Availability and disposition of hydroxyl groups on surfaces of crystalline cellulose II

The relative availabilities of hydroxyl groups at C(2), C(3), and C(6) on the D-glucopyranosyl units of a particular, highly ordered hydrocellulose II have been studied by means of the reaction of N,N-diethylaziridinium chloride, which introduces 2-(diethyl-amino)ethyl substituents. The hydrocellulose II was formed by hydrolysis of fibrous cotton cellulose II during 40 min reflux in 2.5M hydrochloric acid and is designated EHC-II (exemplar hydrocellulose II) because it represents the most highly ordered (crystalline) particles in a series of hydrocelluloses. The deviation in the distribution of substituents among the 2-O-, 3-O-, and 6-O- positions of the D-glucopyranosyl units in EHC-II from that in a disordered cellulose, in which the three types of hydroxyl groups are equally available, is the basis for estimated availabilities of the three types of hydroxyl groups on the surfaces of elementary fibrils in EHC-II. The experimental values of relative availabilities of O(2)H:O(3)H:O(6)H for EHC-II were 1.0:0.26:0.72 compared to estimated values of 1.0:0.0:.075 for surfaces of elementary fibrils of an idealized, perfectly ordered cellulose II, a model that is based on intensities of x-ray diffraction peaks.