Tiêu đề 19. Alcohols, Phenols and Ethers.pdf ✅

Alcohols, Phenols and Ethers 327 19 Alcohols, Phenols and Ethers QUICK LOOK Alcohols: Alcohols are compounds of the general formula ROH, where R is alkyl or substituted alkyl group. The group may be open chain or cyclic, it may contains double bond, a halogen atom, an aromatic ring or additional hydroxyl groups, e.g. 3 2 2 2 Butanol-1 CH CH CH CH OH Alcohols can be classified as, Monohydric Alcohols: Preparation By oxymercuration - demercuration reaction of alkene: 3 THF CH CH CH (CH COO) Hg H O 3 2 3 2 2 CH COOH − = + + → 4 2 6 3 2 NaBH / OH 1/ 2B H 3 CH CH CH | | OH HgOCOCH − −   − −   →   3 3 3 2 propanol CH CH CH Hg CH COO | OH − − − − + + Note: It is fast and convenient. The addition of water to an alkene is anti-Markownikoff and free from rearrangement. Hydroboration of Alkene 2 2 2 3H O 3 2 2 6 3 2 2 3 OH /H O Propene Tripropyl boron Diborane 1 3CH CH CH B H (CH CH CH ) B 2 3CH CH CH OH H BO − = + → − − → − − − − + 3 2 2 3 3 1 propanol 3CH CH CH OH H BO − − − − + Note: In this reaction addition of water to an alkene is syn, anti- Markownikoff and free from rearrangement. Hydrolysis of ethers: 2 4 dil.H SO C H O C H H O 2 5 2 5 2 ∆ − − + → 2 5 2C H OH By reaction of Grignard reagent with formaldehyde/ other aldehydes/ ketones (a) When Grignard reagent reacts with HCHO, it forms primary alcohol. R | H C O RMgX H C OMgX | | H H − = + → − − → (b) Oxirane on reaction with Grignard reagent also forms primary alcohol. (c) Any aldehyde except formaldehyde when treated with Grignard reagent forms secondary alcohol. R | R C O RMgX R C OMgX | | H H ′ ′ − = + → − − (d) When 2-alkyl oxirane reacts with Grignard reagent, secondary alcohol is formed. The ring is opened from least hindered site. 3 2 CH | X RCH C OH Mg | OH H → − − + 3 2 2 CH | O RMgX RCH CH OMgX + → 1 3 2 R | X R C OH Mg | OH H → − − + ′ X OH → + RCH CH OH Mg 2 2 O RMgX RCH CH OMgX + → 2 2 R | X H C OH Mg | OH H − − + ALCOHOLS Dihydric alcohols contains (2-OH groups) e.g.Glycol 2 2 CH OH | CH OH           Trihydric alcohols contains (3-OH groups) e.g. Glycerol 2 2 CH OH | CHOH | CH OH                 Primary 2 (RCH OH) Secondary R CHOH R       Tertiary R R C OH R           Monohydric alcohols Contain (1-OH roup) Benzyl alcohol CH2–OH Cyclohexanol OH (1-cyclo hexene) methanol CH2–OH Cinnamyl alcohol CH=CHCH2OH
328 Quick Revision NCERT - CHEMISTRY (e) When ketone reacts with Grignard reagent, it forms tertiary alcohol. (f) When 2, 2-dialkyl oxirane reacts with Grignard reagent, it forms tertiary alcohol. By reduction of carbonyl compounds The reduction can be carried out by using H2 /catalyst like Ni, Pt, Pd, LiAlH , 4 NaBH , 4 NaH, LiH. When the reduction is carried out by using metal/solvent combination it is known as Bouveault blanc recduction. The intermediates are: R — C — OEt; | O ⋅⋅− R — CH — OEt; | O. R — CH. | O. −⋅⋅ In case of metal hydride the reaction intermediate is R — C — O 2 | H Θ By hydrolysis of ester : R1COOR2+KOH → R1COOK + R2OH By reaction of alkyl boride with CO By reaction of primary amines with nitrous acid