Aromatic compounds, addition alkyl substituents

Because of the generally greater reactivity of >C=C<, -C=C- and aromatic rings toward OH radical addition, H-atom abstraction from alkyl or substituted alkyl groups in the alk-enes, alkynes, and aromatic compounds is generally of minor importance, and Kwok and Atkinson (1995) set the substituent group factors F(>C=C<), F(-C=C-) and F(-C6H5) equal to unity. 

Alkenyl and aryl substituents stabilize the C=0 double bond of carbonyl compounds even more than alkyl substituents. This is due to their pi electron-donating (+M) effect, which allows one to formulate additional zwitterionic resonance forms for carbonyl compounds of this type. Thus, no hydrates, hemiacetals, oligomers, or polymers can be derived from unsaturated or aromatic aldehydes. 

The nucleophilic cleavage of aryl alkyl ethers gives the corresponding phenol with only 1 equiv. of thiophenol in the presence of N-methyl-2-pyrrolidinone (NMP) in a catalytic amount of potassium carbonate. The aromatic nitro and chloro substituents which are displaced with stoichiometric thiolates are preserved by this method. Moreover, a(B-unsaturated carbonyl compounds do not undergo Michael addition of thiolate under these conditions. 

The oxidation of various hydrocarbons such as n-octane, cyclohexane, toluene, xylenes and trimethyl benzenes over two vanadium silicate molecular sieves, one a medium pore VS-2 and the other, a novei, iarge pore V-NCL-1, in presence of aqueous HjOj has been studied. These reactions were carried out in batch reactors at 358-373 K using acetonitrile as the solvent. The activation of the primary carbon atoms in addition to the preferred secondary ones in n-octane oxidation and oxidation of the methyl substituents in addition to aromatic hydroxyiation of alkyl aromatics distinguish vanadium silicates from titanium silicates. The vanadium silicates are also very active in the secondary oxidation of alcohols to the respective carbonyl compounds. V-NCL-1 is active in the oxidation of bulkier hydrocarbons wherein the medium pore VS-2 shows negligible activity. Thus, vanadium silicate molecular sieves offer the advantage of catalysing selective oxidation reactions in a shape selective manner. 

Iron complexes containing bidentate alkyl and aryl phosphorus ligands cleave a variety of C-H bonds under mild conditions, Hydrido acetylide complexes were prepared by oxidative addition of primary acetylenes in the Fe(DPPE)2 and the Fe(DMPE)2 systems [DPPE = bis(diphenylphos-phino)ethane, DMPE = bis(dimethylphosphino)ethane]. The Fe(DMPE)2 system also cleaves C-H bonds of activated methyl groups, aromatic compounds, and certain other sp hybridized molecules. The C-H cleavage reactions are reversible, resulting in equilibrium mixtures of isomeric products in many cases. Studies of substituted benzenes show that while product stability is favored by electron withdrawing substituents, steric effects play a predominant role in the determination of product distribution. 

There are two major variants of ONSH with nucleophiles sensitive to oxidation (a) addition is an irreversible process and (b) equilibrium of the reversible addition is shifted in favor of the adducts. Nucleophilic organometallic compounds, alkyllithium and alkyl-magnesium reagents, are active enough to add irreversibly to nitroarenes in positions occupied by hydrogen to form the adducts [72]. Due to irreversibility of the addition, the SNAr reaction on treatment of ortho- and para-halonitrobenzenes with these C-nucleophiles is not observed. Further oxidation of the formed adducts with a variety of oxidants, preferably KMn04, affords products of oxidative nucleophilic alkylation. This reaction appears to be an important method for direct incorporation of alkyl substituents into aromatic rings (Scheme 14) [72, 73]. 

I itro-DisplacementPolymerization. The facile nucleophilic displacement of a nitro group on a phthalimide by an oxyanion has been used to prepare polyetherimides by heating bisphenoxides with bisnitrophthalimides (91). For example with 4,4 -dinitro monomers, a polymer with the Ultem backbone is prepared as follows (92). Because of the high reactivity of the nitro phthalimides, the polymerkation can be carried out at temperatures below 75°C. Relative reactivities are nitro compounds over halogens, Ai-aryl imides over A/-alkyl imides, and 3-substituents over 4-substituents. Solvents are usually dipolar aprotic Hquids such as dimethyl sulfoxide, and sometimes an aromatic Hquid is used, in addition. 

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