Organometallic Reactions : Identification Of An Unknown Bromide

1317 WordsOct 26, 20166 Pages
LAB 7: ORGANOMETALLIC REACTIONS: IDENTIFICATION OF AN UNKNOWN BROMIDE (Preparative) Introduction The first purpose of the lab was to prepare an unknown organomagnesium bromide, an organometallic reagent, reacting an unknown aryl bromide with magnesium in anhydrous ether. The unknown was chosen from a predetermined list of benzoic acid derivatives with varying molecular weights and melting points (see Supplement C). The second purpose of this lab was to prepare an unknown carboxylic acid by reacting the unknown aryl-magnesium bromide with carbon dioxide and diethyl ether then protonating.The third purpose of this lab was to determine the neutralization equivalence point of the unknown carboxylic acid by titrating with sodium hydroxide. The fourth purpose of this lab was to ascertain the identity of the unknown carboxylic acid, and thus the original unknown aryl bromide, using its molecular weight determined from neutralization and melting point. Data and Results Compound Molecular Weight (g/mol) Melting Point (°C) Unknown Carboxylic Acid (R--COOH) 121.18 116-119 Discussion Organometallic reagents are compounds with carbon-metal (R--M) bond. In the carbon-metal bond, carbon is more electronegative than the metal atom which creates a dipole moment where carbon possesses a partial negative charge and the metal atom possessing a partial positive charge (Rδ---Mδ+). The partial negative charge on the carbon allows it to act as a strong nucleophile or base similar to
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