Phosgene is the acid chloride of carbonic acid. Although phosgene was used as a war gas in World War I, it is now used as a reagent for the synthesis of many useful products. Phosgene reacts like other acid chlorides, but it can react twice.

(a) Predict the products formed when phosgene reacts with excess propan-2-ol.

Verified step by step guidance

1. Step 1: Recognize the structure of phosgene (Cl₂C=O), which is an acid chloride derived from carbonic acid. Acid chlorides are reactive electrophiles that undergo nucleophilic acyl substitution reactions.
2. Step 2: Identify the nucleophile in the reaction. In this case, excess propan-2-ol (CH₃CHOHCH₃) acts as the nucleophile. Alcohols are good nucleophiles due to the lone pairs on the oxygen atom.
3. Step 3: Predict the first reaction step. The nucleophilic oxygen of propan-2-ol attacks the carbonyl carbon of phosgene, displacing one chloride ion (Cl^-) and forming an intermediate ester-like compound: CH₃CHOHCH₃-C(=O)-Cl.
4. Step 4: Predict the second reaction step. Since phosgene can react twice, another molecule of propan-2-ol attacks the remaining carbonyl chloride group in the intermediate, displacing the second chloride ion (Cl^-) and forming the final product: CH₃CHOHCH₃-C(=O)-OCH₃CHOHCH₃.
5. Step 5: Summarize the reaction. The final products are a diester (formed by two molecules of propan-2-ol reacting with phosgene) and two chloride ions (Cl^-) as byproducts.

Key Concepts

Nucleophilic Acyl Substitution

Nucleophilic acyl substitution is a fundamental reaction in organic chemistry where a nucleophile attacks the carbonyl carbon of an acyl compound, leading to the replacement of a leaving group. In the case of phosgene, the nucleophile (propan-2-ol) attacks the carbonyl carbon, resulting in the formation of a tetrahedral intermediate that eventually collapses to yield a carboxylic acid derivative and release the leaving group.

Acid Chlorides

Acid chlorides are a class of reactive organic compounds characterized by the presence of a carbonyl group (C=O) bonded to a chlorine atom. They are highly reactive due to the electronegative chlorine, which makes the carbonyl carbon more susceptible to nucleophilic attack. Phosgene, as an acid chloride of carbonic acid, exhibits similar reactivity, allowing it to participate in nucleophilic acyl substitution reactions.

Reactivity of Phosgene

Phosgene is notable for its ability to react twice with nucleophiles due to its two reactive acyl chloride groups. This property allows it to form products with two nucleophiles, such as propan-2-ol, leading to the generation of a diester. Understanding this reactivity is crucial for predicting the products of reactions involving phosgene and other similar acid chlorides.