Grignard reaction

Sabrina Liao

Purpose

A Grignard reagent will be prepared from a bromide, which will then be used to accomplish a Grignard reaction. Further practice with the techniques of extraction and crystallization will also be gained.

Reaction/ mechanism

Table of reactants and reagents

Reactant/reagent	Amount (g or ml)	Moles (mol)	Molar mass (g/mol)	Density (g/ml)	mp/bp (C)	comments
Magnesium	0.504 g	0.021 mol	24.305	1.738 g/ml	1090C/ 109C	reagant
Petroleum ether	10 ml	0.0794 mol	82.2	0.653 g/ml	-73C/42~62C	reactant
Hydrochloride	7 ml	0.156 mol	36.46	0.81g/ml	-113.2/ -85.1	neutraulizer
bromobenzene	2.1 ml	0.02 mol	157.01	1.5g/ml	-30/156	reactant
Anhydrous ether	37 ml	0.53 mol	24.12 g/mol	0.706 g/ml	-166/35	reactant
Anhydrous sodium sulfate	9ml/5ml	n/a	142.04g/mol	2.66 g/ml	884/1429 C	Drying agent
iodine	1 drop	n/a	126.9	4.93 g/ml	113/184.3	catalyst
benzophenone	2.410 g	0.014 mol	191.27	1.11 g/ml	46.5/305	reagant

Calculations

Procedure

0.504 g of polished magnesium was obtained into a 100 ml round bottom flask. Then, 2.1 ml of bromobenzene was combined with 10 ml of anhydrous ether inside a 50-ml-Erlenmyer flask. Half if the mixture was then transferred into the  100-ml round bottom flask containing the Magnesium while the other half of it was obtained into a seperatory funnel. Then another 7ml of anhydrous ether was added into a seperatory funnel. Since no reaction occurred, a drop of iodine was added into the mixture in order to facilitate the reaction. The mixture was stirred and being refluxed at 110 celsius afterthe reflux apparatus was set up. Although no bubble was observed unexpectedly, the mixture became cloudy and brown indicating the reaction proceeded. After that, the remaining bromobenzene inside the seperaory funnel was added into the 100-ml round bottom flask. Since it was obtained too fast, the reaction was rigorous. The magnesium inside the flask disappeared as reaction came along. The seperatory funnel was then rinsed with 1ml of anhydrous ether which was later added into the mixture. Then the seperatory funnel was replaced by a  stopper. The mixture inside the 100-ml round bottom flask was then refluxed again and the product was cooled down to room temperature within 15 mins. 2.410 grams of Benzophenone was combined with anhydrous ether in a 50 ml Erlenmyer flask and it was then transferred into the seperatory funnel. As the reagent inside the 100 ml round bottom flask being cooled to the room temperature, the separatory funnel was attached to it once again and the benzophenone solution inside the funnel was slowly added inside the Grignard reagent. After the addition was over, the separatory funnel was rinsed by 5ml of anhydrous ether that was then added into the reagent. The mixture turned pink as the reaction proceeded and the product was cooled down to room temperature as reaction stopped. Then, the product was stirred by spatula. Around 7ml of HCL was added to the product and the litmus paper turned red as it reached the mixture. The remained solid inside the mixture was broken down by a spatula. The reagent mixture was then transferred into the separatory funnel which was then shaken and vented. Two layers was observed in the funnel. The bottom layer was drained inside a beaker and the upper layer was stored in an Erlenmyer flask. Then the bottom lawyer was mixed with 5ml ether and the new upper layer was saved and added into the same Erlenmyer flask as before. 1 scoop of granular anhydrous sodium sulfate was added to the solution to get rid of the remaining  water inside the solution. The dried solution was then obtained into a small Erlenmyer flask followed by the previously-used flask being rinsed using a few diethyl ether.  The product was then filtered using filter paper. 10ml of Petroleum ether was then used to remove biphenyl while the solution was then crystalized using vacuum filtration. The melting point of the final product was measured as 163.1 celsius. The final product weighed 2.006 g.

Table of products

product	Yield (g)	yield(mol)	Theoretical yield(g)	Percent yield	Molar mass	Actual mp (C)	literature mp (C)
Triphenylmethanol	2.006 g	0.012 mol	5.2 g	38.58%	260.33 g/mol	160-163	160