O- Xylene derivatives

The preparation of this class of dienes has received considerable attention during the last few years. Scheme 127 depicts the current approaches, such as 1,4-eliminations of o-xylene derivatives via reduction (544) - (M2), thermal dehydrohalogenation ( 5) (542), and fluoride-induced desilylation... 

With substituted cycloproparenes, the regioselectivity of the silver(l)-catalyzed and the uncatalyzed reaction was markedly different. Thus, 2-methylbenzocyclopropene (2) reacted with hydrochloric acid to give predominantly w-xylene 3a (47%), but reacted with silver(I) nitrate in the presence of ethanol or aniline to give preferentially o-xylene derivatives 4b,c. 3-Methyl-benzocyclopropene (5a) gave predominantly the w-xylene 7a with hydrochloric acid, but p-xylenes 6b,c in the silver(I)-catalyzed reaction. 3-Chlorobenzocyclopropene (5b) underwent addition of hydrochloric acid to give a mixture of 3- and 4-chlorobenzyl chlorides 6d and 7d, ° but silver(I)-catalyzed methanolysis gave only the 4-chlorobenzyl ether 7e. ... 

Halogen-substituted xylenes can also be ammoxidized 3,4,5,6,-tetrachloro-phthalodinitrile is formed from the corresponding o-xylene derivative (45 % yield) [80]. 

Chart I shows the structures of the bis(halomethyl) aromatics 18 -- 26 that we have used in our studies. These compounds were commercially available or were prepared by the reaction of N-bromosuccinimide with the corresponding o-xylene derivatives. 

One of the more fundamental methods for generation of the o-xylylene intermediate is 1,4-elimination from o-xylene derivatives. o-Xylene di-, tri-, or tetrabromides undergo intramolecular 1,4-dehalogenation by means of sodium iodide [102], lithium [103], zinc [104], copper [105], iron [106], and chromium [107]. Hoffman degradation of (o-methylbenzyl)trimethylammonium hydroxides [108], as well as the more recently developed fluoride ion-induced elimination from [o-[a-(trimethylsilyl)alkyl]benzyl]trimethylammonium halides [109], have also been effectively utilized in the generation of 2. 

The dinitrile precursors for p-tetra- and p-octatrifluoromethylphlhalocyanines [MPcP(CF3)4] and [MPci (CF3)g] (Scheme 24) were obtained [69] starting from the mono(bis)trifluoromethyl substituted acetylenes 88a,b and 2,3-dimetylbutadiene 89 which easily give the Diels-Alder products 90a,b. These adducts were converted quantitatively upon dehydrogenation with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) to o-xylene derivatives 91a,b. Their oxidation Cr03 in a mixture of acetic and sulfuric acids affords the phthalic acids 91a,b (yield ca. 80 %) which were converted to dinitriles 96a,b and diiminoimides 97a,b in a common way through intermediate anhydrides 93a,b, imides 94a,b, diamides 95a,b. 

The decomposition of the endoperoxide via the o-xylene derivative (48) in an intramolecular electron transfer mechanism would also give the substituents a decisive role in the excitation step itself - not only affecting the fluorescence efficiency of the phthalate dianion. A high fluorescence efficiency is of course a necessary, but not sufficient, requirement in luminol type chemiluminescence [9, 16],... 

Side-Chain Chlorinated Xylene Derivatives Only a few of the nine side-chaia chlotinated derivatives of each of the xylenes are available from direct chlorination. All three of the monochlotinated compounds, a-chloro-o-xylene (l-(chloromethyl)-2-meth5lbenzene [552-45-4] a-chloro-y -xylene (1-(ch1oromethy1)-3-methylhenzene [620-19-9] a-chloro-/)-xylene (1-(ch1oromethy1)-4-methylhenzene [104-82-5]) are obtained ia high yield from partial chlorination of the xyleaes. 1,3-Bis(ch1oromethy1)henzene [626-16-4] can be isolated ia moderate yield from chlorination mixtures (78,79). 

Besides the technical method starting from naphthalene, phthalic acid and its substituted derivatives can be prepared by oxidation of o-xylene to phthalic acid with potassium permanganate. This compound can be subsequently transformed via an anhydride, imide, and amide to a derivative of phthalonitrile, which is the more convenient starting material for several coordination compounds. The synthesis of the ferf-butyl-substituted dicarbonitrile, which is a very common starting material for highly soluble phthalocyanines, is shown below.97,105... 

Blackley548 measured the rates of deuteration of biphenylene, fluorene, tri-phenylene, and phenanthrene relative to o-xylene as 6.15 5.85 1.08 1.32, which is in very good agreement with the values of 8.80 7.00 - 1.14 which may be deduced from the detritiation data in Table 159, obtained using anhydrous trifluoroacetic acid. Aqueous trifluoroacetic acid (with the addition in some cases of benzene to assist solubility) was used by Rice550, who found that triptycene was 0.1 times as reactive per aromatic ring as o-xylene (cf. 0.13 derivable from Table 159) whereas the compound (XXXI) was 0.9 times as reactive as o-xylene. An exactly comparable measure is not available from Table 158, but dihydroanthracene (XXXII), which is similar, was 0.51 times as reactive as o-xylene and... 

