48 SECTIONAL ADDRESSES 
The most recent, and certainly one of the most interesting, examples of 
this kind is found in the phthalocyanines which contain a porphyrazine 
structure, that is the porphin skeleton of the natural porphyrins in 
which some —CH= groups are replaced by —N=. Dr. Linstead will 
shortly give an account of his investigations of these substances and of 
their remarkable properties. 
It was primarily with cognisance of Dr. Linstead’s work that I ventured 
to direct your attention to analogues of natural colouring matters ; this is 
at the technical end of the scale, and in contrast Professor Kuhn has kindly 
consented to describe some novel natural colouring matters of high 
biochemical interest. 
The following sections of this address deal with developments of the 
chemistry of the red, blue and violet colouring matters of flowers and 
blossoms. 
STRUCTURE AND SYNTHESIS OF THE ANTHOCYANINS. 
A brief description of the chemistry of the anthocyanins is necessary at 
this stage. ‘The brilliant and pioneering researches of Richard Willstatter 
and his co-workers (1914— __) established the main features of the chemistry 
of the anthocyanins which were recognised as saccharides, occasionally 
acylated, of the anthocyanidins. They exhibit amphoteric character, 
forming salts with both acids and bases. Thus the violet pigment cyanin, 
which can be isolated from blue cornflowers, red roses, deep red dahlias 
and other flowers, forms a blue sodium salt and a red hydrochloride. 
The hydrolysis of the latter by means of hot aqueous hydrochloric acid 
into cyanidin chloride and glucose is represented by the equation : 
Co7H 51046 Cl + 2H,0 = C,5Hy,06Cl + 2C,H,,0, 
cyanin chloride cyanidin glucose 
chloride 
The constitution of cyanidin chloride (X) has been established by analysis 
and numerous syntheses ; the first of these (Willstatter and Mallison) 
utilised the reduction of quercetin (IX) by means of magnesium in 
aqueous methyl alcoholic hydrochloric acid solution (demonstration). 
Cl 
4 On\ OH HO Oo. OH 
HO 
C OH C OH 
eT) ee 
= (& 
Pan NOH H,+HCl 7 NOH +H,0 
WARNES 2 6 SCH +H, 
(IX) | (X) 
In this process a widely distributed anthoxanthin yields a widely 
distributed anthocyanidin, and the temptation to assume that similar 
reactions occur in the plant laboratory is very great. There is, however, 
very little justification for this view and the experimental support brought” 
forward in its favour will not survive careful scrutiny. The alleged 
