N PREVIOUS papers (13, 14, 16) it was shown that fructose I undergoes dehydration and fragmentation when a concentrated aqueous solution is gently boiled under reflux for a number of hours, After removal of the unchanged fructose by fermentation with baker's yeast, and subsequent purification to remove the yeast and volatile reducing substances, such as 3-hydroxy-2-butanone, hydroxy->propanone, and pyruvaldehyde, the unfermented residue WMI still capable of reducing Fehling solution.It was also found to contain diheterolevulosan, the difructose anhydride first prepared by Pictet and Chavan (11) by the action of cold concentrated hydrochloric acid on fructose, and later by Schlubtwh and Behre ( 1 7 ) , who treated fructose with liquid hydrogen chloride a t room temperature. The preparative work of Pictet and Chavan and that of Sattler and Zerban (13) was repeated by Wolfrom and Blair (80), who showed that diheterolevulosan is a mixture consisting essentially of two di-D-fructose dianhydrides. One of them is a pyranose-pyranose dianhydride whose structural formula corresponds to that proposed by Schlubach and Behre for diheterolevulosan, whereas the second appeared to be a pyranose-furanose dianhydride. The two difructose axihydrides were designated as diheterolevulosan I and diheterolewlomn 11, respectively. The proposed structure for diheterolevulosan I1 was recently confirmed by Wolfrom and his coworkers ($1 ) :
I. Dihetemlevulosan I (di-afructopyranose1,2':2,1 'dianhydride)
Diheterolevulosan I1 (D-fructopyranose-Dfmotofuranose 1,2':2,1 '-dianhydride)A hexamethyldiheterolevulosan was prepared by Sattler and Zerban (19) from the difructose dianhydrides obtained from heated aqueous fructose solution, and on the basis of the information available at that time, it was considered to be one of the isomeric modifications of the hexamethyl derivative of the diheterolevulosan prepared by Schlubach. It is now known that the difructose dianhydridea obtained by the previous methods of preparation, as well as by the action of anhydrous liquid hydrogen fluoride on fructose, consist of mixtures which are composed predominantly of diheterolevulosan I and diheterolevulosan 11. X-ray powder diffraction analysis initiated by the present authors, and with the cooperation of other workers who supplied reference compounds, has revealed tha6 each of the two diheterolevulosans and their hexamethyl derivatives exist in polymorphic modifications, Thus far for each compound there are two known crystalline f o r m , and this, therefore, necessitates a further terminological differentiation. Consequently, such dimorphs will be referred to as hexamethyldiheterolevulosan I, and hexamethyldiheterolevulosan I@, and hexamethyldiheterolevulosan 11, and hexamethyldiheterolevulosan I I p , rwpectively. The hextunethyidiheterolevulosan obtained in former work can accordingly be precisely described as hexamethyldiheterolevulosan 11,.
ACTION OF HYDROGEN FLUORIDE ON FRUCTOSEThe methods of Pictet and Chavan and of Schlubach and Behre involve the trouble...
