The Production of Anthocyanins and Anthocyanidins. 447 



decided to test the pigments obtained by direct extraction of various flowers, 

 in particular with a view to producing anthocyanins from the yellow 

 glucosides present in them. 



Having already shown that oxidation after reduction was not necessary 

 for the production of anthocyan pigments — and this was confirmed in every 

 ease where reduction under ligroin was carried out — particular attention was 

 given to proving that anthocyanins could be produced directly from yellow 

 glucosides without intermediate formation of anthocyanidins, and in this the 

 author was successful. 



The yellow wallflower, yellow daffodil, white narcissus, yellow or white 

 tulip, white primula (obconica), yellow crocus, yellow jasmin, yellow primrose 

 (the presence of yellow pigments in the white flowers was shown by action 

 of dilute ammonia, when, the plant acids being neutralised, the yellow colour 

 appears), and even lemon peel, all yielded by reduction alone red pigments, 

 and, indeed, pigments which upon investigation proved to be in every case 

 an anthocyanin, no trace of anthocyanidin being produced when the reduc- 

 tions were carried out in the cold. No oxidation after reduction was 

 necessary for the production of the anthocyanin pigment, provided that in 

 one or two instances care was taken not to carry the reduction too far. 



Reduction was carried out by zinc (fine granulated) in ca. 2X aqueous acids, 

 and also by electrolysis in 2N sulphuric acid, using lead electrodes (lead 

 has been found to yield salts with anthocyanins, which, however, are decom- 

 posed by acids ; lead salts have no harmful effect upon anthocyanins). 



At first some difficulty was experienced in explaining the observations of 

 Keeble, Armstrong, and Jones* that in the case of yellow wallflower, yellow 

 daffodil, yellow crocus, cream polyanthus, and Chinese primrose oxidation 

 was necessary after reduction in order to obtain a red pigment. A ready 

 explanation was, however, forthcoming when the case of the yellow tulip 

 was examined, for here, when reduction was rapid, there appeared but a 

 transient pink, passing rapidly to a colourless solution, which, however, on 

 addition of hydrogen peroxide immediately developed a red colour. Slow 

 reduction, however, by zinc (very small quantities) and HC1 or, much better, 

 slow electrical reduction gave readily the red pigment, and this proved to 

 be as in the other cases an anthocyanin. The red solution on stronger 

 reduction passed to a colourless one, from which the anthocyanin was again 

 produced by the addition of hydrogen peroxide. 



It has been found that in each case excessive reduction produced to a 

 greater or less extent the above result, and this clearly explains the results 

 of Keeble, Armstrong, and Jones (loc. cit.). 



* 'Eoy. Soc. Proc.,' B, vol. 87, p. 113 (1913). 



