Ortho-, meta-, and para-xylenes

In an attempt to increase Tg of the poly[bis(o-carboxyphenoxy)alkanes], Anastasiou and Uhrich (2000a) replaced the alkane moiety by ortho-, meta-, and para-xylenes producing poly[o-/m-bis(p-carboxyphenoxy)xylene]s (Po-p-CPX, and Pm-p-CPX) and poly[o-/m-/p-bis(o-carboxyphenoxy)xylene]s (Po-o-CPX, Pm-o-CPX, and Pp-o-CPX). They found Po-p-CPX to be relatively insoluble and were unable to synthesize poly[p-bis(p-carboxy-phenoxy)xylene] because of the insolubility of the dicarboxylic acid (Anastasiou and Uhrich, 2000a). Po-o-CPX and Pm-o-CPX demonstrated the most favorable solubility and neither exhibited a melting temperature. All of the polymers synthesized had Tgs between 71 and 101°C (Anastasiou and Uhrich, 2000a). 

Mixed xylenes are commercially available in nitration grades that have tolerances of 3 and 10°F, depending on the specified amount of the hydrocarbon present. Purities of the ortho-, meta-, and para-xylenes are more often than not a matter of negotiation between buyer and seller. 

XYLENE. [CAS 1330-20-7], C6H4(CH3)2, formula weight 106.16. There are three xylenes, ortho-, meta-, and para-xylene. Sometimes referred to as dimethylbenzenes. lire xylenes have the following key physical properties ... 

When 92 is heated with C6D6 at 80°C, a ligand exchange reaction occurs. The thermal reactions of 92 with toluene, ortho-, meta-, and para-xylene, and mesitylene have been monitored by NMR spectroscopy. In all cases... 

Ideal-solution behavior is often approximated by solutions comprised of molecules not too different in size and of the same chemical nature. Thus, a mixture of isomers, such as ortho-, meta-, and para-xylene, conforms very closely to ideal-solution behavior. So do mixtures of adjacent members of a homologous series, as for example, n- hexane/ n- heptane, ethanol/propanol, and... 

Ortho-meta- and para-Xylenes.—The three definite isomeric xylenes have the following physical propertie s which enable us to distinguish them from each other. For the present we may designate them simply as 4, -B, C. 

Product selectivity results from differences in the size of the products produced from a given reaction. In a homogeneous reactions methylation of toluene gives a mixture of ortho, meta and para xylenes but when H-ZSM-5 is used as the acid, p-xylene is the almost exclusive product (Eqn. 10.21) because the passage of this less bulky isomer through the pores of the zeolite is not restricted while the more bulky o- and m-isomers are too large to easily go through them. 2... 

Ungvary G, Tatrai E, Hudak A, et al. 1980b. Studies on the embryotoxic effects of ortho-, meta, and para-xylene. Toxicology 18 61-74. 

This acronym stands for Ifenzene, Toluene, Ethylbenzene, and ortho-, meta- and para -Xylenes (see also Example 8.3 earlier). 

For your information the unknown mixture had been made up from the pure components, and contained 0.420, 0.398, 0.271, and 0.248 g/50 mL of ethylbenzene and of ortho-, meta-, and para-xylene respectively. The (relatively small) differences between these numbers and your results in F 13 F16, of less than 2.5%, are not caused by computational errors, but instead reflect uncertainties in the measured absorbances. Although the infrared absorbances are listed in Table 6.2-1 to three or four digits, they were (conservatively) rated as most likely good to 5% only. 

The intracrystalline diffusivities of llZSM-5 zeolite were directly measured for several hydrocarbons at higher temperatures (373-773 K) by the constant volume method. High silicious HZSM-5 zeolite, which has no activity for reactions, was used as the adsorbent. Aromatics benzene, xylene-isomers ortho-, meta- and para-xylene) and toluene, and paraffins n-hexane, n-pentane, p-octane and iso-octane, were used as adsorbates. Intracrystalline diffusivities of aromatics markedly depended on the minimum size of the aromatics and that of paraffins depended on the carbon number (molecular weight of the paraffins). A method was developed for predicting diffusivity in terras of pore diameter and molecular properties of hydrocarbons. This method was found to well represent the experimental results. 

