• G S Krishna Rao

      Articles written in Proceedings – Section A

    • A note on the formation of quinones by oxidative demethylation and the effect of methylating agents on them

      G S Krishna Rao K Visweswara Rao T R Seshadri

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      Using typical examples, some of which are new, oxidative demethylation of methoxy benzenes, ketones, chalkones and flavones with nitric acid is discussed. The flavones without exception undergo simple conversion into para quinones. The others fall into two categories: (a) 1∶2∶4∶5-Tetramethoxy benzene and its derivatives suffer only oxidative demethylation like the flavones to yield the corresponding para quinones: (b) 1∶2∶3∶5-Tetramethoxy benzene and its derivatives, either ketones or chalkones, on the other hand undergo further change involving demethylation of another methoxyl group yielding hydroxy quinones. In the case of ketones and chalkones this second stage demethylation involves the methoxyl which is situated ortho to the ketonic carbonyl and which is subjected to the combined influence of this carbonyl and the one in the quinone group. These results are of importance in the study of pedicellin-pedicinin conversion.

      Under favourable conditions hydroxy quinones can be methylated by means of dimethyl sulphate and potassium carbonate to the corresponding methyl ethers,e.g. lawsone. In some cases fully methylated ethers of the corresponding quinols could be obtainede.g. gossypetone. This is obviously due to the preliminary dismutation of the quinone into the corresponding quinol and complex products. The action of alkali on benzoquinone and tetramethyl gossypetone has been studied using different conditions.

    • Formation of quinones by oxidative dealkylation - Part II. Constitution of pedicinin

      G S Krishna Rao K Visweswara Rao T R Seshadri

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      An essential point which has not been established in a simple manner by the previous study of pedicinin and its synthesis relates to the position of the methoxyl group. This has now been settled in an unambiguous manner by the reduction of pedicinin with stannous chloride to dihydropedicinin and its ethylation. The product is found to be identical with 4-methoxy-2∶3∶5∶6-tetraethoxy chalkone obtained synthetically starting from 2∶6 dimethoxy quinol. This chalkone undergoes oxidative de-ethylation with nitric acid yielding ethyl pedicinin and eventually pedicinin.

      The toxic properties of dimethyl pedicinin (2∶4∶5-trimethoxy-quino chalkone) have been studied using fish.

    • A new effect of hydrogen bond formation (chelation) - Part II. Constitution of despedicellin, dihydropedicinin and isopedicin

      G S Krishna Rao K Visweswara Rao T R Seshadri

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      Though despedicellin and dihydropedicinin are prepared from chalkones and were earlier given the chalkone constitution, their properties indicate that they are flavanones. This constitution is also in accordance with the recent discovery of the new effect of hydrogen bonds on the stability of flavanones. It is confirmed by the following experiments. (1) The two compounds undergo partial methylation with diazomethane yielding 5-hydroxy-6: 7∶8-trimethoxy-flavanone which forms with nitric acid 6∶7-dimethoxy-quinoflavanone identical with the sample obtained from 5∶6∶7∶8-tetramethoxy flavanone. (2) Dihydropedicinin undergoes oxidation withp-benzoquinone to form allopedicinin which is different from pedicinin. Methylation of this with diazomethane yields 6∶7-dimethoxyquinoflavanone. (3) The estimation of active hydrogen atoms agrees with the flavanone and not chalkone structure for these two compounds. That isopedicin is also a flavanone is confirmed by its methylation with diazomethane to 5∶6∶7∶8-tetramethoxy flavanone. The constitution of the important reference compound, tetramethoxy flavanone is established by its conversion into the corresponding flavonol.

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