Introduction of Alcohol, Preparation and Properties

Chemistry ALCOHOLS, PHENOLS AND ETHERS INTRODUCTION OF ALCOHOL, PREPARATION AND PROPERTIES ALCOHOL, PHENOL& ETHER Hydroxy derivatives Aromatic hydroxy derivatives Aliphatic hydroxy derivatives Alcohols feature oxygen atoms with sp3 hybridization, but there's a notable difference in bond angles: the C – O – H angle in methanol (108.9°) is notably greater than the H – O – H angle in water (104.5°). This discrepancy arises from the relatively larger size of the methyl group compared to a hydrogen atom. The bulkier methyl group offsets the bond angle compression that results from the nonbonding electron pairs of oxygen. While the O – H bond lengths are similar in both water and methanol (0.96 Å), the C – O bond is notably longer (1.4 Å), which re lects the greater covalent radius of carbon compared to hydrogen. O (I) O H 104.5° H H water H C 108.9° H H Methyl alcohol Aliphatic Hydroxy Derivatives Hydroxy derivatives in which —OH is directly attached to sp 3 C (Alcoholic compounds). (II) Aromatic hydroxy derivatives Hydroxy derivatives in which —OH is directly attached to sp 2 C or benzene ring (Phenolic compounds). 1 Chemistry ALIPHATIC HYDROXY DERIVATIVES (a) Classi ication according to number of —OH groups (i) Monohydric [one –OH]  CH3CH2—OH (ii) Dihydric [two –OH] [three –OH]  (iii) Trihydric (iv) Polyhydric (b)  [n –OH]  CH2 CH2 OH OH CH2 CH CH2 OH OH OH CH2 CH -------------CH2  OH OH OH Classi ication according to nature of carbon p or 1° – alcohol  CH3CH2 – OH (ii) s or 2° – alcohol  (CH3)2CH – OH (iii) t or 3° – alcohol  (CH3)3C – OH (i) ALCOHOLS Structure of alcohol Alcohols exhibit a bent molecular structure. The carbon atom bonded to the oxygen atom in the -OH group is sp3 hybridized, and the central oxygen atom is also in an sp3 hybridization state. The bond angle is approximately 108.50 degrees. In the process of sp3 hybridization, the oxygen atom's 2s2, 2px2, 2py1, and 2pz1 orbitals combine to form sp3 hybrid orbitals. :O : 108.5° H H3C sp3 1s Structure of CH3 OH O 2s 2px 2py 2pz Sp3 hybridi sation 2 Chemistry - Non – bonding e pair 𝜎 Bond atom 𝜎 Bond Sp3 + S 108.5ᵒ Hybridised Orbitals Sp3 S H H atom C atom S S H H Out of these four orbitals, two contain one electron each, while the other two contain two electrons each. The orbitals with two electrons do not actively participate in bonding. The remaining two half- illed orbitals form sigma (σ) bonds with the sorbitals of hydrogen atoms and the hybridized orbital of carbon atoms (O-C). Due to the in luence of the lone pair, the bond angle of the tetrahedral oxygen atom is slightly less than the usual tetrahedral structure, measuring 109.028 degrees. MONOHYDRIC ALCOHOL GENERAL METHODS OF PREPARATION (a) From alkanes (By oxidation) (CH3) 