Amine displacement steric factors

However, steric factors appear to play an important role in displacement reactions. Thus, for example, a sterically hindered amine base will not displace an unhindered potentially weaker base such as sulfide. 

Direct amination of 3(2//)-pyridazinones occurs when they are heated with hydrazine hydrate and this is a convenient route to many 4-amino-6-substituted-3(2//)-pyridazinones (Scheme 11). The reaction generally gives high yields and amination is regiospecific when the 6-position is occupied by an aromatic or heteroaromatic ring, but the parent 3(2/ -pyridazinone gives a mixture of the 4- and 5-amino-3(2//)-pyridazinones. The reaction tolerates jV-methyl substitution of the pyridazinone, but is sensitive to steric factors the presence of a 5-substituent causes a marked reduction in reaction rate, and amination does not occur with 4-phenyl-3(2//)-pyridazinone. With maleic hydrazide 4-hydrazination occurs, possibly by displacement of an intermediate amino compound or by oxidation of an intermediate 4,5-dihydro-4-hydrazino adduct both 4-hydrazino- and... 

These transamination reactions differ from the foregoing in that secondary amines are displaced by primary amines or by ammonia. They are controlled by steric factors rather than by volatility (56a). 

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