Dialkyl benzene

Although synthetic lubrication oil production amounts to only about 2% of the total market, volume has been increasing rapidly (67). Growth rates of the order of 20% per year for poly( a-olefin)s, 10% for polybutenes, and 8% for esters (28) reflect increasing automotive use and these increases would accelerate if synthetics were adopted for factory fill of engines by automotive manufacturers. The estimated production of poly( a-olefin)s for lubricants appears to be approximately 100,000 m /yr, esters 75,000, poly(alkylene glycol)s 42,000, polybutenes 38,000, phosphates 20,000, and dialkyl benzene 18,000 (28,67). The higher costs reflected in Table 18 (18,28) have restricted the volume of siUcones, chlorotrifluoroethylene, perfluoroalkylpolyethers, and polyphenyl ethers. 

As shown in Fig. I, product di.stributions varied depending upon the mole ratio of 3 to benzene. When one equivalent or a two-fold excess of benzene was used with respect to 3, the yields of monoalkylated and dialkylated benzenes remained about the same, around 50 and 30%, respectively. As the proportion of 3 to benzene increased, the mono- and dialkylation products decrea.sed and were formed in less than 5% yield, while 4a increased rapidly, becoming the major product (56-58%) at a 6-fold excess or more of 3 to benzene. The yield of 4b increased to 26% at the maximum and then decreased smoothly to 18%>. Products 4c and 4d, however, were produced in yields near 10% regardless of the mole ratios used of 3/benzene. 

Monoalkylbenzene or other aromatic compounds react more rapidly than benzene itself in alkylation with hydrogen fluoride and the dialkyl-benzene react less rapidly in general to form tri and higher alkylated products. The polyalkylated products require more strenuous conditions. To form the monoalkyl product the alkylating agent should be added slowly to a large excess of the aromatic compound. 

Table 2. Values of para-seleotivlty (pS) to different dialkyl-benzenes in reactions of toluene alkylation by ethylene and transalkylation of ethylbenzene.

Octakis (2,3,6-tri-0-methyl-gamma-cyclodextrin) was used to separate enantiomers of methyl esters of deltametrinic acid and permetrinic acid the positional isomers of nitrotoluene were also separated on the same column [17,18]. Various alkyl- and dialkyl-benzenes have been separated on beta- and gamma-cyclodextrin [19]. A complete review of the use of cyclodextrins in chromatography has been published by Hinze [20]. Cyclo-dextrins have been analyzed by packed-column gas chromatography as their dimethylsilyl ethers [21]. 

Fig. 5.33. Friedel-Crafts alkylations of mono- or dialkyl benzenes. This figure depicts a pair of reactions, one of which mainly leads to para-methyl benzophenone, and the other-in combination with a subsequent de-tert-bulylation— exclusively gives ortho-methyl benzophenone, respectively.

Aromatic hydrocarbons substituted by alkyl groups other than methyl are notorious for their tendency to disproportionate in Friedel-Crafts reactions. This tendency has previously limited the application of the isomerization of para- or ortho-)dialkyl-benzenes to the corresponding meta compounds. At the lower temperature of the present modification, disproportionation can be minimized. 

Transition state shape selectivity (or spatioselectivity) occurs when the formation of reaction intermediates (and/or transition states) is sterically limited by the space available near the active sites. This spatioselectivity depends on the size and shape of cages, channels and channel intersections. This type of selectivity was first proposed by Csicsery (34) to explain the absence of 1, 3, 5- trialkylbenzenes in the disproportionation products of dialkyl-benzenes transformation over H-mordenite although these trialkylbenzenes could diffuse in the zeolite channels. The space available in these channels was not sufficient to accommodate the diphenylmethane intermediates involved in the formation of 1, 3, 5-trialkyl benzenes they are bulkier than those involved in the formation of 1, 2, 3 and 1, 2, 4 trialkylbenzenes (Figure 1.5 c). 

