A rapid and efficient method has been found for preparing coumaric acid and 4-methylcoumaric acid from coumarin and 7-methylcoumarin respectively by treatment with mercuric oxide in the presence of cold alkali. 5-nitrocoumaric acid is not produced in the cold and is formed only by boiling the mixture of 6 nitrocoumarin, mercuric oxide and alkali. The action of cold alkali and mercuric acetate or of hot alkali and mercuric oxide on coumarin yields mercurated coumaric acids. From these pure coumaric acid can be produced by using ammonia and hydrogen sulphide.

A rapid and efficient method has been found for preparing coumaric acid and 4-methylcoumaric acid from coumarin and 7-methylcoumarin respectively by treatment with mercuric oxide in the presence of cold alkali. 5-nitrocoumaric acid is not produced in the cold and is formed only by boiling the mixture of 6 nitrocoumarin, mercuric oxide and alkali. The action of cold alkali and mercuric acetate or of hot alkali and mercuric oxide on coumarin yields mercurated coumaric acids. From these pure coumaric acid can be produced by using ammonia and hydrogen sulphide.

Coumaric acids which ordinarily form hydroxystyrenes on heating yield the corresponding coumarins when heated in the presence of mercuric oxide or chloride. The scope of the use of concentrated sulphuric acid and alcohol saturated with hydrogen chloride for producingtrans tocis inversion has been examined. The former is useful for nitrocoumaric acid whereas the latter is suitable for coumaric and methylcoumaric acids. Mercuric chloride in neutral aqueous solution has been found to be very satisfactory for both types of acids.

In methyl alcoholic solution coumarin reacts with mercuric acetate to form 3:6:8-triacetoxymercuri-4-methoxymelilotic anhydride. By the action of sodium hydroxide and hydrogen sulphide β-methoxymelilotic acid is obtained from it and by the action of bromine 3:6:8-tribromocoumarin. 7-methylcoumarin behaves similarly giving a trimercury compound. 6-nitrocoumarin forms 3:8-diacetoxymercuri-6-nitro-4-methoxymelilotic anhydride which, with alkali and hydrogen sulphide, gives 5-nitrocoumaric acid and with bromine 3:8-dibromo-6-nitrocoumarin. It is therefore established that mercuric acetate reacts with the double bond in these coumarins and further mercurates the benzene ring in positions 6 and 8 if they should be free. Mercuric chloride adds on to the double bond in coumarin and 7-methylcoumarin. The reactions of these addition products have been studied. 6-nitrocoumarin does not react with this reagent.

When mercuric acetate reacts with coumarinic acid in cold aqueous solution it adds on to the double bond and mercurates the benzene ring in positions 3 and 5. When the product is dissolved in sodium hydroxide the addenda get eliminated so that 3 ∶ 5-diacetoxymercuri-coumaric acid is produced on acidification. These compounds yield pure coumaric acid on being decomposed with hydrogen sulphide in alkaline solution. 5-Nitrocoumarinic acid adds only at the double bond and does not get mercurated. The product therefore yields the nitrocoumaric acid easily on dissolving in aqueous alkali and subsequently acidifying the solution.

In methyl alcoholic solution mercuric acetate adds on to the double bond in coumaric acids and their esters and mercurates positions 3 and 5 if they should be free. The constitution of these compounds has been established by treatment with bromine in glacial acetic acid and by examination of the action of caustic alkali on the bromocompounds. They give rise to brominated coumarilic acids.

The stabletrans acids, Psoralic and Isopsoralic acids, have been prepared from Psoralen and Isopsoralen. With concentrated sulphuric acid they undergo complex changes whereas in the presence of sunlight and aqueous mercuric chloride they yield the original pyrones. Though Isopsoralic acid undergoes ring closure more easily the difference is not great.

By the action of bromine on coumaric, 4-methylcoumaric and 5-nitrocoumaric acids in boiling glacial acetic acid solution 3∶6∶8-tribromocoumarin, 3∶6∶8-tribromo-7-methylcoumarin and 3∶8-dibromo-6-nitrocoumarin have been obtained in good yield. The primary products are the dibromides of the bromo-compounds produced by the addition at the double bond, subsequent substitution in the nucleus and final ring closure. Hydrogen bromide gets slowly removed during the boiling and during the subsequent crystallisations so as to yield the above-mentioned bromocoumarins. The best method for this however is to use cold alcoholic potash. Small quantities of the lower bromination products are also produced as by-products.

