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Thiamine-Catalyzed Benzoin Condensation


Benzoin was produced by reacting 2 mols of benzaldehyde with the catalyst thiamine to form a new C-C bond. A total of 2.626 grams were recovered. There was a 33% recovery of benzoin. The low percent recovery could be due to the purity of the limiting reactant, benzaldehyde. Upon filtration, the mother liquid appeared oily making it more likely that the low recovery was due to the solution ‘oiling out.’ This could be avoided in the future by maintaining the temperature of the solution below the melting point of the crystals.

Post Lab Questions

4.Upon analysis of the 1H NMR spectrum of benzoin it was determined that the peak at 4.6PPM is the proton from the OH. The peak at 5.99PPM is the CH proton.

II. Introduction

The purpose of this lab was to produce benzoin using thiamine as a catalyst in order to get 2 mols of benzaldehyde to react to form a new carbon-carbon bond according to the equation:

III. Methods and Materials

The procedure used was from Macroscale and Microscale Organic Experiments, chapter 53, pages 655-660. Changes or alterations to the procedure may be found in the laboratory notebook on page 1.

IV. Results

After filtration a small amount of off-white precipitate was recovered. The product was weighed in a tared weigh boat. See Figure 1 for measurement data.

Weigh boat + Benzoin| 4.161g|
Weigh boat| 1.535g|
Benzoin recovered| 2.626g|
V Benzaldehyde| 7.50 mL|
D Benzaldehyde| 1.044g/mL|
Weight Benzaldehyde| 7.83g|
Theoretical Yield of Benzoin| 7.83g|
Percent recovery of Benzoin| 33.5%|
| |


Weight of Benzoin recovered

Weight recovered= (weigh boat + Benzoin)-(weigh boat)=2.626g

Weight of Benzaldehyde used

Weight used=(V Benzaldehyde) x (D Benzaldehyde)=7.83g

Theoretical yield

7.83g Benzaldehyde/106.12g/mol=.074 mol

.074 x (1/2)=.037 mol Benzoin

.037 mol Benzoin x 212.24g/mol=7.83g Benzoin...
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