Aromatic direct synthesis

The direct synthesis in an aromatic hydrocarbon medium is patented, using a triethyl aluminum catalyst (48) in this case, crystallisa tion of the product from a solvent is not needed. 

Reductive carbonylation of nitro compounds (in particular aromatic dinitro compounds) is an important target in industry for making diisocyanates, one of the starting materials for polycarbamates. At present diisocyanates are made from diamines and phosgene. Direct synthesis of isocyanates from nitro compounds would avoid the reduction of nitro compounds to anilines, the... 

Transition metal complexes have been used in a number of reactions leading to the direct synthesis of pyridine derivatives from acyclic compounds and from other heterocycles. It is pertinent also to describe two methods that have been employed to prepare difficultly accessible 3-alkyl-, 3-formyl-, and 3-acylpyridines. By elaborating on reported194,195 procedures used in aromatic reactions, it is possible to convert 3-bromopyridines to products containing a 3-oxoalkyl function196 (Scheme 129). A minor problem in this simple catalytic process is caused by the formation in some cases of 2-substituted pyridines but this is minimized by using dimethyl-formamide as the solvent.196... 

The reaction with the siloxy derivative 29 is an interesting example because the product 30 is a 1,5-dicarbonyl derivative (Equation (36)).96 1,5-Dicarbonyls are classically prepared by a Michael addition, but the synthesis of 30 by a Michael addition is not possible because it would require addition to the keto form of 1-naphthol. The acetoxy derivative 31 resulted in a different outcome, leading to the direct synthesis of the naphthalene derivative 32 (Equation (37)).96 In this case, the combined C-H activation/Cope rearrangement intermediate was aromatized by elimination of acetic acid before undergoing a reverse Cope rearrangement. 

Since zeolite catalysts are successfully introduced in the refining and petrochemical industries, it is not surprising that most of the recent advances concern incremental improvements of existing processes with the development of new generations of catalysts (e.g., dewaxing, ethylbenzene and cumene synthesis). The number of newer applications is much more limited, for example, direct synthesis of phenol from benzene and aromatization of short-chain alkanes, etc. However, both the improvement and development of processes contribute significantly to environmental advances. 

Both aromatic and aliphatic fluoroformates 7 can be readily prepared from phenols or alcohols and carbonyl difluoride and treated with sulfur tetrafluoride without isolation. Hydrogen fluoride evolved in the reaction of hydroxy compounds with carbonyl di fluoride serves as a catalyst for the consecutive reaction with sulfur tetrafluoride.15<)-162 This provides a general, convenient, direct synthesis of aryl and alkyl trifluoromethyl ethers 5 from phenols and alcohols. When the intermediate fluoroformate 7 is isolated prior to treatment with sulfur tetrafluoride, at least one mole equivalent of hydrogen fluoride is necessary to promote the fluorination reaction. 159 163 Representative examples of the conversion of hydroxy compounds 6 into trifluoromethyl ethers 5 via intermediate fluoroformates 7 are given (for other examples 7 -> 5, see Houben-Weyl, Vol. E4, pp 628. 629). 

Olah et al.466 observed immediate formation of protonated benzenesulfinic acid upon addition of SO2 to benzenium ion formed in H SO3F-Sb I 5-SO2C11 solution at —78°C. Based upon this observation, Laali and Nagvekar467 developed a method for the synthesis of aromatic sulfoxides [Eq. (5.169)]. Product formation was interpreted in terms of dehydration of protonated benzenesulfinic acid followed by nucleophilic attack by the aromatic to the formed arenesulfinyl cation. Mixed sulfoxides (4-fluorophenyl-4-methylphenyl and 4-fluorophenyl-3-trifluoromethyl sulfoxides) were also prepared by sequential addition of the two aromatics. The direct synthesis of symmetric diaryl sulfoxides in high yields (room temperature, 2—48 h, 50-95%) has been reported through the electrophilic activation of thionyl chloride with triflic acid.468... 

In a closely related publication, carboxylic acids were employed instead of acid chlorides in a microwave-assisted direct synthesis of 2-substituted benzoxazoles [79]. The reactions with 2-aminophenol were performed in a household microwave oven and worked well with aromatic, heteroaromatic, aj/i-unsalurated and arylalkyl carboxylic acids (35-82% yields). Phthalic acid formed only mono-benzoxazoles, while the use of succinic acid led to a mixture of mono- and bis-benzoxazoles. Phthalic and succinic anhydrides could... 

Dietrich-Buchecker, C.O., Mamot, P.A. and Sauvage, J.P. 1982. Direct synthesis of disubstituted aromatic polyimine chelates, Tetrahedron Lett., 23, 5291-5294. 

Fig. 8 The two applied approaches to catenane synthesis prior to 1983. (a) The first statistical synthesis [58] relied upon the macrocyclization of a linear compound (7) in the presence of a deuterated cycloalkane (III) to achieve small amounts of the catenane V. (b) The first example [59] of directed synthesis by covalent templation was a catenane that formed after cleaving the covalent bonds around the aromatic core in compound 16. Reproduced with permission from [58] (copyright 1960 American Chemical Society), [59] (copyright 1964 Wiley-VCH)...

The heterobenzene ( -C5H5P)2Cr can be directly prepared by the metal-ligand vapor cocondensation technique. This heterocycle is aromatic and prefers ( -coordination to -coordination. For pyridine, cr-coordination via a lone pair is highly preferred over bonding that utihzes the tt-electron system. Therefore the direct synthesis of jj -pyridine metal complexes requires the N-atom to be blocked by means of substitution in the 2,6-positions ... 

Okamoto et al. [19] described the direct synthesis of the benzimidazo [2,1-a] isoquinoline (x) ring system by a microwave-accelerated tandem process in which a sonogashira coupling, 5-endocyclization, oxidative aromatization and 6-endo cyclization can be performed in a single synthetic operation. 

Gil, M., Ji, X., Li, X., Na, H., Hampsay, J., Lu, Y. (2004). Direct synthesis of sulfonated aromatic poly(ether ether ketone) proton exchange membranes for fuel cell applications. /. Membrane Sci. 234, 75-81. 

Luminescence spectra of a series of Ce(III) compounds containing halide, alkyl, aryl, ether, nitrile, and cyclic aromatic hydrocarbon ligands have been recorded under a range of conditions auid a matrix isolation UV study of the direct synthesis of (C2H4>f Eu using europium atoms has been reported. ... 

The direct synthesis of anthraquinone from phthalic anhydride and benzene has been reported to proceed over zeolite Beta [50] in a shape selective manner. In a conventional anthraquinone synthesis, anthracene is used as a feedstock for oxidation. Once there is a shortage of it in the market, additional anthracene could be produced by isomerization of its isomer, viz. phenanthrene. This, however, is not possible by direct isomerization of the trinuclear aromatic system but involves the partially (symmetrically) hydrogenated species. Consequently, isomerization of symmetrical octahydrophenanthrene to symmetrical octahydro-anthracene was studied by Song and Moffatt [51]. As sketched in Figure 3, a high yield of symmetrical octahydroanthracene can be obtained over zeolite H-mordenite (ngj/nyy = 8) at 250 °C (liquid phase, decalin as solvent). These examples show that (shape selective) catalysis on zeolites is more and more expanding into the conversion of polycyclic aromatics, and we foresee continued interest and success in this field of zeolite catalysis. 

A direct synthesis of the aromatic aldehydes by means of the Friedel-Crafts reaction could not be brought about until recently, because of the instability of formyl chloride, which, if formed, decomposes immediately into carbon monoxide and hydrochloric add ... 

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