Alcohols & Phenols, Synthesis & Chemical Properties, Lecture notes of Organic Chemistry

Download Alcohols & Phenols, Synthesis & Chemical Properties and more Lecture notes Organic Chemistry in PDF only on Docsity! ALCOHOLS & PHENOL: SYNTHESIS & CHEMICAL PROPERTIES BS-Chemistry (Semester-II) By Dr. Aliya Ibrar Dated: 22-05-2021 Eh Grignard reactions of carbonyl compounds = Formaldehyde (H,C=O) reacts with Grignard reagents giving primary alcohol. H R-MgX + c= -c-0 * -CH.- 9 fees EO MgX —75, R-CH,-OH or H i) ether R-MgX + > = a= es C=O oP -R-CH»-OH Example: HL i) ether Hl CH3CH2CH2CH2-MgBr + se 0 Tae CH,CH,CH,CH,-C- OH il 4 butylmagnesium bromide 1-pentanol (92%) = Aldehydes reacts with Grignard reagents giving secondary alcohols. ' R' ether R R-MgX + 4oo=0 —_> R-G-O H or R' i) ether R' R-MgX + ~Sc=o ——» R- C-OH H ii) H30* H Example: H3C th CHjCHyMgBr 5 Nexo =. H ii) H30* R' + I MgX ee R-C—OH oH, CH3CH2-C-OH H = Ketones reacts with Grignard reagents giving tertiary alcohols. R' R' R' R-MgX + c= fag va g ame Sher” ~R-C-O MgX 75-2 R-C-OH R" R" or R' i) ether R' R-MgX + Bye-c=0 ——> p-C-0H ii) H30* R" Example: Oo OH i) ether CH;CH-MgBr 4 H C-C-CH,CH,CH, ae CHCH,-C-CH,CH,CH, Il) Fig CH, a INDUSTRIAL AND LABORATORY PREPARATION OF ETHANOL = There are three principle ways to get the simple alcohols that are the backbone of aliphatic organic synthesis. These methods are: a) hydration of alkenes obtained from the cracking of petroleum b) the oxo process from alkenes, carbon monoxide and hydrogen c) fermentation of carbohydrate Sth REDUCTION OF ALDEHYDES, KETONES AND CARBOXYLIC ACIDS = Aldehydes and ketones can be reduced to alcohols using: a) lithium aluminium hydride (LiAIH,) b) sodium borohydride (NaBH,) Cc) catalytic hydrogenation Ul rd H* a R—C—H + LiAIH, or NaBH, or Hn, Ni —s R—C—H ———» Rp—c—H aldehyde [ 4 1° alcohol ll 7 + OH R—C—R'+ LiAIH, or NaBH, or H,Ni —p» R—C—R' —”_5 p/p. ketone L | H H* = diluted acid such as H2SO, 2° alcohol Examples: ° ° 2 CH;—C—H + LiAIH, —»CH,—C—H Tt CHs—C—H ethanal L H ethanol . 4 fe CH,—C—CH3, + H,/Ni—® CH;—C—CH,;—"_» CH,—C—CH; propanone \ hi 2-propanol eS REACTIONS OF ALCOHOLS = Reaction with sodium = Oxidation = Esterification = Halogenation and haloform reactions = Dehydration = Formation of ether (Williamson ether synthesis) 2 —F— Reaction with sodium = Alcohols reacts with Na at room temperature to form salts (sodium alkoxides) and hydrogen. 2R-O-H + 2Na — 2R-O° Na* + H, = For example: alcohol sodium ethoxide = Reactivity of alcohols towards the reactions with sodium: CH,>1 >2 >3 | “ H 1° alcohol i i H 1° alcohol Oxidation Pyridinium chlorochromate ee) CH,Clp, 25°C Cu or Cr3O/pyridine A Cr30/pyridine = Collins reagent i a a H 1° alcohol KMn0O,/H* or K,Cr,07/H* or CrO3/H* t R-C=O aldehyde " R-C=O aldehyde 0 I R-C-OH carboxylic acid ——_— Esterification = Esterification: - the reaction between an alcohol and a carboxylic acid to form an ester and H,O. O II H" II R—C—O—H| +|}H7O—R' === R—C—O-—R' + |H,O carboxylic acid alcohol ester EXAMPLES i . i CH3CH2-O;H CH3——C-;O—H CH3—C—OCH.CH3 ethanol ethanoic acid ethyl ethanoate ft oO CHs-OfH] + C--OH| —— €)-£-och, +|H,O methanol benzoic acid methyl benzoate H+ = catalyst + H20 Esterification also occurs when alcohols react with derivatives of carboxylic acids such as acid chlorides CH,-O}H | methanol O Il + CH,-C— Cl ethanoyl chloride O II a a CH3;-C—OCH, methyl ethanoate + HCl eee Halogenation and haloform reactions 1) Hydrogen halides (HBr or HCl or Hl) R-OH + H-X — R-X + H,O Example: C,H;-OH +H-Br ——- C,H.