The action of alkali on a number of coumarins with methyl groups in the 4-position has been studied in detail. Each of them yields readily only one acid which, though fairly stable, has the property of undergoing change into the corresponding coumarin under the action of heat and dehydrating agents. The acids, however, cannot be converted into stabler isomers by methods which are definitely effective in convertingcis intotrans acids. The methyl ethers of the acids are easily obtained by methylating the acids or the original pyrones in the presence of alkali in an aqueous alcoholic medium. Their properties are those of ethers of thetrans acids since they cannot be converted into isomeric compounds by methods which are definitely successful in convertingcis intotrans ethers. It is therefore concluded that the acids and their ethers derived from 4-methylcoumarins aretrans compounds. The comparatively ready formation of these acids and their ready conversion again into the coumarins are explained on the basis of the tautomeric mechanism which renders the geometrical inversion very facile.

From the seeds ofErythrina indica a fixed oil and a water-soluble alkaloid have been isolated. The properties of the oil have been compared with those of the oil of the Formosan variety and found to differ in the degree of unsaturation. The alkaloid has been identified as hypaphorine. The bark contains, besides a large amount of mineral matter and resin, the same base which is also present in the leaves to a smaller extent.

The action of mercuric acetate in methyl alcoholic solution on (1) umbelliferone, (2) 4-methylumbelliferone and (3) 4: 7-dimethylcoumarin has been investigated. With umbelliferone addition at the double bond and substitution in positions 6 and 8 take place whereas in the case of its 4-methyl derivative position 8 alone is mercurated to yield a monoacetoxymercuri-compound. In regard to the last compound the reaction stops with addition at the double bond and mercuration of the 6th position, the position 8 escaping the attack of the reagent. It is concluded that owing to the influence of the substitutent groups the reactivity of the three active centres of the coumarin molecule are differently affected.

The action of diazomethane on herbacetin yields 3∶7∶8∶4′-tetramethylherbacetin. The pentamethyl ether is obtained by the further methylation of the above tetramethyl compound with dimethyl sulphate and sodium hydroxide in aqueous acetone medium.

The constitution of Herbacitrin is established as the 7-glucoside of Herbacetin by methylating the glucoside through the acetyl derivative and isolating 7-hydroxy-3: 5: 8: 4′tetramethoxy flavone from the hydrolysis of the methylated glucoside. Similarly, the constitution of Quercimeritrin is confirmed as the 7-glucoside of Quercetin.

The acetyl derivatives of coumaric, 4-methylcoumaric, 5-nitrocoumaric, psoralic and isopsoralic acids have been prepared and their behaviour studied under conditions which bring abouttrans tocis inversion. Under the influence of sunlight, the first three acids produce the corresponding coumarins on prolonged exposure. When heated to above their respective melting points all the acetyl compounds undergo inversion to an extent of 60–80%. Along with the pyrones, highly polymerised resinous compounds are also produced on heating. Treatment with equimolecular amounts of mercuric chloride in aqueous or aqueous alcoholic medium brings about inversion in all the cases with almost theoretical yields.

By the action of methyl iodide and potassium carbonate, quercetin underwent complete methylation, while herbacetin and gossypetin yielded 3∶7∶8∶4′-tetramethyl ether and 3∶7∶8∶3′∶4′-pentamethyl ether respectively. This reagent, therefore, resembles diazomethane in the methylation of the naturally occurring flavonols.

On treatment with diazomethane, butrin gives rise to a monomethyl ether which yields on hydrolysis with acids a mixture of 4′-O-methylbutin and 4′-O-methylbutein, the latter being the major component. The constitutions of these two products have been established by alkaline oxidation, yielding isovanillic acid and comparison with synthetic samples. It is, therefore, concluded that butrin is 3′: 7-diglucoside of butin, and thus it is the first instance of a glycoside to contain the sugar residues in two different positions amongst the group of anthoxanthins and also the first instance to carry a sugar group in the side phenyl nucleus amongst both anthoxanthin and anthocyanin pigments.

The colouring matter of the flower petals ofHibiscus cannabinus consists mostly of the glucoside cannabiscitrin along with small quantities of the corresponding aglucone cannabiscetin. The properties and reactions of these two substances are described along with those of some of their derivatives.

Cannabiscetin forms a hexaacetate and a hexamethyl ether. It is a flavonol exhibiting similarities with gossypetin and herbacetin particularly in regard to alkali colour reactions and gossypetone reaction. It yields gallic acid on being subjected to alkali fission, its methyl ether producing trimethyl gallic acid. It is, therefore, concluded to be 3:5:8:3′:4′:5′ hexahydroxy flavone.

The final constitution of cannabiscitrin has been established. It is a monoglucoside of the flavonol cannabiscetin, carrying the sugar group in the side phenyl nucleus in the 3′-position. This has been arrived at from the following considerations:—It gives the gossypetone reaction and after complete methylation and hydrolysis, it yields a pentamethyl cannabiscetin which on decomposition produces 4∶5-dimethyl gallic acid. The same acid is also obtained by first decomposing cannabiscitrin with alkali, and then subjecting the products to methylation and subsequent hydrolysis. Thus the glucoside belongs to an unusual type and resembles butrin.

