Triphenylmethanol, triphenylmethyl cation

Carbocations are a class of reactive intermediates that have been studied for 100 years, since the colored solution formed when triphenylmethanol was dissolved in sulfuric acid was characterized as containing the triphenylmethyl cation. In the early literature, cations such as Ph3C and the tert-butyl cation were referred to as carbonium ions. Following suggestions of Olah, such cations where the positive carbon has a coordination number of 3 are now termed carbenium ions with carbonium ions reserved for cases such as nonclassical ions where the coordination number is 5 or greater. Carbocation is the generic name for an ion with a positive charge on carbon. 

In a 25-mL Erlenmeyer flask place 8.75 mL of acetic anhydride, cool the tube, and add 0.44 g of fluoboric acid. Add 1 g of triphenylmethanol with thorough stirring. Warm the mixture to give a homogeneous dark solution of the triphenylmethyl fluoborate, then add 0.4 g of cycloheptatriene. The color of the trityl cation should fade during this reaction and the tropilium fluoborate begin to precipitate. Add 10 mL of anhydrous ether to the reaction tube, stir the contents well while cooling on ice, and collect the product by filtration on the Hirsch funnel. Wash the product with 10 mL of dry ether and then dry the product between sheets of filter paper. 

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