3 C—H (b) / (CH3) 3 C — OH ∆ From alkenes (i) By hydration CH3- CH – CH3 CH3 — CH = CH2 O H (ii) By hydroboration oxidation CH3— CH = CH2 / CH3- CH2 – CH2 OH (1ᵒ alcohol) 3 Chemistry (iii) By oxymercuration demarcation () CH3—CHCH2 (c) ( ) , CH CH OH From alkyl halides (By hydrolysis) . CH3—CH2—Cl (d) CH3 ( ) CH3CH2 — OH From carbonyl compounds (By reduction) > CO ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯  > CH—OH Reducing agents may be, LiAlH4/H NaBH4/H Na + EtOH [Bouveault-blanc Reduction] NaH [Darzen reduction] Ni / H2 R— CHO R C R—CH2—OH NaBH H R O R – CH – R OH CH3 C CH3 O LiA1H4 H+ ? MECHANISM H CH3-C-CH3 O H LiA1H4 CH3-C-CH3 O H H CH3-C-CH3 OH H 4 Chemistry OD H LiA1H4 D O OH D NaBD4 H CH3—CHCH—CHO CH3—CHCH—CH2—OH Crotonaldehyde Ph—CH = CH—CHO Ph—CH2—CH2—CH2—OH / Cinnamaldehyde (e) From ethers . ⎯⎯⎯⎯⎯⎯⎯ R—O—R ⎯⎯⎯⎯⎯⎯⎯ CH3—O—CH2CH3 (f) R—OH + R—OH . CH3—OH + CH3CH2—OH From acid and derivatives (By reduction) R— COOH R— CH2— OH + H2O R R— CH2— OH + HCl C Cl O R C OR R — CH2— OH + R— OH O R C O C O R C OR R— CH2— OH + R — CH2— OH O NY2 R — CH2— NH2 + H2O O (g) From esters (By hydrolysis) (i) By alkaline hydrolysis R C O OR ⎯⎯⎯⎯ R C ONa + R OH O 5 Chemistry (ii) By acidic hydrolysis R C H OR H2O (excess) O CH3 C 18 OC2H5 H3O R C OH + R OH O CH3 C 18 OH + C2H5OH O O This reaction is reversible reaction and it's order is 1 and it is also called PseudoUnimolecular reaction. (h) From p-amines R—NH2 R—OH + N2 + H2O CH3CH2—NH2 CH3CH2—OH + N2 + H2O ⎯⎯⎯⎯ MECHANISM CH3CH2–NH2 ⎯⎯⎯⎯⎯⎯⎯⎯⎯ OH Cl CH3 = CH2 CH3CH2+ N2+Cl CH3CH2 - N2 Cl Unstable O- N = O -H CH3CH2 - OH [Major] CH3CH2 - Cl CH3CH2 – O – N = O CH2 = CH2 Inter mediate is carbocation so rearrangement may be possible. Ex. CH3CH2CH2—NH2 ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ ? Sol. Mechanism CH3CH2CH2 — ⎯⎯⎯⎯⎯⎯⎯⎯⎯ CH3CH2CH2 —  N2 Cl  CH3CH2CH2  6 Chemistry CH HO CH3 CH  CH3 CH 3 OH Exception: CH3 – NH2 (i) H CH3 CH3 –O - CH3 ⎯⎯⎯⎯⎯ From Grignard reagent p-alcohol R—Mg—X + [O]  R — O — MgX ⎯⎯ R—OH [Same C-p-alcohol] R R -8 +8 R Mg X+H C H H C H2O H OMg H +8 X + CH2 R Mg CH2 O (ii) H OH [one C more p-alcohol] x R R -8 C CH2 CH2 2 2 H2O CH2 OmgX CH2 OH Two C more p-alcohol s-alcohol R R Mg C X+R H C R C ⎯⎯⎯⎯ R OMgX O H C OH C R Mg X +H C OR H R R MgX H2O H O O (iii) C C R OH t-alcohol R R Mg X +R C O R R C R R OMgX ⎯⎯⎯⎯ R C R OH 7 Chemistry R Mg X+R C OR R C O R O R MgX R R H2O C R OH PHYSICAL PROPERTIES OF ALCOHOL (i) C1 to C11 represent clear, colorless liquids, while higher alcohols are in solid form. (ii) The density of monohydric alcohols is lower than that of water (H 2O). (iii) Density is directly proportional to the molecular weight for monohydric alcohols. (iv) Solubility  The initial three members can fully dissolve in water, whereas the higher members are nearly insoluble in water but can dissolve in organic solvents such as benzene and ether.  