Seidel, F.; Thier, W.; Uber, A.; Dittmer, J. published the artcile< The formation of ""triacetylacetic ester."" II>, Safety of (9Z,12Z)-Methyl octadeca-9,12-dienoate, the main research area is .
It had been reported that in the preparation of Ac2CHCO2Et according to Claissen there is also formed Ac3CCO2Et (I), since the reaction product gave with N2H4 a product (II) assumed to be Et 3,5-dimethylpyrazole-4-acetyl-4-carboxylate (III). v. Auwers (C. A. 27, 62) doubts the existence of I and the correctness of the structure III for II. It has now been found that II changes above its m. p. into β-(5-hydroxy-3-methyl-4-pyrazolyl)crotonolactone (IV), and hence II is not a condensation product of I with N2H4 but Et β-(5-hydroxy-3-methyl-4-pyrazolyl)crotonate (V). The N2H4 first deacetylates the Ac2CHCO2Et in the reaction mixture, forming AcCH2CO2Et and AcNHNH2 (the greater part of the N2H4 thus escaping further reaction), and the unchanged N2H4 condenses with a part of the AcCH2CO2Et to 3-methyl-5-pyrazolone which combines with the rest of the AcCH2CO2Et to form V with loss of water. All attempts to prepare the true III (which is isomeric with IV) were unsuccessful, but they yielded hitherto unknown intermediate products which not only contributed to the knowledge of the reactivity of the pyrazoles and pyrazolones but also helped to establish the structure of V with certainty. Et 3,5-dimethylpyrazolone-4-carboxylate (VI), from Ac2CHCO2Et (reacting in the mono-enolic form, of which the equilibrium mixture contains 91.8%) and N2H4, gives with AcCl the 1-Ac derivative (VII) which, after saponification, is decarboxylated to 1-acetyl-3,5-dimethylpyrazole (VIII). The structure of VIII is established: (1) by condensing Ac2CH2 (76% enol) with N2H4 to 3,5-dimethylpyrazole (IX) and acetylating IX to VIII with AcCl in pyridine; (2) by synthesis of VIII from Ac2CH2 and NH2NHAc. Direct replacement of the 4-H atom on the pyrazole nucleus by acyl is not possible; to obtain 3,5-dimethyl-4-acetylpyrazole (X), CHAc3 (88.3% enol at equilibrium) must be condensed with N2H4. It reacts with AcCl to form the 1,4-di-Ac derivative (XI). It was hoped that IV (or the free acid) might be obtained by saponifying isodehydracetic ester to HO2CCH:CMeC(CO2Et):C(OH)Me and condensing the latter with N2H4, but the product was always only 3-methyl-5-pyrazolone, the isodehydracetic ester evidently breaking down into AcCH2CO2Et under even the mildest conditions. Definite proof that 3-methyl-5-pyrazolone reacts at the 4-position with AcCH2CO2Et to form V was obtained indirectly. Reaction through the NH group is excluded, for 3,4,4-trimethyl-5-pyrazolone does not react with AcCH2CO2Et but 1-phenyl-3-methylpyrazolone does, yielding Et (β-5-hydroxy-1-phenyl-3-methyl-4-pyrazolyl)crotonate (XII), which splits off EtOH at 165° to form the lactone (XIII). Further evidence that the NH group is not involved in the condensation is afforded by the fact that IV forms a Bz derivative V, obtained in 24 g. yield from a charge of 638 g. AcCH2CO2Et, 88.6 g. Na and 600 g. AcCl, m. 188°, is also obtained readily by Wolff’s method (Ber. 38, 3038(1905)); it is stable toward boiling MeOH and alc. NH3 but with PhNHNH2 and concentrated KOH gives 3-methyl-5-pyrazolone. IV, m. 246°. Free acid, from IV and 10% NaOH at 15-20°, m. 154° (decomposition), regenerates IV on heating in vacuo at 15-20° or in hot alc. VII (6.2 g. from 7.0 g. VI), m. 69°; free acid, similarly obtained (6.0 g.) from the free acid (5.0 g.) of VI, m. 164°. VIII, b12 70°, b23 84°. 1-Bz analog, b12 158°. X, needles with 1 H2O, m. 121° (decomposition) and (anhydrous) 128°. XI, m. 50°. XII, m. 88°. XIII, light yellow, m. 132°. 1-Bz derivative of VI, m. 181°.
Berichte der Deutschen Chemischen Gesellschaft [Abteilung] B: Abhandlungen published new progress about 112-63-0. 112-63-0 belongs to class esters-buliding-blocks, and the molecular formula is C19H34O2, Safety of (9Z,12Z)-Methyl octadeca-9,12-dienoate.
Referemce:
Ester – Wikipedia,
Ester – an overview | ScienceDirect Topics