Trityl fluoborate

Reaction of triphenylmethanol with fluoboric acid in the presence of acetic anhydride generates the stable salt, trityl fluoborate. The fluoboric acid protonates the triphenylmethanol, which loses the elements of water in an equilibrium reaction. The water reacts with the acetic anhydride to form acetic acid and thus drives the reaction to completion. 

Tris (dimethylamido) phosphite added with cooling to a soln. of trityl fluoborate in methylene chloride until the color disappears, and the product precipitated with ether trityltris-(dimethylamido) phosphonium fluoborate. Y ca. 100%. 

Abstraction of hydride ions from tropylidenes by nitrosyl or trityl tetra-fluoborates leads to 2-imino-3-arylthiazolotropylium salts like 640a,b [94H(38)2691] and to cycloheptaazaazulenium salt 643 or (unstable) 14-77-electronic pyrrolotropylium salt 647 [Scheme 173 94JCS(P1)2579]. 

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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See also in sourсe #XX -- [ ]

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