The objective of this experiment was to synthesize the alkyne product Diphenlyac

Question

The objective of this experiment was to synthesize the alkyne product Diphenlyacetylene by performing a double elimination reaction in which two HBR molecules are removed from 1,2-Dibromo-1,2-diphenylethane. In addition to purifying the product Diphenlyacetylene by recrystallizing it from ethanol

I have 2 questions regarding lab report.
1) why was the crude sample generated from trans stillbene and bromine not recrystallized?
2) how would the purity of reagent 1,2-Dibromo-1,2-diphenylethane affect the yield of diphenylacetylene?

Synthesis of Diphenylacetylene Laboratory Report Write a standard laboratory report following the guidelines given in the syllabus. Refer to the laboratory syllabus for the template for writing the report. The lab report should be word processed using 12 point font. Include the following: Equation for the synthesis (Do not include the mechanism, just the reaction equation.) Equations can be neatly hand-drawn-they do not need to be computer generated. A Table of Reagents and Products using the exact amounts of reagents and products from the laboratory data collected. Some of this table will be a duplicate of the table generated for the pre-lab assignment, but some of it will be based on the data generated in the lab. You are using a student generated sample of crude 1,2-dibromo-1,2-diphenylethane in this experiment. Use physical appearance and melting point to discuss the purity of the 1,2-dibromo- 1,2-diphenylethane. Why was the crude sampie (generated from trans-stilbene and bromine) not recrystallized? How would the purity of the 1,2-dibromo-1,2-diphenylethane affect your yield of O diphenylacetylene? Use physical appearance and melting point to discuss the purity of the diphenylacetylene. Discuss your yield of diphenylacetylene. What were potential sources of loss of material in your experiment other than personal error? Calculate the yield of the reaction. Show your calculations. The yield in grams (and moles) and the experimental melting point range should be included in the Table of Reagents and Products.

Explanation / Answer

1) Sample dissolved in the solvent is too little (weight) and some of it will not dissolve in the solvent
during recrystallization and as result the melting point will not vary. Hence the crude sample is not
recrystallized.

2) 1,2-Dibromo-1,2-diphenylethane is the limiting reagent in this reaction, so the amount (gms) of final product
produced totally depends on the moles of the limiting reagent. The actual yield might get reduced
as the pure moles of limiting reagent decrease. However there will be no significant change in the yield
as the final product is purified and filtered.

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