This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Reduction of Pyridine”.
1. What will be the product if reaction with hydrogen gas in the presence of Raney nickel takes place?
c) Pyrylium salt
Explanation: Hydrogen-saturated piperidine is obtained through reaction with hydrogen gas in the presence of Raney nickel.
2. What is name of the reaction when piperdine is converted by pyridine commercially?
d) Transfer hydrogenation
Explanation: Piperidine is commercially obtained by the hydrogenation of pyridine using nickel catalyst at about 200℃.
3. By which of the following agent there will be incomplete reduction of pyridine?
a) Na-NH2, EtOH
b) H2/RaNi, 200℃
Explanation: NaNH2 in presence of ethanol will form 1, 4-dihydropyridine when undergoes partial hydrogenation of pyridine take place.
4. When Lithiumtetrahydroborate in the presence of water reacts with pyridine, which product is formed?
Explanation: Selective synthesis of 1,4-dihydropyridine is achieved in the presence of organometallic complexes of magnesium and zinc, and Lithiumtetrahydroborate in the presence of Water.
5. When lithium aluminium hydride reacts with pyridine, which product is not formed?
Explanation: Partially hydrogenated derivatives are obtained under milder conditions, reduction with lithium aluminium hydride yields a mixture of 1,4-dihydropyridine, 1,2-dihydropyridine, and 2,5-dihydropyridine.
Explanation: Hydrogen-saturated piperidine is obtained through reaction with hydrogen gas in the presence of Raney nickel. Group –COOH will remain same.
7. Pyridine undergoes nucleophilic substitution with phenyl lithium at 100℃ to give which of the following?
Explanation: Nucleophilic substitution takes place preferentially at the 2- and 4- positions as the intermediate anion is stabilised by the electronegative nitrogen.
Explanation: A benzyne intermediate is generated when bromide leaves. This intermediate can be attacked on either carbon-3 or carbon-4, giving you both possible products. Path 1 gives you 4-aminopyridine, and path 2 gives you 3-aminopyridine.The mechanism finishes when the basic reactant donates electrons to acquire a proton and regenerate the reactant NH−2. This is obviously hard (you’re generating an extremely strong base, which prefers not to be free!), so it’s one of the reasons why heat is needed.
Sanfoundry Global Education & Learning Series – Organic Chemistry.
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