Triphenylmethyl reactions

The selectivity relationship merely expresses the proportionality between intermolecular and intramolecular selectivities in electrophilic substitution, and it is not surprising that these quantities should be related. There are examples of related reactions in which connections between selectivity and reactivity have been demonstrated. For example, the ratio of the rates of reaction with the azide anion and water of the triphenylmethyl, diphenylmethyl and tert-butyl carbonium ions were 2-8x10 , 2-4x10 and 3-9 respectively the selectivities of the ions decrease as the reactivities increase. The existence, under very restricted and closely related conditions, of a relationship between reactivity and selectivity in the reactions mentioned above, does not permit the assumption that a similar relationship holds over the wide range of different electrophilic aromatic substitutions. In these substitution reactions a difficulty arises in defining the concept of reactivity it is not sufficient to assume that the reactivity of an electrophile is related... 

Cesium forms simple alkyl and aryl compounds that are similar to those of the other alkah metals (6). They are colorless, sohd, amorphous, nonvolatile, and insoluble, except by decomposition, in most solvents except diethylzinc. As a result of exceptional reactivity, cesium aryls should be effective in alkylations wherever other alkaline alkyls or Grignard reagents have failed (see Grignard reactions). Cesium reacts with hydrocarbons in which the activity of a C—H link is increased by attachment to the carbon atom of doubly linked or aromatic radicals. A brown, sohd addition product is formed when cesium reacts with ethylene, and a very reactive dark red powder, triphenylmethylcesium [76-83-5] (C H )2CCs, is formed by the reaction of cesium amalgam and a solution of triphenylmethyl chloride in anhydrous ether. 

Triphenylmethyl thioethers have been formed by reaction of the thiol with tri-phenylmethyl alcohol/anhydrous CF3COOH (85-90% yield) or with triphenyl-methyl chloride (75% yield). 

If (A i[X ]/A 2[Y ]) is not much smaller than unity, then as the substitution reaction proceeds, the increase in [X ] will increase the denominator of Eq. (8-65), slowing the reaction and causing deviation from simple first-order kinetics. This mass-law or common-ion effect is characteristic of an S l process, although, as already seen, it is not a necessary condition. The common-ion effect (also called external return) occurs only with the common ion and must be distinguished from a general kinetic salt effect, which will operate with any ion. An example is provided by the hydrolysis of triphenylmethyl chloride (trityl chloride) the addition of 0.01 M NaCl decreased the rate by fourfold. The solvolysis rate of diphenylmethyl chloride in 80% aqueous acetone was decreased by LiCl but increased by LiBr. ° The 5 2 mechanism will also yield first-order kinetics in a solvolysis reaction, but it should not be susceptible to a common-ion rate inhibition. 

In the case of t-butyl substituted a,/3-unsaturated ketones, however, no reaction with ketones occurred in the presence of triphenylmethyl fluoroborate instead, a 1,2-methyl shift in the unsaturated ketone accompanied by cyclization afforded a crystalline dihydro-furylium salt. ... 

On treatment with a strong base such as sodium hydride or sodium amide, dimethyl sulfoxide yields a proton to form the methylsulfinyl carbanion (dimsyl ion), a strongly basic reagent. Reaction of dimsyl ion with triphenylalkylphosphonium halides provides a convenient route to ylides (see Chapter 11, Section III), and with triphenylmethane the reagent affords a high concentration of triphenylmethyl carbanion. Of immediate interest, however, is the nucleophilic reaction of dimsyl ion with aldehydes, ketones, and particularly esters (//). The reaction of dimsyl ion with nonenolizable ketones and... 

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. 

A further extension of the MIMIRC reaction is seen in the synthesis of enantiomerically pure cyclohexanones. A successful diastereoselective MIMIRC reaction with 2-(rer/-butyldimethylsi-lyloxy)-4-phenyl-l,3-butadiene and an optically pure (Z)-y-alkoxy-substituted enone was performed using catalytic amounts (5 mol%) of triphenylmethyl perchlorate at — 78 ,C 360,408 (for a further example see Section 1.5.2.4.4.1.). 

The combination of carbon-centered radicals usually involves head-to-head (a,a ) coupling. Exceptions to this general rule occur where the free spin can be delocalized into a n-system. The classic example involves the triphenylmethyl radical (13) which combines to give exclusively the a-para coupling product (26), Scheme I.8).27 This chemistry is also seen in cross reactions of 13 with other tertiary radicals.146... 

