B.—CHEMISTRY 51 
a pigment of red poppies which is now recognised by synthesis as 
cyanidin 3-gentiobioside. There is very little doubt that pelargonidin 
Beligcric LORE 
sGeee 
a Aiak geal er Cs ena a 
O 
O 
(XXII) 
3-rhamnoglucoside colours the scarlet gloxinia and that pelargonidin 
3-biosides are of widespread occurrence, for example, in the ordinary 
orange-red nasturtium and in the flowers of the scarlet runner bean. 
The anthocyanins of groups (a), (6) and (c), when derived from the same 
anthocyanidin, exhibit similar behaviour as indicators. ‘Thus chry- 
santhemin, keracyanin and mecocyanin all give a violet solution in aqueous 
soda and this becomes blue on the addition of caustic alkali. On partial 
hydrolysis mecocyanin and antirrhinin actually yield chrysanthemin. 
The anthocyanins of class (d) are the most widely distributed and best- 
known members of this series of natural pigments ; they include pelar- 
gonin (XXIII), the colouring matter of the scarlet pelargonium and 
possibly the first anthocyanin to be obtained in a crystalline condition 
(Molisch’s experiment), also cyanin (XXIV), the isolation of which from 
the blue cornflower by Willstatter and Everest in 1914 was the first of 
an impressive series of investigations. 
Cl 
—— 
HO“ AN _ on HONS _< on 
| hey oa 
O-C,H,,0; ee O-C,H,,0; 
C,H,,0,:0 C,H,,0,;°0 
(XXIII) (XXIV) 
Peonin from the deep red peony and malvin (XXV) from the wild 
mallow or from certain primulz, are the peonidin and malvidin repre- 
sentatives in this group, which is completed by petunin and hirsutin. 
Quite recently the delphinidin member has been isolated from Salvia 
patens. 
The anthocyanins of group (d) differ from those of groups (a), (6) and 
(c) in their alkali-colour-reactions and in their marked instability to 
aqueous sodium hydroxide. ‘Thus cyanin, which compares with meco- 
cyanin in group (c), gives a pure blue solution in aqueous soda and the 
dilute solution becomes very quickly yellow on the addition of sodium 
hydroxide (demonstration). 
Pelargonin, cyanin, peonin, malvin and hirsutin have been synthesised 
