading to polyalkylation. Use of excess aromatic compound minimizes polyalkylation in the lab. docsity.com The electrophile in Friedel Crafts alkylation is a carbocation: R-X + AlX3  R+ R-OH + H+  R+ | | — C = C — + H+  R+ Carbocations can rearrange!  docsity.com rearrangement + CH3CH2CH2-Br, AlCl3 CH CH3H3C AlCl3 + C CH3H3C CH3 + H+ isopropylbenzene tert-butylbenzene 2-methyl-2-phenylbutane carbocation rearrangements are possible! CH3CCH2CH3 CH3 CH3CHCH2-Br CH3 CH3CCH2-OH CH3 CH3 docsity.com NR with rings less reactive than bromobenzene Br + CH3CH2-Br, AlCl3 Br Br CH2CH3 CH2CH3 + COOH NO2 + CH3-Br, AlCl3 + CH3CH2 -OH, H+ NR NR -CHO, -COR -SO3H -COOH, -COOR -CN -NR3 + -NO2 docsity.com NR with –NH2, -NHR, -NR2 NH2 + CH3CH2-Cl, AlCl3 NR NH2 + AlCl3 NH2 AlCl3 Lewis base Lewis acid deactivated to EAS docsity.com Friedel-Crafts limitations: a) Polyalkylation b) Possible rearrangement c) R-X cannot be Ar-X d) NR when the benzene ring is less reactive than bromobenzene e) NR with -NH2, -NHR, -NR2 groups In syntheses it is often best to do Friedel-Crafts alkylation in the first step! docsity.com Alkylbenezenes, oxidation: NR NR NR NR NR KMnO4 KMnO4 heat CH3CH3 H2 C CH3 COOH docsity.com + KMnO4, heat + KMnO4, heat COOH COOH COOH + 2 CO2 docsity.com Oxidation of alkylbenzenes. 1) Syn 2) identification C8H10: H2C CH3 CH3 CH3 CH3 CH3 CH3 CH3 COOH COOH COOH COOH COOH COOH COOH bp 136oC bp 144oC bp 139oC bp 138oC mp 122oC mp 231oC mp 348oC mp 300oC docsity.com CH2CH3 benzyl free radical > 3o > 2o > 1o > CH3 CHCH3 CHCH3CHCH3 CHCH3 . . . . X2 2 X. + X . docsity.com Alkenylbenzenes, syntheses: 1. Modification of side chain: a) dehydrohalogenation of alkyl halide b) dehydration of alcohol c) dehalogenation of vicinal dihalide d) reduction of alkyne (2. Friedel-Crafts alkylation) docsity.com Alkenylbenzenes, synthesis modification of side chain CHCH3 CHCH3 CHCH2 C CH=CH2 CH Br OH Cl Cl styrene KOH(alc) H+, heat Zn H2, Pd-C docsity.com Alkenylbenzenes, reactions: 1. Reduction 2. Oxidation 3. EAS 4. Side chain a) add’n of H2 j) oxymercuration b) add’n of X2 k) hydroboration c) add’n of HX l) addition of free rad. d) add’n of H2SO4 m) add’n of carbenes e) add’n of H2O n) epoxidation f) add’n of X2 & H2O o) hydroxylation g) dimerization p) allylic halogenation h) alkylation q) ozonolysis i) dimerization r) vigorous oxidation docsity.com Alkenylbenzenes, reactions: reduction CH=CH2 CH=CH2 + H2, Ni + H2, Ni, 250 oC, 1,500 psi CH2CH3 H CH2CH3 docsity.com Alkenylbenzenes, reactions oxidation CH=CH2 CH=CH2 CH=CH2 CHCH2 COOH CH=O OHOH + CO2 + O=CH2 KMnO4 heat 1. O3 2. Zn, H2O KMnO4 docsity.com Alkenylbenzenes, reactions side chain: CH=CHCH3 CH2CH2CH3 CHCHCH3 CHCH2CH3 CHCH2CH3 Br Br Br OSO3H H2, Ni Br2, CCl4 HBr H2SO4 docsity.com Benzyl carbocation CH=CHCH3 + H + CHCH2CH3 CHCH2CH3CHCH2CH3 CHCH2CH3 resonance stabilization of benzyl carbocation > 3o > 2o > 1o docsity.com CH=CHCH3 CHCH2CH3 CHCHCH3 CHCH2CH3 CH2CHCH3 OH OH Br OH OH H2O, H + Br2, H2O 1. H2O, Hg(OAc)2 2. NaBH4 1. (BH3)2 2. H2O2, NaOH docsity.com Alkynylbenzenes, syntheses: Dehydrohalogenation of vicinal dihalides CH=CH2 CHCH2 Br Br C CH Br2 1. KOH 2. NaNH2 H C CH3 Br KOH(alc) H2 C CH3 CH2=CH2 HF docsity.com Alkynylbenzenes, reactions: 1. Reduction 2. Oxidation 3. EAS 4. Side chain a) reduction e) as acids b) add’n of X2 f) with Ag + c) add’n of HX g) oxidation d) add’n of H2O, H + docsity.com Alkynylbenzenes, reactions: reduction C C CH3 + 2 H2, Ni CH2CH2CH3 + (xs) H2, Ni heat & pressure C C CH3 + Li, NH3 + H2, Pd-C anti- syn- docsity.com Alkynylbenzenes, reactions: side chain: C C H C=CH C CCH3 Br Br Br Br Br Br C Br Br H C=CH2 Br Br2 2 Br2 HBr 2 HBr docsity.com C CH H2O, H + CCH3 O C CH C CH Na Ag+ C C C-Na+ C-Ag+ C CCH3 Ag+ NR, not terminal docsity.com Arenes: alkylbenzenes alkenylbenzenes alkynylbenzenes As expected, but remember that you cannot do EAS on alkenyl- or alkynylbenzenes. docsity.com