• G Viswanath

      Articles written in Proceedings – Section A

    • Nuclear oxidation in flavones and related compounds - Part XXV. Isomers of pedicinin

      K J Balakrishna T R Seshadri G Viswanath

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      The structure of 6-methoxy-4 ∶ 5 ∶ 7-trihydroxy-benzal-coumaranone was suggested by Saloojaet. al.3 for one of the forms of pedicinin. A substance of this constitution has now been synthesised by applying the two stage process of nuclear oxidation to an appropriate compound of the benzalcoumaranone series. The synthetic product differs markedly from pedicinin. Similar difference has been noticed earlier with the flavanone isomer, allo-pedicinin. It is concluded therefore that the two melting points noted for pedicinin are due to the existence of two crystal forms.

    • Formation of quinones by oxidative demethylation - Part IV. Isomers of methyl pedicinin

      K J Balakrishna T R Seshadri G Viswanath

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      Two isomers of methyl pedicinin are synthesised and studied: (1) 4: 7-dihydroxy-5: 6-dimethoxy-benzal-coumaranone and (2) 5: 6-dimethoxy-4: 7-quino-benzyl-coumaranone. The first is made from 2-hydroxy-3: 4: 5: 6-tetramethoxy-chalkone by conversion into the corresponding benzal-coumaranone, oxidative demethylation to 4: 7-quinone and reduction to the quinol. The second synthesis condenses pentamethoxy-benzene with α-bromo-β-phenyl-propionyl chloride to yield tetramethoxy-benzyl-coumaranone and oxidises it with nitric acid to the quinone. Their properties are different from methyl pedicinin and they do not undergo conversion into it. It is therefore concluded that methyl pedicinin should be given only the quinone chalkone formula and that the alternative formulations are not valid. Further the possibility of reversible isomeric change between chalkones and benzylcoumaranones does not find experimental support.

    • A note on 4:5:6-trimethoxy-coumaran-3-one

      K J Balakrishna T R Seshadri G Viswanath

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      4:5:6-Trimethoxy-coumaranone is obtained from quercetagetol-tetramethyl ether by treatment with hydrobromic acid and methylation of the product. It is conveniently synthesised from 2:6-dimethoxy-quinol which undergoes Friedel and Craft’s reaction with chloracetyl chloride satisfactorily.

    • A note on the determination of resacetophenone by Koppeschaar’s method

      K Neelakantam G Viswanath

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      Quantitative studies on the bromination of resacetophenone showed that the reaction was slow and progressive and its magnitude depended primarily on the amount of bromate initially added in excess of the theoretical equivalent so that reproducible results could not be obtained directly by Koppeschaar’s method. However, on plotting the volume of bromate initially added against the excess found by titration, a linear graph was obtained which on extrapolation to zero excess gave the value of bromate equivalent to di-bromination of the ketone present in solution. The estimated maximum error involved was of the order of 5%.

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