The solubility of lower alcohols arises from the formation of hydrogen bonds between the polar O–H groups of alcohol molecules and water.  As the molecular mass increases, the solubility of alcohols in water diminishes.  Among isomeric alcohols, solubility decreases as the degree of branching in the chain increases. C1 to C3 and t-butyl alcohol is completely soluble in H2O due to H–bonding. solubility  No. of side chains  1 Molecular weight Order of solubility C4H9OH > C5H11OH > C6H13OH CH3 CH3CH2CH2CH2OH < CH3CH2CH OH < OH < CH3CH CH2 OH OH C OH CH3 CH3 CH3CH2CH2 CH3 < CH2 CH CH2 OH OH OH 8 Chemistry [Number of —OH increases, H-bonding increases] (v) Boiling points: B.P.  molecular weight If molecular wt. is same then B.P.  1 branching Order of BP C5H11OH < OH > C4H9OH < CH3CH3CH2CH2OH > CH3CH2CH C6H13OH CH3 CH3 CH3 < CH3CH2CH2 CH3 OH C OH CH3 CH CH2 OH OH < CH2 CH CH2 OH OH OH [Number of OH increases, H-bonding increases] CHEMICAL PROPERTIES OF ALCOHOL Monohydric alcohol shows following reactions (A) Reaction involving cleavage of O H (B) Reaction involving cleavage of OH C (C) Reaction involving complete molecule of alcohol (A) Reaction involving cleavage of O CH3—OH > (i) CH3CH2—OH Acidic nature H2O > R—OH > : Reactivity order (Acidic nature) is H > (CH3)2CH—OH CHCH > > (CH3)3C—OH NH3 (Acidic strength) Alcohols are less acidic than H2O and neutral for litmus paper and gives H2 with active metals (Na, K) R—OH + Na  R—OH + K (ii)  Reaction with CS2 R— OH + Na R— ONa + S C R—ONa + H2 R—OK + H2  R— ONa + H2 S   R O C S Na S 9 Chemistry (iii) Sodium alkyl xanthate (Used as loating agent) Alkylation /∆ ⎯⎯⎯⎯⎯⎯⎯ R— OH ⎯⎯ R— OH (iv) R— O— CH2 — H R— ONa ⎯⎯⎯⎯ R—O—R (Williamson synthesis) Acylation R OH + Cl C R  R O O R OH + Cl C CH3  R O C CH3 O (Acetylation) OH O C ⎯⎯⎯⎯⎯⎯ COOH O Salicylic acid R COOH Acetoxy benzoic acid Acetyl salicylic acid Aspirin [Used as analgesic] Benzoylation: (Schotten Baumann's Reaction) R OH + Cl C Ph   R O C Ph O O (Benzoylation) Esteri ication: Conc. H2SO4 is used as catalyst and dehydrating agent. R OH + R C OH . ⎯⎯⎯⎯⎯⎯⎯⎯⎯ O  R C OR + H2O O MECHANISM H2SO4 H+ + HSO : : (vi) R O (Acylation) O (v) C R—C—O—H + H+ O R—C—O—H OH R-C-O-H OH +RO H O H R-C-OH O H R’ 10 Chemistry OH OH R − C − OH OH R −C R − C OR′ -H+ R – C – OR’ O OR′ OR′ Note: This is a laboratory method to prepare ester. 