Experiment 56 Postlab

Topics: Thiamine, Acetic acid, Benzoin Pages: 2 (263 words) Published: December 6, 2012
Submitted On:
Thursday, July 17th, 2012

Experimental Procedure and Observations: See Attached Pages


Measured Weight of Product: 8.577 g benzil
Theoretical Weight of Product: 15.765 g benzil

Percent Yield: 8.577 g * 100% = 54.4%
15.765 g

Melting Point of Intermediate (Benzoin)Melting Point of Product (Benzil) Trial 1 – 129-131°C
Trial 2 – 133-135°C
Trial 3 – 132-135°C
Trial 1 – 92-93°C
Trial 2 – 92-94°C
Trial 3 – 93-95°C

Average Melting Point Observed (Intermediate): 131.3-133.6°C Average Melting Point Observed (Product): 92.3-94°C
Theoretical Melting Point of Benzoin: 132°C
Theoretical Melting Point of Benzil: 94.5°C

Discussion and Conclusions:
The purpose of this experiment was to prepare benzil by first converting benzaldehyde to benzoin by the benzoin condensation, then oxidizing benzoin to benzil. The benzoin condensation was carried out using thiamine hydrochloride, or vitamin B1, as a catalyst.

The percent yield of the product was sub-par. It was found to be 54.4%, which may have been due to the formation of other byproducts during the experiment. For example, the benzoin and copper(II) acetate mixed with ammonium nitrate and acetic acid could have caused the copper(II) acetate to not fully react with the benzoin. This side-reaction led to less benzoin intermediate which in turn led to a less yield of benzil product. Additionally, the melting points found were similar to that of accepted values of benzoin and benzil, so there is no discrepancy in purity of the products.
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