Peculiarities of formine layer derivatization with phenyl isocyanate
Chemical interesterification reaction of rapeseed oil with methyl formate yields two layers of product - upper biofuel containing layer and lower glycerol formates containing layer. Our aim was to develop a method for analysis of lower layer of interesterification product containing glycerol, monoformin (MFG), diformin (DFG), and triformin (TFG). Underivatized glycerol and MFG cannot be determined with HPLC-PDA-MS. Derivatization was performed with phenyl isocyanate in acetonitrile. 2-3 mg of sample, halfmililiter of acetonitrile, 10 microliters of phenyl isocyanate, 10 microliters of N,N-dimethylaminopyridine solution in acetonitrile (20 micrograms DMAP) were heated at 45 deg. Celsius for 2 hours. The products of derivatization was sought in reactions of some possible impurities of the lower layer: formic acid, ortophosphoric acid, and tertbutanol (does not react). Isopropanol and n-butanol were tested for possible use as internal standards for quantitative determination. When the developed method is applied to the analyzable mixture, the results are not as expected - two extra peaks are formed and glycerol and MFG peaks are small or even nonexistent in some cases, when all phenyl isocyanate has reacted. The extra peak about RT=16 was identified as triphenyl isocyanurate, which is formed in the presence of catalysts - potassium salts contained in lower layer. A table was drawn, summarizing all identified intermediates, products, and overreacted compounds of this derivatization reaction. Attempts to purify the lower layer from potassium salts were made. Drying with sodium sulphate gave little bit better results. Purification with acid ion exchange resin from Dowex removed potassium, but also glycerol and possibly other formins. Subsequent drying and acid removal after ion exchange were also studied. A suitable method for pufification and analysis of lower layer was not found. We concluded that this derivatization reaction is not suitable to our needs, because it has many side reactions.
Date
28.01.2019.
Keywords
derivatization, phenyl isocyanate, glycerol
