Grignard Reaction

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The Wurtz-type reaction is the side reaction that contributed the most to a deviation in expected yield. At 47.9% the yield for 2-methyl-3-heptanol was fairly poor, however, the results could have been improved. If the Pasteur pipette was instead a calibrated syringe that distributed even and exact amounts of the ethereal solution the yield for 2-methyl-3-heptanol would have been larger. Instead of chopping the magnesium in the preparation of the Grignard and it was finely grounded the reaction would have had more of the reagent producing a higher yield. After the preparation of the Grignard reagent, the synthesis of 2-methyl-3-heptanol was time devoted to two distillation paths. The first was the simple distillation removing the diethyl ether, and the second was a short path distillation that distilled a small amount of octane and a majority of 2-methyl-3-heptanol. However, because of the impurity of octane and starting material present in solution the short path distillation started at approximately 140 °C and ended at 145 °C. This range is relatively lower than the true literature value for 2-methyl-3-heptanol at 167°C.

In order to see if 2-methyl-3-heptanol was present a comparative test between the actual IR and the one obtained was needed. The final mixture was a colorless, slightly opaque solution. Compared to the actual IR results (image 1) for 2-methyl-3-heptanol the graphs almost aligned perfectly. The most noticeable similarity being the broad dip at approximately 3457 cm-1. This indication of the hydroxyl group is present in both IR results. The carbon-to-carbon sp2 and sp3 bonds are also nearly identical. However, one difference between the two graphs is a larger stretch at around 1700 cm-1. The 1700 cm-1 most likely suggests a C=O as an aldehyde remains in solution. This means the reagent 2-methyl-propanal also known as isobutyraldehyde was still in part in the final solution. This means the 1.26 grams of 2-methyl-3-heptanol was also mixed in with unreacted starting material, which should lower the actual yield. Even the actual image of 2-methyl-3-heptanol contains a slight dip at the 1700 cm-1 wavelength suggesting there is difficulty in removing the all the starting material and getting a pure solution. Regardless this experiment required a multitude of steps that needed to be performed with precision and accuracy.

Actual IR for 2-methyl-3-heptanol:

[pic 5]

Image 1