Ch7Summary Alcohol

<<Alcohols>>P H Y S I C A L P R O P E RT I E S ~ ~ 1) Melting points, boiling points: Relatively high due to intramolecular Hbonds. 2) Solubility in water: -OH group form H-bond with water molecules, so miscible with water in all proportions. For members with >6 carbons, degree of significance of -OH group decrease, so less or not soluble. 3) Highly inflammable for short-chained members. 4) Characteristic deep, broadband between 3300 cm-1 to 3600 cm-1 in IR spectrum due to presence of -OH group. 5) Relatively neutral. C H E M I C A L P R O P E RT I E S ~ ~ Reactions involving breakage of C-O bond: 1) Dehydration of alcohols: (a) Intramolecular dehydration (alkenes formation): -alcohol heat with excess conc. sulphuric acid. -heat with pumice stone ,Al2O3. ease : 3。>2。>1。 (b) Intermolecular dehydration (ether formation ): -Excess alcohols heat with conc. H2SO4. (Reversible) 2) Halide formation: (a) With hydrogen halide: - R-OH + HX ---> R-X + H2O -Lucas Reagent ,ZnCl/HCl --- rate of cloudiness exist:3。>2。>1。. (b) With phosphorus halide: - 3 R-OH + PX3 ---> 3 R-X + H3PO3 - R-OH + PX5 ---> R-X + POX3 + HX Reactions involving breakage of O-H bond: 1) Reaction with active alkali metals (alkoxide formation): - R->-OH <----> R->-O- + H+ - the alkoxide ion formed is destablised by the +ve inductive conferred by the electron donating alkyl group, equilibrium position shift to the left. 1。alcohol ---> aldehyde ---> carboxylic acid . this multiple bond character confers it a strong C-O bond. (orange to green) .Formed by refluxing with carboxylic acids.of the ring.Elimination: product is not stable due to high angle strain. Relatively acidic. 4) Triiodomethane formation (Iodoform test): . so it's well stabilized and more acidic.oxidizing agents commonly used: KMnO4/H+ (aq). C H E M I C A L P R O P E RT I E S ~ ~ 1) Alkoxide formation: . .Oxidation: complex polymers formed.Due to the acidity.2) Esterification: .2。alcohol ---> ketone .e. . 2) Other reactions of the -OH group: .alcohols with -C(CH3)H-OH group + I2/NaOH (aq) ---> R-COO-Na+ + CHI3. H2SO4.3。alcohol ---> no reaction.The negative charge is dispersed throughout the phenoxide ion(conjugate base) by conjugation with the π. reaction with NaOH(aq) can be used to distinguish between them. . acid anhydrides under catalyst of conc. it react with NaOH(aq) but alcohols do not. acyl chlorides.Halide formation: slow/no reaction. (violet to colorless) K2Cr2O7/H+ (aq). <<Phenols>> P H Y S I C A L P R O P E RT I E S ~ ~ Solubility in water: slightly dissolved. . The lone pair of O is partially overlap with the ring system. .Green colour changes from orange forms the basis of the breathalyser. 3) Oxidation: . .Esterification: slow reaction.1 General properties of Hydrox Compounds Alcohol: The hydroxyl group(OH) is attached to a sp3 C atom CH3 CH3 C CH3 tertiary(3。) ROH 3C attached to the C containing OH OH 2-methylpropan-2-ol CH3CH2 CH OH CH3 secondary(2。)ROH 2C attached to the C containingOH butan-2-ol CH3CH2CH2 OH primary (1。) ROH 1 C attached to the C containing OH propan-1-ol Phenol: OH is directly attached to a sp2 C atom in an aromatic ring. Due to the presence of the polar O-H group & the ability to from hydrogen bond with water.. Hydrogen bonding: alcohol & phenol molecules can form intermolecular H-bonds. OH OH phenol OH benzene-1. It has usually higher melting point & boiling point than other carbon compounds with the same no. of carbon atoms(except RCOOH).2Preparation of ROH: A. Phenols are slightly soluble in water. warming (3。) R-X(l) + H2O(aq)---------------------------------> (3。)ROH(aq) + HX(aq) .4-diol In alcohols R-O-H. alcohols with 1 to 6 C atoms are very soluble in water.Reaction with NaHCO3: no reaction but carboxylic acids do. Can be modified by using acyl chlorides instead of acids and converting phenol into phenoxide ion. . (Identification of phenols. a means for distinguishing the two.Reaction with neutral Iron(Ⅲ) chloride: Violet coloration. the O is sp3 hybridized (similar to H 2O) In phenols Ar-O-H.) Topic: Hydroxy Compounds LSC 1. reflux (1。/ 2。)R-X(l) + OH (aq)------------------------> (1。/2。)ROH (aq) + X (aq) AgNO3(aq)/ethanol. 1. the O is mainly sp2 hybridized because the lone pair of O has to overlap with the p orbitals of the benzene ring so that the C-O bond has some double bond character. Therefore. It is more difficult to break. Then. Hydrolysis of RX KOH(aq). ~~2。 turn cloudy at about 5 minutes (not precipitation) ~~1。 does not change( only dissolves in the acid. R-C-CH2R` H H H H D. HCI) ~~3。 turn cloudy at once.of CHI 3.3 Test for Phenol & ROH: ROH & Phenols react with Na but NOT Mg (RCOOH react vigorously with both Na and Mg) ROH do not decolorize cold Br 2/CCI4 or Br2(aq) in the absence of light but >phenols decolorize Br 2(aq) with the formation of a white ppt. due to the formation of ROH2 positive ion).R-C-CI LiAIH 4 does not react with C=C bonds NaBH4 only react reduces aldehyde & ketone C. Hydration of alkene: H2SO/cold OSO3H H 2O OH R-C=C-R` ----------- R. RCOOR`----------------------- 1。ROH LiAIH 4 is a very powerful reducing agent.H 2O OH ketone R-C-R`------------------------------------- R-CH-R` 2。 aldehyde.C-CH2R --------.} B. reduction of ketone .NOT phenols) react immediately with PCI 5 to give HCI(g) which fumes with NH3(g) CH3 O >-CH-OH group(& -C-CH 3 too ) can be identified by the iodoform test(I2/NaOH) BECAUSE OF formation of yellow ppt. > heating is usually not required because the reaction is already vigorous(especially for aldehydes) O LiAIH 4 can also reduce RCOOH.) >Phenol can form a coloured( usually violet )complex with neutral FeCI3(aq). RCOOH. > ROH (RCOOH . It is better to warm with AgNO 3(aq) + ethanol mixture. Water soluble ROH (1 to 6C) can be distinguished by the Lucas test(by mixture with saturated ZnCl 3 + conc. From 1。 aliphatic amine: RCH2NH2 +NaNO2/HCI-- RCH2OH +N2(effervescence) 1.{3。RX undergo elimination easily if heating under reflux with KOH(aq) in addition to substitution .RCOOR`. >Further reaction for ROH & phenol: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~ . at room temperature (Note that phenylamine also react with Br 2(aq) to give a white ppt. aldehyde & carboxylic compound (NOT for 3。ROH) O LiAIH4/dry ether . O . [no catalyst]. N2 ------- OH dil H positive above 5. The fact that phenol is soluble in Naoh(aq) can be used in isolation of phenol from other organic compounds(except RCOOH). OH O Na + + Na OH ------ +H 2O alcohols do not react with NaOH. phenol is a much stronger than alcohol.6 ESTERIFICATION alcohol react with mineral acid or organic acid (with H 2SO4(l) or dry HCIas catalyst ) to give ester& water Ester can be found when alcohol reacts with acid chloride or acid anhydride.Method | +acidified K2Cr2O7 ROH | phenol | | no observable change | acidified K 2Cr2O7 from orange to green ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~ +NaOH+ | | | BENZENEDIZONIUM | orange ppt | no observable change | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~ 1. Phenol is more acidic than ROH because a phenoxide ion is more stable than an alkoxide ion due to the delocalization of e while the e donating alkyl group in ROH destabilizes the alkoxide ion. 1to 5 Carbon alkanols are only miscible NaOH(aq).Therefore.O < R.H > R.5 reaction phenol phenol reacts with NaOH .O H2O is more acidic than ROH because RO is less stable than OH . 1.4 Preparation of Phenols FROM diazonium salt ( an important intermediate in synthesis ) The diazonium ion will begin to breakdown with the resulting formation of phenol and effervescence of nitrogen at above 278K. ~ LEE SUN CHUN 7B 23~ .OH O < H.`C 1. 1.6 Acidity of Alcohols & Phenols A CI D I T Y : B A S I C S T R E N GT H : OH > H . 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