1 -Hexene aromatization

These results indicate the formation of 1-hexene from -hexane in both helium and hydrogen. The absence of cyclohexane is due to the lack of its formation and not to its rapid further reaction to benzene. The rate of hexene aromatization is more rapid than that of hexane (52, 54). 

Rhodium- and cobalt-catalyzed hydrogenation of butadiene and 1-hexene [47, 48] and the Ru-catalyzed hydrogenation of aromatic compounds [49] and acrylonitrile-butadiene copolymers [50] have also been reported to be successful in ionic liquids. 

The second aromatization reaction is the dehydrocyclization of paraffins to aromatics. For example, if n-hexane represents this reaction, the first step would be to dehydrogenate the hexane molecule over the platinum surface, giving 1-hexene (2- or 3-hexenes are also possible isomers, but cyclization to a cyclohexane ring may occur through a different mechanism). Cyclohexane then dehydrogenates to benzene. 

For conjugated, non-aromatic substances, both the molar absorptivity and wavelength of maximum absorption increase. An example of this is the comparison of 1-hexene that absorbs at 177 nm with a molar absorptivity of 12,000 while 1,3,5-hexatriene absorbs at 268 nm and has a molar absorptivity of 42,500. 

The hydrogenation of simple alkenes, such as hexene, cyclohexene, cyclo-hexadiene and benzene, has been extensively studied using biphasic, alternative solvent protocols. These hydrocarbon substrates are more difficult to hydrogenate compared to substrates with electron withdrawing groups. Benzene and alkyl substituted aromatic compounds are considerably more difficult to hydrogenate... 

Representatives of the subfamilies Omaliinae and Proteininae (omaliine group) possess an abdominal defensive gland reservoir that opens out between sternite 7 and 8 [ 120]. The multi-component mixtures contained in these glands are used for defence. In Omaliinae and Proteininae the secretion is characterized by mixtures of acids (e.g. 2-methylpropanoic acid, hexanoic acid, 2-octenoic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, butyric acid, and tiglic acid), aldehydes (( )-2-hexenal, heptanal, octanal, nonanal), ketoaldehydes such as 4-oxo-2-hexenal 41 (Scheme 5), 6-methyl-5-hepten-2-one, alcohols (octanol, ( )-2-hexen-l-ol, 2-methylbutan-l-ol), alkanes (nonadecane), esters (2-methylbutyl tiglate 42, various propanoates, 2-hexenyl 3-methylbutanoate, 2-methylbutyl 2-methylbutanoate, octanoates,butanoates), and aromatic compounds (e.g. 2-phenethyl 3-methylbutanoate 43). Unusual compounds are 2-... 

Lund and coworkers [131] pioneered the use of aromatic anion radicals as mediators in a study of the catalytic reduction of bromobenzene by the electrogenerated anion radical of chrysene. Other early investigations involved the catalytic reduction of 1-bromo- and 1-chlorobutane by the anion radicals of trans-stilhene and anthracene [132], of 1-chlorohexane and 6-chloro-l-hexene by the naphthalene anion radical [133], and of 1-chlorooctane by the phenanthrene anion radical [134]. Simonet and coworkers [135] pointed out that a catalytically formed alkyl radical can react with an aromatic anion radical to form an alkylated aromatic hydrocarbon. Additional, comparatively recent work has centered on electron transfer between aromatic anion radicals and l,2-dichloro-l,2-diphenylethane [136], on reductive coupling of tert-butyl bromide with azobenzene, quinoxaline, and anthracene [137], and on the reactions of aromatic anion radicals with substituted benzyl chlorides [138], with... 

