Alcohol Notes

ALCOHOL, PHENOL & ETHER ALCOHOLS Alcohols are bent molecules. The carbon atom (linked with 3 'O' atom of –OH group) is sp3 hybridised. The central 'O' atom is also in sp3 state of hybridisation. The bond angle is 108.50 . In sp3 hybridisation of O - 2s2,2px2 2py1 2pz1 orbitals hybridised to form sp3 orbitals H3C 3 H sp 1s Structure of CH3OH In these four orbitals two containing one electron each and two containing two electrons each. Orbitals containing two electrons do not take part in bonding. Other two half filled orbitals form  bond with s-orbitals of H -atom and hybridised orbital of C-atom (O—C). Due to lone pair effect the bond angle of tetrahedral oxygen atom is lesser than normal tetrahedral structure (109028'). MONOHYDRIC ALCOHOL GENERALMETHODS OF PREPARATION (a) From alkanes (By oxidation) :  H / KMnO4 Δ (CH3)3 C—H (b) (CH3)3 C — OH From alkenes : (i) By hydration : CH3 — CH = CH2 (ii)  H H2O By hydroboration oxidation : CH3— CH = CH2 BH3 H2O2/HO CH 3 CH 2 CH2 (1° alcohol) OH (iii) By oxymercuration demercuration : CH3—CH CH2 (i) Hg(OAc)2,H2O (ii) NaBH4,HO CH3 CH OH 3 3 :O: sp sp 108.5° 1s sp Structure of alcohol CH 3 (c) From alkyl halides (By hydrolysis) : Aq. KOH or Moist Ag2O CH3—CH2—Cl (d) From carbonyl compounds (By reduction) : >C  CH3CH2 — OH O Reducing agent > CH—OH Reducing agents may be, LiAlH4/H NaBH4/H Na + EtOH [Bouveault-blanc Reduction] NaH [Darzen reduction] Ni / H2 R— CHO LiAlH4  H R—CH2—OH R NaBH4 H R C R O CH3 CH R OH C CH3 LiAlH4  H ? O MECHANISM : CH3—CH CH—CHO Crotonaldehyde Ph—CH = CH—CHO Cinnamaldehyde (e) LiAlH4   H /OH CH3—CH CH—CH2—OH Ph—CH2—CH2—CH2—OH From ethers : R—O—R CH3—O—CH2CH3 (f) LiAlH4  H dil. H2SO4 dil. H2SO4 R—OH + R—OH CH3—OH + CH3CH2—OH From acid and derivatives (By reduction) : R— COOH LiAlH4  H R— CH2— OH + H2O ALCOHOL, PHENOL & ETHER R C Cl LiAlH4  H R— CH2— OH + HCl R O C OR LiAlH4  H R — CH2— OH + R— OH R O C O C O R (g) OR LiAlH4  H R— CH2— OH + R — CH2— OH O C LiAlH4  H NH2 R — CH2— NH2 + H2O O From esters (By hydrolysis) : (i) By alkaline hydrolysis : R C OR NaOH R O (ii) C ONa + R OH O By acidic hydrolysis : R C R OR O CH3 C OH + R OH O C 18 OC2H5 H3O  CH3 C 18 OH + C2H5OH O O This reaction is reversible reaction and it's order is 1 and it is also called Pseudo-Unimolecular reaction. (h) From p-amines : R—NH2 CH3CH2—NH2 NaNO2+HCl or HNO2 HNO2 R—OH + N2 + H2O CH3CH2—OH + N2 + H2O MECHANISM : CH3CH2 –NH2 NaNO2+HCl CH3CH2– N2 Cl CH 3CH2+ N2 + Cl Unstable OH [Major] Inter mediate is carbocation so rearrangement may be possible. Ex. Sol. CH3CH2CH2—NH2 Mechanism : NaNO2+HCl CH3CH2CH2—NH2 NaNO2+HCl Exception : (i) ?   