The efficiency of these inhibitors may depend on reaction conditions. For example the reaction of radicals with stable radicals (e.g. nitroxides) may be reversible at elevated temperatures (Section 7.5.3) triphenylmethyl may initiate polymerizations (Section 7.5.2). A further complication is that the products may be capable of undergoing further radical chemistry. In the case of DPPH (22) this is attributed to the fact that the product is an aromatic nitro-compound (Section 5.3.7). Certain adducts may undergo induced decomposition to form a stable radical which can then scavenge further. 

The kinetics of alkylation by triphenylmethyl compounds have been studied. Hart and Cassis353 found that the alkylation of phenol and o-cresol by triphenylmethyl chloride in o-dichlorobenzene gave non-linear kinetic plots which were, however, rendered linear by presaturation of the reaction mixture with hydrogen chloride, precise third-order kinetics, equation (182)... 

This method is a modification of the method originally published by Kursanov and Vol pin.6 Tropylium salts have also been prepared by bromination-dehydrobromination of tropili-dene,6 and by the hydride-exchange reaction between tropilidene and triphenylmethyl carbonium ion.7... 

Okamoto and his colleagues60) described the interesting polymerization of tri-phenylmethyl methacrylate. The bulkiness of this group affects the reactivity and the mode of placement of this monomer. The anionic polymerization yields a highly isotactic polymer, whether the reaction proceeds in toluene or in THF. In fact, even radical polymerization of this monomer yields polymers of relatively high isotacticity. Anionic polymerization of triphenylmethyl methacrylate initiated by optically active initiators e.g. PhN(CH2Ph)Li, or the sparteine-BuLi complex, produces an optically active polymer 60). Its optical activity is attributed to the chirality of the helix structure maintained in solution. 

CIDNP has also been reported in reactions of organomercurials. Emission is observed from the couphng product of p-methylbenzyl-mercuric bromide and triphenylmethyl bromide (Beletskaya et al., 1971), while thermolysis of organomercury derivatives of tin such as t-C4H9HgSn(CH3)3 gave mixtures of isobutene and isobutane (by disproportionation of uncorrelated pairs of t-butyl radicals) showing A/E polarization (Mitchell, 1972). 

In weaker acid systems, other reactions involving the triplet state supervene to the exclusion of dimerization. Photolysis of 85 in 3-3% sulfuric acid, 96-5% acetic acid, and 0-2% water gave as products tri-phenylmethane (93), 9-phenylfluorene (94), 6is-9-phenylfluorenyl peroxide (95) and benzophenone (96). When benzene was present, tetra-phenylmethane (97) was also formed in addition to the other products. When the triphenylmethyl cation is irradiated in 3-3% H2SO4, 80 1% HOAc, 16-4% toluene, and 0-2% H2O, the products observed were... 

The results obtained from the decomposition reaction of (triphenylmethyl)-methyldichlorosilane to (diphenylmethyl)methyldichlorosilane in benzene solvent in the presence of aluminum chloride are summarized in Table XV. 

A.s. shown in Table XV, the decomposition of (triphenylmethyl)methyldichloro-silane did not occur at room temperature, but occurred at the reflux temperature of benzene to give (diphenylmethyl)methyldichlorosilane in 10 and 20% yields after I and 2 h reaction periods. The results indicate that the decomposition occurs in the alkylation reaction conditions of benzene with (trichloromethyl)chlorosilanes a.s observed in the decomposition of tetraphcnylmethane to triphenylmethane. ... 

To confirm the production of benzene from the decomposition reaction of methyl(triphenylmethyl)dichlorosilane, the decomposition reaction of methyKdi-phenylmethyl)dichlorosilane in the presence of aluminum chloride was carried out in toluene solvent at 80 C. In this reaction, the exchange reaction between phenyl groups on the methyl group of (diphenylmethyl)(inethyl)dichlorosilane and toluene occurred to give [phenyl(tolyl)methylJ(methyl)dichlorosilane and (di-tolylmethyl)(methyl)dichlorosiIane (Scheme 1). " ... 

An interesting X-ray structure of the highly strained, sp hybridized vinyl cation 8 was recently reported by Muller et al. The synthesis of 8 was accomplished by the reaction of alkynylsilane 7 and triphenylmethyl (trityl) cation. 

---