Pyrazoline chemical properties

The features of the electronic structure of aryl-substituted pyrazolines influence their chemical properties. For example, in the case of 3-substituted 7V-phenyl-pyrazolines 100 reactions of formylation, acylation, nitration, sulfonation, azocoupling and other electrophilic processes involve the para position of the 7V-phenyl ring, with formation of compounds 101 [103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113]. On the other hand, some electrophilic reactions, including nitration, bromination, chlorination, formylation and azocoupling, for 3-unsubstituted pyrazolines 102 occur at position 3, yielding heterocycles 103 and in some cases as a mixture with 104 [108, 114, 115] (Scheme 2.26). This fact provides evidence for orbital control of these reactions. 

The most outstanding chemical property of 2-pyrazolin-5-ones is the activity of the hydrogen atoms at C-4. This position is very reactive, undergoing the characteristic condensations and substitutions of the active methylene group. Aldehydes and ketones react readily at this position, giving in the simpler cases a mixture of products as shown in eq 04 22.34.110.296.311.333,633.702.809.980,1123.1241.1250.1263,1288,1351 This... 

These differences in film morphology were also reflected as differences in film formation conditions, film adhesion, and in electrochemical properties. The pyrazoline beads readily formed films from solvents such as benzene. For the phenoxy TTF system, however, only CH2Cl2 was effective in forming films. In general, the TTF cross-linked polymers were found to be less adherent to the metallized substrates than the pyrazoline cross-linked polymers. Electro-chemically, it was found that the pyrazoline films showed complete activity after one potential sweep. The TTF polymer films, on the other hand, required from 5 to 20 cycles to reach full electrochemical activity as evidenced by a constant voltammogram with cycling. Furthermore, it was observed that the TTF polymer films were much less electroactive than the pyrazoline materials as shown by optical densities and total coulombs passed which were several times less for the TTF systems. 

Most chemical and physicochemical properties of aromatic substituted pyrazolines as well as isoxazolines are formed by the 7i,/ ,7i-system of the diarylhydrazone (oxime) moiety. 

In the last 20 years the pyrazole ring has attracted much attention, as it has become fairly accessible and shows diverse properties. Besides the traditional interest in pyrazole derivatives which have been the basis of numerous dyes and drugs, a number of pyrazole anesthetics have appeared.12 Recently it was established that pyrazolines are not only of interest as intermediates in the synthesis of cyclopropanes, but also as effective chemical bleaching agents, and as luminescent and fluorescent substances.3-8 The ease with which... 

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