Meta-Diethylbenzene

Recently, the results of the isomerization and transalkylation of isomeric diethylbenzenes with benzene in the presence of triflic acid have been reported. The aim is to find the best condition for the preparation of ethylbenzene.283 285ort/ta-Diethylbenzene and benzene reacting in 1 1 molar ratio at 35°C gave ethylbenzene in 49% yield in 6h 285 An even higher yield was obtained with /mra-diethylbenzene (51% at 22°C), whereas meta-diethylbenzene produced ethylbenzene only in 29% yield.283 Both decreasing temperature and decreasing diethylbenzene/benzene ratio resulted in decreasing yields. 

Evaluating the catalytic shape-selectivities of these materials by use of the disproportionation of ethylbenzene (23.24) at 523 K at a conversion of 2% in differential reactor mode, it was observed that larger crystals of sample A gave 85% para-diethylbenzene and 15% meta-diethylbenzene. The smaller crystals of sample B with the smoother aluminium gradient yielded 96% para-diethylbenzene and only 4% meta-isomer. In a second series, samples of crushed large crystals with mean sizes of 1-10 (m were examined. No increase in activity was observed as is expected when the reaction is controlled by the diffusion limitation of molecules in the large crystals. However, this treatment created larger non-selective external surface area and hence a smaller selectivity of 87% para-diethylbenzene for sample B was recorded. 

Short-chain alkylated biphenyls are the principal biphenyl derivatives in commercial use. They are generally produced by Hquid-phase Friedel-Crafts alkylation of biphenyl with ethylene, propylene, or mixed butenes. A series of mixed ethylated biphenyl heat-transfer fluids (trademarked Therm S-600, 700, 800) is marketed by Nippon Steel. A mixed diethylbenzene—ethylbiphenyl heat-transfer fluid is also available from Dow (63). Monoisopropylbiphenyl [25640-78-2] largely as a mixture of meta- and para-isomers is produced by Koch Chemical Co. Monoisopropylbiphenyl (MIPB) was selected by Westinghouse (64,65) as a PCB replacement in capacitors and this is its primary appHcation today. For a time MIPB was also employed as a PCB replacement in pressure sensitive copy paper, but this outlet has since given way to other dye solvents. A similar product consisting of a mixture of j -butylbiphenyl isomers [38784-93-9] (66) is currently the favored dye solvent for pressure sensitive copy paper (67) manufactured in the United States. 

The high acidity of the Nafion-H catalyst is further demonstrated by its ability to promote both polyalkylation and isomerization. In reaction between benzene and ethylene at 190°C, 20% of the alkylated products are diethylbenzenes.187 The isomer distribution of the diethylbenzenes is 1 % of the ortho, 75% of the meta, and 24% of the para isomers. This composition is very close to the equilibrium composition of diethylbenzenes determined in solution chemistry with AICI3 catalyst and indicates that the reaction is thermodynamically controlled. 

The predominance of meta-diethyl benzene in the isomerization of diethylbenzenes is easily rationalized. Since isomerization reaction proceeds via arenium ion intermediates, the cr-complex derived from mefa-diethylbenzene is the most stable one. Moreover, mefa-diethylbenzene is also the most basic of the isomeric diethylben-zenes. Therefore, more acidic catalysts increase the amount of the meta isomer at the expense of the para (and ortho) isomers, due to the increased stability of the substrate-catalyst complex. 

Which of the diethylbenzene isomers (ortho, meta, or para) corresponds to each set of NMR spectral data ... 

The gas-phase tram-alkylation reaction was performed in an automated micro-flow apparatus containing a quartz fixed-bed reactor (i d. 10 mm) at lO Pa [16 vol% benzene (1, p.a., dried on molsieve), 3.2 vol% diethylbenzene (2, consisting of 25% ortho, 73% meta, 2% para isomers, dried on molsieve), N2 balance (50 mL/min), WHSV =1.5 h ] with 2.0 mL of the tube reactor filled with catalyst particles (500-850 pm sieve fraction, typically 1.4 g). Two separate saturators were connected to the inlet of the reactor for the supply of 1 and 2. The partial vapor pressure of 1 and 2 was controlled by adjusting the temperature of the saturator-condensers and the N2 flow rate. After equilibration for 30 min at the applied reaction temperatures (473 K and 673 K, heating rate 10 K/min) within a dry N2 flow (50 mL/min), benzene (1) and diethylbenzene (2) were passed throu the reactor. To prevent condensation of both reactants and products prior to GC analysis [Hewlet Packard 5710 A, column CP-sil 5CB capillary liquid-phase siloxane polymer (100% methyl) 25 m x 0.25 mm, 323 K, carrier gas N2, FID, sample-loop volume 1.01 pL], tubes were heat-traced (398 K). FID sensitivity factors and retention times were determined using ethene (99.5 %, dried over molsieve) and standard solutions of 1, 2, and ethylbenzene (3, 99%) in methanol (p.a.). The conversion of 2 was measured as a function of time [8]. 

The significant finding was that the xylene fraction was 99% para. The other fractions are not lost. Toluene can be disproportionated to p-xylene and benzene with H-ZSM-5 treated with a little hexamethyldisiloxane to give 99% p-xylene, so that the usual separation of the ortho- and meta isomers with another zeolite would not be required.177 Benzene can be transalkylated with the higher aromatics to give toluene. Ethylbenzene can be isomerized to p-xylene. Ethylbenzene can be alkylated with ethanol in the presence of a modified ZSM-5 catalyst to produce p diethylbenzene with 97% selectivity.178... 

DIETHYLBENZENE (25340-17-4, mixed isomers 1300-82-9, para- 141-93-5, meta- 135-01-3, ortho-) Forms explosive mixture with air (flash point ortho-, 135°F/57°C meta-andpara-,132° — 133°F/55°—56°C cc). Strong oxidizers may cause fire and explosions. Flow or agitation of substance may generate electrostatic charges due to low conductivity. Rubber on long immersion, will swell, then soften. 

Note that diethylbenzene has three isomers in orto-, meta-, and para- ring positions. Up to six substitutions at the benzene ring might be theoretically possible. Propylene present in ethylene as impurity may also produce cumene and higher alkylates as byproducts. Using an excess of benzene can improve the yield by converting the polyalkylbenzene into ethylbenzene, as for example ... 

Write the graphic formulas of the monobromo derivatives of ortho-, meta-, and para-diethylbenzene. 

Moreover, the macro - and micro -FTIR techniques enable us to obtain spectra in situ from a working catalyst, since the cells used (see Sect. 2.1.1) may be operated as flow-through reactors. Thus, coking of zeolite catalysts upon reaction of ethane or ethylbenzene was investigated in situ, and the decrease of diffusivities (e.g., of benzene) in the coking samples was measured as a function of the amount of coke deposited [15]. Similarly, the sorption of para-, meta-, and ortho-diethylbenzene from the gas phase into H-ZSM-5... 

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