Para-xylene , nitration

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. 

Ksilil (Russ, Xylitej in Fr, Ksylit in Polish, TNX). A term given to commercial Trinitro-xylene (TNX) which consists chiefly of the trinitro derivatives, of meta-, with some ortho-and para-xylenes. It is a greyish-yellow substance prepd by the nitration of commercial xylene by mixed nitric-sulfuric acid. It is insol in w. Ksilil is slightly more, sensitive to initiation, and about as sensitive to impact and bullet test as TNT. It was used in composite expls as a partial substitute for TNT Refs 1) PATR 2145 (1955), p Rus 10-L 2) Gorst (1957), 100 3) Urbanski 1 (1964),... 

Since the nitro compound is made by nitration of a benzene ring, the preferred symmetry is very different from that needed for the Fischer synthesis. Nitration of para-xylene (1,4-dim ethylbenzene) is a good example. 

The rest of the synthesis is more straightforward the nitro group can be reduced to an amine, which immediately forms an enamine by intramolecular attack on the more reactive carbonyl group (the ketone) to give the aromatic indole. Since the nitro compound is made by nitration of a benzene ring, the preferred symmetry is very different from that needed for the Fischer synthesis. Nitration of para-xylene (1,4-dimethylbenzene) is a good example. 

The yields of the main reaction products in reactions of aromatics with NO3 were determined by GC-MS after sampling on a carbon column or a XAD-2 trap [7] For benzene only nitro-benzene was identified as a product, but benzene was essentially unconverted in the reaction with NO3. Benzaldehyde and benzyl nitrate were identified in the reaction with toluene. For ortho-, meta-, para-xylene and 4-fluorotoluene the corresponding aldehydes and nitrates were identified as main products, which suggests that the below mechanism for toluene and the xylenes is the main reaction pathway [8] ... 

Nitration of m xylene is directed ortho to one methyl group and para to the other... 

Schrader prepared the ester (38) in 60% yield by reaction of sodium p-nitrophenate with diethyl chlorophosphate, using xylene as solvent for the reaction. He made it, but in lower yields, from p-nitrophenol and diethyl chlorophosphate, using, respectively, pyridine and sodium cyanide as acceptors for hydrogen chloride. Schrader also prepared it in 96% yield by nitrating diethyl phenyl phosphate at 0° C. or below. Under the conditions he used, Schrader claims that the nitro group is directed to the para position. No yield is given for the diethyl phenyl phosphate, which he presumably made from sodium phenate and diethyl chlorophosphate. Diethyl chlorophosphate may be prepared in high yield (30) from diethyl phosphite and chlorine. 

Production of p-xylene via p-xylene removal, i.e., by crystallization or adsorption, and re-equilibration of the para-depleted stream requires recycle operation. Ethylbenzene in the feed must therefore be converted to lower or higher boiling products during the xylene isomerization step, otherwise it would build up in the recycle stream. With dual-functional catalysts, ethylbenzene is converted partly to xylenes and is partly hydrocracked. With mono-functional acid ZSM-5, ethylbenzene is converted at low temperature via transalkylation, and at higher temperature via transalkylation and dealkylation. In both cases, benzene of nitration grade purity is produced as a valuable by-product. 

Nitration of monosubstituted aromatics, toluene in particular, has been extensively studied using zeolites in order to direct the reaction towards the formation of the desired para-isomer. Toluene has been nitrated para-selectively with benzoyl nitrate over zeolite catalysts.[14,15] For example, when mordenite is used as a catalyst, MNTs are formed in almost quantitative yields, giving 67 % of the para-isomer in 10 min, but tetrachloromethane is required as solvent. However, the main problems associated with the use of benzoyl nitrate are handling difficulties due to its sensitivity toward decomposition, and the tendency toward detonation upon contact with rough surfaces. Nagy et a/.[19 21] reported the nitration of benzene, chlorobenzene, toluene and o-xylene with benzoyl nitrate in the presence of an amorphous aluminosilicate, as well as with zeolites HY and ZSM-11, in hexane as a... 

Before spectroscopy was invented, Komer s absolute method was used to determine whether a disubstituted benzene derivative was the ortho, meta, or para isomer. Komer s method involves adding a third group (often a nitro group) and determining how many isomers are formed. For example, when o-xylene is nitrated (by a method shown in Chapter 17), two isomers are formed. 

Of the three isomeric xylenes, each of which yields nitro products, it is the meta-xylene or i-3-di-methyl benzene which is most easily nitrated. The number of isomeric nitro xylenes possible has been previously explained (pp. 472 and 482). In the case of meta-xylene three such nitro compounds are possible but only one is readily obtained. It is I-3-di-methyl 4-nitro benzene that is, the nitro group enters the ring ortho to one methyl group and para to the other. This is just what we should expect from the influence of the methyl group upon subsequent substitution (p. 506). The nitro xylenes are not so important as nitro benzene or the nitro toluenes, but have some use in dyestuff manufacture. 

Whereas it could be argued, that the iscmer distribution differences in the nitration of toluene are not large (see, however, the 50% variation in ortho/para ratios in Table XV) these differences are becoming much more significant when comparing data of nitrations in similar media for -xylene, anlsole, and chlorobenzene (TABLE XVI). 

The nitration reactions also exhibit high selectivity when the reactions proceed at the encounter controlled diffusion limit. To Illustrate, the nitration of anisole yields little meta product the ortho and para isomers are produced almost exclusively. Similarly, the substitution products of m-xylene... 

Since tertiary carbocations are more stable than secondary carbocations, the activated complex for mesitylene is more stable than for benzene. Therefore, mesitylene is more reactive toward ring nitration than is benzene. Looking at the other compounds activated complexes for ortho, para substitution, we find Toluene has two secondary carbocations and one tertiary carbocation m-xylene has one secondary carbocation and two tertiary carbocations p-xylene has two secondary carbocations and one tertiary carbocation. We see that toluene and p-xylene have the same number of secondary and tertiary carbocations in the activated complex. The activated complex for p-xylene is, however, more stable than for toluene because of the presence of an extra methyl group. The methyl group has an activating effect on the entire molecule. Prom the relative... 

Because of the inefficiency of the nitrodeiodination reaction and the faster rate of nitration of o-xylene relative to 4-iodo-o-xylene, I2 cannot be used as a catalyst to alter the substitution pattern in the nitration of o-xylene. ° Mononitration of m-xylene with HNO3 in a liquid mixture of m-benzenedisulphonic acid and phosphoric acid gives excellent yields and a 4-nitro-isomer content higher than that obtained by the usual method. In a typical experiment, the yield was 96% and the 4- to 2-isomer ratio ca. 7.5. A white product obtained during the nitration of toluene has been identified as (46). The catalytic para-nitration of substituted benzenes, especially toluene, has been reviewed, but in Japanese. 

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