CompoundLucas ReagentChromic acid 1-butanol (A) 2-butanol (B) 2-methylpropan-2-ol (C) Phenol (D) Unknown (E) Iron(III) chloride Water pH=7 pH=4.5 pH=7 Explain why phenol reacts with NaOH while it does not react with NaHCO 3.. Explain the difference in reaction of the compounds toward Lucas Reagent. Explain the difference in reaction of the compounds with chromic acid. Suggest a test reagent for Phenol. Explain your choice briefly. State TWO methods for the formation of each of the alkanols A-C and phenol. Account for the browning of an apple on exposure to air for some time.
Alcohols are soluble in water. An alcohol has two parts: hydrophilic –OH group and hydrophobic hydrocarbon part. The large hydrocarbon in long-chain alcohols limits the aqueous solubility of such alcohols. Unlike alcohol, phenol is weakly acidic as the conjugate base is resonance-stabilized. However, its acidic strength is strong enough to neutralize OH - but not strong enough to neutralize NaHCO 3. It cannot liberate CO 2 from HCO 3 -. Tertiary alcohols rapidly react with Lucas reagent to form tertiary chloride, which produces immediate turbidity in the reagent. Primary alcohols cannot form stable primary carbocation upon protonation with Lucas reagent and thus show very slow or negative Lucas test.
Primary alcohols can be oxidized by acidified K 2 Cr 2 O 7 or chromic acid to carboxylic acid. Secondary alcohols can be oxidized to ketone while tertiary alcohols can only be oxidized in severe conditions. Unlike alcohol, phenol gives violet coloration with neutral iron(III) chloride as a result of complex formation. Benzenesulphonic acid reacts with NaOH at 300 o C to give phenol. Aniline reacts with HNO 2 at 0 o C to give stable aryl diazonium salt which easily gives phenol upon hydrolysis. Primary and secondary alcohols can be formed from the hydration of alkenes in acidic medium. They are also formed respectively from aldehyde and ketone by reduction with NaBH 4. Tertiary alcohols are formed by the hydrolysis of tertiary chloride at lower temperatures.
Browning of apple occurs as phenol derivatives present in apple easily air-oxidizes into quinone. CQA quinone and its interaction with catechins in the enzymatic browning of apple were examined. When an apple is cut into or is bruised, the result is brown flesh. This browning is caused by the introduction of oxygen into the delicate plant cells. It is called oxidation. When the chloroplast cells (replete with polyphenol oxidase enzymes) oxidize from an injury, phenolic compounds starts to produce o-quinones in the apple's flesh. Although o-quinones are colorless, they are the first step in the reaction of the amino acids that produce a brown compound.