Grignard Reaction - Lab Report Example

Grignard Reaction Table of Contents Grignard Reaction: 3 Introduction 3 Results and Discussion 5 Summary 10 Experimental 11 2References 12Grignard Reaction: Abstract This paper details the results of experiments surrounding the synthesis of a Grignard reagent in the form of phenylmagnesium bromide, for later use in the synthesis of benzhydrol, leveraging the power of Grignard reagents to accomplish the task. The final product was verified using NMR spectral analysis, and validated to be in accordance with expectations from the theory and from the reagents and methods used to synthesize the final products (Experiment Handout, 2015; Rakita and Silverman, 1996). Introduction The overarching rationale of the experiment is gaining an understanding of the way Grignard reagents that are organometallic in nature can be employed in the generation of so-called carbon-carbon bonds. Organometallic compounds in themselves are of great use in many synthesis reactions in organic chemistry, and reactions involving such compounds have great utility in this scientific discipline. Employing such reagents of organometallic origin allow for synthesizing high-yield bonds that are carbon-carbon and ones of very high levels of specificity. Grignard reagents belong to such highly valuable organometallic reagents, being among the most prized and responsible for many important synthetic reactions in organic chemistry (McMichael, 2001; Organic Chemistry Portal, 2015). They refer to arylmagnesium and alkyl halides in the main, and are named after Victor Grignard, the chemist from France who got the 1912 Nobel for the scientific discipline. Those reagents are basically substances that contain bonds between carbon and metal constituents. To synthesize Grignard reagents, what are needed are magnesium metal in a solvent made of ether, reacting with either an alkyl halide or an aryl halide. Taking a step back therefore, the Grignard reaction in general generally refers to a process that is made out of two steps, one involving the synthesis of the Grignard reagent as discussed above, and second the generation of a product from making the Grignard reagent react with a substrate that is either inorganic or organic in nature, with the reaction in general being additive or involving reactions by substitution (Rakita and Silverman, 1996, pp. 1-7; Experiment Handout, 2015). To further discuss, the Grignard reaction as discussed above is essentially a series of steps that end up in the formation of compounds with carbon to carbon bonds. Grignard who was an organic chemist came to this set of reactions in the early years of the past century in the course of his investigations into the nature of reactions between magnesium on the one hand and so-called bromoalkanes on the other. When the reactions were conducted in ether media, the discovery was that there was a dissolution of the magnesium, with heat being formed and dissipated, and the outcome Te was a dark gray solution. The addition of an aldehyde or a ketone resulted in the formation and dissipation of heat once more, and the generation of alight gray product. The incorporation of an aqueous mixture at the end of the process to the light gray product from the previous step yielded an alcohol with a carbon-carbon bond, with the carbonyl atom now being bonded to the atom of bromine. The graphic below depicts these processes from the formation of the Grignard reagent to the formation of the alcohol with the carbon to carbon bond (McMichael, 2001): Graphic Source: McMichael, 2001 In the main, when a compound contains a magnesium to carbon bond, that is called a reagent of Grignard. Magnesium inserts into a prior bromine to carbon bond, in a process that is mapped and understood poorly, even as there is also a poor picture in scientific understanding with regard to the exact structural configuration of the Grignard reagent itself (McMichael, 2001; Rakita and Silverman, 1996). Results and Discussion The experiment itself mirrors the process discussed above, from McMichael (2001). The first step is the synthesis of the Grignard reagent, which in this case is phenylmagnesium bromide. The second step is making this Grignard reagent react with acetophenone, which is a ketone, for the production of 1,1-diphenylethanol, also called an alcohol of the tertiary kind. (Experiment Handout, 2015). In the first experiment, the generation of the Grignard reagent called phenylmagnesium bromide was achieved through the reaction of magnesium with the bromobenzene ether solution. The effects of magnesium being inserted between the bromine and the carbon bond includes giving the carbon component a strong negative charge, as well as upping the level of reactivity of the resulting compound, so that the reagent becomes a nucleophile with strength (Rakita and Silverman, 1996). In the next experiment, this reagent is made to react with acetophenone, to produce benzoic acid and the tertiary alcohol discussed above, respectively . On the other hand, the handout also notes that the Grignard reagent is a potent nucleophile and a potent base, and so reacts with acids and water readily. This necessitates making sure that the Grignard reagent is handled in conditions sans water, as well as oxygen molecules to which it also reacts readily with, prior to the desired reactions in order to maximize product yields (Experiment Handout, 2015; McMichael, 2001). In essence what we are looking for in the NMR and the spectroscopy data are