Dimethylaniline amines :alkyl anilines

In acid solution aromatic amines form resins with formaldehyde. This reaction in olves the formation of nuclear methylene linkages similar to those which occur in phenol-formaldehyde resins. The reaction type characteristic of the aromatic nucleus rather than of the activating amine group, whose presence merely facilitates reaction. As a result, resins can be obtained even with tertiary amines such as dimethylaniline. Under these conditions the amine reacts as an ammono-phenol. Studies of the mechanism by which formaldehyde reacU with X-alkyl anilines in acid elution indicate that the primary reaction involves the nitrogen atom. 

A AlI lation. A number of methods are available for preparation of A/-alkyl and A[,A/-dialkyl derivatives of aromatic amines. Passing a mixture of aniline and methanol over a copper—zinc oxide catalyst at 250°C and 101 kPa (1 atm) reportedly gives /V-methylaniline [100-61-8] in 96% yield (1). Heating aniline with methanol under pressure or with excess methanol produces /V, /V-dimethylaniline [121 -69-7] (2,3). 

The extent to which secondary and tertiary amines are formed by reductive alkylation is controlled to some degree by the steric bulk of the amine and the carbonyl compound. The more hindered the system, the higher the temperature and hydrogen pressure needed to affect the reaction. While the reductive alkylation of secondary aliphatic amines with formaldehyde takes place under mild conditions (Eqn.l9.52X N,N-dimethylaniline was prepared by reductive alkylation over palladium at 120°C and 15 atmospheres pressure (Eqn. 19.53). 153 54 Reductive alkylation of aniline with acetone over palladium gave a 67% yield of the monoalkylaniline at 100°C and 40 atmospheres pressure but secondary amine formation using the more sterically accessible ketones, 2-tetralone or 2-indanone, took place at room temperature and 4 atmospheres pressure (Eqn. 19.54). 55 Palladium was the preferred catalyst in these reactions since with platinum or rhodium ring hydrogenation was also observed. 54,155... 

N,A-Dimethylaniline 355 cf-1044 A mixture of aniline (93 g), pure methanol (105 g), and 94% sulfuric acid (9.4 g) is heated at 215° for 6 h in an autoclave with a cast-iron lining. Some of the amine is alkylated thereby to the quaternary salt, and to cleave this to the tertiary base the reaction product is treated, after cooling, with 30% sodium hydroxide solution (25 g) and heated again in the autoclave for 5 h at 170°. The autoclave contents are then distilled in steam, and the amine is salted out of the distillate, separated in a separatory funnel, and distilled through a column. This gives almost pure A,jV-dimethylaniline (117 g, 96%), b.p. 192°. 

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