Diphenylmethane structures

The most likely lignin condensation reaction during the kraft cook is the formation of diphenylmethane structures 29, 30). These structures are also proposed 14) as being already present in native lignin. Phenolic diphenylmethanes do not exhibit any color, but they can easily be dehydrogenated to quinonemethides 20, 23) or quinonemethide radicals (P). 

Funaoka M, Abe I (1982b) The reaction of lignin under the presence of phenol and boron trifluoride VI The behavior of lignin units unable to form the diphenylmethane structure Mokuzai Gakkaishi 28 529-534... 

D. S., Alkaline oxidative degradation of diphenylmethane structures Activation energy and computational analysis of the reaction mechanism, Can. J.Chem. 79, 1394-1401 (2001). 

Departure of the molecular structure from the basic diphenylmethane structure so far considered produces interesting effects on the aggregation characteristics. All of the drugs included in Table 4.4 retain sufficient flexibility to form micellar aggregates (see Fig. 4.7 for structures). The effect on micellar properties of modifications of the chemical structure of the hydrophobic groups... 

The excited triplet states of quinones can be fairly readily populated by irradiation and nuclear polarization observed (Cocivera, 1968). Hydrogen atom abstraction leads to the relatively stable semiquinone radicals and, in alkaline media, radical anions. Recombination of radical pairs formed in this way can give rise to CIDNP signals, as found on irradiation of phenanthraquinone (20) in the presence of donors such as fluorene, xanthene and diphenylmethane (Maruyama et al., 1971a, c Shindo et al., 1971 see also Maruyama et al., 1972). The adducts are believed to have the 1,2-structure (21) with the methine proton appearing in absorption in the polarized spectrum, as expected for a triplet precursor. Consistently, thermal decomposition of 21 as shown in equation (61) leads to polarization of the reactant but now in emission (Maruyama... 

The practical route for oxidizing leuco diphenylmethanes 15 demands inital conversion to an imine salt 16. The imine salt is obtained by heating a mixture of diphenylmethane, sulfur, ammonium chloride, and sodium chloride at 175°C in a current of ammonia or by heating a mixture of diphenylmethane, urea, sulfamic acid, sulfur, and ammonia at 175°C (Scheme 3). Dyes 16 can be represented as the quinonoid resonance structure 17. Dyes of this class, known as auramines, are all yellow, with the only commercial representative being auramine O 16a. Due to its poor lightfastness and instability to hot acids and bases, its use has been restricted to dyeing and printing cotton, paper, silk, leather, and jute. 

A clay mineral and/or its acid-treated products109,110 are used as color developers. A diphenylmethane derivative of structure 82 has been micro-... 

Estimate the critical constants for diphenylmethane using Lydersen s method normal boiling point 537.5 K, molecular mass 168.2, structural formula ... 

Based on the above studies, the identity of the diisocyanate component in BPUla was deduced by the presence of fragments at ra/z 250 [methylene-bis(4)phenyl-isocyanate] (MDI), 224 (4-amino-4 -iso-cyanato-diphenylmethane), and 198(diamino-diphenylmethane).27 The presence of the diamine, as the chain extender was evident from the presence of the fragments m/z 324, assignable to 1,l -bisCB-iso-jg cyanatoethyl)ferrocene, and 298, assignable to the structure 10. 

It can be seen that primary and secondary R02 radicals disproportionate with the participation of the a-C—H bond. This explains why the substitution of D in the a-position for H retards the recombination of R02 [/tn//tD =1.9 for ethylbenzene, h/ d = 2.1 for styrene, and h/ d=1-37 for diphenylmethane [179]). Because of this, R02 radicals of unsaturated compounds with a double bond in the a-position to the peroxyl free valence disproportionate more rapidly than structurally analogous aliphatic peroxyl radicals (at 300 K, 2kt = 2x 107 and 3.8 x 106 L mol-1 s-1 for R02 radicals of cyclohexene and cyclohexane, respectively [180]). Among the products of secondary peroxyl radicals disproportionation, carbonyl compound and alcohol were found in a ratio of 1 1 at room temperature (in experiments with ethylbenzene [181], tetralin [103], and cyclohexane [182-184],... 

