Durene

Durene is recovered from reformer residues by low-temperature crystallization recovery by distillation is not possible, because of the virtually identical boiling point of isodurene. Furthermore, durene occurs in gasoline produced by the recently developed Mofe//process (see Chapter 3.4.1) high concentrations in these methanol-derived gasolines can lead to blockages in the carburetor, a result of the tendency of durene to crystallize. 

Durene is predominantly oxidized to pyromellitic dianhydride this anhydride can also be produced by oxidation of the corresponding triisopropyltoluenes and diisopropylxylenes. The favored process is gas-phase oxidation with V2O5 as a catalyst, at temperatures from 400 to 600 C. 

Pyromellitic dianhydride is mainly used in the production of polyimides, e.g. by reaction with an aromatic diamine, such as 4,4 -diaminodiphenyl ether the high-temperature resistant plastic Kapton Du Pont) is obtained by this method. 

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When the concentration of 2-phenylethanesulphonate anion was >0-5 mol 1, or when 2-mesitylethanesulphonate anion (v), " mesitylene-a-sulphonate anion, or iso-durene-a -sulphonate anion were nitrated, the initial part of the reaction deviated from a first-order dependence on the concentration of the aromatic towards a zeroth-order dependence. 

The rates of nitration of mesitylene-a-sulphonate anion (iii) and iso-durene-a -sulphonate anion (iv) in mixtures of aqueous nitric and perchloric acid followed a zeroth-order rate law. Although the rate of exchange of oxygen could not be measured because of the presence of perchloric acid, these results again show that, under conditions most amenable to its existence and involvement, the nitric acidium ion is ineffective in nitration. 

Work on the nitration of durene also gives evidence for the importance of the speed of mixing in nitration with nitronium salts. ... 

Pentamethylbenzene and anthracene react very rapidly with nitronium tetrafluoroborate in sulpholan to give cr-complexes, which decompose slowly (see below), and durene behaves similarly with nitronium hexafluorophosphate in acetonitrile. ... 

Duranol dyes Duranon Tick Repellent Duraphyl Dura Se bolus Durasoft Durazym Durene [95-93-2]... 

See also Durene.) pHTHALIC ACID AND OTHERBENZENEPOLYCARBOXYLIC ACIDS] (Vol 18)... 

Fluoroalkjiations are frequentiy performed indirectly using tandem reactions. Arenes react with sodium borohydride in trifluoroacetic acid to afford otherwise difficult to obtain l,l,l-trifluoro-2,2-diarylethanes. Presumably sodium borohydride reacts initially with the trifluoroacetic acid to produce the trifluoroacetaldehyde or its equivalent, which rapidly undergoes Friedel-Crafts-type condensation to give an intermediate carbinol. The carbinol further alkylates ben2ene under the reaction conditions giving the observed product. The reaction with stericaHy crowded arenes such as mesitylene and durene... 

Properties. Table 4 contains typical gasoline quaUty data from the New Zealand plant (67). MTG gasoline typically contains 60 vol % saturates, ie, paraffins and naphthenes 10 vol % olefins and 30 vol % aromatics. Sulfur and nitrogen levels in the gasoline are virtually lul. The MTG process produces ca 3—7 wt % durene [95-93-2] (1,2,4,5-tetra-methylbenzene) but the level is reduced to ca 2 wt % in the finished gasoline product by hydrodealkylation of the durene in a separate catalytic reactor. 

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). 

High purity mesitylene, hemimellitene, and durene are often produced synthetically, whereas pseudocumene is obtained from extracted reformate by superfractionation. The composition of a typical extracted Cg reformate and the hoiling points of the nine Cg isomers present are shown in Table 5. Pseudocumene is separated in high purity (>98%) by superfractionation alone, whereas mesitylene, hemimellitene, and durene cannot be cleanly separated because of the presence of close hoiling compounds, eg, 2-ethyltoluene, indane, and isodurene, respectively. 

