Aromatic directive

Although the bicyclic sulfide (2S3) does not appear to have been aromatized directly to the highly reactive thieno[3,4-6]thiophene (8), a methoxycarbonyl derivative (258) has been converted to the acid (259), decarboxylation of which furnished (8 Scheme 88) (67TL761). 

V Snieckus, Regioselective Synthetic Processes Based on the Aromatic Directed Metalation Strategy, ... 

V. Snieckus, Regioselective synthetic processes based on the aromatic directed metalation strategy, PureAppl. Chem. 1990, 62, 671. 

Mechanistically, this sequence can be rationalized by initial alkynone formation upon coupling of acid chloride 7 and aUcyne 4 furnishing the alkynone 8, which now can act as a dipolarophile (Scheme 18). The amount of triethylamine is sufficient to deprotonate the l-(2-oxoethyl)pyridinium bromide 25 giving rise to the zwitter-ionic pyridinium ylide 27, an allyl-type dipole suitable for the subsequent 1,3-dipolar cycloaddition to give the dihydroindolizine 28. Under either aerobic or anaerobic conditions in the final cycloaddition step oxidative aromatization directly furnishes the desired indolizines 26. 

Direct fluorination of aliphatics and non-C moieties Direct fluorination of benzenoid aromatics Direct fluorination of heterocyclic aromatics Oxidations of alcohols, diols and ketones with fluorine Photo-oxidation of a-terpinene and cyclopentadiene Oxidation of benzyl alcohol to benzaldehyde Homogeneously catalyzed oxidation of butyraldehyde Oxidation of sulfite to sulfate Photochlorination of aromatic isocyanates... 

Vapor-phase adsorption isotherms of benzene and thiophene on various sorbents including CuY and AgY were measured first in order to assess their suitabilities for sulfur removal, as well as for the removal of aromatics. Direct correlations have yet to be established between the vapor-phase isotherms and the liquid-phase isotherms. However, some efforts have already been made in this direction by using the potential theory approach where log (Cs/C) replaces log (Ps/P) in the potential energy expression (Cj is the saturated concentration in solution and Pg is the saturated vapor pressure, see Manes, 1998). A sorbent capable of adsorbing thiophene at very low partial pressures in the gas phase should also be able to do so in the liquid phase. 

Correlations have been found between certain absorption patterns in the infrared and the concentrations of aromatic and paraffinic carbons given by the ndA/method (see article 3.1.3.). The absorptions at 1600 cm due to vibrations of valence electrons in carbon-carbon bonds in aromatic rings and at 720 cm (see the spectrum in Figure 3.8) due to paraffinic chain deformations are directly related to the aromatic and paraffinic carbon concentrations, respectively. )... 

For hydrocarbon studies, analyses can be made without prior assumptions, since the carbons not carrying protons can be excited directly, this of course not being the case for hydrogen (e.g., quaternary carbons in alkanes, substituted carbons in aromatic rings). 

The smoke point corresponds to the maximum possible flame height (without smoke formation) from a standardized lamp (NF M 07-028). The values commonly obtained are between 10 and 40 mm and the specifications for TRO fix a minimum threshold of 25 mm. The smoke point is directly linked to the chemical structure of the fuel it is high, therefore satisfactory, for the linear paraffins, lower for branched paraffins and much lower still for naphthenes and aromatics. 

Figure 5.13 shows that the luminometer index depends directly on the mono-aromatic and di-aromatic contents. For this reason, the specifications... 

The potential advantages of LPG concern essentially the environmental aspects. LPG s are simple mixtures of 3- and 4-carbon-atom hydrocarbons with few contaminants (very low sulfur content). LPG s contain no noxious additives such as lead and their exhaust emissions have little or no toxicity because aromatics are absent. This type of fuel also benefits often enough from a lower taxation. In spite of that, the use of LPG motor fuel remains static in France, if not on a slightly downward trend. There are several reasons for this situation little interest from automobile manufacturers, reluctance on the part of automobile customers, competition in the refining industry for other uses of and fractions, (alkylation, etherification, direct addition into the gasoline pool). However, in 1993 this subject seems to have received more interest (Hublin et al., 1993). 

These properties concern paraffins that are part of food packaging materials. Their potential toxicity could be attributable to aromatic residues. The latter are thereby characterized directly or indirectly by ... 

The special case of pericyclic reactions is an appropriate means of introducing the subject These reactions are very common, and were extensively studied experimentally and theoretically. They also provide a direct and straightforward connection with aromaticity and antiaromaticity, concepts that mm out to be quite useful in analyzing phase changes in chemical reactions. 

Since aliphatic hydrocarbons (unlike aromatic hydrocarbons, p. 155) can be directly nitrated only under very special conditions, indirect methods are usually employed for the preparation of compounds such as nitroethane, CjHsNO. When ethyl iodide is heated with silver nitrite, two isomeric compounds are formed, and can be easily separated by fractional distillation. The first is the true ester, ethyl nitrite, C,HiONO, of b.p. 17° its identity is shown by the action of hot sodium hydroxide solution, which hydrolyses it, giving ethanol and... 

A further difference between aliphatic and aromatic hydrocarbons is that only the latter are capable of direct sulphonation. Thus benzene when heated with concentrated sulphuric acid gives benzenesulphonic acid, a reaction which proceeds more readily, however, if chlorosulphonic acid is used instead of sulphuric acid an excess of chlorosulphonic acid however may convert the sul phonic acid into the sulphonyl chloride (c/. p. 181). 

A halogen atom directly attached to a benzene ring is usually unreactive, unless it is activated by the nature and position of certain other substituent groups. It has been show n by Ullmann, however, that halogen atoms normally of low reactivity will condense with aromatic amines in the presence of an alkali carbonate (to absorb the hydrogen halide formed) and a trace of copper powder or oxide to act as a catalyst. This reaction, known as the Ullmant Condensation, is frequently used to prepare substituted diphenylamines it is exemplified... 

This reaction is given by most aromatic aldehydes having the aldehyde group directly joined to the benzene ring it is also given by formaldehyde, with the formation of methanol and formic acid. Other aliphatic aldehydes do not give Cannizzaro s reaction under these conditions. 

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