1 Steric hinderence (i) Reactivity for esterification  . (ii) Reactivity of R – OH [If acid is same]: CH3 – OH > 1° > 2° > 3° alcohol (iii) Reactivity of RCOOH [If alcohol is same] CH3 H C OH > CH3 O (vii) C OH > CH3 CH C OH CH3 > CH3 O O C C OH CH3 O Reaction with CHCH CHCH + 2CH3—OH BF3/HgO  OCH3 CH3CH OCH3 Methylal CHCH + 2CH3CH2— OH BF3/HgO  OC2H5 CH3CH OC2H5 Ethylal (viii) Reaction with carbonyl compounds R—CHO + 2R—OH ⎯⎯⎯ R ⎯⎯⎯ C R + 2R OH O CH3CHO + 2CH3—OH (ix) R R R CH OR OR Acetal C OR OR Ketal ⎯⎯⎯ CH3CH OCH3 OCH3 Methylal Reaction with Grignard reagent R—Mg—X + H—OR ⎯⎯⎯ R H + Mg X OR 11 Chemistry (x) Reaction with Ketene: Ketene is used as acetylating agent. OR CH2 = C = O + R—OH  CH2 C OR OH + CH3  CH2 C O OC2H5 OC2H5 CH2CO + C2H5—OH C + OH CH3 C O Ethyl acetate (xi) Reaction with isocyanic acid: Ethyl urethane is used in preparation of urea OC2H5 OC2H5 NHC O + H—OC2H5  NH (xii) OH  +  NH2 C O Ethyl urethane C Reaction with oxirane OR R OH + CH2 CH2 CH2 H+ O (B) Reaction involving cleavage of C CH3—OH (i) < CH3CH2—OH CH2 OH OH : Reactivity order or basic nature is < (CH3)2CH—OH < (CH3)3 C—OH Reaction with halogen acid ZnCl2 R—CH2—OH + HCl ZnCl2 R2CH—OH + HCl R—CH2—Cl + H 2O R2CH—Cl + H 2O 20 alcohols Reactivity of the acids is HI > HBr > HCI > HF (ii) Reaction with inorganic acids R OH + H O N=O O  R O N=O+H2O O Nitric acid Alkyl nitrate R—OH + HHSO4  R—HSO4 + H2O Alkyl hydrogen sulphate 12 Chemistry (iii) Reaction with phosphorous halides 3R—OH + PCl3 (iv) R—Cl + POCl3 + HCl R—Cl + SO2  + HCl ⎯⎯⎯⎯⎯⎯⎯ (gas) Reaction with NH3: Alumina (Al2O3) is used as dehydrating agent. R OH + HNH2 (vi) 3RCl + H3PO3 R—OH + PCl5  Reaction with thionyl chloride (SOCl2) R—OH + SOCl2 (v)  Al2O3 250°C R—NH2 + H2O Reaction with halogens: Oxidation and chlorination takes place simultaneously. CH3CH2OH + Cl2(dry)  CH3CHO + 2HCl (Oxidation) CCl3CHO + 3HCl (chlorination) chloral CH3CHO + 3Cl2 (C) Reaction involving complete molecule of alcohol (i) Dehydration: Removal of H2O by two type. (a) Intermolecularly removal of H2O [form ether] (b) Intramolecularly removal of H2O [form alkene] 0 ᵒC C2H5OH+H2SO 4 (conc.) 100 ᵒC (C2H5)2SO4 C2H5HSO 4 140 ᵒC C 2H O C2H5 (Williamson’s Synthesis) 5 170 ᵒC C2H5HSO (Elimination) 4 C2H5OH+Al2 O3 (Alumina) 250 ᵒC 350 ᵒC C2H5 O C2H5 CH2 = CH2 Ease of dehydration follow the order: 3° ROH > 2° ROH > 1° ROH > CH 3OH 13 Chemistry (ii) Catalytic Dehydrogenation: This reaction is useful in distinction of 1°, 2° and 3° alcohols. CH3CH2OH → ° CH3CHO + H2 (p- alcohol ) CH3 CH (Acetaldehyde) CH3 C CH3 → ° O OH (s- alcohol) (acetone) CH3 CH3 CH3 C OH → ° CH3 C CH2 + H2O[dehydration] (Iso - butylene) CH3 (t. alcohol) (iii) CH3 + H2 Oxidation: This reaction is useful in distinction of 1°, 2° and 3° alcohols. R—CH2 —OH H/KMnO4or [0] RCHO RCOOH Room temp. H/K2Cr2O7 (p-alcohol) (same carbon acid) [O] R R’ C H OH (s- alcochol) R R C H/ K2Cr2O7 R high temp. CH CH3 C R Room temp. O (Same carbon) [O] Room temp. OH (t-alcohol) CH3CH2 H/ KMnO4 or R [O] high temp. Acids (less carbon) No reaction Acids (less carbon) C CH3CH2 O OH (iv) high temp. No reaction CH3 [ ] ⎯ CH3COOH + CH3COOH Carbonyl group goes with smaller alkyl group Reaction with phosphorous pentasulphide R—OH + P2S5  R—SH + P2O5 Thio alcohol 14 Chemistry (v) Reaction with salts CuSO4 CH3OH CaCl2 MgCl2 (vi) CuSO4. 