1 CH3CH2CH2— N2 Cl  CH 3CH CH CH 3 – NH 2 HNO2 CH 3 – O – CH 3 From Grignard reagent : (i) p-alcohol : R—Mg—X + [O]  R — O — MgX H2O R—OH [Same C-p-alcohol] OH [one C more p-alcohol] (ii) s-alcohol : (iii) t-alcohol : ALCOHOL, PHENOL & ETHER PHYSICAL PROPERTIES (i) C1 to C11 are colourless liquids and high alcohols are solids. (ii) Density of monohydric alcohol is less than H2O. (iii) Density  mol. wt. (for monohydric alcohol). (iv) Solubility : • The first three members are completely miscible with water. The higher members are almost insoluble in water but are soluble in organic solvents like benzene, ether etc. • The solubility of lower alcohols is due to the existence of hydrogen bonds between water and polar O–H groups of alcohol molecules. • The solubility of alcohols in water decreases with increase in molecular mass. • Among the isomeric alcohols the solubility decrease with branching of chain increases. C1 to C3 and t-butyl alcohol is completely soluble in H2O due to H–bonding. solubility  No. of side chains   Order of solubility : C4H9OH > C5H11OH > 1 molecular weight C6H13OH CH3 CH3CH2CH2CH2OH < CH 3CH 2CH < OH CH3 < CH 3 CH < CH 2 OH OH OH [Number of —OH increases, H-bonding increases] (v) OH CH3 CH3 CH 3CH2CH 2 C CH2 CH CH2 OH OH OH Boiling points : B.P.  molecular weight If molecular wt. is same then B.P.  Order of BP : C4H9OH < 1 branching C5H11OH < C6H13OH CH3 CH3CH2CH2CH2OH > CH3CH2CH OH > CH3 CH3 CH 3CH2CH 2 OH < CH 3 CH C OH CH3 CH 2 OH OH [Number of OH increases, H-bonding increases] < CH2 CH CH2 OH OH OH Ex. Sol. Boiling point of alcohol is more than corresponding ether. Why ? Reason : H-bonding in alcohol. O H ---------- O H ------------- O H ------------- O H ---------- R R R R Ex. Boiling point of alcohol is less than corresponding carboxylic acid. Why ? Sol. Reason : Dimer formation in carboxylic acid. R O C H OH O O C R CHEMICAL PROPERTIES Monohydric alcohol show following reactions (A) (A) Reaction involving cleavage of O H (B) Reaction involving cleavage of C OH (C) Reaction involving complete molecule of alcohol Reaction involving cleavage of O CH3—OH (i) > H : Reactivity order (Acidic nature) is CH3CH2—OH > (CH3)2CH—OH > (CH3)3C—OH > CH > NH3 Acidic nature : H2O > R—OH CH (Acidic strength) Alcohols are less acidic than H2O and neutral for litmus paper and gives H2 with active metals (Na, K) 1 R—OH + Na R—ONa + H2 2 R—OH + K  R—OK + (ii) 1 H 2 2 Reaction with CS2 : R— OH + Na R— ONa + S  C S  R— ONa + R O 1 H 2 2 C S Na S Sodium alkyl xanthate (Used as floating agent) (iii) Alkylation: R— OH CH2N 2/ R— OH Na R—O—CH2—H R— ONa RX R—O—R (Williamson synthesis) (iv) Acylation : R OH + Cl C O R  R O C R O (Acylation) ALCOHOL, PHENOL & ETHER R OH + Cl C CH3  R O C CH3 O O (Acetylation) O OH C O COOH CH3COCl COOH R Salicylic acid Acetoxy benzoic acid Acetyl salicylic acid Aspirin [Used as analgesic] (v) Benzoylation : (Schotten Baumann's Reaction) : R OH + Cl C Ph R  O O (vi) C Ph O (Benzoylation) Esterification : Conc. H2SO4 is used as catalyst and