Selective absorption of durene from heavy gasoline (bp 150—225°C) is possible using a version of UOP s Sorbex technology where the X zeoHte is made selective for durene by replacing the exchangeable sodium cations with lithium ions (16). 

Mesitylene can be synthesized from acetone by catalytic dehydrocyclization (17). Similarly, cyclotrimerization of acetylenes has produced PMBs such as hexamethylbenzene (18). Durene has been recovered from Methanex s methanol-to-gasoline (MTG) plant in New Zealand (19). 

Koch Chemical Company is the only U.S. suppHer of all PMBs (except hexamethylbenzene). Its process has the flexibility of producing isodurene, prehnitene, and pentamethylbenzene, should a market develop. Koch s primary process (20) is based on isomerization, alkylation, and disproportionation conducted in the presence of a Friedel-Crafts catalyst. For the synthesis of mesitylene and hemimellitene, pseudocumene is isomerized. If durene, isodurene, or prehnitene and pentamethylbenzene are desired, pseudocumene is alkylated with methyl chloride (see Alkylation Friedel-CRAFTSreactions). 

Kocb s process also permits recovery of prebnitene, isodurene, and pentametbylbenzene by fractionation. In tbe case of isodurene, only 85% purity is acbieved wben tbe filtrate from tbe durene crystallization unit is redistilled durene is tbe principal impurity. Altbougb bexametbylbenzene can be synthesized via the trimethylation of the readily available pseudocumene, its high melting point (105.5°C) presents more of a processing challenge. 

The only significant U.S. producer of PMBs is Koch Chemical Company. The only PMBs produced ia any sizable quantity ate pseudocumene, durene, mesitylene, and hemimellitene. Koch s production capabiUty for pseudocumene is ca 35,000 t/yr the combiaed production rate of the other PMBs is less than 5,000 t/yr. 

Pseudocumene is shipped ia barges, tank cars, tank tmcks, isocontainers, and dmms. Mesitylene is shipped ia tank tmcks, isocontainers, and dmms, whereas durene is shipped molten ia heated tank tmcks, isocontainers, and occasionally as a cast soHd in dmms. Mesitylene, pseudocumene, and hemimellitene are classified as flammable Hquids the higher homologues are classified as combustible. The higher melting PMBs requite additional precautions when handled in the molten state to avoid thermal bums. Detailed shipping and handling procedures are described in manufacturers material... 

Durene. The oxidation of durene (4) yields pyromeUitic acid [89-05-4] (17) or pyromeUitic dianhydride [89-32-7] (18) directly. The oxidation can be carried out with dilute nitric acid ia solution, with air and catalyst either ia the vapor phase over a soHd vanadium pentoxide-based catalyst or ia the... 

The first observation of the enantioselective properties of an albumin was made in 1958 (28) when it was discovered that the affinity for L-tryptophan exceeded that of the D-enantiomer by a factor of approximately 100. This led to more studies in 1973 of the separation of DL-tryptophan [54-12-6] C22H22N2O2, on BSA immobilized to Sepharose (29). After extensive investigation of the chromatographic behavior of numerous racemic compounds under different mobile-phase conditions, a BSA-SILICA hplc column (Resolvosil-R-BSA, Macherey-Nagel GmvH, Duren, Germany) was... 

Bis-(chloromethyl)durene [3022-16-0] M 231.2, m 197-198 . Crystd three times from benzene, then dried under vacuum in an Abderhalden pistol. 

The pyromellitic dianhydride is itself obtained by vapour phase oxidation of durene (1,2,4,5-tetramethylbenzene), using a supported vanadium oxide catalyst. A number of amines have been investigated and it has been found that certain aromatic amines give polymers with a high degree of oxidative and thermal stability. Such amines include m-phenylenediamine, benzidine and di-(4-amino-phenyl) ether, the last of these being employed in the manufacture of Kapton (Du Pont). The structure of this material is shown in Figure 18.36. 

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