(a) Methyl chloromethyl sulfone reacts with strong alkali to yield ethylene and sodium sulfite. Write a mechanism for this reaction which is in accord with the reagents and the products. (b) Butadiene when heated with sulfur dioxide undergoes 1,4 -addition with formation of an unsaturated cyclic sulfone. How might this sulfone (in conjunction with the reaction which gives an alkene from an a-halosulfone) be used in a synthesis of cyclobutadiene?

We're given methyl chloromethyl sulfone, which has the formula ClCH_2SO_2CH_3. The strong alkali can be represented as OH^-. We need to find a mechanism that leads to the formation of ethylene (C_2H_4) and sodium sulfite (Na_2SO_3).

The mechanism for this reaction can be described as follows: 1. The nucleophilic hydroxide ion (OH^-) attacks the sulfur atom of the ClCH_2SO_2CH_3 molecule, breaking the S-Cl bond. 2. A new bond is formed between the sulfur atom and the oxygen atom of the hydroxide ion, leading to an intermediate with a negative charge on the sulfur atom. 3. The intermediate molecule undergoes an intramolecular S_N2 reaction, in which the negatively charged sulfur atom attacks the methylene carbon (CH_2) adjacent to the sulfur, creating a new C-S bond and expelling a chloride ion. 4. The resulting intermediate further breaks the C-C bond on the other end of the molecule, and ethylene (C_2H_4) is released. What remains is the ion SO_3^2-, which can form sodium sulfite by binding with two sodium ions (Na^+). The final products are ethylene (C_2H_4) and sodium sulfite (Na_2SO_3). #Part (b)#

When butadiene (C_4H_6) is heated with sulfur dioxide (SO_2), it undergoes a 1,4-addition reaction to form an unsaturated cyclic sulfone. The reaction mechanism involves nucleophilic addition of sulfur dioxide to the conjugated double bonds, creating a cyclic sulfone intermediate with a double bond still present within the ring.

To use the unsaturated cyclic sulfone in the synthesis of cyclobutadiene, we need to perform the α-halosulfone reaction, which converts α-halosulfone into an alkene. Since the unsaturated cyclic sulfone already contains an alkene, the reaction should go through the following steps: 1. Add a halogen atom (e.g., chlorine) adjacent to the sulfur atom in the sulfone group. This will form an α-chlorosulfone intermediate. 2. The α-chlorosulfone intermediate reacts with a strong base (e.g., an alkoxide, RO^-) in a manner similar to the reaction described in part (a). The base attacks the sulfur atom, breaking the S-Cl bond and forming a new S-O bond. This causes the ring to open and releases a molecule of alkene. 3. The elimination process is repeated once more, releasing another molecule of alkene as the product. 4. The final product obtained after these multiple elimination steps will be the desired compound, cyclobutadiene (C_4H_4).