Chemical/Physical. Under atmospheric conditions, the gas-phase reaction with OH radicals and nitrogen oxides resulted in the formation of p-tolualdehyde (Atkinson, 1990). Kanno et al. (1982) studied the aqueous reaction of p-xylene and other aromatic hydrocarbons (benzene, toluene, o-and /n-xylene, and naphthalene) with hypochlorous acid in the presence of ammonium ion. They reported that the aromatic ring was not chlorinated as expected but was cleaved by chloramine forming cyanogen chloride. The amount of cyanogen chloride formed increased at lower pHs (Kanno et al, 1982). Products identified from the OH radical-initiated reaction of p-xylene in the presence of nitrogen dioxide were 3-hexene-2,5-dione, p-tolualdehyde, and 2,5-dimethylphenol (Bethel et al., 2000). 

The solubilities of aromatic compounds in the ionic liquid are dramatically higher than those of saturated compounds. Benzene has a solubility of 4.9mol/mol of ionic liquid, and thiophene has a solubility of 6.7mol/mol of ionic liquid. A dramatic steric effect was observed on the solubility of aromatics the alkyl-substituted aromatics showed reduced solubility. Although the solubility of hexene in the ionic liquid is considerably lower than that of the aromatics, it is still measurably higher than that of hexane. Similar structure-solubility relationships characteristic of organic molecules were observed with the ionic liquids [BMIM]BF4, [BMIM]PFg, and [EMIM]BF4 (Fig. 10) (27). 

In order to produce additional evidence for the above mecheuiism for aromatization over Ga203 HZSM-5 catalysts the reactions of n-hexene, 1,5 hexadiene, methylcyclopentane, methylcyclopentene, cyclohexene, cyclohexadiene at 773 K over H-2SM-5 and Ga-HZSM-5 were comparatively studied. In these exj riments low pressure and low contact were employed to observe the primary kinetic products uncomplicated by secondary reactions. The relative rates of the formation of benzene from the various hydrocarbons cited above are listed in Table 4. 

The reaction of n-hexene at 773 K and high dilution over H-ZSM5 produced almost exclusively cracked products propene. Under these conditions the formation of aromatics and paraffins were not observed. In contrast over Ga-HZSN-5 the main products were propene and benzene. The very rapid dehydrogenation of n-hexene over Ga-HZSM-5 into hexadiene and hexatriene which could easily form cyclic hydrocarbons by Intramolecular alkylation catalyzed by H will explain the different behaviour of H-ZSM-5 and Ga-HZSM-5 in the reaction of highly diluted n-hexene. These suggestions are consistent in view of the finding that Ga-HZSM-5 shows dehydrogenating properties. 

Wiesen, E., I. Barnes, and K. H. Becker, Study of the OH-Initiated Degradation of the Aromatic Photooxidation Product 3,4-Dihy-droxy-3-hexene-2,5-dione, Environ. Sci. Technol., 29, 1380-1386... 

The edible portion of broccoli Brassica oleracea var. italica) is the inflorescence, and it is normally eaten cooked, with the main meal. Over 40 volatile compounds have been identified from raw or cooked broccoli. The most influential aroma compounds found in broccoli are sulfides, isothiocyanates, aliphatic aldehydes, alcohols and aromatic compounds [35, 166-169]. Broccoli is mainly characterised by sulfurous aroma compounds, which are formed from gluco-sinolates and amino acid precursors (Sects. 7.2.2, 7.2.3) [170-173]. The strong off-odours produced by broccoli have mainly been associated with volatile sulfur compounds, such as methanethiol, hydrogen sulfide, dimethyl disulfide and trimethyl disulfide [169,171, 174, 175]. Other volatile compounds that also have been reported as important to broccoli aroma and odour are dimethyl sulfide, hexanal, (Z)-3-hexen-l-ol, nonanal, ethanol, methyl thiocyanate, butyl isothiocyanate, 2-methylbutyl isothiocyanate and 3-isopropyl-2-methoxypyrazine... 

Parsley (Petroselinum crispum) is a member of the Apiaceae family. The fresh leaves of parsley and the dried herb are widely used as flavouring. More than 80 compounds have been identified in the volatile fraction, and the aromatic volatiles of parsley are mainly monoterpenes and the aromatics myristicin and api-ole. It is suggested that the characteristic odour of parsley is due to the presence ofp-mentha-l,3,8-triene, myrcene, 3-sec-butyl-2-methoxypyrazine, myristicin, linalool, (Z)-6-decenal and (Z)-3-hexenal [227, 228]. Furthermore, /3-phellan-drene, 4-isopropenyl-l-methylbenzene and terpinolene contribute significantly... 

