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McGill University
CHEM 222
David Harpp

Chemistry 222 Fall 2012 Experiment 2: Grignard Reaction – Report Sheet Last Name: Siva First Name: Krishnaa Date: September 27, 2012 Section Number: 005 Objective: 1 mark (What is the purpose of this experiment?) The purpose of this experiment is to study the formation of the carbon- carbon single bond which is largely found in organic chemistry. This is studied with the help of the Grignard reaction. In a Grignard reaction the carbon of an organic group of the Grignard reagent bonds with the carbonyl carbon of a ketone to form an alcohol. The method to produce a Grignard reagent is also studied in this experiment. Introduction: 2 marks (Brief description of the concept/reaction studied – Grignard reactions) This lab begins with the formation of the Grignard reagent. Magnesium turnings were mixed with bromobenzene and absolute ether in a round bottom flask and was heated on a steam bath to produce a brown substance called phenyl magnesium bromide (the Grignard reagent). The focal point of this experiment involves the reaction of phenyl magnesium bromide, the Grignard reagent, and benzophenone, a ketone, to produce the crystalline alcohol triphenylcarbinol and MgBr(OH). This overall reaction is known as the Grignard reaction. It is important to note that this reaction also involves the production of an intermediate product which is an organomagnesium salt. This salt forms when the reaction mixture with the phenyl magnesium bromide and benzophenone, is mixed with the 10% sulfuric acid, ethyl ether and ice. Following this step, the organic layer is separated from the aqueous layer, and then filtered through a cone of anyhydrous sodium sulfate. Following some evaporation processes and cooling, the crystalline alcohol triphenylcarbinol is finally obtained through a suction filtration process. At this point, a carbon-carbon single bond gets formed between the carbon of the Grignard reagent's organic group and the carbonyl carbon of the ketone. To verify that it is indeed the crystalline alcohol triphenylcarbinol, the melting point of the product is taken at the end. Reaction Equation: 2 marks (Include proper structures and data [molar mass, concentration, density, volume, mass, moles, etc – as appropriate – including theoretical yield] for reactants and products) (The reaction equation with the table containing the proper information is on the following pages.) 1 Chemistry 222 Fall 2012 Molar mass Melting Point Boiling Density Volume/ (g/mol) C) Point ( C) g·cm−3) Mass Moles Bromobenzene 157.010 -30.8 156.0 1.495 3.6 mL 0.034 Magnesium 24.305 650.0 1091.0 1.738 0.8 g 0.033 Benzophenone 182.217 47.9 305.4 1.110 2.0 g 0.011 Theoretical: Theoretical: Theoretical: Crystalline 161.5 C 2.86 g 0.011 Alcohol Experimental: 360.0- Experimental: Experimental: Triphenylcarbinol 260.330 151- 154 C 380.0 1.199 0.25 g 0.0009603195944 Table 1. Results – Yield and Physical Properties of Triphenylcarbinol 5 marks Triphenylcarbinol Yield (g) 0.25 g Yield (%) 8.74 % Appearance White crystalline structures Melting Point 151 C - C Discussion Questions: 10 marks 1. Suggest at least one chemical reason why your percent yield is less than 100%. (Incomplete reactions? Side reactions? Stability of reagents?) To begin with, the formation of the impurity, biphenyl, is one reason the percent yield is less than 100%. Biphenyl gets produced when the phenyl magnesium bromide reacts with the unreacted bromobenzene (Williamson and Masters, 2011). Benzophenone should have been added gradually in this experiment to keep the formation of the primary impurity of biphenyl to a minimal. With the slow addition, the bromobenzene concentration would be kept to a minimal and the bromobenzene would more likely react with the magnesium instead of the formerly made phenyl magnesium bromide. This impurity is somewhat removed near the end of the experiment with
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