RNH HNO ROH N H O 2 2 2 2 + → + + From glucose: Zymase C H O 2CH CH OH 2CO 6 12 6 3 2 2 → + Industrial method for methanol and ethanol are as follows: Heat CH H O CO 3H ;CO 2H 4 2 2 2 + → + + ZnO CrO3 400 C,200atm CH OH 3 + → ° for ethanol we take ethylene obtained from petroleum : H PO 3 4 CH CH H O(steam) CH CH OH 2 2 2 3 2 300 350 C − ° = + → It is an Oxo process. Primary, Secondary and Tertiary alcohols can be distinguished by Victor Meyer’s Method: (a) HI OH AgNO2 NO 2 2 2 2 Primary alcohol RCH OH RCH I RCH NO → → → NaOH 2 2 Nitrolic acid Red sodium salt or nitrolic acid R — C — NO R — C — NO || || NOH NONa → (b) (c) Dihydric Alcohol /Glycol (Ethane – 1, 2- Di-Ol) Preparation 2 2 4 2 3CH CH 2KMnO 4H O = + + → 2 2 2 (Glycol) CH — OH 3 2MnO 2KOH | CH — OH + + Trihydric Alcohol Glycerol (Propan - 1, 2, 3 - Triol) Preparation By saponification of oils and fats 2 2 CH — OCOR | CH — OCOR NaOH | CH — OCOR + → 2 Soap 2 (Glycerol) CH — OH | CH — OH 3RCOONa | CH — OH + Phenols: Phenols are the organic compounds in which –OH group is directly linked to aromatic ring system. The simplest formula of such compound is phenol 6 5 (C H OH). Structure of some common phenols is as follows: O H Phenol O H CH3 p-Cresol OH o-Cresol CH3 OH m-Cresol CH3 HI HNO2 − − → − − → –C OH – C I No reaction R R R R R R NaOH 2 Pseudonitolic acid C NO Bluecolour | NO − → R R → OHNO HI CHOH → R R R R CHI → AgNO2 R R CH NO − 2 LiBH4 3 2 2 2 O || OH R B CO R — B — C — R R BCH RCH OH + → → → 2 OH 3 2 2 2 H O || OH R B CO R — B — C — R R BCH RCH OH R Θ + → → → OH C 2H C H == + → 1 1 2 2 2 2 R R R | | X RMgX RCH — C — OMgX RCH — C — OH Mg R | | OH R R + → → + O 1 1 1 2 2 2 2 2 R R R | | X RMgX RCH — C — OMgX RCH — C — OH Mg R | | OH R R + → → + R R R R | R | X C O RMgX C — OMgX C — OH Mg R R R OH ′ ′ ′ == + → → + ′′ ′′ ′′ R R R R | R | X C O RMgX C — OMgX C — OH Mg R R R OH ′ ′ ′ == + → → + ′′ ′′ ′′
Alcohols, Phenols and Ethers 329 Preparation: (1) Phenols can be prepared by reaction of benzene sulphonic acid with NaOH. (2) Phenols can also be obtained by warming diazonium salt solution with hot dilute acid solution. (3) Phenols can be prepared from aryl halides, (4) By reaction of phenolic acid with soda lime. Kolbe Reaction or Kolbe-schmidt Reaction: When sodium phenoxide reacts with CO2 at 120°C under 5-7 atmosphere followed by acidification with H, ⊕ it forms salicylic acid. The reaction intermediate (s) are: Phthalein Reaction note that H para to OH is removed. Ledrer-manasse Reaction: When phenol reacts with formaldehyde in the presence of acid or alkali, it forms bakelite, a thermostat polymer. Liebermann’s Nitroso Reaction Phenol → NaNO / conc. H SO 2 2 4 deep green or blue colour →H O2 Red → NaOH green or blue colour. The reactions are as follows: 2 4 ; H SO O H O H NaNO /H SO 2 2 4 → ↽ ⇀ O H p-nitrosophenol NO O H quinone monoxime NOH Sodium salt (Blue) O N O N Phenol indophenol ← ← NaOH H O2 O N O H Phenol indophenol hydrogen sulphate (Blue) OH ⊕ N O H HSO4 Θ HCHO H or OH → + Θ O H O H CH OH 2 O H CH2 O H Bakelite ← + CH2 CH2 → −H O2 O H O H O H O || C O C || O Phthalic anhydrolic + 2 4 2 3 conc. H SO → or ZnCl or AlCl C O O H O H C || O Phenolphthalei n ; ; O ⊝ O ⊝ COO ⊝ O H COO ⊝ H ⊕ → COOH O H Saliylic acid 120 C CO2 5 7 atm ° − + → COON ON O H O H COOH O H + → + NaOH(CaO) Na CO 2 3 Cl O H 300 C NaOH + NaCl 200 atm ° + → N X2 O H H 2 + HX + N + → + Na SO 2 3 (i) NaOH H O2 (ii) HCl + → O H + → NaOH SO H3 SO Na 3 O H OH Quinol Catechol OH OH O H Resorcinol O H
