Triphenylmethanol preparation

Triphenylmethanol, prepared in the experiment in Chapter 31, has played an interesting part in the history of organic chemistry. It was converted to the first stable carbocation and the first stable free radical. In this experiment triphenylmethanol is easily converted to the triphenylmethyl (trityl) carbocation, carbanion, and radical. Each of these is stabilized by ten contributing resonance forms and consequently is unusually stable. Because of their long conjugated systems, these forms absorb radiation in the visible region of the spectrum and thus can be detected visually. 

Table 20-1. N-Substituted imidazoles and triazoles prepared by transfer reactions of azolides A—F with tertiary alcohols of the triphenylmethanol type and analogues.

Triphenylmethyl fluoroborate is prepared by dissolving 27 g. (0.104 mole) of triphenylmethanol ( purum, Fluka A G) in 260 ml. of propionic anhydride by warming on a steam bath. With an acetone-dry ice bath the solution is cooled to 10° and maintained between 10° and 20° while 31 ml. of 43% w/w fluoroboric acid is added portionwise with swirling. The yellow solid is collected, washed well with dry ether, and dried in a desiccator under vacuum to yield 34 g. (90-99%). The product is very hygroscopic, taking up water with hydrolysis. It is desirable to prepare this reagent immediately before use. 

Alternatively it may be prepared from triphenylmethanol (10 g) by heating under reflux in dry benzene (5 ml) with redistilled acetyl chloride (6.0 ml) for 30 minutes. The mixture is cooled, diluted with light petroleum (10 ml, b.p. 

Triphenylmethyl bromide, m.p. 153-154 °C, may be prepared in a similar manner from triphenylmethanol and acetyl bromide. 

Preparation from the triphenylmethanol, by reaction with sulfinyl chloride, also often gives problems of pressurisation, associated with the appearance, and then reaction, of an aqueous phase. 

The S-trityl ether of cysteine has been prepared by reaction of the amino add with triphenylmethanol in acetic add in the presence of trifluoroborane etherate43 or with triphenylmethanol in neat trifluoroacetic add.44 Slightly lower mp and spedfic rotation were recorded for the product obtained by the more... 

Prelab Exercise Prepare a flow sheet for the preparation of triphenylmethanol. Through a knowledge of the physical properties of the solvents, reactants, and products, show how the products are purified. Indicate which layer in separations should contain the product. 

Triphenylmethanol can also be prepared from the reaction of ethyl benzoate with phenylmagnesium bromide and by the reaction of diethylcarbonate... 

If the ethyl benzoate used to prepare triphenylmethanol is wet, what by-product is formed ... 

Bromobenzene was converted to the Grignard with activated magnesium , and the Grignard was then reacted with benzophenone (12) in analogy with the procedure of Bachmann and Hetzner.32 Triphenylmethanol (13) was obtained in 87% yield, compared to the literature32 value of 89—93%. Next, the Grignard was prepared at —78 °C (Dry Ice-acetone bath) and reacted with (12) at —78°. Reaction for 2.5 hr yielded (13) in 28% yield, and the yield was raised to 73% after 17 hr reaction at —78 °C. 

All students will prepare the Grignard reagent, phenylmagnesium bromide. At the option of the instructor, you should proceed to either Experiment 33A (triphenylmethanol) or Experiment 33B (benzoic add). 

Outline a synthetic reaction scheme for the preparation of triphenylmethanol from... 

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