In order to obtain compounds with Ti-O-P and Zr-O-P units, the hexaethoxy-derivative, NsPaCOEOg, was treated with titanium and zirconium tetrachlorides. In each case, hygroscopic solids of the type NaPaCOEOiOaMCU (M = Ti or Zr) and ethyl chloride were obtained. The degree of polymerization of these solids was 1.6—1.8, and on the basis of their i.r. and n.m.r. spectra, two alternative structures, (46) and (47), were proposed. In an alternative route to the same type of compound, N3P3CI6 was treated with tetra-n-butoxytitanium in o-xylene. Butyl chloride was liberated and a solid was obtained which has been assigned the structure (48). Its thermal decomposition was studied by differential thermal analysis. 

An experimental probe for the presence of radical intermediates resulting from thermally induced homolytic cleavage of the N-0 bond was derived by incorporating an alkene into a model substrate to act as a potential intramolecular radical trap (Scheme 6.25) [11]. In a control experimental, thermal reaction of 73 gave the desired product 74 in 66% isolated yield. On the other hand, thermal rearrangement of the unsaturated compound 75 under our typical conditions gave the desired hydroxypyrimidinone 76 in only 38% isolated yield. When the vinyl ami-doxime mixture 75Z/E was heated in o-xylene at 125 °C in the presence of a... 

Some examples of the lateral cyclization of suitable O-allyl and O-propargyl derivatives were discussed in CHEC-11(1996) <1996CHEC-II(8)747>. Thermal reaction of silyl diazoacetate 303 in xylene provides unspecific decomposition and a minor amount (about 2%) of a colorless solid can be precipitated with ether. The X-ray diffraction analysis identified the structure 305, which is a product of the lateral criss-cross cycloaddition of primarily formed azine 304 (Scheme 43) <2000T4139>. 

Although the mass of the fluorinated benzocyclobutene analogue is significantly higher than that of the hydrocarbon it should be noted that the incorporation of fluorine often enhances the volatility of derivatives beyond the expected levels, e.g., tetrafluorobenzocyclobutene with a mass of 176 boils only 10° higher than o-xylene with a mass of 106 (153°C vs. 143°C). 

Recently195, the hydrogen bond basicity scale (p.K hb as logarithm of the formation constant of 4-fluorophenol/base complexes in carbon tetrachloride, equilibrium 21) has been measured for several nitro derivatives (nitromethane, nitrobenzene, IV-nitrocamphorimine, 2-nitropropane, 4-nitro-o-xylene, 4-nitroanisole, lV,./V-diethyl-4-nitroaniline, l-dimethylamino-2-nitroethylene, l-piperidino-2-nitroethylene) ... 

Fig. 18. Comparison of ciajtrans ratios obtained from o-xylene and its tetrahydro derivatives 1,2- and 2,3-dimethyIcycIohexene as a function of hydrogen pressure PtOj (97).

More recently Hartog and Zwietering (103) used a bromometric technique to measure the small concentrations of olefins formed in the hydrogenation of aromatic hydrocarbons on several catalysts in the liquid phase. The maximum concentration of olefin is a function of both the catalyst and the substrate for example, at 25° o-xylene yields 0.04, 1.4, and 3.4 mole % of 1,2-dimethylcyclohexene on Raney nickel, 5% rhodium on carbon, and 5% ruthenium on carbon, respectively, and benzene yields 0.2 mole % of cyclohexene on ruthenium black. Although the cyclohexene derivatives could not be detected by this method in reactions catalyzed by platinum or palladium, a sensitive gas chromatographic technique permitted Siegel et al. (104) to observe 1,4-dimethyl-cyclohexene (0.002 mole %) from p-xylene and the same concentrations of 1,3- and 2,4-dimethylcyclohexene from wi-xylene in reductions catalyzed by reduced platinum oxide. 

Phthalazine and its homologs and derivatives are easily hydrogenolyzed. Electroreduction in alkaline medium gave 1,2-dihydrophthalazines [495], while in acidic media [495] and on catalytic hydrogenation [496], the ring was cleaved to yield o-xylene-a,a -diamine. 

In 1983, Sasaki et al. obtained rough first approximations of the mid-infrared spectra of o-xylene, p-xylene and m-xylene from multi-component mixtures using entropy minimization [83-85] However, in order to do so, an a priori estimate of the number S of observable species present was again needed. The basic idea behind the approach was (i) the determination of the basis functions/eigenvectors V,xv associated with the data (three solutions were prepared) and (ii) the transformation of basis vectors into pure component spectral estimates by determining the elements of a transformation matrix TsXs- The simplex optimization method was used to optimize the nine elements of Tixi to achieve entropy minimization, and the normalized second derivative of the spectra was used as a measure of the probability distribution. 

There are only two top 50 chemicals, terephthalic acid and dimethyl terephthalate, derived from /7-xylene and none from o- or m-xylene. But phthalic anhydride is made in large amounts from o-xylene. 

Cyclic amidoxime 327 was reacted with DMAD (dimethyl acetylenedicarboxylate) in CH3CN and then in refluxing o-xylene to give after addition of BZ2O a bicyclic pyrimidine derivative 328 in 31% yield (equation 142) °°. The adducts 330, prepared in situ... 

The engine characteristics of aromatic hydrocarbons seem strongly dependent upon the nature of the side chain. The alignment of the knock resistance of the polymethyl-benzenes with structure corresponds quite closely with that found to be characteristic of the physical constants. The vicinal derivatives o-xylene, hemimellitine, and prehnitene... 

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