Question

Find the number of moles of $Br_2$ used if the product (Y) is treated with excess of $Br_2/CCl_4$?

Answer 1

3

Answer 2

The starting material is cyclopropane-1,2,3-tricarboxylate. Its structure is a cyclopropane ring with three ethoxycarbonyl groups ($-\text{COOC}_2\text{H}_5$) attached to each carbon of the ring.

Reaction with $LiAlH_4$ reduces the ester groups to primary alcohols. Thus, product (X) is cyclopropane-1,2,3-trimethanol.

Product (X) is treated with $H^+/\Delta$. This involves acidic conditions and heating, which can cause dehydration of alcohols and ring opening of the strained cyclopropane ring. A likely product under these conditions is benzene, which is a stable aromatic compound and can be formed from a $C_6$ precursor with sufficient unsaturation. Cyclopropane-1,2,3-trimethanol has the formula $C_6H_{12}O_3$. Dehydration to form benzene ($C_6H_6$) involves the loss of $12-6=6$ hydrogen atoms, which corresponds to the loss of 3 molecules of water ($3 \times H_2O$). The degree of unsaturation of $C_6H_{12}O_3$ is 1 (due to the cyclopropane ring). The degree of unsaturation of $C_6H_6$ is 4 (benzene ring). This is consistent with the formation of a benzene ring, which requires ring opening and rearrangement. While the exact mechanism might be complex, the formation of benzene from a $C_6$ precursor with appropriate functional groups under strong acidic conditions and heating is a plausible outcome, especially when considering the stability of the aromatic product.

So, product (Y) is benzene.

Benzene is then treated with excess $Br_2/CCl_4$. The reaction of benzene with $Br_2$ in the absence of a catalyst is slow and requires UV light for radical substitution.

Let's assume that the question is asking about the reaction of product (Y) with excess $Br_2/CCl_4$, and the intended reaction is addition to any double bonds present. If (Y) is benzene, it has 3 formal double bonds. Addition of $Br_2$ to a double bond is a 1:1 reaction. So, if addition occurs to all three double bonds, it would consume 3 moles of $Br_2$.

The product would be hexabromocyclohexane. This reaction can occur under UV light or high pressure. Given the context of JEE/NEET level questions, and the common reactions of benzene, it is possible that the question intends to test the addition reaction of benzene with excess bromine.

Let's assume that product (Y) is benzene and the reaction with excess $Br_2/CCl_4$ refers to the addition reaction. In this case, 3 moles of $Br_2$ are added to the three double bonds of benzene to form hexabromocyclohexane.

Therefore, the number of moles of $Br_2$ used is 3.