Benzene 1,4-dimethylbenzene

Solid + Liquid Equilibria in Less Ideal Mixtures We should not be surprised to find that the near-ideal (solid + liquid) phase equilibria behavior shown in Figures 8.20 and 8.21 for (benzene + 1,4-dimethylbenzene) is unusual. Most systems show considerably larger deviations. For example, Figure 8.22 shows the phase diagram for. vin-C Hw +. The solid line is the fit of the... 

Figure 14.17a summarizes the effect of pressure on the melting temperature, while Figure 14.17(b) shows the effect of temperature on the melting pressure, for the (benzene +1,4-dimethylbenzene) system. The... 

It is unusual to find systems that follow the ideal solution prediction as well as does (benzene+ 1,4-dimethylbenzene). Significant deviations from ideal solution behavior are common. Solid-phase transitions, solid compound formation, and (liquid 4- liquid) equilibria often complicate the phase diagram. Solid solutions are also present in some systems, although limited solid phase solubility is not uncommon. Our intent is to look at more complicated examples. As we do so, we will see, once again, how useful the phase diagram is in summarizing a large amount of information. 

Aromatics - Benzene, Methylbenzene (Toluene) Dimethylbenzene (Xylenes) Naphthenes - Cyclopentane, Cyclohexane... 

The PMBs, when treated with electrophilic reagents, show much higher reaction rates than the five lower molecular weight homologues (benzene, toluene, (9-, m- and -xylene), because the benzene nucleus is highly activated by the attached methyl groups (Table 2). The PMBs have reaction rates for electrophilic substitution ranging from 7.6 times faster (sulfonylation of durene) to ca 607,000 times faster (nuclear chlorination of durene) than benzene. With rare exception, the PMBs react faster than toluene and the three isomeric dimethylbenzenes (xylenes). 

At 320 °C, cesium tetrafluorocobaltate converts benzotrifluoride to /n-fluo-robenzotrifluoride, 2f/-heptafluorotoluene, octafluorotoluene, pertluoro-l -meth-ylcyclohexene, and perfluoromethylcyclohexane [29] l,3-Bis(trifluoromethyl)-benzene is convened at 420 °C to 4,5,6-trifluoro-l,3-bis(trifluoroethyl)bcnzene, perfluoro-l,3-dimethylbenzene, and perfluoro-l,3-dimethylcyclohexane [29], p-Xylene gives at 350 °C l,4-bis(difluoromethyl)tetrafluorobenzene, 1-di-fluoromethyl-3-trifluoromethyltetrafluorobenzene, perfluoro-1,3-dimethyl-benzene, and perfluoro-1,3-dimethyloyclohexane... 

If several groups are attached to the benzene ring, their names as well as their relative positions should be indicated. For example, dimethylbenzene or xylene, CgH (CH,)2, has three geometric isomers, with prefixes ortho-, meta-, and para-, indicating the relative positions of the two methyl groups. 

Simple aromatic hydrocarbons come from two main sources coal and petroleum. Coal is an enormously complex mixture made up primarily of large arrays of benzene-like rings joined together. Thermal breakdown of coal occurs when it is heated to 1000 °C in the absence of air, and a mixture of volatile products called coal for boils off. Fractional distillation of coal tar yields benzene, toluene, xylene (dimethylbenzene), naphthalene, and a host of other aromatic compounds (Figure 15.1). 

Below the equilibrium lines, but above the eutectic temperature, a liquid and solid are in equilibrium. Under line ac, solid benzene, and liquid Li, whose composition is given by line ac, are present. Under line be, the phases present are solid 1,4-dimethylbenzene and liquid Li, whose composition is given by line be. Below point c, solid benzene and solid 1,4-dimethylbenzene are present. In the two phase regions, one degree of freedom is present. Thus, specifying T fixes the composition of the liquid, or specifying X2 fixes the temperature.cc Finally, at point c (the eutectic) three phases (solid benzene, solid 1,4-dimethylbenzene, and liquid with x2 = vi.e) are present. This is an invariant point, since no degrees of freedom are present. 

As the mixture freezes, 1,4-dimethylbenzene is removed from solution, the liquid mixture becomes richer in benzene, and the melting temperature falls along line be. For example, when the temperature given by point h is reached, solid 1,4-dimethylbenzene (point i) and a liquid solution with a composition given by point g are present. The lever rule gives the ratio of solid to liquid as... 

Benedict-Webb-Rubin equation 252. 256-7 benzene, vapor pressure 260-1 benzene + I, 4-dimethylbenzene mixture, phase equilbria 420-2, 424... 

