Question

The compound which produces propane on heating with $HI$ and red phosphorus is
A.\[C{H_3}C{H_2}C{H_2}I\]
B.\[C{H_3}C{H_2}CHO\]
C.\[C{H_3}C{H_2}C{H_2}OH\]
D.All of theses

Answer 1

Hint: We must have to know that HI and red phosphorus are used for reduction of substrate. Propane is a saturated molecule that has all single bonds. Saturated molecules are the class of hydrocarbons which have zero degree of saturation. They do give a non sooty flame on combustion. They also cover the highest surface area compared to other hydrocarbons.

Complete Answer:
As we know that red phosphorus and $HI$ are used in reduction. Hence, they will help in addition of hydrogen to the substrate molecule. Reduction is defined as the addition of hydrogen or removal of oxygen from the substrate molecule.
Considering option (a) 1-iodopropane \[\left( {C{H_3}C{H_2}C{H_2}I} \right)\] . The reaction goes as such:
\[C{H_3}C{H_2}C{H_2}I + HI + red phosphorus \to C{H_3}C{H_2}C{H_3} + {\text{ }}{I_2}\]
The reaction of 1-iodopropane with red phosphorus and HI results in the formation of alkane. The HI and red phosphorus acts as a reducing agents and remove the iodine atom present and add hydrogen atom which forms propane.
Now considering option (b) that is Propanal. The reaction says:
\[C{H_3}C{H_2}CHO + HI + red phosphorus \to C{H_3}C{H_2}C{H_3} + {I_2} + {H_2}O\]
During the reaction the oxygen present in the molecule gets removed as water molecule and instead of that a hydrogen atom takes its place which leads to formation of alkane that is propane.
Now considering option (c) Propanol . The reaction goes as such :
\[C{H_3}C{H_2}C{H_2}OH + HI + red phosphorus \to C{H_3}C{H_2}C{H_3} + {I_2} + {H_2}O\]
As in the reaction for propanol similarly the oxygen atom gets removed in propanol and hydrogen atom from HI takes the place and leads to formation of alkane that is propane.
Thus, all the options on reaction with HI and red phosphorus results in the formation of alkane in this case propane.

Thus, option (d) all of these are correct.

Note:
We need to know that this reaction is used in the interconversion of functional groups. These reactions have high application in the synthesis reaction of particular compounds. The reaction can reduce all the functional groups like aldehydes, ketones and carboxylic acids. Red phosphorus is highly harmful for humans, causing respiratory tract irritation, cough and various other problems. Hence, it is advised to use it carefully.