The dehydrogenation of paraffins to olefins, while it does not take place to a large extent at typical reforming conditions (equilibrium conversion of n-hexane to 1-hexene is about 0.3% at 510°C. and 17 atm. hydrogen partial pressure), is nevertheless of considerable importance, since olefins appear to be intermediates in some of the reactions. This matter will be discussed in more detail in a subsequent section. The formation of olefins from paraffins, similar to the formation of aromatics, is favored by the combination of high temperature and low hydrogen partial pressure. The thermodynamics of olefin formation can play an important role in determining the rates of those reactions which proceed via olefin intermediates, since thermodynamics sets an upper limit on the attainable concentration of olefin in the system. 

As shown in Scheme 1.30, the chiral titanocene catalyst 34 hydrogenates unfunctionalized, disubstituted styrenes under 136 atm of hydrogen at 65°C to give the saturation products with 83 to >99% ee [156]. A high enantioselectivity is now realized only with aryl-substituted olefins. The enantioselectivity of 41% ee attained 2-ethyl-1-hexene and 34 as catalyst is the highest for hydrogenation of non-aromatic olefins. 

Clearly significant separations can be effected, especially between aromatics and aliphatics. The size basis for the effect is clear in the comparison of hexane and hexene results the presence of the 1-hexene double bond does not seem to enhance its inclusion into the liquid clathrate phase greatly. Also clear is the strong dependence on the dimensions of the anion, with the smaller, more compact materials giving better separations. 

There are different methods to cleave benzyl ether bonds. The most common one is hydrogenolysis with palladium on carbon or platinum as catalysts under H2 atmosphere. The standard solvents are ethanol or ethyl acetate. Pd is the preferred and milder one, because the use of Pt at any rate results in aromatic ring hydrogenation. Also a number of methods have been developed in which hydrogen is generated in situ, e. g. from cyclo-hexene, -hexadiene or formic acid (see Chapter 7). 

We have recently broadened those investigations to study the origin of the enantioselectivity in the dihydroxylation of terminal aliphatic n-alkenes. The dihydroxylation of the series from propene to 1-decene was studied by means of the IMOMM method [97]. Experimental studies on propene, 1-butene, 1-pentene, 1-hexene and 1-decene showed that the reaction was enantioselec-tive in all cases, leading to the R product. Moreover, the results show a dependence of the enantioselectivity on the chain length it sharply increases from propene to 1-pentene, and after that the enantioselectivity remains practically constant for 1-hexene and 1-decene. The explanation for this dependence of the enantioselectivity with the chain length remained elusive. On the other hand, the -stacking interactions that were found to be critical for styrene cannot be responsible for the observed enantioselectivity for these terminal aliphatic n-alkenes because they do not have aromatic rings. 

The ruthenium-catalyzed addition of C-H bonds in aromatic ketones to olefins can be applied to a variety of ketones, for example acetophenones, naphthyl ketones, and heteroaromatic ketones. Representative examples are shown in the Table 1. Terminal olefins such as vinylsilanes, allylsilanes, styrenes, tert-butylethy-lene, and 1-hexene are applicable to this C-H/olefin coupling reaction. Some internal olefins, for example cyclopentene and norbornene are effective in this alkylation. The reaction of 2-acetonaphthone 1 provides the 1-alkylation product 2 selectively. Alkylations of heteroaromatic ketones such as acyl thiophenes 3, acyl furans, and acyl pyrroles proceed with high yields. In the reaction of di- and tri-substitued aromatic ketones such as 4, which have two different ortho positions, C-C bond formation occurs at the less congested ortho position. Interestingly, in the reaction of m-methoxy- and m-fluoroacetophenones C-C bond formation occurs at the congested ortho position (2 -position). 

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