Question

1. How would you explain a percent recovery over 100% with an observed melting point higer than the literature melting point during an extraction lab?

2. How you you explain a low percent recovery during an extraction lab?

3. How does emulaion fomration affect the results of an extraction lab?

Answer 1

1. When the percent recovery is higher than 100% in the extraction process, it means that the isolated product is not pure and some impurities have been isolated along with the product. The difference in the melting point also points to this. As the melting point is higher than the expected value, most probably, an inorganic impurity (salt or base) is present in the product. If you can share the reaction you are doing, more information on the impurity can be provided.

2. If the percent recovery is lower than expected then it may be due to couple of reasons.

a) entire product was not extracted properly. Some of the product was still present in the aqueous layer and was not completely extracted into the organic layer ( this assumes that your product is soluble in organic layer and impurities are being washed out in the aqueous layer)

b) the layer separation was not done properly. Some of the organic layer was removed along with the aqueous layer.

b) there is also a possibility that your reaction was not complete. The reaction was quenched and work up was started for the reaction mixture that still had unreacted starting material. During extraction, product was extracted into organic layer and remaining starting material was washed out in the aqueous layer.

3. Emulsion formation impacts the extraction process. When emulsion forms, the separation between the organic layer and aqueous layer is not clear. This will make you miss the exact separation point. There are two scenarios

a) you may remove some organic layer along with the aqueous layer. In this case you will get lower yield

b) you may not separate the layers properly and some aqueous layer may be present in the organic layer. In this case you will have impurities in your product.

Note: try to correlate the two scenarios in answer 3 with the results in first 2 questions.