Organic Synthesis and Multi-step Routes: Practice Questions

In the laboratory preparation of aspirin, a student purifies the crude solid product by recrystallisation. Which of the following methods should the student use to best confirm the purity of the dried product?

An organic chemist intends to synthesize 2-methylbutan-2-ol using a Grignard reagent. Which of the following reaction sequences would successfully produce this tertiary alcohol as the major product?

State the reagents and conditions required to synthesize 2-methylpropan-2-ol from propanone using a Grignard reagent.

Outline a reaction sequence to convert 1-bromopropane into butanoic acid, identifying the intermediate compound and the reagents for each step.

Propan-2-ol is a common solvent that can be synthesized in the laboratory through several routes. One method involves the use of a Grignard reagent to increase the carbon chain length starting from smaller organic precursors.

(a) Describe how a chemist would prepare a solution of methylmagnesium iodide starting from iodomethane. Include the necessary reagents and the specific solvent required to ensure the reagent remains stable. (2 points)

(b) The prepared Grignard reagent is then reacted with ethanal, followed by the addition of dilute hydrochloric acid. Draw the structural formula of the organic product formed and provide its IUPAC name. (2 points)

(c) The final product is a liquid. State the name of the technique used to verify the purity of the liquid product by comparing its experimental physical constant to a data book value. (1 point)

A target molecule, 3-methylpentan-3-ol, needs to be synthesized starting from ethane. A student proposes a four-step reaction scheme to achieve this increase in carbon chain length.

(a) In Step 1, ethane is converted to chloroethane. In Step 2, chloroethane is reacted to form ethylmagnesium chloride. State the reagents and conditions for both steps. (2 points)

(b) In Step 3, the ethylmagnesium chloride reacts with a ketone to form an intermediate alkoxide. Identify the specific ketone required to produce 3-methylpentan-3-ol and draw its structural formula. (2 points)

(c) After the addition of dilute acid in Step 4, the product is found in an organic layer. Describe how a separating funnel is used to isolate the organic layer and name a suitable drying agent used to remove traces of water from the final product. (2 points)

(d) A sample of the target molecule (\( M_r = 102.0 \)) undergoes complete combustion. Calculate the mass of water, in grams, produced when \( 2.04 \text{ g} \) of 3-methylpentan-3-ol is burned. (2 points)