Question

Show how to convert \((R)\)-2-pentanol to \((S)-2\)-pentanethiol via a tosylate.

Short answer

Question: Describe the process of converting (R)-2-pentanol to (S)-2-pentanethiol via a tosylate. Answer: To convert (R)-2-pentanol to (S)-2-pentanethiol via a tosylate, follow these steps: 1) React (R)-2-pentanol with tosyl chloride (TsCl) in the presence of pyridine to form (R)-2-pentanol tosylate; 2) Invert the stereochemistry of the chiral center by reacting the (R)-2-pentanol tosylate with a strong nucleophile, like sodium thiolate ion (NaSH), resulting in (S)-2-pentanethiol and sodium tosylate as products.

Step-by-step solution

Convert alcohol to tosylate

In this step, we're converting the (R)-2-pentanol to its tosylate derivative. This is done by reacting (R)-2-pentanol with tosyl chloride (TsCl) in the presence of a base like pyridine. The reaction takes place as follows: (R)-2-pentanol + TsCl + Pyridine -> (R)-2-pentanol tosylate The pyridine is there to act as a base and neutralize the byproduct, HCl.

Invert the stereochemistry

In this step, we need to invert the stereochemistry of the chiral center from (R) to (S). This inversion can be done through an SN2 reaction. To accomplish this, react the (R)-2-pentanol tosylate with a strong nucleophilic species, capable of causing the inversion of stereochemistry by attacking from the opposite side of the tosylate group. A suitable nucleophile for this reaction is the sodium thiolate ion (NaSH), which is the conjugate base of the desired thiol compound. The reaction proceeds as follows: (R)-2-pentanol tosylate + NaSH -> (S)-2-pentanethiol + NaTs (sodium tosylate) In this step, the strong nucleophilic thiolate anion attacks the tosylate group from the opposite side, effectively displacing it and inverting the stereochemistry from (R) to (S).

Confirmation of the product

Now that the two steps for the conversion of (R)-2-pentanol to (S)-2-pentanethiol via a tosylate have been completed, we can confidently confirm the product obtained as the desired (S)-2-pentanethiol.