Triphenylmethyl chloride, color

The idea of carbonium ions is quite old in organic chemistry. Olah has traced the early history (15). In 1902 Von Baeyer wrote of carbonium salts in explaining the deep color formed when triphenylmethyl chloride was dissolved in sulfuric acid. Carbonium ions as reaction intermediates were proposed by Meerwein in 1922, and much used by Ingold, Hughes, and others in England soon thereafter. F. C. Whitmore in the USA from 1932 on showed how carbonium ions as reaction intermediated could explain the acid-catalyzed reactions of alkylation, polymerization, and isomerization. His studies were summarized in a review article in 1948 ( ). More recently, of course, there have been many spectroscopic studies of stable carbonium ions formed in highly acidic solutions at low or moderate temperatures, as, for example, in the works of N. C. Deno and G. A. Olah. 

In 1902 Norris and Kehrman independently discovered that colorless triphenyl-methanol gave deep yeUow solutions in concentrated sulfuric acid (Scheme 2.1). Triphenylmethyl chloride similarly formed orange complexes with aluminum and tin chlorides. Adolf von Baeyer recognized in 1902 the salt-Hke character of the compounds formed. He dubbed the relationship between color and salt formation halochromy, of which malachite green is a prime example. 

Before 1900 chemists considered carbon to be tetrasubstituted in virtually all organic compounds. Then, Gomberg s attempt to prepare hexaphenylethane from the reaction of triphenylmethyl chloride (5) with zinc dust (equation 5.1) gave colored solutions that reacted with reagents such as iodine (equation 5.2) to produce stable products. The results were interpreted in terms of an equilibrium between hexaphenylethane (6) and triphenylmethyl radicals. ... 

An activation energy of this magnitude would lead to an unobservably slow reaction at normal temperature. There is an abundance of evidence that carbocations can be intermediates in nucleophilic substitution reactions. Carbocation formation in solution is feasible because of the solvation of the ions that are produced. One of the earliest pieces of evidence for the existence of carbocation intermediates was the observation that triphenylmethyl chloride (trityl chloride) gave conducting solutions when dissolved in liquid sulfur dioxide, a polar non-nucleophilic solvent. Trityl chloride also reacted with Lewis acids, such as aluminum chloride, to give colored salt-like solids. 

Advantage can be taken of the ionizing and dissociating effects produced by a solvent to activate inert molecules and initiate a polymerization. For instance, triphenylmethyl chloride in pure sulfuric acid solution undergoes an instantaneous ionization and produces a triphenylmethylium cation with a characteristic red color ... 

Methylsulfinyl carbanion (dimsyl ion) is prepared from 0.10 mole of sodium hydride in 50 ml of dimethyl sulfoxide under a nitrogen atmosphere as described in Chapter 10, Section III. The solution is diluted by the addition of 50 ml of dry THF and a small amount (1-10 mg) of triphenylmethane is added to act as an indicator. (The red color produced by triphenylmethyl carbanion is discharged when the dimsylsodium is consumed.) Acetylene (purified as described in Chapter 14, Section I) is introduced into the system with stirring through a gas inlet tube until the formation of sodium acetylide is complete, as indicated by disappearance of the red color. The gas inlet tube is replaced by a dropping funnel and a solution of 0.10 mole of the substrate in 20 ml of dry THF is added with stirring at room temperature over a period of about 1 hour. In the case of ethynylation of carbonyl compounds (given below), the solution is then cautiously treated with 6 g (0.11 mole) of ammonium chloride. The reaction mixture is then diluted with 500 ml of water, and the aqueous solution is extracted three times with 150-ml portions of ether. The ether solution is dried (sodium sulfate), the ether is removed (rotary evaporator), and the residue is fractionally distilled under reduced pressure to yield the ethynyl alcohol. 

In an attempt to demonstrate the existence of pentavalent nitrogen, Schlenk and Holtz studied the reaction of triphenylmethyl sodium with tetramethylammonium chloride (52). The highly colored material was strongly conducting in polar solvents and could be identified as a salt, the stability of which is due to the resonance stabilization of the triphenyl-methide anion. In the absence of such stabilizing substituent effects (53), as with n-butyl or another alkyllithium reagent, a metalation of the tetramethylammonium cation occurs, which leads to type I products (18) ... 

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