dehydrating agent. R C OH + R OH  Conc. H2SO4  R C OR + H O 2 O O MECHANISM : : : H2SO4 H+ + HSO4– + R—C—O—H + H R—C—O—H O OH Note : This is a laboratory method to prepare ester. Ex. CH3 C OH + H OC 2H5 conc. H2 SO4 CH3 C O Ex. Ph C OC2 H5 + H2O O OH + H 18 OC2H5  conc. H2SO4  Ph C O 18 OC2H5 + H2O O Dry HCl can be used as dehydrating agent. Ex. CH3 C O OH + H OC 2H5 Dry HCl CH3 C O OC2 H5 + H2O KEY POINTS ETOOS KEY POINTS 1 . Steric hinderence (i) Reactivity for esterification  (ii) Reactivity of R – OH [If acid is same] : (iii) Reactivity of RCOOH [If alcohol is same] : CH3 – OH > 1° > 2° > 3° alcohol CH3 H OH > CH3 C O O (vii) OH > CH3 C Reaction with CH CH CH C CH3 O OH > CH3 C C OH CH3 O CH : CH + 2CH3—OH BF3/HgO  OCH3 CH3CH OCH3 Methylal CH CH + 2CH3CH2— OH BF3/HgO  CH3CH OC2H5 OC2H5 Ethylal (viii) Reaction with carbonyl compounds : R—CHO + 2R—OH R CH OR OR Acetal R C R + 2R R OH OR C OR R Ketal O CH3CHO + 2CH3—OH CH3CH OCH3 OCH3 Methylal (ix) Reaction with Grignard reagent : R—Mg—X + H—OR (x) R H + Mg X OR Reaction with Ketene : Ketene is used as acetylating agent. OR OR CH2 = C = O + R—OH  CH2 C OH ‡ˆ ˆˆ ˆ† ˆˆ CH3 C OC 2H5 OC 2H5 CH2 C O + C2H5—OH  CH2 C O ˆˆ CH3 OH ‡ˆ ˆˆ ˆ† C O Ethyl acetate ALCOHOL, PHENOL & ETHER (xi) Reaction with isocyanic acid : Ethyl urethane is used in preparation of urea OC2H5 OC2H5 NH C O + H—OC2H5  NH C OH ‡ˆ ˆˆ ˆ† ˆˆ NH2 C O Ethyl urethane (xii) Reaction with oxirane : R (B) OR OH + CH2 Reaction involving cleavage of C (i) CH3—OH < O CH2 H + CH2 CH2 OH OH : Reactivity order or basic nature is CH3CH2—OH< Reaction with halogen acid : ZnCl2 R—CH2—OH + HCl  ZnCl2 R2CH—OH + HCl  (CH3)2CH—OH R—CH2—Cl < + H 2O R2CH—Cl + H2O 20 alcohol Reactivity of the acids is HI > HBr > HCl > HF (ii) Reaction with inorganic acids :  Nitric acid R—OH + HHSO4 Alkyl nitrate  R—HSO4 + H2O Alkyl hydrogen sulphate (iii) (iv) Reaction with phosphorous halides : 3R—OH + PCl3  3RCl + H3PO3 R—OH + PCl5  R—Cl + POCl3 + HCl Reaction with thionyl chloride(SOCl2) : R—OH + SOCl2 (v) Pyridine R—Cl + SO2  + HCl (gas) Reaction with NH3 : Alumina (Al2O3) is used as dehydrating agent. R OH + HNH2 Al2O3 250°C R—NH2 + H2O (CH3)3 C—OH (vi) (c) Reaction with halogens : Oxidation and chlorination takes place simultaneously. CH3CH2OH + Cl2(dry)  CH3CHO + 2HCl (Oxidation) CH3CHO + 3Cl2  CCl3CHO + 3HCl (chlorination) chloral 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°C C2 H5 OH + H2SO4 (conc.) C2H5 OH +Al2O3 (Alumina) (C2H5)2 SO4 100°C C2H5HSO4 140°C C2H5 170°C CH2 250°C C 2H 5 350°C CH2 O C2H5 (Williomson's synthesis) CH2 (Elimination) O C 2H 5 CH 2 Ease of dehydration follow the order : 3° ROH > 2° ROH > 1° ROH > CH3OH (ii) Catalytic Dehydrogenation : This reaction is useful in distinction of 1°, 2° and 3° alcohols. Cu 300°C CH3CH2OH CH3CHO + H2 (p- alcohol ) CH3 CH (Acetaldehyde) CH3 