the indications that the reactants and the expected products from the reactions are present as they should be for the different experiments under this exercise, from the generation of the tertiary alcohol to the generation of benzoic acid making use of the Grignard reactant in step one and making that reactant react with acetophenone in the second experiment. The peaks corresponding to the expected peaks indicating the presence of the desired products and peaks for the reactants would confirm the success of the reactions and the expected products from theory. Indeed looking at the data for both MACM for carbon and HMQC spectra we find that the expected product from acetophenone and the Grignard reagent was present following the reactions. The resulting NMR plots can therefore be interpreted in terms of how those spectra reveal the presence of the desired products versus the expectations of how the reactions will proceed, as well as the spectra for telltale leftover reactants from the experiments. For instance, looking at the resulting NMR plot for experiment 2, one can see that the plot closely resembles the NMR spectrum plot for 1,1-diphenylethanol in the literature, confirming that indeed, the actual product from the reaction of the Grignard reactant with the acetophenone (ChemicalBook, 2008): In the NMR plot above, the two large peaks at 128.54 and 128.27 correspond to the unique NMR spectrum for the tertiary alcohol as detailed in the literature, which occurs around the same values, even as there are four other peaks that are not as prominent in the plot above but are part of the unique signature for this alcohol as well. The plot above confirms the presence of the tertiary alcohol from the reaction of the Grignard reagent with the acetophenone (ChemicalBook, 2008). On the other hand, looking at the MACM plot below, the NMR spectrum derived from the final product conforms with the NMR spectrum as reflected in the literature, which again basically is a confirmation that indeed, the derived product from making the Grignard reagent react acetophenone. This reflects the accuracy in the synthesis of the Grignard reagent in the first part of the experiment too, the fact that the latter two experiments yielded products in accordance with expectations (Schaller, n.d.): The plot above correlates with established HNMR plots for benzhydrol, with peaks at between 7 and 8, confirming the successful synthesis of the benzhydrol from the Grignard reagent and acetophenone (ChemicalBook, 2008b). The HMQC spectral plot reinforces the above findings on the correlation between expected product from the literature with the actual product generated from the experiment, affirming that indeed the expected Grignard reagent synthesis and the subsequent synthesis of the final product match with theory (ChemicalBook, 2008b): Summary The overarching goal of the experiments was to understand the nature of Grignard reagents and how they effect the synthesis of carbon-carbon bonds in suitable reactions. The first experiment was an experiment in Grignard reagent synthesis, and entails understanding the formation of the reagent with magnesium and bromobenzene, to form a magnesium and carbon bond, the essence of what makes a reagent a Grignard reagent. The second experiment entail forming final products in the form of a tertiary alcohol from making the Grignard reagent react with acetophenone. The resulting products were analyzed for their NMR spectra to verify that the final products were indeed the ones that were expected to be produced from the reactions. More controlled experimental setups that more closely track the level of moisture that were inevitably made part of the reaction, which hampered the reactivity of the Grignard reagent, would be beneficial in future experiments. Other factors that affected the amount and purity of the final products need also to be further explored in future experiments and appropriately controlled (Experiment Handout, 2015). Experimental The first experiment entails producing the Grignard reagent for use in later experiments, in this case phenylmagnesium bromide, from bromobenzene and magnesium in an ether medium. The resulting Grignard reagent is then used to synthesize 1,1-diphenylethanol from its reaction with acetophenone in ether. The resulting product was examined with NMR spectroscopy to determine whether the expected and final products are the same, conforming to theory (Experiment Handout, 2015). 1 2 References Silverman, G. and Rakita, P. (ed) (1996). Handbook of Grignard Reagents. New York: Marcel Dekker Inc. / Google Books. Retrieved from books.google.com ChemicalBook (2008). 1,1-DIPHENYLETHANOL(599-67-7)13CNMR. Chemical Book. Retrieved from http://www.chemicalbook.com/SpectrumEN_599-67-7_13CNMR.htm ChemicalBook (2008b). Benzhydrol(91-01-0)1HNMR Chemical Book. Retrieved from http://www.chemicalbook.com/SpectrumEN_91-01-0_1HNMR.htm Experiment Handout (2015). Grignard Synthesis McMichael, K. (2001). Grignard Reagent and its Synthetic Uses. Washington State University Organic Chemistry Pages, Hosted by California State University. Retrieved from http://chemistry2.csudh.edu/rpendarvis/grignard.html Organic Chemistry Portal (2015). Grignard Reaction/Grignard Reagents. Organic-Chemistry.org. Retrieved from http://www.organic-chemistry.org/namedreactions/grignard-reaction.shtm Silverman, G. and Rakita, P. (ed) (1996). Handbook of Grignard Reagents. New York: Marcel Dekker Inc. / Google Books. Retrieved from books.google.com Read More