Alcohols
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I am using PCl5 to distinguish between a tertiary alcohol and an ester, but I don't know what quantities I should use.
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Igloo replies
Given that a positive result gives off TOXIC gaseous hydrogen chloride and that the reaction is strongly exothermic, the reaction MUST be carried out in a fume cupboard using the smallest quantities possible. There is no need to measure out quantities accurately. Simply follow the procedure below.
Use a clean and dry teat pipette to place a few drops of the tertiary alcohol or ester in a boiling tube. Don’t forget to keep the remainder of the liquid away whilst you add the phosphorus pentachloride. Use a spatula and transfer a very small amount (about half a spatula full) of the solid PCl5 into the boiling tube, pointing the open end of the tube away from you during the addition. Replace the lid on the remainder of the PCl5. Shake the mixture gently.
A positive result is shown by a fizzing from the mixture, and if you carefully place a finger on the base of the boiling tube it should be warm or even hot.
Risk assessment
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updated: 12 February 2008
