ORGANIC HYDROXY COMPOUNDS
hydroxy cpds: contain -OH group
hydroxy cpds:
-alcohol (-OH attached to aliphatic C chain) (monohydric alcohol: 1 -OH, diol: 2 -OH, triol: 3 -OH)
-phenol (-OH attached to C atom of benzene ring)
Monohydric alcohols
general formula: C_nH_2n+2O or C_nH_2n+1OH [n=1,2,..]
functional group: hydroxy group, -OH

Types of alcohols
primary (1°) alcohol: C atom attached to -OH group has 2 H atoms attached
secondary (2°) alcohol: C atom attached to -OH group has 1 H atom attached
tertiary (3°) alcohol: C atom attached to -OH group has no H atoms attached

Isomerism in alcohols
C_nH_2n+2O:- general formula for alcohols(-C-OH) & ethers (-C-O-C-)

Industrial preparation
Fermentation of glucose to form ethanol
-Hydrolysis of starch: starch >(enzyme)> glucose
(C₆H₁₀O₅)_n + nH₂O >(enzyme)> nC₆H₁₂O₆
-Fermentation of glucose: glucose >(yeast)> ethanol + CO₂
C₆H₁₂O₆>(yeast)> 2CH₃CHOH + 2CO₂
ethanol produced is purified by distillation (bp: 78.5°C)
Catalytic Hydration of alkenes

alkene + steam >(H₃PO₄, 300°C, 70 atm)> alcohol
Lab preparation
Hydrolysis of halogenoalkanes
R-X + NaOH(aq) >(heat, reflux)> R-OH + NaX
halogenoalkane + aqueous sodium hydroxide, heat under reflux > alcohol + sodium halide
Reaction between 1° amine & nitrous acid
reagent: sodium nitrite, NaNO₂, acidified w/ dil HCl [NaNO₂ + HCl > HNO₂]
conditions: ice-cold temp (0°C-10°C)
R-NH₂ + HNO₂ >( ice-cold temp)> R-OH + H₂O + N₂ [amino group replace by hydroxy group]
observation: bubbles of gas appear (N₂)

Physical properties
-characteristic smell
-lower members: colourless liquids, higher members: white waxy solids [as RMM ^ > VDW forces ^ > solid-like]
-compared to cpds w/ similar RMM, alcohols have higher mp + bp (H-bonds bet alcohol molecules)
-1^st 3 alcohols completely soluble in water (H-bond bet water & alcohol molecule) (higher members: H-bonds bet alcohol molecules to strong to be overcome by H-bonding in water)

Chemical properties Reactions: -reactions involving -OH group (-reaction w/ Na, -conversion to halogenoalkane, -esterification)
-dehydration
-oxidation
-triiodomethane test
-combustion

Reaction involving -OH group
Reaction w/ electrophile metals (eg. sodium)
reagent: Na metal
condition: room temp
2R-OH(l) + 2Na(s) > 2R-O^-Na⁺(aq) + H₂(g)
observation: if excess alcohol -sodium metal dissolves > colourless liquid of sodium alkoxide (R-ONa), -effervescence of hydrogen gas
Conversion to halagenoalkane
-OH group replaced by halogen, used to prepare halogenoalkanes
Replacing w/ chloride group, Cl ^-
reagent: phosphorus (V) chloride, PCl₅ (phosphorus pentachloride)
condition: room temp
R-OH + PCl₅ > R-Cl + POCl₃(l) + HCl(g)
observation: white fumes of HCl gas evolved > indicates presence of -OH group
Replacing w/ iodide group, I ^- or bromide group, Br^-
reagent: red phosphorus + halogen, X (X = bromine / iodine)
condition: heat under reflux
  2P(s) + 3X₂ >(heat)> 2PX₃ (phosphorus tribromide/ triiodide)
  3R-OH + PX₃ >(red P, X, heat, reflux)> 3R-X + H₃PO₃ (phosphorus (III) acid)

Formation of ester
Esterification
reagent: alkanoic acid + conc H₂SO₄
condition: heat under reflux

reaction is reversible, so conc H₂SO₄ added to favour forward reaction by absorbing water, conc H₂SO₄ is also a catalyst by providing H⁺(aq)
observation: if poured into beaker of H₂O- ester floats on H₂O surface > oily patches of sweet, fruity smelling ester

Alkanoylation/ Acylation of alcohol
reagent: alkanoyl chloride = acyl chloride, R(=O)Cl
condition: room temp

observation: -sweet, fruity smell of ester, -steamy white fumes of HCl gas

Dehydration of alcohol to form alkene
reagent: conc H₂SO₄
conditions: -conc H₂SO₄ in excess, -heat under reflux, temp: ~180°C


Dehydration of alcohol to form ether
reagent: conc H₂SO₄
conditions: -alcohol in excess, -heat under reflux, temp: ~140°C


Oxidation of alcohols
reagent: oxidising agent- acidified potassium dichromate(VI), K₂Cr₂O₇/H⁺ [or KMnO₄/H⁺]
observation: excess alcohol- orange K₂Cr₂O₇ > green (Cr³⁺(aq) formed) [purple KMnO₄ decolourised (v.pale pink)]
1° alcohol:
conditions: (1)heat & distil > aldehyde obtained, (2)heat, reflux > aldehyde >(further oxidised) >alkanoic acid
formation of aldehyde:


formation of alkanoic acid:


2° alcohol:
condition: heat under reflux


3° alcohol: resistant to oxidation

Triiodomethane test
only works for alcohols / carbonyl cpds w/ following structure


reagents: -aq. I₂ sol [I₂ dissolved in KI(aq)], -NaOH(aq)
condition: warm mixture

observation: yellow ppt w/ antiseptic smell of CHI₃
(R-CH(OH)CH₃: -CH₃ part forms triiodomethane, R-CH(OH)- part oxidised > sodium salt of alkanoic acid)
(ethanol: only 1° alcohol that tests +ve)
[triiodomethane test:
  2NaOH + I₂ > NaI + NaOI + H₂O
  R-CH(OH)CH₃ + NaOI > R-C(=O)CH₃ + NaI + H₂O
  R-C(=O)CH₃ + 3NaOI > CHI₃ + R-C(=O)O^-Na⁺ + H₂O]

Combustion
alcohol(ethanol) burns in air w/ pale blue flame (clean + non-luminous) due to oxygen content (-OH group)

Aromatic hydroxy compounds part 2


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