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Organic Chemistry

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Alkynes

Question
14 out of 16
 

Alkynes are hydrocarbons with carbon-carbon triple bonds in them. The simplest alkyne can be prepared by the process shown in Reaction 1.

image\Ch 17 pass react 1,2.png

Also consider the following reactions.

image\Ch 17 pass react 3,4.png

Quinoline is a heterocyclic amine.


Lindlar's catalyst is often used for the reduction of alkynes to alkenes. The catalyst consists of palladium which is deposited in a finely divided state of barium sulfate, which is subsequently treated with a heterocyclic amine called quinoline. Which of the following is the most likely function of quinoline?

A To speed up the reaction so that the alkyne is completely converted to its most reduced form of hydrocarbon
B To slow down the reaction, because the function of a catalyst is to slow down the reaction
C To moderate the catalytic activity to facilitate a restrictive reduction
D It acts as an oxidizing agent so that the alkyne is reduced.
Ans. C Oxidizing agents oxidize other compounds; they do not reduce! This rules out Choice D. Choice B does not make any sense either. The alkyne is not being reduced to an alkane, but is being reduced to an alkene. This is not the most reduced form. Choice A is incorrect. The function of quinoline is to moderate the activity of the catalyst so that the double bonded alkenes that are formed will not undergo further reduction to form alkanes. Moreover, quinoline is not the actual catalyst.

Alkynes Flashcard List

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