4 intro.docx

Synthesis of Triphenyl Carbinol and Benzoic Acid by Grignard Reagent - Introduction Grignard reagents are the intermediates of the formation of alcohol formation from a compound containing a carbonyl group and an alkyl halide. They are used because these two types of compounds do not readily interact to form alcohols themselves. The Grignard reagent is formed through the reaction of a zero valent magnesium atom with an alkyl halide. The magnesium atom inserts itself in between the halide-carbon bond. The formed Grignard reagent then goes on to react with an ether compound to produce an alcohol. The reaction first takes place by the of the benzene ring of the Grignard reagent to the carbonyl carbon atom of the methylbenzoate, breaking the double bond whose negative character then breaks the bond between the alpha carbon and the methoxy group to reform the initial carbonyl group. This creates the intermediate benzophenone. Benzophenone then goes back to react in the same way with another benzene ring of a Grignard reagent to add another benzene ring to the compound, but this time the oxygen stays negatively charged. The negative charge of the oxygen then pulls a hydrogen atom off a hydronium ion in order to form an alcohol substituent. This ends with the formation of triphenyl carbinol, with the remaining magnesium bromide from the Grignard reagent coordinating with the chloride from the added hydrochloride solution to form a neutral species. A problem can occur in the formation of benzene from the Grignard reagent, this is when the reagent reacts with water to displace the magnesium bromide with a hydrogen atom. This is faster than the nucleophilic attack that occurs in the above reaction, so water is removed from the apparatus before the experiment is performed to minimize this side reaction.