330 Quick Revision NCERT - CHEMISTRY Nitrosation: Hydrogenation: Oxidation Phenols turn pink or red or brown when exposed to air and light due to slow oxidation. The exact nature of these oxidation products is not known; but probable products are quinones and phenoquinones. When phenols is oxidised with potassium persulphate in alkaline solution, it forms quinol and the reaction is known as Elbs persulphate oxidation. Structure and Nomenclature of Ethers Ethers are compounds of the general formula R–O–R, Ar–O–R, or Ar – O –Ar. To commonly name ethers we usually name the two groups that are attached to oxygen, and follow these names by the word ether: If one group has no simple name, the compound may be named as an alkoxy derivative: 3 2 2 2 3 3 3 Methoxyhexane CH CH CH CHCH CH | OCH − 2 2 2 3 2 Ethoxyethanol CH CH | | HO OCH CH − The simplest aryl alkyl ether has the special name of anisole. If the two groups are identical, the ether is said to be symmetrical (e.g., diethyl ether, diphenyl ether), if different, unsymmetrical (e.g., methyl tert-butyl ether, anisole). Preparation of Ethers In the laboratory, the Williamson synthesis of ethers can be used to make unsymmetrical ethers as well as symmetrical ethers. In the Williamson synthesis an alkyl halide (or substituted alkyl halide) is allowed to react with a sodium alkoxide. R X Na O R + − − + − → ′ R O R Na X+ − − − +′ Example 3 3 3 3 Sodium tert-butoxide CH | CH Br Na O — C — CH | CH + − + → 3 3 3 3 tert-Butyl methyl ether CH | CH — O — C — CH | CH Reaction involves nucleophilic substitution of alkoxide ion for halide ion; it is strictly analogous to the formation of alcohols by treatment of alkyl halides with aqueous hydroxide. Since alkoxides and alkyl halides are both prepared from alcohols, the Williamson method ultimately involves the synthesis of ether from two alcohols. If we wish to make unsymmetrical dialkyl ether, we have a choice of two combinations of reagents; one of these is nearly always better than the other. In the preparation of tert-butyl ethyl ether, for example, the following combinations are conceivable: 3 3 2 3 3 tert-Butyl ethyl ether CH | CH CH — O — C — CH | CH 2 5 p Ethoxybenzoic acid C H O COOH − Nucleophile Leaving group Substrate R O R — X R O — R X − − ′ ′ + → + OCH3 Anisole 3 3 Isopropyl phenyl ether CH | CH — C — O — | H 3 3 3 3 Methyl tert-butyl ether CH | CH — O — C — CH | CH 2 5 2 5 Ethyl ether C H OC H Phenyl ether − − O O H O H quinol O K S O 2 2 8 OH  →Θ O H O quinone O 2 O 2 − H O +  → OH HOC H ⋯⋯ 6 5 6 5 Phenoquinone O HOC H ⋯⋯ 6 5  → 2C H OH O H O H Cyclohexanol Ni 2 150 200 C 3H − ° + → O H O H p-nitrosophenol NO o H 2 10 C HNO ⊕ + →