Dimethyl by-products

An advantage of this method is that separating acidic (10) from the neutraJ dimethylated by-product is very easy. 

Under the same conditions (batch or GL-PTC) discussed for CHg-acidic compounds, primary aromatic amines also react with DMC. In this case, although the reaction yields selectively the mono-A-methylated amines with no dimethylated by-products, sizable amounts of methyl carbamates (ArNHCOgMe) are formed. ° Much better results can be gathered in the presence of zeolites, particularly alkali metal exchanged Y and X faujasites. These aluminosilicates posses pseudospheri-cal cavities (supercavities) of 11-8 A in diameter, which can be accessed through channels whose size is 7.4 kP ... 

Among the different synthetic procedures available for the preparation of hydratropic acids (e.g., indirect methylation of arylacetic acids,4 asymmetric hydroformylation of styrenes,5 rearrangements of a-bromoalkyl aryl ketals,6 etc.), direct methylation of arylacetic acid derivatives seems the most attractive from both economical and synthetic aspects the reagents are easily accessible and a one-pot reaction is involved. Nevertheless, this procedure is seldom used since the yields of the monomethyl derivatives are severely limited by the low selectivity of the reaction. Sizeable amounts of dimethylated by-products form.2 Even under phase-transfer catalysis conditions, high selectivity in monomethylation is elusive.7-8... 

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See also in sourсe #XX -- [ ]

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