Pyridazon

A piridazine ring forms the nucleus for a rather unusual nontricyclic antidepre.ssant. Condensation of the keto ester 136 with hydrazine leads to the cyclic hydrazide 137. Oxidation, for example with bromine, gives the corresponding pyridazone 138. The oxygen is then replaced by chlorine by reaction with phosphorus oxychloride. Displacement of the halogen in 139 with N-ethylami-nomorpholine affords minaprine 140 [30]. 

Yoon and co-workers prepared perchlorinated pyridazines via chlorination of pyridazone 164 <00JHC1049>. They reported that the chlorination of 164 using phosphorus oxychloride gave only 165 in 81% yield. However, a solution of phosphorus pentachloride and cyclohexane provided only 166 in 81% yield. Furthermore, other reaction conditions gave a mixture of 165 and 166 in varying ratios depending upon the solvent, temperature, and reaction time. 

The protonation site of pyridazone [142] appears also to be the exocyclic oxygen, since a hypsochromic change occurs in the ultraviolet absorption upon protonation (Cookson and Cheeseman, 1972). The p/iTa-values of the 6-substituted derivatives follow a correlation with Op-constants of the substituents ... 

When two amide groups in a six-membered aromatic ring are in opposition to each other, as in maleic hydrazide, the oxo structure [143] is not so highly stabilized and tautomerism is observed in which the 6-hydroxy-3-pyridazone form [144] predominates (Katritzky and Lagowski, 1963). The p/fj-value of this compound is... 

The site of protonation of amino-substituted pyridazones [145] is not firmly established (Cookson and Cheeseman, 1972). Protonation on the ring nitrogen leading to a cation stabilized by amidinium-type resonance appears unlikely, since it would be expected to produce a bathochromic shift in the ultraviolet absorption. The reverse is observed and therefore oxygen protonation is more likely. 

Another series of compounds which are easily accessible from levulinic acid are pyridazone and pyridazine derivatives. Levulinic acid and its esters condense almost quantitatively with hydrazine to ve 6-methyl-3-P3rridazinone (XLVI), which is readily dehydrogenated by means of bromine to give 6-methyl-3-pyridazone (XLVII). 

Chlorination of the pyridazone yields 3rchloro-6-methyl-pyridazine (XLVIII) which on treatment with ammonia gives 3-amino-6-methyl-pyridazine (XLIX). The sulfanilamide derivative (L) has promising... 

Other derivatives of this class of compound show marked analgesic and antipyretic activity. Thus 2,6-dimethyl-3-pyridazone (LI, R = CHs)... 

The principal couplers for yellow images are the benzoylacetanilides and the pivaloyl-acetanilides. Dyes from the latter are better for light stability but are less active in forming dye. Reactivity is higher in two-equivalent couplers like the pyridazone (49) than in the parent four-equivalent couplers (75BRP1402511). 

There are few reports of the nitration of the pyridazines and pyrazines. The nitration of phenylpyridazines has been stated to occur exclusively in the phenyl ring (73MI1). The use of fuming nitric acid at 0°C forms only the 4-nitrophenyl derivative (95%), as does 4-chloro-2-phenyl-3-pyridazone (100%), and 4-amino-2-phenyl-3-pyridazone (60%) (47JCS549). 

Crathome [16] reported a method for the determination of Pyrazon (5-amino-4-chloro-2-phenyl-3-pyridazone) in non saline waters. Pyrazon was isolated from water samples (500mL) by rotary evaporation to dryness in vacuo, extraction of the solid residue with methanol (2><25mL) and further evaporation of the methanol extract (to approx. 2mL). Final concentration (to 0.5mL) was achieved by removal under a stream of nitrogen. 

With SH , P4S10, and thiols, displacement of halogens inpolyhalopy-ridazines and pyridazones proceeds usually at elevated temperatures with all halogens present in the nucleus. 

PHENOSANE 1-PHENYL-4-AMINO-5-CHLORO-PYRIDAZON-(6) (GERMAN) 1-PHENYL-4-AMINO-5-CHLOROPYRIDAZONE-6 1-PHENYL-4-AMINO-5-CHLORO-6-PYRIDAZONE PYRAMINE PYRAMIN RB PYRAZON PYRAZONE PYRAZONL... 

C9H20O 2,6-dimethyl-4-heptanol 108-82-7 -65.15 1.0257 2 18540 C10H6CI2N2O 1-phenyl-4,5-dichioro-6-pyridazone 1698-53-9 25.00 1.4528 2... 

Treatment of the methoxylactol (198) with ethanolic hydrazine afforded the novel ring-A-fused pyridazone (237). Diazomethane reacts sufficiently readily with iminium salts, e.g. (238), to allow the preparation of aziridinium salts (239) in the presence of diazomethane-sensitive carbonyl groups.Addition of cyanamide and halogen to 2- and 5-enes affords uic-halogeno-cyanoamines which give cyanoimines on contact with base. ... 

The herbicidal properties of the pyridazine group were described by Fischer in 1962, and the first of them, pyrazon, 5-amino-4-chloro-2-phenyl-3-pyridazone (1), was introduced in 1962 by the BASF AG under the trade name Pyramin . 

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