If (0.05 mol) 1-chloro-2,4-dinitrobenzene is reacted with an excess of pyridine
ID: 518600 • Letter: I
Question
If (0.05 mol) 1-chloro-2,4-dinitrobenzene is reacted with an excess of pyridine and sodium methylcyclopentadienide, what is the theoretical (100%) yield of the desired 1-methylazulene product (molar mass = 142.2 g/mol)?
a. 66.7 g
b. 7.11 g
c. 0.015 g
d. 2.12 g
e. 2844 g
The crude product solution (in cyclohexane) was passed through silica gel to purify it. Before this step, the TLC showed a low Rf spot (yellow) and a high Rf spot (blue), but afterwards the yellow spot was mostly removed. How did this purification work?
a. Silica gel does not absorb strongly colored materials, so these pass through with the cyclohexane
b. Substances towards the red end of the color spectrum (red, orange & yellow) are absorbed more strongly on silica gel than those at the blue end of the color spectrum
c. Polar materials (such as the impurity) are tightly held on silica gel, whereas non polar materials (such as the methylazulene) are not held on the silica gel and so are washed through in the cyclohexane.
d. The impurity reacts with silica gel to form an imine, which is a solid
e. The impurities are strongly basic, and so are absorbed by the acidic silica gel
Explanation / Answer
0.05 mol of starting material is used. If yield is 100 % , 0.05 mol of product will be obtained
0.05 x 142.2 = 7.11 g is the 100% theoretical yield.
c)Polar materials (such as the impurity) are tightly held on silica gel, whereas non polar materials (such as the methylazulene) are not held on the silica gel and so are washed through in the cyclohexane.
High Rf molecules eluted first in silica gel column chromatography. In other words non polar molecules eluted before polar molecules. As the elutant polarity is increases, polar molecules or low Rf molecules will come out column chromatography.
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