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Chem. 262 Notes 6

Chem. 262 Notes 6 - temperatures 2 Alcohol oxidations are...

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Experiment VI: In this experiment you will use chromic acid to oxidize isoborneol to camphor, which will be purified by sublimation. The direct conversion of a solid to a gas without going through a liquid phase is termed sublimation (an example is dry ice). Solids that readily vaporize at relatively low temperatures can be purified by sublimation. Impure iodine, for example, can be purified by sublimation, wherein the iodine is vaporized at low heat, leaving nonvolatile impurities behind and affording pure gaseous iodine that can be cooled back to a solid. 1. (a) Define sublimation. (b) When is it a useful method for purifying a compound? Sublimation is the direct conversion of a solid to a gas without going through the liquid phase. Sublimation is particularly useful in purifying compounds that readily vaporize at relatively low
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Unformatted text preview: temperatures 2. Alcohol oxidations are often performed with pyridinium chlorochromate (PCC) in dichloromethane solvent instead of by aqueous chromic acid. (a) Why? Alcohol oxidations are often used with PCC instead of chromic acid because if chromic acid is used to oxidize a primary alcohol, the carboxylic acid will be made. (b) Why is PCC not needed for this reaction? PCC was not needed for this reaction because isoborneol is a secondary alcohol, so chromic acid could be used to oxidize it. (d) What other factor(s) are important in choosing an oxidant? Which oxidant would you prefer based on these factors? The strength of the oxidant is important to consider; I would prefer to use chromic acid because it is very strong....
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