Excimer formation is observed quite frequently with aromatic hydrocarbons. Excimer stability is particularly great for pyrene, where the enthalpy of dissociation is A// = 10 kcal/mol (Fbrster and SeidI, 1965). The excimers of aromatic molecules adopt a sandwich structure, and at room temperature, the constituents can rotate relative to each other. The interplanar separation is 300-350 pm and is thus in the same range as the separation of 375 pm between the two benzene planes in 4,4 -paracyclophane (13), which exhibits the typical structureless excimer emission. For the higher homologues, such as 5,5 -paracylophane, an ordinary fluorescence characteristic of p-dialkyl-benzenes is observed (Vala et al., 1965). 

Like the other aromatic substrates with electron-withdrawing groups, the radical anions derived from 1,3-benzenedicarbonitrile dimerize reversibly as indicated by the persistence of a—low-intensity—ESR spectrum of the radical anion [262 and refs, therein]. Results obtained by CV put a value of 10 M on K i, and also in this case kdim increases upon addition of water [262]. The reversible dimerization of the radical anions of dialkyl benzene-1,3-dicarboxylate (92a), dialkyl pyridine-1,3- dicarboxylate (92b), and their sulfur analogues (Y = S) [Eq. (58)] has been characterized by CV and ESR spectroscopy [263], and values of 10 —lO" M s and of kpreparative scale, a competing slow, but irreversible, first-order reaction gave the monocarboxylate anions as the sole product [263]. 

Cg, mainly C4), ALK (monoalkylated benzenes with a molecular weight in 92 to 120 range) and DIALK (dialkylated benzenes with a molecular weight in the 148 to 190 range, mainly 1-ethylpropyl-3-ethylbenzene). 

The only disquieting note is that the enthalpies of formation (cf. Reference 6) of m- and p-tcrt-hutyltoluene are —54 2 and —57 2 kJ mol , which suggests the para-isomer is more stable, unUke the case for most other dialkylated benzenes. 

The lower cost dialkyl benzenes are used in a wide variety of industrial and metalworking products. In particular, their sulphur-free chemistry has led to extensive use as rolling and drawing oils for copper. The synthesised alkyl benzenes, even when their chemistry is optimised, generally exhibit poorer properties than PAOs. However, their excellent solvency and low pour point make them suitable for lubricants designed for extremely low-temperature operations in arctic greases, gear oils, hydraulic and power transmission fluids. 

Silanation of zeolites through chemical vapour deposition of tetraethyl orthosilicate has been proved to be a very convenient and useful laboratory technique to modily zeolite characteristics in order to make it highly selective for para-dialkyl benzenes specially with... 

Cejka, J. and Wichterlova, B. 2002. Acid-catalyzed synthesis of mono- and dialkyl benzenes over zeolites active sites, zeolite topology, and reaction mechanisms. Catal. Rev. 44 375-421. 

Numerous azobenzenes and imines have been used to prepare cyclopalladated ctmiplexes, and the liquid crystal properties of some of die products have been investigated. 1 Cyclometallated derivatives have also been prepared from 2-phenylpyiidines, > 2,6-diphenylpyridine, 6-phenyl bipy. O and 6-(2-thienyl) bipy.509 Other substrates subjected to cyclopalladation include amidines, thio- and selenoamides, ll> l N-phenylsulftmyl glycine, hydroxyquinoline derivatives, the drugs diazepam and prazepam, and PBu 3. Doubly cyclopalladated complexes have been prepared from 1,3-diacetylbenzene dioxime and also from N,N-dialkyl benzene-l,3-dicarbaldimines. The 2D NMR spectra of cyclopalladated 8-methylquinoline and benzo-(h)-quinoline show that a CH bond occupies a fifth coordination position above the square plane.520... 

Measurement of the equilibrium constants for such processes allows one to estimate the relative electron affinities (in solution) of different aromatic compounds. Measurements of this kind for the equilibria between benzene and various monoalkyl and dialkyl benzenes, i.e.. 

Chem. Descrip. Dialkyl benzene sulfonic acid Chem. Analysis 2.0% max. free sulfuric acid Uses Emulsifer and demulsifer in oil field recovery systems Features Can be neutralized with various bases to produce the salts of the sulfonic acid for use in neutral systems... 

---