This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Source of Pyridine Compounds”.
1. Which of the following plant is the natural source of pyridine?
a) Atropa belladonna
b) Ocimum tenuiflorum
c) Azadirachta indica
d) Ficus religiose
View Answer
Explanation: Pyridine is not abundant in nature, it is present in the leaves and roots of belladonna (Atropa belladonna).
2. Why is extraction of pyridine from coal tar or as a byproduct of coal gasification ineffective?
a) Less concentration of desired compound
b) This method is expensive
c) Reactive is rare
d) Dangerous procedure
View Answer
Explanation: The process was labor-consuming and inefficient because coal tar contains only about 0.1% pyridine, and therefore a multi-stage purification was required, which further reduced the output.
3. Which of the following derivative of pyridine is mostly found in mycobacterium tuberculosis?
a) Niacin
b) Nicotinamide
c) Nicotinic acid
d) Strychnine
View Answer
Explanation: The bacteria Mycobacterium tuberculosis and Escherichia coli produce nicotinic acid by condensation.
4. Mycobacterium tuberculosis and Escherichia coli produce nicotinic acid by condensation of which of the following compounds?
a) Glyceraldehyde 3-phosphate
b) Amino acid
c) Pyrrole
d) acetylene
View Answer
Explanation: The bacteria Mycobacterium tuberculosis and Escherichia coli produce nicotinic acid by condensation by glyceraldehyde 3-phosphate and aspartic acid.
5. Which of the following derivative of pyridine is mostly found in mammals?
a) Nicotinamide
b) Vitamin B6
c) Nicotinic acid
d) Strychnine
View Answer
Explanation: Mammals synthesize nicotinic acid through oxidation. The coenzyme forms of nicotinic acid are nicotinamide adenine dinucleotide (NAD). These compounds assist dehydrogenase enzymes in the catabolism of fat, carbohydrates, and amino acids, and in the enzymes involved in synthesis of fats and steroids and other vital metabolites.
6. Mycobacterium tuberculosis and Escherichia coli produce nicotinic acid by condensation of which of the following compounds?
a) Glyceraldehyde 3-phosphate
b) Kynurenine
c) Pyrrole
d) Tryptophan
View Answer
Explanation: Mammals synthesize nicotinic acid through oxidation of the amino acid ‘tryptophan’, where an intermediate product, aniline, creates a pyridine derivative, kynurenine.
7. What is the name of the reaction given below when condensation of acrolein and acetaldehyde take place?
a) Chichibabin synthesis
b) Dealkylation of alkylpyridine
c) Hantzsch pyridine synthesis
d) Bonnemann cyclisation
View Answer
Explanation: The reaction can be described as a condensation reaction of aldehydes, ketones, α, β-unsaturated carbonyl compounds, or any combination of the above, in ammonia. In particular, unsubstituted pyridine is produced from acetaldehyde, which are inexpensive and widely available.
8. In the synthesis of pyridine by Chichibabin synthesis, synthesis of acroloien is done which method?
a) Knoevenagel Condensation
b) Aldol condensation
c) Dieckmann condensation
d) Claisen condensation
View Answer
Explanation: Acrolein is formed in a Knoevenagel condensation from the acetaldehyde and formaldehyde. It is then condensed with acetaldehyde and ammonia into dihydropyridine.
9. Which of the following reagent can’t be used as the reagent in the dealkylation of alkylpyridines in the pyridine synthesis?
a) Vanadium oxide
b) Nickel based catalyst
c) Silver or platinum-based catalyst
d) Copper catalyst
View Answer
Explanation: The oxidative dealkylation is carried out either using air over vanadium(V) oxide catalyst, by vapor-dealkylation on nickel-based catalyst, or hydrodealkylation with a silver- or platinum-based catalyst. There are no evidences found when copper is used as catalyst in this reaction.
10. What is the name reaction of the following reaction?
a) Chichibabin synthesis
b) Dealkylation of alkylpyridines
c) Hantzsch pyridine synthesis
d) Bönnemann cyclization
View Answer
Explanation: The Hantzsch pyridine synthesis typically uses a 2:1:1 mixture of a β-keto acid (often acetoacetate), an aldehyde (often formaldehyde), and ammonia or its salt as the nitrogen donor.
11. Which of the following catalyst can be used in the synthesis of pyridine by Bönnemann cyclization?
a) Vanadium oxide
b) Nickel based catalyst
c) Silver or platinum-based catalyst
d) Cobalt catalyst
View Answer
Explanation: The trimerization of a part of a nitrile molecule and two parts of acetylene into pyridine is done with CoCp2(cod) (Cp = cyclopentadienyl, cod = 1,5-cyclooctadiene) as a catalyst, and can be performed even in water.
12. What is the name reaction of the following reaction?
a) Chichibabin synthesis
b) Dealkylation of alkylpyridines
c) Hantzsch pyridine synthesis
d) Bönnemann cyclization
View Answer
Explanation: The trimerization of a part of a nitrile molecule and two parts of acetylene into pyridine is called Bönnemann cyclization.
13. What is the name reaction of the following reaction?
a) Chichibabin synthesis
b) Ciamician–Dennstedt rearrangement
c) Kröhnke pyridine synthesis
d) Bönnemann cyclization
View Answer
Explanation: The Ciamician–Dennstedt rearrangement entails the ring-expansion of pyrrole with dichlorocarbene to 3-chloropyridine.
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