Nitro with reactive methylene compounds

Aromatic nitro compounds are often strongly colored. They frequently produce characteristic, colored, quinoid derivatives on reaction with alkali or compounds with reactive methylene groups. Reduction to primary aryl amines followed by diazotization and coupling with phenols yields azo dyestuffs. Aryl amines can also react with aldehydes with formation of Schiff s bases to yield azomethines. 

Compounds with Reactive Methylene Groups. In this group the coupling components with the greatest industrial importance are the A-acetoacetyl derivatives of aromatic amines (acetoacetarylides) CH3COCH2CONHAr. Anilines substituted by halogen, alkyl, alkoxy, nitro, and acylamino groups are most suitable (e.g., Napthol AS-IRG). 

Coupling with phenols is usually effected more easily than coupling with amines, and naphthols couple considerably more readily than hydroxybenzene derivatives. Reactive methylene compounds behave similarly to phenols of the benzene series. Negative substituents (halogen, nitro, sulfo, carboxyl, carbonyl, etc.) accelerate coupling when... 

Since various substituents are tolerated, the Friedlander reaction is of preparative value for the synthesis of a large variety of quinoline derivatives. The benzene ring may bear for example alkyl, alkoxy, nitro or halogen substituents. Substituents R, R and R" also are variable. The reaction can be carried out with various carbonyl compounds, that contain an enolizable a-methylene group. The reactivity of that group is an important factor for a successful reaction. 

In a variation of the Michael condensation, nitroparaffins having active methylene groups add to reactive olefinic compounds including ot,/3-unsaturated esters (method 301), a.,y6-unsaturated cyanides (method 388), and a-nitro olefins. Interaction of primary or secondary aliphatic nitro compounds with the unsaturated nitro compounds in the presence of sodium ethoxide in alcohol yields 1,3-dinitroparaffins. The reaction is general, but the yields vary, depending on the degree of polymerization that the nitro olefin undergoes and the amount of addition of alcohol to it as well as on the reactivity of the product toward further condensation. 

Active methylene compounds have been nitrated directly with nitric acid. Since the nitro group thus introduced also activates the carbon adjacent to it, the product resulting from the direct nitration of an active methylene compound is frequently highly reactive and consequently may be quite unstable—in fact, explosive. Therefore, as with all aliphatic nitro compounds, precaution must be taken to reduce the hazards of explosion to personnel and equipment. A typical example of the reaction is given in the following preparation. 

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