Ethers, aliphatic methoxylation

Aliphatic amines are mainly converted to a-substituted products [99,100], whereby especially the a-methoxylation leads to valuable reagents for synthesis. The intermediate iminium salts can be directly trapped by silyl enol ethers to form Mannich bases [108]. If the a-position is blocked or steric conditions favor it, N,N coupling to hydrazo or azo compounds occurs (Table 5, numbers 17-19). 1,1-Disubstituted hydrazines are dimerized to tetrazenes in fair to excellent yields (Table 5, numbers 20-24). The intermediate diaze-nium ions can attack enolizable carbonyl compounds to form aza-Mannich bases [109]. Arylazonaphthols undergo anodic oxidation, producing radical cations. These couple to biphenylbisazo compounds (up to 34%) or can be trapped by anisidine to form azodiphe-nylamines (up to 74%) [110a]. 

It would appear that most of the benzene ring structures in humic substances have two or more substituents, such as carbonyl, carboxyl, hydrocarbon, hydroxyl, and methoxyl and other ether functional groups. The evidence from identification of the products of degradation reactions, and more recently from NMR data, suggests that aliphatic hydrocarbons and aliphatic and aromatic ether groups link the core components in the macromolecules, and that carbonyl, carboxyl, and hydroxyl substituents are likely to be attached to some of the aliphatic hydrocarbons (Hayes and Swift, 1978). 

Ethers of tertiary aliphatic ethers give the halides smoothly when treated with hydrogen chloride.8 Benzyl ethers are also easily cleaved both benzyl groups of l,3-dibenzyloxy-2,5-dimethoxybenzene are removed in one hour by hydrochloric acid at 65°, but the methoxyl groups remain unaffected 9... 

Further investigation by Chapman and co-workers using physical methods has revealed that a-lumicolchicine is a dimer of j3-lumicol-chicine (57). UV- and IR-spectra showed the absence of an enol ether group and indicated the presence of only the styrene chromophore. The NMR-spectrum of a-lumicolchicine is similar to that of j8-lumicolchicine except that (1) the vinyl proton observed in jS-lumicolchicine is missing, (2) a-lumicolchicine exhibits one more aliphatic proton than the ]8-isomer, and (3) the methoxyl resonance at 3.63 ppm in j8-lumicolchicine has shifted to unusually high field in a-lumicolchicine (3.02 ppm). This... 

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