Diphenylmethane and Triphenylmethane

The oxidations of toluene, diphenylmethane and triphenylmethane are second order , relative rates at 22 °C being... 

The transition state does not involve a large degree of charge separation and hence the relative rates of oxidation of toluene, diphenylmethane and triphenylmethane may be explained in terms of an ionic mechanism. 

Such a pre-equilibrium closely parallels that suggested by Dewar et for the manganic acetate oxidations of several aromatic ethers and amines (p. 405). Other features of the reaction are a p value of —0.7 and identical activation energies of 25.3 kcal.mole for oxidation of toluene, ethylbenzene, cumene, diphenylmethane and triphenylmethane. 

Use of benzotriazole in the preparation of diphenylmethanes and triphenylmethanes has been reviewed." Benzotriazole is condensed with an aldehyde and then allowed to react with naphthols to form a diphenyl-methane benzotriazole derivative such as 69 (Scheme 9). The benzotriazole moiety in 69 is displaced by a Grignard reagent to give triphenylmethanes.79 100 This method allows for the preparation of triarylmethanes which contain three different aromatic rings. Compounds 70-72 are prepared by this method. 

Diphenylmethane and triphenylmethane dyes are monomethine dyes with two or three terminal aryl groups, of which at least one, but preferably two or three, are substituted by a donor group para to the methine carbon atom. The most important donor is the amino group. Important dyes belonging to this class include the well-known malachite green (12) [9] and crystal violet (13) [10], which are some of the oldest synthetic cationic dyes ... 

Acetoxylation of hydrocarbons. I n a paper of 1923Dimroth reported preliminary observations on the oxidation of aromatic hydrocarbons and olefins with lead tetraacetate. Toluene, he found, affords benzyl acetate in very low yield oxidation of diphenylmethane and triphenylmethane proceeded more readily but offered nothing of preparative promise. Dimroth observed also that anethole reacts to give in small yield a product of addition of two acetoxyl groups to the olefin linkage. 

Early application of these methods gave estimates of the pAT of toluene of about 45 and propene of about 48. Methane was estimated to have a pAT in the range of 52-62. ° More recent electrochemical measurements in DMF provided the results in Table 3.37. These measurements put the pAT of methane at about 48, with benzylic and allylic stabilization leading to values of 39 and 38 for propene and toluene, respectively. The electrochemical values that overlap with the pATo so scale for compounds such as diphenylmethane and triphenylmethane are in reasonable agreement. 

The implication here is that diphenylmethane and triphenylmethane are not able, because of their nonplanarity, to form a sodium addition compound. Neither are they acidic enough to react directly with sodium in a displacement reaction at the moderate temperatures employed. They are, however, acidic enough to react with the disproportionated form of the sodium addition compound of naphthalene, which is a much stronger base than sodium itself. Fluorene, because of its planarity, is able to form the addition compound, which then is able to act as a base toward two other fluorene molecules. 

One way to assess the stabilization of an anion is to regard it as the conjugate base of an acid and to compare the acid s pAT with other substances. The weaker the conjugate base, the more strongly held is the unshared electron pair. For the case of benzyl anion, we compare toluene with other hydrocarbons—methane, diphenylmethane, and triphenylmethane. 

For uniformity with the stmctures given in the Colourindex the ammonium radical (9) is used for the amino-substituted xanthenes and the keto form for the hydroxy derivatives. The xanthene dyes may be classified into two main groups diphenylmethane derivatives, called pyronines, and triphenylmethane derivatives (eg, (4)), which are mainly phthaleins made from phthaUc anhydride condensations. A third much smaller group of rosamines (9-phenylxanthenes) is prepared from substituted ben2aldehydes. The phthaleins may be further subdivided into the following fluoresceins (hydroxy-substituted) rhodamines (amino-substituted), eg, (6) and mixed hydroxy/amino-substituted. 

Diphenylmethane is significantly more acidic than benzene, and triphenylmethane is more acidic than either. Identify the most acidic proton in each compound, and suggest a reason for the trend in acidity. 

If the alkyl halide contains more than one, equally reactive C-halogen centers, these will generally react each with one aromatic substrate molecule. For example dichloromethane reacts with benzene to give diphenylmethane, and chloroform will give triphenylmethane. The reaction of tetrachloromethane with benzene however stops with the formation of triphenyl chloromethane 7 (trityl chloride), because further reaction is sterically hindered ... 

The effect of solvent upon k2 has been reported , and it was concluded that the activated complex is not sufficiently polar to be called ionic . The oxidations of toluene and triphenylmethane exhibit primary kinetic deuterium isotope effects of 2.4 and ca. 4 respectively. No isotopic mixing occurred during formation of the Etard complex from a mixture of normal and deuterated o-nitrotoluene . The chromyl chloride oxidation of a series of substituted diphenylmethanes revealed that electron-withdrawing substituents slow reaction while electronreleasing groups have the opposite effect, the values ofp andp being —2.28 + 0.08 and —2.20 + 0.07 respectively . ... 

The value given is that found in cyclohexylamine. F. G. Bordwell and W. S. Matthews, J. Amer. Chem. Soc., 96, 1214 (1974), report 29 (corrected to the present scale) in dimethylsulfoxide. c In liquid NH3 corrected to triphenylmethane = 31. d Reported to be between diphenylmethane and toluene. e Estimated by B B from electrochemical data. 

In a subsequent study, Shudo and co-workers244 showed that benzaldehydes with electron-withdrawing groups (N02, CF3) react with 2 equivalents of benzene in the presence of triflic acid to give substituted triphenylmethanes in good yields [Eq. (5.90)]. They also observed that pura-fluorobenzaldehyde and biphenyl-4-carboxaldehyde yield diphenylmethane and triphenylmethanol under similar conditions, and the same products were also isolated in the reaction of triphenylmethane (Scheme 5.29). 

All the protons in benzene are equivalent. In diphenylmethane and in triphenylmethane, protons are attached either to the. v/r-hybridized carbons of the ring or to the v/T-hybridized carbon between the rings. The large difference in acidity between diphenylmethane and benzene suggests that it is not a ring proton that is lost on ionization in diphenylmethane but rather a proton from the methylene group. 

Activation of organolithium compounds [1, 926, before references]. Potassium f-butoxide enhances the reactivity of organolithium compounds. For example, benzene is not metalated by n-butyllithium at room temperature, but if potassium /-butoxide is present phenyllithium is formed in 77% yield as shown by the reaction with carbon dioxide to give benzoic acid. Triphenylmethane. diphenylmethane, and toluene are also rapidly metalated.71... 

Isocyanates are used as a cross-linker in EPI adhesive systems. Theoretically, any isocyanate with two or more NCO groups would be suitable. In practice two main parameters are important for the choice of isocyanate The volatility and reactivity of the isocyanate [1, 12]. The use of isocyanates with low volatility, low vapor pressure, is preferred to minimize the health risks concerned with the use and handling of the isocyanate. Isocyanates that are typically used, or have been used, as cross-linkers in EPI adhesive systems are based on the following isocyanate monomers toluene diisocyanate (TDl), diphenylmethane diisocyanate (MDl), hexamethylene diisocyanate (HMDI), 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI) and triphenylmethane-triisocyanate (TTl)... 

Another case where resonance influences carbon acidities is the comparison of toluene to diphenylmethane and lastly triphenylmethane (pK s = 41.2,33.0, and 31.5, respectively). The large shift between toluene and diphenylmethane is due to additional resonance stabilization of the conjugate base. However, the third additional phenyl ring has little effect. Several factors are involved to account for this small change. One is that the phenyl rings cannot all be planar with the anionic carbon, which is required for full resonance stabilization (examine the trityl radical discussed in Chapter 2), and instead a propeller twist develops in the anion. This is an example of a steric inhibition of resonance. A second factor is called a resonance saturation effect. Once the charge on the conjugate base is stabilized via resonance, the additional resonance is not as effective at stabilization. 

Diphenylmethane has been prepared with aluminum chloride as a catalyst from methylene chloride and benzene, from chloroform and benzene as a by-product in the preparation of triphenylmethane, and from benzyl chloride and benzene. It has been prepared by the reduction of benzophenone with hydriodic acid and phosphorus, or with sodium and alcohol. It has also been made by heating a solution of benzyl chloride in benzene with zinc dust, or with zinc chloride. The above method is only a slight modification of the original method of Hirst and Cohen. ... 

This tri-isocyanate is reported to impart good light stability and weather resistanee in polyurethane eoatings and is probably the most widely used aliphatic isocyanate. A number of other aliphatic polyisocyanates have been introduced recently in attempts to produce polyurethanes with improved light stability. Amine derivatives of diphenylmethane are made by reacting aniline of toluidines with formaldehyde. These can lead to a mixture of di-isoeyanates, the diphenylmethane di-isocyanates (MDIs) of commerce. Triphenylmethane-pp p"-tny tri-isocyanate is produced from leucorosaniline. 

The influence of different additives on the apparent pKa values of diphenylmethane, 4-methyl-pyridine and the deprotonation rate of triphenylmethane was investigated 3 TM EDA caused the highest enhancement. 

The apparatus required is similar to that described for Diphenylmethane (Section IV,4). Place a mixture of 200 g. (230 ml.) of dry benzene and 40 g. (26 ml.) of dry chloroform (1) in the flask, and add 35 g. of anhydrous aluminium chloride in portions of about 6 g. at intervals of 5 minutes with constant shaking. The reaction sets in upon the addition of the aluminium chloride and the liquid boils with the evolution of hydrogen chloride. Complete the reaction by refluxing for 30 minutes on a water bath. When cold, pour the contents of the flask very cautiously on to 250 g. of crushed ice and 10 ml. of concentrated hydrochloric acid. Separate the upper benzene layer, dry it with anhydrous calcium chloride or magnesium sulphate, and remove the benzene in a 100 ml. Claisen flask (see Fig. II, 13, 4) at atmospheric pressure. Distil the remaining oil imder reduced pressure use the apparatus shown in Fig. II, 19, 1, and collect the fraction b.p. 190-215°/10 mm. separately. This is crude triphenylmethane and solidifles on cooling. Recrystallise it from about four times its weight of ethyl alcohol (2) the triphenylmethane separates in needles and melts at 92°. The yield is 30 g. 

Triphenylmethane leuco dyes are far more important than the diphenylmethanes in terms of practical value. Use of triphenylmethane dyes for traditional applications of dyes is limited to dyeing wool, silk, leather, and polyacrylonitrile fibers. The largest portion of the annual production of this class of leuco dyes is consumed in the manufacturing of various copying papers. 

Buncel and Menon (1977) have studied reactions of potassium hydride solubilized in tetrahydrofuran by 18-crown-6 [3]. Very weak carbon acids such as triphenylmethane [ 151J (pAa = 31.5), diphenylmethane [152] (pAa = 33.1), and di-/j-tolylmethane [153] (pAa = 35.1) were completely metallated. After... 

The strongly basic properties of potassium hydroxide are apparent from the work of Dietrich and Lehn (1973) who reported that the liquid-solid system KOH/THF/[2.2.2]-cryptand was capable of generating the anions of weak carbon acids such as triphenylmethane [142], diphenylmethane [143], and fluorene. The same anions could be generated using NaNH2 instead of KOH. 

Conversion of tight ion pairs into crown ether-separated ion pairs leads in many cases to increased basicity. For example, Dietrich and Lehn (1973) have shown that a homogeneous solution of sodium t-amyloxide in benzene is unable to deprotonate triphenylmethane, whereas the reaction occurs rapidly in the presence of [2.2.2]-cryptand [37]. In THF or diethyl ether, alkali metal enolates do not react with triphenyl- or diphenylmethane (Pierre et al.,... 

---