Although treated as separate classes in the Colour Index, these structural types are closely related and the few diphenylmethane dyes such as auramine (1.28 Cl Basic Yellow 2) are now of little practical interest. Commercial usage of the triarylmethane dyes and pigments has also declined considerably in favour of the major chemical classes. They were formerly noteworthy contributors to the acid, basic, mordant and solvent ranges, primarily in the violet, blue and green sectors. Numerous structural examples are recorded in the Colour Index. The terminal groupings can be amine/quinonimine, as in auramine and crystal violet (1.29 Cl Basic Violet 3), hydroxy/quinone, or both. The aryl nuclei are not always benzenoid (section 6.5). 

In comparison, both the free ligand and the dinuclear Cu(I) cryptate of an analogous macrobicyclic structure possessing a diphenylmethane group as a central unit display only two resonances for the CH2CH2 fragment, as is the case here only for the complexes 91 and 92. This points to the special conformation features of the free macrobicycles 89 and 90. 

Cyclophanes consist of a class of artificial hosts featured with well-defined hydrophobic cavities constructed by aromatic rings incorporated in their macrocy-clic structures, and also with high design versatility because they are totally synthetic.The first direct evidence of the formation of an inclusion complex with an organic guest was obtained for tetraazacyclophane 62, the cavity of which is constructed with diphenylmethane units bridged by tetramethylene chains. 

For uniformity with the structures given in the Colourlndex 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 triphenyknethane derivatives (eg, (4)), which are mainly phthaleins made from phthalic anhydride condensations. A third much smaller group of rosamines (9-phenylxanthenes) is prepared from substituted benzaldehydes. The phthaleins may be further subdivided into the following fluoresceins (hydroxy-substituted) rhodamines (amino-substituted), eg, (6) and mixed hydroxy/amino-substituted. 

In the course of the previous work we have prepared compounds for comparative purposes, one of which has been reported by Gierer. He and his co-workers 15) synthesized an unsymmetrical diphenylmethane by acid-catalyzed condensation of syringyl alcohol and 2-methoxy-4-methyl-phenol and assumed substitution in the 6-position of the guaiacol nucleus. We repeated this synthesis and prepared an isomeric material by base-catalyzed condensation of the same starting materials. Our interpretation of the modes of synthesis and the NMR spectra of the two compounds is that Gierer s compound most probably is 3, 4-dihydroxy-6 -methyl-3,4, 5-trimethoxydiphenylmethane and that the compound prepared under basic conditions is 2, 4-dihydroxy-5 -methyl-3,3, 5-trimethoxydiphenylmethane, the structure claimed by Gierer. We do not, however, have unequivocal structural evidence and our data are summarized under Experimental. 

Pearl and Dickey (20) isolated 3,3 -dimethoxy-4,4 -dihydroxybenzo-phenone, an analog of the diphenylmethanes apparently present in our product mixture. They suggest that the ketone is a rearrangement product of vanillil. In our system the corresponding diphenylmethanes could also be produced by a coupling reaction of phenolic methylols or quinonemethides, and at present they cannot be considered proved structural elements native to lignin. 

Reactivities of isocyanates depend on their structure. Table 2.6 gives the main isocyanates used for polymer network synthesis. Conjugation with aromatic nuclei makes ArNCO particularly reactive. The reactivity of diisocyanates is well documented in the literature. For symmetric diisocyanates such as diphenylmethane 4,4 -diisocyanate (MDI) or para-phenylene 4,4 -diisocyanate (PPDI), both NCO groups have initially the same reactivity. But as the NCO group itself exhibits an activating effect on isocyanate reactivity, the fact that one NCO group has reacted introduces a substitution effect that usually decreases the reactivity of the second NCO group. 

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