Degree Name

Master of Science (MS)

Semester of Degree Completion

1979

Thesis Director

Jerry W. Ellis

Abstract

The purpose of this study was to prepare the 1,1-dimethylpyrazolium-5-oxides from a variety of N,N-dimethylhydrazones which can be prepared from the corresponding β-ketoesters.

Substitution of a methyl group at α-position of β-ketoesters makes the formation of N,N-dimethylhydrazones more difficult. The electron-withdrawing group (-NO2) and the electron-releasing group (-OCH3) as a parasubstituent of the benzene ring have the electrostatic effect to the nucleophilic attack of dimethylhydrazine to form the N,N-dimethylhydrazones.

It was found that N,N-dimethylhydrazones exist as a mixture of keto and enol tautomers based on the ir and nmr spectra. A semiquantitative analysis of the tautomerism of dimethylhydrazones was carried out by comparing the characteristic absorption of the quaternary methyl group at δ2.45 and the weak, broad peak at δ8.8 and the relative ratio of keto to enol tautomers was determined. The intramolecular hydrogen bonding shifts the ir and nmr absorptions to upfield and stabilizes the enol forms. The substitution of a methyl group in the α-position results in an decrease of the enol tautomers because of the steric and inductive effect. However, the strong electron-withdrawing -NO2 substituent at the benzene ring favors the enol form for ethyl p-nitrobenzoylacetate dimethylhydrazone.

The N,N-dimethylhydrazones were subjected to conditions conducive to cyclization to 1,1-dimethylpyrazolium-5-oxides. Two new examples of this novel heterocyclic system were prepared and fully characterized.

The nmr spectra of the synthesized 1,1-dimethylpyrazolium-5-oxides show three characteristic peaks: a strong singlet at about δ3.0 is due to the quaternary methyl group and the other two absorptions are contributed to the substituents R and R'. The UV absorption maxima of 1,1,4-trimethyl-3-phenylpyrazolium-5-oxide is shifted to longer wavelengths compared with 1,1,3,4-tetramethylpyrazolium-5-oxide.

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