The use of bromine in the estimation of cellulose in plant materials.

A number of methods are available for the quantitative estimation of cellulose in plant materials and have been reviewed by Doree (1933). Almost all of them are based upon the original procedure of Cross & Bevan (1903), who used chlorine gas for the removal of lignin as 'lignone chloride' followed by hot sodium sulphite extraction. Since then Jenkins (1930) and Norman & Jenkins (1933) have proposed the use ofchlorine in solution as sodium hypochlorite to obviate the inconvenience of using gaseous chlorine. The defects in the original Jenkins (1930) method were subsequently discussed by Norman & Jenkins, who developed a modified method which eliminated them. Chlorination in this method is effected by acidification of dilute hypochlorite solution and, since the gas is liberated in contact with the material, treatment is effective and sometimes reduces the number of chlorinations necessary. Although the use of chlorine in solution is advantageous it is difficult to obtain and store sodium hypochlorite in the tropics owing to its instability. In order to obviate a return to the use of gaseous chlorine, it was thought that sodium hypobromite, which is more easily prepared than the hypochlorite, might prove equally useful in cellulose determination, or that, alternatively, nascent bromine might well be liberated in contact with the material by aoidifving a mixed solution containing bromide and bromate. After a few tests the method seemed to work satisfactorily enough to warrant the working out of a detailed analytical procedure based on the principles laid down in the chlorination processes. Althouglh Doree (1933) and Norman (1937), two of the more recent authors on cellulose chemistry, make no reference to the use of bromine in cellulose determination, Schwalbe (1938) has referred to the application of bromine for this purpose by Hugo Muller in 1877 in the form of hypobromous acid, and by Willstatter in 1913 as bromine water. Since the concentration of bromine available in these reagents for the bromination of cellulosic material is so small, the number of brominations has to be indefinitely increased. Consequently the process becomes long and laborious. The improved method described in this communication eliminates most of these defects. The reactions involved are identical in kind with those for chlorine, either gaseous or in solution. Instead of the 'lignone chloride' a corresponding bromide is formed which under acid conditions possesses a yellow colour like the chloride; it produces a purple colour in cold sodium sulphite, although the intensity of colour is lower than with the chloride, and this colour disappears on heating. Nascent bromine is liberated according to the following equation: