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Organic Chemistry-III 1. Methanol [CH3OH] : (a) Laboratory Preparation : When methyl halides are boiled with aqueous sodium hydroxide, hydrolysis takes place with the formation of methanol. boiling CH3Cl + NaOH (aq) NaCl + CH3OH (methanol) boiling NaBr + CH3OH (methanol) CH3Br + NaOH (aq) (b) Industrial preparation : When water gas ( a mixture of CO and H2) is mixed with hydrogen and passed over heated catalyst (Cr2O3 or ZnO) at 350 C, it reacts to form methanol. Cr2O3 ZnO [CO + H2] + H2 CH3OH [Methanol] (c) Physical Properties : (i) It is a colourless liquid, highly inflammable in nature and has a strong alcoholic smell. (ii) It is highly toxic in nature. Small quantities of it on consumption damage liver and cause blindness. Large dose of it can prove fatal. (iii) It is soluble in water as well as organic solvents. (d) Chemical properties : (i) It reacts with sodium at room temperature to form sodium methoxide and hydrogen gas. 2CH3OH + 2Na 2CH3ONa + H2 (g) (ii) It reacts with phosphorus trichloride at room temperature to form phosphorus acid and methyl chloride. 3CH3OH + PCl3 H3PO3 + 3CH3Cl (iii) It reacts with conc. H2SO4 at 140 C to form dimethyl ether. 140 C 2CH3OH + H2SO4 (conc.) CH3OCH3 + H2SO4.H2O (iv) When vapours of methyl alcohol are passed over heated copper oxide at 300 C, it oxidised to formaldehyde. 300 CH3OH + CuO Cu + HCHO + H2O 1 Key Points (v) Acidified potassium dichromate oxidises methanol to formic acid. Acidified CH3OH + 2[O] HCOOH + H2O K 2Cr2O 7 (e) Uses (i) It is used as solvent in paints and varnishes. (ii) It is used for making methylated spirit. (iii) It is used for making useful organic compounds, such as formaldehyde and formic acid. (iv) It is used as antifreeze in automobile radiators. 2. Ethyl alcohol or Ethanol [C2H5OH] : (a) Laboratory Preparation : (i) When ethyl halides are boiled with aqueous sodium hydroxide, they hydrolyse to form ethanol. C2H5Cl + NaOH (aq) NaCl + C2H5OH (ethanol) C2H5 Br + NaOH (aq) NaBr + C2H5OH (ethanol) (b) Industrial Preparation : (i) Ethene is first dissolved in conc. H2SO4 under 30 atoms. pressure at 80 C to form ethyl hydrogen sulphate which on boiling with water hydrolyse to form ethyl alcohol. 30 atoms 80 C C2H4 + H2SO4 (conc.) C2H5.HSO4 C2H5 . HSO4 + H2O H2SO4 + C2H5OH (ii) From starch or molasses : When starch [C6H10O5)n is warmed with malt extract at 60 C, the enzyme diatase present in it converts starch to maltose, a sugar solution. Diatase 2(C6H10O5)n + (H2O)n (C12H22O11)n [maltose] The maltose is mixed with yeast containing maltase and zymase enzymes and allowed to ferment for 3-4 days, when the following reaction takes place with the formation of ethanol. Maltase C12H22O11 + H2O 2C6H12O6 Zymase C6H12O6 2C2H5OH + 2CO2 30 C 2 Key Points The ethanol is separated from mixture by fractional distillation. (c) Physical Properties : (i) It is colourless, inflammable liquid having a strong alcoholic smell. (ii) If consumed in larger quantities over condrable time, it can damage liver and kidneys. (iii) It is soluble in water and organic solvents. (d) Chemical Properties : (i) It reacts with sodium at room temperature to form sodium ethoxide and hydrogen gas. 2C2H5OH + 2Na 2C2H5ONa + H2 (g) (ii) When ethanol vapours are passed over heated copper oxide, it is oxidised to acetaldehyde 300 C C2H5OH + CuO Cu + H2O + CH3CHO (iii) When ethyl alcohol is treated with acidified potassium dichromate, it is oxidised to acetic acid. Acidified C2H5OH + 2[O] CH3COOH + H2O K 2Cr2O 7 (iv) When a mixture of ethanol and conc. H2SO4 is heated at 170 C, it forms ethene gas. Conc H 2SO 4 C2H5OH C2H4 + H2O 170 C 3. The continuous use of alcohol damages liver and kidneys. 4. Ethyl alcohol which is used for industrial purposes is denatured (made unfit for drinking) by adding poisonous agents like pyridine, methyl alcohol, copper sulphate, etc. 3 Key Points

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