Lab #5: Grignard Reaction – Synthesis of Triphenylmethanol John Kang
Date submitted: ________________
Lab Partners: Sang Lee, Vicky Lai
TA: John Stanko
This experiment explored the synthesis of triphenylmethanol through the use of Grignard reagents. The percent yield of the product was 10% on a relatively humid day. The melting point was calculate to be 127.2oC with a literature value of 162oC. An IR spectrum of the product was taken and used for positive identification of the product. The mechanism of the formation of triphenylmethanol was explored. Byproducts were also considered and their mechanisms duly noted.
This experiment explores the use of organometallic reagents in addition reactions. Organometallic compounds have a carbon-metal bond, such as a carbon-magnesium or carbon-lithium bond. Transition metals can also be used such as rhodium or iridium. Organometallic compounds have a wide range of uses, including being consumed as a reagent and acting as a catalyst. Grignard reagents are a very common organometallic compound. Grignard reagents are formed from the reaction of an alkyl, cycloalkyl, or aryl halide and magnesium metal. This reaction is shown below as Figure 1. [pic]
Fig. 1: Formation of a Grignard reagent
The carbon bonded to the metal is an excellent nucleophile and base. This carbon with carbanion character can partake in typical nucleophilic reactions such as nucleophilic substitution or carbonyl addition. The experiment performed is an example of carbonyl addition using a Grignard reagent. On critical aspect of the a reaction involving a Grignard reagent is that it must be performed under dry conditions. The carbanion is a very strong base and can abstract protons from water, allowing less carboanions to undergo the desired reaction. In this experiment, phenylmagnesium bromide is the prepared Grignard reagent. Its synthesis...
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