The interaction of different nitriles (acetonitrile, pivalonitrile and benzonitrile), of branched aliphatic compounds (2,2-dimethylbutane, reri-butyl-alcohol, methyl-rert-butylether, methyl and dimethylcyclohexanes) and of aromatics (benzene, toluene, ortho-, meta- and para-xylene, pyridine, picolines and lutidine) has been studied over four different ZSM5 zeolites, over silicalite-1 and titanium silicalite-1 and over boralite BOR-C. Internal, external and extraframework sites have been characterized and the access to the cavities discussed. 

Xylenes for solvent purposes consist of a mixture of three dimethylbenzene isomers, ortho-, meta- and para-xylene, and ethylbenzene. The physical properties quoted are for a typical mixture and the only property that is significantly altered by the ratio of the isomers is the flash point of the mixture. This can be significant in the UK and other countries where legislation primarily aimed at the safe storage of petrol regulates the storage and handling of hydrocarbons with flash points of less than 73 °F (22.8 °C) by the Abel method. 

The list (see Appendix 6.1) contains 170 substances said to have the potential to cause significant water pollution. The majority are not solvents. The important solvents included on the list are the major chlorinated hydrocarbons toluene ortho, meta and para xylenes ethyl benzene and some long chain aliphatics (C8 upwards). Pollution authorities in EU member states refer to this list in setting their own national lists for control. 

Xylenes ortho-, meta-, and para-Xylene occur together in technical xylene, m-xylene predominating. Ethylbenzene also contaminant in technical xylene... 

Figure 4.17. Zeolite transition-state selectivity. Toluene alkylation with methanol catalyzed by H-MOR showing the energies of the key reaction intermediates . Reaction energy diagram for ortho-, meta- and para-xylene are compared.

Isomers of organic ligands of course will give rise to isomeric forms of the corresponding rc-complexes. For example, there are three isomers of xylenechromium tricarbonyl derived from ortho-, meta-, and para-xylene [5-14]-[5-16]. Similar examples are found for olefin 7t-complexes such as butenepalladium chloride [5-17]-[5-19]. 

Styrene and propylene oxide, Ortho-, meta- and para-xylenes, cumene,n-propyl benzene, iso-butyl benzene, alpha-methyl styrene and mixed meta-/para-diethyl benzenes, tert-, sec- and n-butyl benzenes, ortho-methyl styrene, mixed meta-/para-mediyl styrenes and n-undecane, meta- and para-ethyl toluenes, ortho-ethyl toluene. 

Much of the production of xylene comes from the re-forming of naphtha (C8) streams, with mixtures of ortho-, meta-, and para-xylenes, which must be separated and purified. 

In the years 1900-1909, Autenrieth, Beuttel, and Kotz [91-93] studied syntheses and reactions of the a,a-dimercaptanes of ortho-, meta-, and para-xylene. The main purpose of the condensation reactions with aldehydes, ketones, and dibromoalkanes was the isolation of cyclic compounds. For instance, oligomeric condensates were obtained when the meta dimercaptane was reacted with aldehydes, whereas a crystalline cyclic dimer was isolated with acetone as reaction partner (see Formula 2.5). In the case of the para dimercaptane crystalline dimeric cycles were also obtained with aromatic aldehydes. The condensations of the para dimercaptane with dibromoalkanes yielded several crystalline compounds which were interpreted as cyclic monomers (see Formula 2.5), although in most cases the monomeric structure is unlikely for reasons of ring strain. Another unlikely ring structure, namely a dimeric disulfide, was postulated by Zincke and Kruger [94] for the oxidation product of meta-dimercaptobenzene (see Formula 2.5). 

---