Quercetagitrin, a monoglucoside of quercetagetin, has for the first time been isolated from the flowers of the African Marigold (Tagetes erecta). It is not a 3-glucoside since it gives a red precipitate with lead acetate and does not undergo easy hydrolysis with acids. Further it is easily oxidised in cold alkali, and after methylation the products of decomposition yield veratric acid. The glucose group, therefore, is not present in the side phenyl nucleus. By complete methylation and subsequent hydrolysis of the glucoside, a pentamethyl quercetagetin is obtained. This ether is a new compound, and differs from 3∶6∶7∶3′∶4′-pentamethyl quercetagetin in all its properties, and hence the free hydroxyl group in it is in either the 6th or the 7th position. The allyl ether of this new pentamethyl quercetagetin smoothly undergoes the Claisen Rearrangement, indicating thereby that the ortho-position with respect to the allyloxy group is unsubstituted. Hence the allyl ether should be 3∶5∶6∶3′∶4′-pentamethyl-7-allyl quercetagetin, and the new pentamethyl ether should have the constitution of 3∶5∶6∶3′∶4′-pentamethyl quercetagetin. Consequently quercetagitrin is the 7-glucoside of quercetagetin.

A new flavonol, patuletin has been isolated from the petals of the flowers ofTagetes patula (French Marigold). It contains five hydroxyl groups and yields a pentaacetate and a pentamethyl ether. It is, therefore, isomeric with quercetin and herbacetin. On oxidation in cold alkali, the substance decomposes into protocatechuic acid which could be isolated after methylation as veratric acid. The completely methylated ether also yields veratric acid on boiling with potash. Assuming that a hydroxyl group is present in position 5, as is the case with most of the naturally occurring flavones and flavonols, the remaining hydroxyl group in the compound is concluded to be in position 6 in view of the properties of the flavonol and its resemblance to quercetagetin. Hence patuletin is represented as 3∶5∶6∶3′∶4′-pentahydroxy flavone.

Luteolin is present in the form of its glucoside in the yellow variety of the flowers ofChrysanthemum indicum, whereas the red, scarlet red and the deep red variety contains the anthocyanin, chrysanthemin. Just as the simultaneous occurrence of quercetin and cyanidin is frequent, a similar correlation between the corresponding flavone, luteolin and cyanidin may also be common.

A new flavonol glycoside has been isolated from the flower petals ofHibiscus sabdariffa, and has been named Hibiscitrin. Its aglycone, Hibiscetin is a hexahydroxy flavonol forming a heptaacetyl derivative on acetylation. When decomposed with boiling 50% alkali, its heptamethyl ether produces trimethyl gallic acid, indicating thereby the existence of hydroxyl groups in 3′, 4′ and 5′ positions in hibiscetin. On oxidation withp-benzoquinone, the pigment yields the corresponding quinone, and hence it should contain two hydroxyl groups in positions 5 and 8. It resembles gossypetin in many of its properties especially the colour changes with alkaline buffer solutions, and also occurs along with it in the flowers. It is, therefore, expected that the benzopyrone part of hibiscetin would be just the same as in gossypetin, and hence it is assigned the structure of 3∶ 5∶ 7∶ 8∶ 3′∶ 4′∶ 5′-heptahydroxy-flavone.

The flower petals ofHibiscus sabdariffa contain hibiscitrin as the main component. Gossypitrin is present to a smaller extent. Besides these two, a small amount of a new compound named sabdaritrin has also been isolated. On boiling with dilute sulphuric acid it yields a new hydroxyflavone called sabdaretin.

A sample of the flower-petals ofThespasia populnea is found to contain populnin (0·33%), populnetin (0·07%) and herbacetin (mostly as its glucoside, 0·03%). The proportions vary with different samples depending on seasonal and other factors. Besides these three yellow pigments, a colourless phenolic compound called populneol is also present (0·16%).

Populnetin seems to be a new tetrahydroxy flavone and populnin is its monoglucoside.

The new non-glycosidic substance obtained from the Indian cotton flowers has been shown to consist mostly of populnetin from a comparison of the methyl ethers. The characteristics of the methyl ether of populnetin are described.

A convenient method of preparing 2∶4-dihydroxy-ω∶3∶6-trimethoxyacetophenone (I) directly from 2∶6-dibenzyloxy-1∶4-dimethoxybenzene is described. By the condensation of (I) with the sodium salt and anhydride of trimethylgallic acid, 7-hydroxy-3∶5∶8∶3′∶4′∶5′-hexamethoxyflavone (II) is obtained. Methylation of (II) yields a heptamethyl ether (III) identical with heptamethyl hibiscetin. Demethylation of (II) gives rise to a heptahydroxy flavone (IV) which is found to be identical with hibiscetin in all its properties and reactions. The constitution of hibiscetin is therefore confirmed by synthesis as 3∶5∶7∶8∶3′∶4′∶5′-heptahydroxy flavone.