Anthraquinone itself is traditionally available from the anthracene of coal tar by oxidation, often with chromic acid or nitric acid a more modern alternative method is that of air oxidation using vanadium(V) oxide as catalyst. Anthraquinone is also produced in the reaction of benzene with benzene-1,2-dicarboxylic anhydride (6.4 phthalic anhydride) using a Lewis acid catalyst, typically aluminium chloride. This Friedel-Crafts acylation gives o-benzoylbenzoic acid (6.5) which undergoes cyclodehydration when heated in concentrated sulphuric acid (Scheme 6.2). Phthalic anhydride is readily available from naphthalene or from 1,2-dimethylbenzene (o-xylene) by catalytic air oxidation. 

Synonyms AI3-17612 BRN 0636244 Caswell No. 907A CCRIS 721 4,6-Dimethylphenol 2,4-DMP EINECS 203-321-6 EPA pesticide chemical code 086804 1-Hydroxy-2,4-dimethyl-benzene 4-Hydroxy-l,3-dimethylbenzene NSC 3829 RCRA waste number UlOl UN 2261 1,3,4-Xylenol 2,4-Xylenol /n-Xylenol. 

Synonyms AI3-52255 BRN 1901563 CCRIS 910 Chromar 1,4-Dimethylbenzene p-Dlmethyl-benzene EINECS 203-396-5 p-Methyltoluene NSC 72419 Sclntlllar UN 1307 1,4-Xylene 4-Xylene p-Xylol. 

Xylene (dimethylbenzene) has been substituted for benzene in many solvent degreasing operations. Like toluene, the three xylenes do not possess the myelotoxic properties of benzene, nor have they been associated with leukemia. Xylene is a central nervous system depressant and a skin irritant. Less refined grades of xylene contain benzene. See Table 56-1 for the TLVs. 

When flushing a gasoline-contaminated soil in a laboratory column with clean water, Mackay et al. (1996) observed that after 5 pore volumes (i.e., after 5 times replacing the water in the column), the benzene concentration in the effluent decreased from initially 370 to about 75 iig-L, while the 1,2-dimethylbenzene concentration increased from 1200 to 1400 jug-L-1. Try to explain these findings. 

Aromatic hydrocarbons which have methyl side chains mainly behave like toluene and form aldehydes, while combustion is stimulated and selective oxidation of the nucleus is repressed. The oxidation of methyl-naphthalene, for example, exhibits a low selectivity with respect to phtha-lic anhydride formation, combustion and maleic acid formation being the dominating reactions. Durene is a special case because it resembles o-xy-lene. The oxidation of durene over a V—W—O catalyst at 420° C is reported to produce pyromellitic dianhydride, phthalic and maleic anhydride, although combustion dominates (Geiman et al. [122]). 1,2,4-Trimethyl-benzene yields dimethylbenzene and trimellitic acid if oxidized on a Sn— V—O catalyst. Kinetic data have been measured by Balsubramanian and Viswanath [37]. 

The classical argument concerting the equivalence of the positions on the benzene ring is based on the existence of three (ortho, meta. para) isomers of xylene (dimethylbenzene). How many isomers ore there of dimelhylhorazine ... 

When there are two or more substituents on a benzene ring, structural isomerization can result. For instance, there are three possible isomers of xylene (dimethylbenzene). The isomers are commonly designated as ortho, meta, and para. A letter (o, m, or p) designates the isomeric position. 

Perfluoro(l,3-dimethylbenzene) and sodium methoxide yield, depending on the amount of the nucleophile used, l,2,4-trifluoro-6-methoxy-3,5-bis(trifluoromethyl)benzene (19) or 1,4-di-fluoro-2,6-dimethoxy-3,5-bis(trifluoromethyl)benzene (20).94... 

The presence of a phenyl group in a compound can be ascertained with a fair degree of certainty from its infrared spectrum. For example, in Figure 22-1 we see the infrared spectra of methylbenzene, and of 1,2- 1,3-, and 1,4-dimethylbenzene. That each spectrum is of a benzene derivative is apparent from certain common features. The two bands near 1600 cm-1 and 1500 cm-1, although of variable intensity, have been correlated with the stretching vibrations of the carbon-carbon bonds of the aromatic ring also, the sharp bands near 3030 cm-1 are characteristic of aromatic C-H bonds. Other bands in the... 

Further complications arise from the fact that the alkylation reactions sometimes are under equilibrium control rather than kinetic control. Products often isomerize and disproportionate, particularly in the presence of large amounts of catalyst. Thus 1,2- and 1,4-dimethylbenzenes (ortho- and para-xylenes) are converted by large amounts of Friedel-Crafts catalysts into 1,3-dimethyl-benzene (meta-xylene) ... 

Benzene and many of its derivatives are manufactured on a large scale for use in high-octane gasolines and in the production of polymers, insecticides, detergents, dyes, and many miscellaneous chemicals. Prior to World War II, coal was the only important source of aromatic hydrocarbons, but during the war and thereafter, the demand for benzene, methylbenzene, and the dimethyl-benzenes rose so sharply that other sources had to be found. Today, most of tbe benzene and almost all of the methylbenzene and the dimethylbenzenes produced in the United States are derived from petroleum. 

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