(4) THE CARBOHYDRATES OF BARLEY STRAW
(Chem. Soc. J. 1898, 459).
C. F. cross, E. J. Bevan, and Claud Smith.
These are a series of investigations mainly devoted to establishing the identity of the furfural-yielding group which is a characteristic constituent.
This 'furfuroid' while equally resistant to alkalis as the normal cellulose group with which it is associated, is selectively hydrolysed by acids. Thus straw cellulose dissolves in sulphuric acids of concentration H2SO4.2H2O - H2SO4.3H2O, and on diluting the normal cellulose is precipitated as a hydrate, and the furfuroid remains in solution. But this sharp separation is difficult to control in mass. By heating with a very dilute acid (1 p.ct. H2SO4) the conditions are more easily controlled, the most satisfactory results being obtained with 15 mins. heating at 3 atm. pressure.
(1) Operating in this way upon brewers' grains the furfuroid was obtainable as the chief constituent of a solution for which the following experimental numbers were determined:—Total dissolved solids, 28.0 p.ct. of original 'grains'; furfural, 39.5 p.ct. of total dissolved solids, as compared with 12.5 p.ct. of total original grains; cupric reduction (calc. to total solids), 110 (dextrose = 100) osazone; yield in 3 p.ct. solution, 35 p.ct. of weight of total solids.
| Pentosazone | ||||
| Analysis | N | 17.1 | 17.3 | 17.07 |
| C | 62.5 | 62.3 | 62.2 | |
| H | 6.4 | 6.5 | 6.1 | |
| Melting-point | 146°-153° |
From these numbers it is seen that of the total furfuroids of the original 'grains' 84 p.ct. are thus obtained in solution in the fully hydrolysed form, which is that of a pentose or pentose derivative. It was, however, found impossible to obtain any crystallisation from the neutralised (BaCO3) and concentrated solution, the syrup being kept for some weeks in a desiccator. It was noted at the same time that the colour reaction of the original solution with phloroglucol and hydrochloric acid was a deep violet, in contradistinction to the characteristic red of the pentoses. On oxidation with hydrogen peroxide, in the proportion of 1 mol. H2O2 to 1 mol. of the carbohydrate in solution, carbonic anhydride was formed in quantity = 20.0 p.ct. of the latter.
Fermentation (yeast) experiments also showed a divergence from the resistant behaviour of the pentoses, a considerable proportion of the furfuroid disappearing in a normal fermentation.
(2) The quantitative methods above described were employed in investigating the barley plant at different stages of its growth. The green plant was extracted with alcohol, the residue freed from alcohol and subjected to acid hydrolysis.