Essay On Multistep Synthesis

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Multistep Synthesis of Benzilic Acid from Benzaldehyde

Cambria M. Miller
March 24, 2014

Texas A&M University at Galveston, Galveston, Texas

INTRODUCTION
Benzilic acid (fig. 1) is a white crystalline solid often used in organic synthesis of certain pharmaceuticals and drugs (1). It is thought that benzilic acid may have success in anti-aging products. Benzilic acid is an alpha hydroxy acid and other alpha hydroxy acids have been used in the same manner (2).

Figure 1. Benzilic acid structure.

The purpose of this experiment was to successfully synthesize benzilic acid from benzaldehyde. Benzaldehyde is an organic molecule used to make bitter almond oil, and to synthesize many different organic compounds (3). This experiment is a multistep synthesis which means there are multiple parts that require the product of the previous step to be used as a reactant in the following step. Thus it is very critical to have high yields and accuracy at each step.
Traditionally cyanide was used as a catalyst in this reaction since Von Liebig first discovered it in his research with almond oil. However, cyanide is very poisonous and harmful to health. More recently it was discovered that Vitamin B1, a coenzyme by the name of thiamine hydrochloride may be used to catalyze the benzoin condensation, which is preferable to using cyanide. This experiment will test whether thiamine can effectively catalyze the reaction (2).
The experiment begins with the condensation of benzoin (eq. 1). In the presence of the thiamine catalyst, the 2 benzaldehyde molecules condense to produce benzoin when they are heated with sodium hydroxide and ethanol.

Equation 1: Benzoin Condensation.

The production of benzil (eq. 2) is a redox reaction. The b...

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...uced in part C using the product from part B. Another source of error was that on two different occasions recrystallization was omitted from the procedure. While this probably does not have a huge effect, crystallizing the product helps to eliminate impurities.
The overall product yield for this reaction is 90.53%. Although this number seems high, indicating a very successful synthesis, it does not account for the fact that Part C began with a new sample of benzil. Had it been continued using the product from part B, the yield would be much lower. Product may have been lost through residue being left in different glassware used due to inefficient transferring as well as reactions not running to completion. The purpose of this experiment was to produce benzilic acid, not to have high yields so in that sense there was success (excluding the formation of benzil).

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