Cu 300°C CH3 CH3 CH3 C CH3 + H2 O (acetone) OH (s- alcohol) CH3 C OH Cu 300°C CH3 C CH2 + H2O [dehydration] (Iso - butylene) CH3 (t. alcohol) (iii) Oxidation : This reaction is useful in distinction of 1°, 2° and 3° alcohols. R—CH2—OH  H/KMnO4or  H /K2Cr 2O7 RCHO [O] Room temp. (p-alcohol) RCOOH (same carbon acid) Acids (less carbon) R R C R OH (t-alcohol) [O] Room temp. high temp. No reaction Acids (less carbon) ALCOHOL, PHENOL & ETHER CH3CH2 CH CH3 [O] high temp. CH3CH2 OH C CH3 [O] CH3COOH + CH3COOH O Carbonyl group goes with smaller alkyl group (iv) Reaction with phosphorous pentasulphide : R—OH + P2S5 R—SH  + P2O5 Thio alcohol (v) Reaction with salts : CuSO4 CH3OH CuSO4. 2CH3OH CaCl2 CaCl2. 4CH3OH MgCl2 MgCl2 . 6CH3OH (vi) Distinction between 1°, 2° and 3° alcohols : (a) Lucas test : A mixture of HCl(conc.) and anhydrous ZnCl2 is called Lucas reagent. p-alcohol ZnCl2 + HCl No turbidity at room temp. [On heating within 30 minutes.] s-alcohol ZnCl2 + HCl Turbidity appears within 5 minutes. ZnCl2 + HCl t-alcohol Turbidity appears within 1 minute. 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°] R2CH—OH [2°] R3C—OH [3°] R—CH2—I R2CH—I R3C—I RCH2—NO2 R2CH—NO2 R3C—NO2 R—C—NO2 R2C—NO2 No reaction (b) N OH N Soluble (Red) (vii) Dichromate test : 1° Alcohol Insoluble (Blue) H/K2Cr2O7 orange [Cr+6] Acid + Cr+3 [green] Colourless (White) 2° Alcohol H/K2Cr2O7 orange [Cr+6] 3° Alcohol H/K2Cr2O7 orange [Cr+6] Ketone + Cr+3 [green] No oxidation, No green (viii) Test of alcoholic group : R—OH (ix) 1 H 2 2 [effervescence of H2] R—ONa + Na R—OH PCl5 R—OH Cerric ammonium nitrate R—Cl + POCl3 + HCl NH3 NH4Cl [White fumes] Red colour Distinction between CH3 – OH and C2H5OH CH3 OH CH3 CH2 OH B.P. 65°C 78°C I2 + NaOH Cu/300°C No ppt Yellow ppt of CHI3 No smell Smell of formalin [HCHO] Salicylic acid Smell of oil of wintergreen No smell OH CH3OH COOH3 Methyl salicylate (Oil of wintergreen) COOPh Phenyl salicylate Salol (Internal antiseptic) OH OH Ph—OH COOH O C CH3 O COOH CH3COCl Aspirin (Analgesic) ADDITIONAL REACTIONS (a) Oxidation by HIO4 [per iodic acid] : CH2 OH CH2 CH 2 OH OH CH CH2 OH OH CH2 HIO4 OH + HO OH HIO4 HO CH2  2H O 2 HCHO + HCHO OH CH 2+HO CH OH OH OH + HO CH2  3H O 2 HCHO+HCOOH+HCHO OH (Glycerol) 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. ALCOHOL, PHENOL & ETHER Ex. Ex. Ex. (b) Pinacole - Pinacolone Rearrangement : CH3 CH3 CH3 CH3 C C CH3 conc. H2SO4 CH3 OH OH Pinacole MECHANISM : C C O CH3 CH3 Pinacolone AROMATIC HYDROXY DERIVATIVES Phenolic compounds : Compounds in which —OH group is directly attached to sp2 C [Benzene ring] OH OH OH COOH CH3 Phenol o-cresol OH OH Salicylic acid OH OH OH OH catechol resorcinol quinol All phenolic compounds give characteristic colour with neutral FeCl3.\ Ph—OH CH3CH2—OH neutral FeCl3 neutral FeCl3 Violet colour No colour