Synthesis of Grignard Reagents
Abstract:
The purpose of this lab is to prepare phenylmagnesium bromide, a Grignard reagent, and react it with benzophenone to give triphenylmethanol. Once made, the Grignard reagent will do a nucleophilic attack on the carbonyl carbon of the ketone, benzophenone. The result is an alkoxide that is then protonated to give the alcohol, triphenylmethanol. The purity of the final product will then be considered by melting point and IR spectroscopy. Final purified triphenylmethanol weighed 8.02 grams and melted at 158.5-162 degrees Celsius.
Introduction:
Grignard reagents are the most useful way to form primary, secondary or tertiary alcohols from a carbonyl group. The Grignard reaction involves the nucleophilic addition of an organomagenesium complex to a carbonyl carbon followed by acid work-up. This reaction involves a single electron transfer between the carbonyl group and the grignard reagent. Once the Grignard reagent is synthesized it can work as a base by abstracting a proton or it can work as a good nucleophile. When it works as a base it can be added to water, alcohols, amines, acids, terminal alkynes and etc. When it works as a nucleophile, its nucleophilicity reacts with the electrophilic carbon in a carbonyl group forming a new carbon-carbon bond. Grignard reagents when synthesized are very reactive and thus must be made in an environment free of water or any other potential proton donor. Thus in order to synthesize the grignard reagent it is run in ether which is unreactive with the grignard reagent. The grignard reagent works as a nucleophile in this experiment and when added to the ketone, benzophenone it reacts with the carbonyl and forms the triphenylmethanol.
Then using experimental techniques the triphenylmethanol is purified, and melting point and IR spectrum are recorded. Melting points are very specific and usually melt in a range of temperatures. An impure compound will have a much lower and larger range of melting points
The purpose of this lab is to prepare phenylmagnesium bromide, a Grignard reagent, and react it with benzophenone to give triphenylmethanol. Once made, the Grignard reagent will do a nucleophilic attack on the carbonyl carbon of the ketone, benzophenone. The result is an alkoxide that is then protonated to give the alcohol, triphenylmethanol. The purity of the final product will then be considered by melting point and IR spectroscopy. Final purified triphenylmethanol weighed 8.02 grams and melted at 158.5-162 degrees Celsius.
Introduction:
Grignard reagents are the most useful way to form primary, secondary or tertiary alcohols from a carbonyl group. The Grignard reaction involves the nucleophilic addition of an organomagenesium complex to a carbonyl carbon followed by acid work-up. This reaction involves a single electron transfer between the carbonyl group and the grignard reagent. Once the Grignard reagent is synthesized it can work as a base by abstracting a proton or it can work as a good nucleophile. When it works as a base it can be added to water, alcohols, amines, acids, terminal alkynes and etc. When it works as a nucleophile, its nucleophilicity reacts with the electrophilic carbon in a carbonyl group forming a new carbon-carbon bond. Grignard reagents when synthesized are very reactive and thus must be made in an environment free of water or any other potential proton donor. Thus in order to synthesize the grignard reagent it is run in ether which is unreactive with the grignard reagent. The grignard reagent works as a nucleophile in this experiment and when added to the ketone, benzophenone it reacts with the carbonyl and forms the triphenylmethanol.
Then using experimental techniques the triphenylmethanol is purified, and melting point and IR spectrum are recorded. Melting points are very specific and usually melt in a range of temperatures. An impure compound will have a much lower and larger range of melting points
References: 1. Huston, Ericka, Ryan Weiss, Nicole Kennedy, and George Bandik, Organic Chemistry 2 Laboratory Manual. Hayden-McNeil, LLC: 2012. 2. Padias, Anne B., Making the Connections: A How-To Guide for Organic Chemistry Lab Techniques, 2nd ed.; Hayden-McNeil, LLC: Plymouth, MI, 2011. 3. Grignard Synthesis, Grignard Synthesis of Carbonyl Groups. http://www.bc.edu/schools/cas/chemistry/undergrad/org/spring/Grignard.pdf 3/10/12.