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Alcohol
- 1. Alcohols P.M. Jadhav Assistant Professor Dept.of Chemistry M.S.P. Mandals, Shri Muktanand college, Gangapur, Dist: Aurangabad.
- 2. Alcohols Organic compounds whichcontains one or more hydroxyl (-OH) groups CH3OH CH3CH2OH CH3CH2CH2OH Ethyl alcoholMethyl alcohol Propyl alcohol CHH3C CH3 OH CHH3C CH3 CH2 OH Isobutyl alcoholIsopropyl alcohol CH3C CH3 CH3 OH t-butyl alcohol H2C OH CH2 1,2-ethane diol OH H3C CH OH CH2 OH H2C CH2 CH2 OH OH 1,2-propane diol 1,3-propane diol CH2 CH CH2 OH OH OH 1,2,3-propanetriol (Glycerol) Monohydric alcohols Dihydric alcohols Trihydric alcohols
- 3. IUPAC Nomenclature : •Select the longest chain containing –OH group. • Name gives to alcohol by replacing -e of the corresponding alkane by suffix – ol i.e. alkanol. • The position of -OH group is indicated by a number, usually the lowest possible number from the end that gives the -OH a lower number. • Substituents on parent chain indicated by name in alphabetical order along with their position. • If more than one hydroxyl group is present, the prefix di, tri, to indicate the number of hydroxyls. (Ethyl alcohol) (Propyl alcohol) CHH3C CH3 OH CHH3C CH3 CH2 OH (Isopropyl alcohol) H3C CH2 OH H3C CH2 CH2 OH 12 123 Ethanol 1-propanol 1 2 3 2-propanol 123 2-methyl-1-propanol H3C CH OH CH2 OH H2C CH CH2 OH OH 1,2-dihydroxy propanol 1,2,3-trihydroxy propanol 123 OH 1 2 3
- 4. Preparation methods: Reductionof carbonyl compounds: • Carbonyl compounds such as aldehydes, ketones, carboxylic acids and esters on reduction with reducing agents such as of LiAlH4, NaBH4, (H2) and metals catalyst ( Pt, Pd or Ni ) or Na/C2H5OH. • Aldehyde, carboxylic acids and esters gives primary alcohols. • Ketone gives secondary alcohols. R C X O R C H 2 O H A lc o h o l R e d u c in g a g e n ts X = H (a ld e h y d e ), R (k e to n e ), O H (c a rb o x y lic a c id ), O R (e s te rs )
- 5. Acidic nature ofalcohol: • Alcohols are weak acid because hydroxyl group deprotonate to give hydrogen ion in presence of strong base. The acidic character of alcohol is due to polarity of –OH group. R O H R O H conjugate base • The alkyl or aryl group influence acidity of alcohol as electron donating group increase the electron density on oxygen atom leading to decrease the polarity of – OH bond their by decrease in acidity of alcohol. Primary alcohol > Secondary alcohol > Tertiary alcohol H3C CH2 CH2 OH 1-Propanol CH3C CH3 CH3 OH t-butyl alcohol CHH3C OH CH3 2-propyl alcohol
- 6. Chemical Reactions: • EsterFormation: Reaction of an alcohol with a carboxylic acid under acidic conditions produces an ester, this reaction is called as esterification and is reversible in nature. • Formation of Alkoxides: Alcohols are weak acid react with strong base like sodamide (NaNH2), sodium hydroxide or potassium hydroxide to give the respective alkoxides and form hydrogen gas. • Alkyl Halides formation: Alkyl halide formed by the reaction of alcohol with HX (hydrogen halide such as HCl, HBr or HI) in in presence of acidic condition. • Dehydration: Alcohol undergoes dehydration in presence of catalyst to give product alkenes and water. • Dehydration to form Ethers: Intermolecular dehydration of alcohols on heating to gives ethers. • Oxidation: Oxidation of Alcohols with oxidizing agents such as potassium permanganate (KMnO4), K2Cr2O7/H2SO4 or chromic acid to give a carbonyl compounds like aldehyde, ketone or carboxylic acid. R C OR O R-OHR COOH Ester HCl / H2SO4 H2O carboxylic acid alcohol H3C CH2 OH Ethanol NaNH2 H3C CH2 O Na H2 Ethoxide 2. 2. R OH HX R X H2O Alcohol Alkyl halide H3C CH2 OH H2C CH2 1800 C H2SO4 H2O Ethyl alcohol Ethylene Ethanol K2Cr2O7 H2SO4 H3C CH2 OH H3C C OH O Acetic acid CH3 OH CH3 O CH32. Heat Methanol Dimethyl ether H2O
- 7. Physical Properties ofAlcohols: • Hydrogen Bonding: The polar -OH group forms hydrogen bonds because the partial positive charge on H atom of the -OH group has no electrons other than the electron pair in the O-H bond, it interacts with unshared electron pairs on oxygen atoms of neighboring alcohol molecules and forms a weak hydrogen bond with a partially negative oxygen atom of a neighboring alcohol molecule. • Boiling Point: Alcohols forms hydrogen bond to each other, they have higher boiling points than alkanes. The boiling point of alcohols increases as the molecules become larger. • Solubility: Alcohols are soluble in water. The presence of hydroxyl group in alcohol which is able to forms hydrogen bonds with water molecules. • Polarity: Alcohol is polar due to its hydrogen bonding ability and the presence of oxygen atom in the molecule. • Viscosity: The viscosity of alcohol increases as the size of molecule increase. R O H O H R H O R H O R Intramolecular Hydrogen bonding R O H O H H H O H H O R Intermolecular Hydrogen bonding (alcohol & water)
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