0.5 Grignard reaction  (Page 3/5)

The product obtained is a 2° alcohol, 4-methyl-3-heptanol. A mixture of diastereomeric products is formed as the product contains two chiral centers. It is possible to vary the structure of both the Grignard reagent and the aldehyde; a wide variety of 2° alcohols is prepared by this route. Primary alcohols result when formaldehyde is used as the aldehyde. Secondary alcohols may also be obtained with these reagents when ethyl formate, an ester, acts as the electrophile. This latter reaction, however, requires two molar equivalents of the Grignard reagent. The mechanism for the reaction is as follows.

PreLab Questions (Total 10 points)

Click here for the Pre-Lab

Name(Print then sign): ___________________________________________________

Lab Day: ___________________Section: ________TA__________________________

This assignment must be completed individually and turned in to your TA at the beginning of lab. You will not be allowed to begin the lab until you have completed this assignment.

1. A small crystal of iodine is used during the preparation of ‘Grignard reagent’-Why? (1 point)

2. Which solvent can we use in the preparation of GR except ether? (1 point)

3. Why is the addition of the GR to propanal solution done over the period of 30 minutes? (2 points)

4. Write the major product of the following reactions: (4 points)

5. How will you synthesize the following molecule? (2 points)

from tertBu-Br, dry ether, $D_{2}O$ and Mg(0).

Grading

You will be assessed on:

• Completion of Pre lab questions.
• Write-up in your Lab Notebook (see Lab Notebook Guidelines )
• Analysis of product by Infrared and NMR Spectroscopy
• Completion of Post lab questions.

Materials required

Equipment Chemicals

• Water Bath 1. 2-bromopentane
• Stir bar 2. Mg metal, Iodine crystals
• Round bottom flask (10mL) 3. Propanal
• Hirsch funnel 4. Diethyl ether
• Beaker 5. 3M HCl, NaOH
• Glass rod (for recrystalisation) 6. Sodium sulfate (anhydrous)

Safety

Wear gloves all the time, especially working with NaOH, HCl. Keep safety glasses on all the time.

Experimental procedure

Part 1: Preparation of Grignard reagent

Part 2: Grignard reaction

Part 3: Isolation of product

Part 4: Characterization of product

NOTE: All the glassware used in the preparation of the Grignard reagent should be cleaned and dried in an oven at 110°C for at least 30 minutes, so you will need to plan on attending 15 minutes early on that day, dry your glassware and then attend the pre-lab lecture. (Use your glassware when it reaches room temperature, pressure builds up inside the apparatus) You will dry your glassware in the following way.  Show up to the lab 15 minutes early and dry your glassware in the oven.  The TA in charge of the lecture will then start his/her lecture on schedule.  Place all your glassware that you will need into a beaker with your name on it.  Place this in one of the ovens in the lab.  Do not put any non-glass parts in the oven.

NOTE: Check septum you are going to use for Grignard reaction. There should be no "open" holes. If septum has an obvious hole, it should be replaced with a new one.