Analysis of Mixtures of Hydroxyl Compounds Using Differential Reaction Rates.

Primary Hydroxyl Content of Soybean Polyols

“…At the concentrations of PI used in the present study ([PI] \ 5 mmol/50 mL) the Beer's law is totally respected: a perfect linear relationship between absorbance and molar concentration of the absorbing species (PI) was obtained, with the values of the absorbance units always being lower than 1 (Table 1). This perfect linearity between absorbance and PI concentrations was proven by Willeboordse and Crithchfield [15]. The absorbance can be converted into the molar concentration of PI at any time using the calibration curve presented in Fig.…”

“…The primary hydroxyl content is determined graphically from a second order kinetics plot of ln[(b -x)/(a -x)] as a function of time t, where a is the initial concentration of hydroxyl groups (a = 4.6 mmol/50 mL); b is the initial concentration of PI (b = 5 mmol/50 mL); x is the concentration of OH groups, in millimoles (equal to the concentration of PI groups) reacted at time t. The procedure for graphical determination of primary hydroxyl is described in detail in the literature [13,15,16]. The modifications to the method, as applied here for the first time to soybean polyols, consist in the use of DABCO as the catalyst instead of stannous octoate (stannous octoate loses the catalytic activity with time [15] while the catalytic activity of DABCO does not change with time) and the use of different concentrations of reagents.…”

“…The modifications to the method, as applied here for the first time to soybean polyols, consist in the use of DABCO as the catalyst instead of stannous octoate (stannous octoate loses the catalytic activity with time [15] while the catalytic activity of DABCO does not change with time) and the use of different concentrations of reagents. We experimentally proved that for the same polyol, a DABCO solution stored for 3 months at room temperature, in a volumetric flask, leads to identical kinetic curves as a freshly prepared DABCO solution.…”

“…If the water content is higher than 0.1%, the soy polyol has to be heated for 1-2 h at 100-110°C in a vacuum (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Water reacts with isocyanates at a higher rate than secondary hydroxyl [8] and leads to an artificial increase of primary hydroxyl content.…”

“…In order to correctly evaluate the primary hydroxyl of soybean polyols, we have applied a kinetic method, based on the difference in reactivity of primary and secondary hydroxyl of soybean polyols with a common reagent, phenyl isocyanate (PI), and evaluated the method precision. The determination of primary hydroxyl content in alcohol mixtures or of polyether polyols by kinetic methods has been described in several papers [13][14][15][16][17][18][19][20]. All of these methods include second order kinetics of the reaction of polyols with acetic anhydride [13], phthalic anhydride [14] or phenyl isocyanate [15,16] and pseudo-first order kinetics using a high excess of hydroxyl groups [15] or an excess of phenyl isocyanate or p-methyl-phenyl isocyanate [16,17], or the large difference in reactivity of primary and secondary hydroxyl with triphenylchloromethane [18] or 3-nitrophthalic anhydride [19].…”