Formates, triphenylmethyl

Although styrene polymerized by ionic mechanism is not utilized commercially, much research was devoted to both cationic and anionic polymerizations. An investigation of cationic polymerization of styrene with an A1(C2H5)2C1/RC1 (R = alkyl or aryl) catalyst/cocatalyst system was reported by Kennedy.The efficiency (polymerization initiation) is determined by the relative stability and/or concentration of the initiating carbocations that are provided by the cocatalyst RCl. A/-butyl, isopropyl, and j c-butyl chlorides exhibit low cocatalytic efficiencies because of a low tendency for ion formation. Triphenylmethyl chloride is also a poor cocatalyst, because the triphenylmethyl ion that forms is more stable than the propagating styryl ion. Initiation of styrene polymerizations by carbocations is now well established. 

Von Baeyer (Nobel Prize, 1905) should be credited for having recognized in 1902 the saltlike character of the compounds formed. He then suggested a correlation between the appearance of color and salt formation—the so-called halochromy. Gomberg (who had just shortly before discovered the related stable triphenylmethyl radical), as well as Walden, contributed to the evolving understanding of the structure of related cationic dyes such as malachite green. 

Photochromism Based on Dissociation Processes. Both heterolytic and homolytic dissociation processes can result in the generation of a photochromic system. An example of an heterolytic process is the reversible formation of triphenylmethyl cation, by photolysis of... 

Boron trifluoride etherate (in HOAc, 60-80°, 15 min, high yields) also catalyzes formation of 5-diphenylmethyl and 5-triphenylmethyl thioethers from aralkyl alcohols. 

NO2C6H4SCI, AcOH (results in disulfide formation), followed by NaBH4 or HS(CH2)20H or dithioerythritol, quant." 5-Triphenylmethyl, 5-4,4 -di-methoxydiphenylmethyl, and 5-acetamidomethyl groups are also removed by this method. 

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. 

Carbon-centered organic radicals are highly reactive trivalent species with only one nonbonding electron. While most known radicals have their unpaired electron in a pure p- or a delocalized Ji-orbital, there are also examples of radicals centered in s/t" hybrid o-orbitals, such as the well known phenyl and cyclopropyl radicals. The first radical reported in the literature is credited to Gomberg s landmark paper in 1900 when he postulated the formation of triphenylmethyl radical 36, also known as tri-fyj 99,100 jj-jjyj j-adical is an example of a persistent radical that exists in equilibrium... 

Here the radical 1 acts as a strong terminator to prevent the formation of oligomers and polymers. On the other hand, it is expected that the substituted diphenylmethyl radicals which are less stable than 1 serve as both initiators and primary radical terminators. In fact, it was reported [84] that the apparent polymerization reactivities decreased in the following order diphenylmethyl, phenylmethyl, and triphenylmethyl radicals, which were derived from the initiator systems consisting of arylmethyl halides and silver. 

Sodium amalgam rather than sodium is used in the preparation of triphenylmethyl from the halide the mercury prevents the formation of sodium triphenylmethyl and of Chichibabin s hydrocarbon. 

The type of reactivity shown by the formation of Chichibabin s hydrocarbon extends to the activation of substituents other than hydrogen as well. For example, molecular silver will not usually remove fluorine from organic compounds, not even from triphenylmethyl fluoride. Yet the radical parafluorophenyldiphenylmethyl reacts with molecular silver to give silver fluoride.88... 

The reduction of hydroxylamine by titanous salts in water produces the free amino radical, a reaction analogous to the formation of triphenylmethyl from the carbinol and a reducing agent.138 The amino radical will attack benzene to give diaminocyclohexadiene and di-(aminocyclohexadienyl) it converts cyclohexene into cyclohexyl-amine.139... 

A bulky methacrylate, triphenylmethyl methacrylate (TrMA), is a unique monomer which gives an almost 100% isotactic polymer in anionic polymerization with n-butyllithium both in nonpolar and polar solvents. Moreover, even free-radical polymerization affords a highly isotactic polymer from this monomer.23 The isotactic specificity of TrMA polymerization is ascribed to the helical formation of the main chain. When TrMA is polymerized in toluene at —78°C... 

A simple example of such abstraction of proton is the formation of triphenylmethyl carbanion by NaNH2 in presence of liquid ammonia. 

The interpretation of reactions catalysed by metal halides was complicated and confused further by the formation of 7t-complexes between these catalysts and olefins, and the unfortunate fact that many of these complexes formed from aromatic olefins have a colour which to the unaided eye is indistinguishable from that of the triphenylmethyl and related cations. There is no evidence that these complexes are catalytic, and quite a lot that they are not. 

Schmidlin s experiment here described shows very clearly the equilibrium between hexaphenylethane and triphenylmethyl. The disappearance of the colour on shaking the substance with air indicates that the yellow radicle, present in equilibrium, is removed as (colourless) peroxide. The re-establishment of the equilibrium by renewed dissociation of (colourless) hexaphenylethane proceeds so slowly that the formation of the yellow radicle in the decolorised solution can be observed without difficulty. 

Romanian scientists compared one-electron transfer reactions from triphenylmethyl or 2-methyl benzoyl chloride to nitrobenzene in thermal (210°C) conditions and on ultrasonic stimulation at 50°C (lancu et al. 1992, Vinatoru et al. 1994, Chivu et al. 2006). In the first step, the chloride cation-radical and the nitrobenzene anion-radicals are formed. In the thermal and acoustic variants, the reactions lead to the same set of products with one important exception The thermal reaction results in the formation of HCl, whereas ultrasonic stimulation results in CI2 evolution. At present, it is difficult to elucidate the mechanisms behind these two reactions. As an important conclusion, the sonochemical process goes through the inner-sphere electron transfer. The outer-sphere electron transfer mechanism is operative in the thermally induced process. 

To obtain complete conversion of ketones to enolates, it is necessary to use aprotic solvents so that solvent deprotonation does not compete with enolate formation. Stronger bases, such as amide anion ( NH2), the conjugate base of DMSO (sometimes referred to as the dimsyl anion),2 and triphenylmethyl anion, are capable of effecting essentially complete conversion of a ketone to its enolate. Lithium diisopropylamide (LDA), which is generated by addition of w-butyllithium to diisopropylamine, is widely used as a strong... 

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