2CH3OH CaCl2.4CH3OH MgCl2. 6CH3OH Distinction between 1°, 2° and 3° alcohols (a) Luca’s test: A mixture of HCl(conc.) and anhydrous ZnCl2 is called Luca’s reagent. p-alcohol ⎯⎯⎯⎯⎯⎯⎯⎯ No turbidity at room temp. [On heating within 30 minutes.] s-alcohol ⎯⎯⎯⎯⎯⎯⎯⎯ Turbidity appears within 5 minutes. t-alcohol ⎯⎯⎯⎯⎯⎯⎯⎯ Turbidity appears within 1 minute. (b) Victor - Meyer test: This is colour test for alcohol (pri. sec. & tert.). p-alcohol  Red colour s-alcohol  Blue colour t-alcohol  No colour R—CH2—OH [1°] P+I2 R—CH2—I AgNO2 RCH2—NO2 HNO2 R2CH—OH [2°] P+I2 R2CH—I AgNO2 R2CH—NO2 HNO2 R3C—OH [3°] P+I2 R3C—I AgNO2 R3C—NO2 HNO2 15 Chemistry R—C—NO2 N R2C—NO2 N OH Soluble No reaction O NaOH NaOH Insoluble (Blue) (vii) NaOH (Red) Colourless (White) Dichromate test 1° Alcohol H/K2Cr2O7 Orange [Cr+6] Acid + Cr+3 [green] 2° Alcohol H/K2Cr2O7 Orange [Cr+6] Ketone + Cr+3 [green] 3° Alcohol H/K2Cr2O7 Orange [Cr+6] No oxidation, No green (viii) Test of alcoholic group (ix) R—OH ⎯⎯⎯ R—ONa + H2 [effervescence of H2] R—OH ⎯⎯⎯⎯ R—Cl + POCl3 + HCl R—OH ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ ⎯⎯⎯⎯ NH4Cl [White fumes] Red color Distinction between CH3 – OH and C2H5OH CH3OH CH3CH2OH B.P. 65ᵒC 78ᵒC I2 + NaOH No ppt Yellow ppt of CHI3 Cu/300°C Smell of formalin [HCHO] No smell Salicylic acid Smell of oil of wintergreen No smell 16 Chemistry OH CH3OH Methyl salicylate (Oil of wintergreen) COOPh Phenyl salicylate Salol (Internal antiseptic) OH OH Ph-OH COOH O C CH3 Aspirin (Analgesic) O COOH CH3COCl (a) COOH3 ADDITIONAL REACTIONS Oxidation by HIO4 [per iodic acid] CH2 CH2 OH OH CH2 CH2 HIO4 OH O CH CH2 OH OH OH (Glycerol) OH + HO CH2 -2H2O OH HO CH CH2 + HO HIO4 OH HCHO+HCHO OH+HO OH CH2 OH -3H2O HCHO + HCOOH+HCHO  (b) Condition for oxidation by HIO4 At least 2 —OH or 2 > C=O or 1 —OH and 1 > C=O should be at adjacent carbons. Pinacole - Pinacolone Rearrangement CH3 CH3 CH3 CH3 C C 𝐜𝐨𝐧𝐜.𝐇𝟐 𝐒𝐎𝟒 CH3 CH3 C ⎯⎯⎯⎯⎯⎯⎯⎯⎯ C O OH OH Pinacole CH3 OH3 Pinacolone MECHANISM CH3 CH3 C OH CH3 C OH CH3 H CH3 CH 3 CH3 C C OH OH2 CH3 CH3 -H2O CH3 C C OH OH OH 17 Chemistry CH3 C C O CH3 CH3 CH3 CH3 CH3 -H CH3 C C CH3 CH3 C C CH3 H CH3 OH CH3 (Complete octet more stable) AROMATIC HYDROXY DERIVATIVES Phenolic compounds Compounds in which —OH group is directly attached to sp 2 C [Benzene ring] OH OH OH COOH Phenol O-cresol Salicylic acid OH OH OH OH OH catechol resorcinol OH quinol All phenolic compounds give characteristic colour with neutral FeCl 3.\ Ph—OH ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ Violet colour CH3CH2—OH ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ No colour 18