VIIl] 



AROMATIC COMPOUNDS 



119 



Of the methylated compounds, myrtillidin and oenidin may be re- 

 presented thus: 



CI 



Ho 



fY^^ 



PH 



OH 

 OH 



HO 



fV\ 



^^^ C-OCH. 



HO H 



Myrtillidin 



PH 



OCH3 

 OH 



H 



HP 



Oenidin 



Expt, 113. Preparation and reactions of pelargonin chloride. Extract the flowers 

 from two or three large bosses of the Scarlet Geranium {Pelargonium zonale) in a 

 flask with hot alcohol. Filter ofi* and concentrate on a water-bath. Then pour the 

 hot concentrated solution into about half its volume of strong hydrochloric acid. On 

 cooling, a crystalline precipitate of pelargonin chloride separates out. Examine under 

 the microscope and note that it consists of sheaves and rosettes of needles. Filter oflF 

 the crystals, take up in water and make the following experiments with the solution : 



{a) Add alkali. A deep blue-violet colour is produced. 



(6) Take two equal quantities of solution in two evaporating dishes. To one add 

 as quickly as possible some solid sodium chloride. The colour in the solution without 

 salt will rapidly fade owing to the formation of the colourless isomer in neutral 

 solution : this change is prevented to a considerable extent in the solution containing 

 salt owing to the formation of an addition compound of the pelargonin with the 

 sodium chloride which prevents isomerization (see p. 115). To portions of the water 

 solution (without sodium chloride) which has lost its colour add respectively acid 

 and alkali. The red colour returns with acid owing to the formation of the red acid 

 oxonium salt : with alkali a greenish-yellow colour will be produced due to the 

 formation of the salt of the colourless isomer. If alkali is added to the portion of the 

 pigment solution containing the sodium chloride, it will be found that it still gives 

 a violet colour. 



(c) Add sulphuric acid and amyl alcohol. The alcohol does not take up the 

 colour. Add amyl alcohol after acidifying another portion of the solution with 

 sulphuric acid and heating on a water-bath. The alcohol now abstracts some of the 

 colour. This shows that the glucoside pelargonin exists in the first case, but is de- 

 composed into the non-glucosidal pelargonidin after heating with acid. 



{d) Acidify with hydrochloric acid and add zinc dust : the colour disappears and 

 returns again after filtering. 



Expt. 114. Preparation of the acetic acid salt of pelargonin. Make an alcoholic 

 extract of petals as in Expt. 113. Evaporate down and pour into glacial acetic acid 

 instead of hydrochloric acid. The crystals of the salt formed are smaller and more 

 purple in colour than those of the chloride. 



In considering the anthocyan pigments, the question now arises — 

 What is the chemical significance of the various shades in the living 

 plant? Apparently the same pigment may be present in two flowers 

 of totally different colours, as in the blue Cornflower and the magenta 