-Br + H,O Reactivity of hydrogen halides decreases in order HI > HBr > HCI Reactivity of alcohols with hydrogen halides: sa> 2 > 1 = Reactivity of alcohols towards dehydration: See > 1 = Reagents for dehydration: i) Concentrated H,SO, CH,-CH,-OH conc. H,SO, A CH,=CH, + H,O ii) With phosphoric (v) acid OH icy 85% H3PQ,, 165-170°C O + H,O — iii) Vapour phase dehydration of alcohols Al,O, heat CH,CH,OH CH,=CH, +H,O  Formation of ether (Williamson ether synthesis) = Involves the S,2 attack of an alkoxide ion on an unhindered primary alkyl halides. = The alkoxide is made by adding Na, K or NaH to the alcohol. R-O- + R’-X — R-O-R’ + X alkoxide (R’ must be primary) = The alkyl halides (or tosylate) must be primary, so that a back-side attack is not hindered. = If the alkyl halides is not primary, elimination usually occurs to form alkenes. Se EXAMPLES CH3CH2-OH + Na ——> CH,CH,-O Na* + CHgl CH,C H,-O-CH3, + Nal or 1) Na 2) CH3I eo 1) Na cr’ —_ 2) CH3CHz-OTs cyclohexanol ethoxycyclohexane CH3CH2-OH CH,CH,-O-CH, + Nal a ESTERIFICATION EXAMPLES Cron MoH NaOH ( prone “ondios ©)y-ollen, + Nacl =o nSOH | sodium phenoxide a " Oro pone Opal + no phenyl benzoate a HALOGENATION = More reactive towards electrophilic substitution than benzene. = ortho-para director. OH OH X X + 3x, ——com _» + 3HX temperature X EXAMPLES OH OH Br. Br + 3Br. Oot _» + 3HBr temperature Br 2,4,6-tribromophenol (white precipitate) OH 2a + 3cl, ———a__» + 3HCI temperature pieces (white precipitate) * Monobromophenols are obtained if the bromine is dissolved in a non-polar solvent such as CCl, OH OH Oo Br 0 + 2Br>(CCl,) —— Cy + O + 2HBr H Br TESTS TO DISTINGUISH CLASSES OF ALCOHOLS 1) Lucas Test - The alcohol is shaken with Lucas reagent (a solution of ZnCl, in concentrated HCl). - Tertiary alcohol - immediate cloudiness (due to the formation of alkyl chloride). - Secondary alcohol - Solution turns cloudy within about 5 minutes. - Primary alcohol - No cloudiness at room temperature. CHs Hs CH,;—C—CH, HCI/ZnCl CH;—C—CH, | room temperature | OH Cl 3° alcohol (cloudy solution almost immediately) CH3-CH-CH,CH, ___HCIZnCln__ CH,-CH-CH,CH; I room temperature | OH Cl 2° alcohol (cloudy solution within 5 minutes) CH3;CH.CH.CH,OH HCI/ZnCl, room temperature no reaction 1° alcohol 2) Oxidation of alcohols - only primary and secondary alcohols are oxidised by hot acidified KMnO, or hot acidified K,Cr,0, solution. - the alcohol is heated with KMnO, or K,Cr,0, in the presence of dilute H,SO,. - 1° or 2° alcohol: — the purple colour of KMnO, solution disappears. — the colour of the K,Cr,0, solution changes from orange to green. - 3° alcohol do not react with KMnO, or K,Cr,0,.  H | CH3—C—R + 4I, + 6NaOH —+| CHI, (s) |+ RCOONa + 5Nal + 5H,O triiodomethane OH (iodoform) yellow precipitate where R = hydrogen, alkyl or aryl group ¢ The iodoform test can distinguish ethanol from methanol ' Oo CHz—C—-H| + 4lp + 60H —* CHI; (s) + 5l + 5H2O + H—-C—O7 a iodoform methanoate ethanol positive iodoform test H | H—C—H + 4l, + 60H —+ no reaction OH negative iodoform test methanol * The iodoform test can distinguish 2-propanol from 1-propanol r’ 0 CH3—C—H + 41, + 60H —* CHI; (s) + 5I + 5H20 +CH,—C—O Oa iodoform ethanoate 2-propanol positive iodoform test ier | ) + 41, + 60H —* noreaction H H OH negative iodoform test 1-propanol * TERTIARY ALCOHOLS DO NOT GIVE POSITIVE IODOFORM TEST 2) BROMOFORM H | =; + 4Br. + 6NaOQH —*> CHBr, (s) + RCOONa + 5NaBr + 5H,O OH bromoform where R = hydrogen, alkyl or aryl group reagent sample iodoform