Mechanism of the transition-metal-catalyzed mutarotation reaction of N-(p-chlorophenyl)-beta-D-glucopyranosylamine in methanol.
Rate constants for the mutarotation reaction of N-(p-chlorophenyl)-beta-D-glucopyranosylamine (NGlc) in methanol have been determined in the presence of transition metal chlorides (MCl(2)), at 25 degrees C. The activity of the metal ions catalyzing the alpha-pyranoside<-->beta-pyranoside interconversion has been found to increase in the following series: Mn(2+)<Co(2+)<Ni(2+)<Zn(2+)<Cu(2+). The pHs of the methanolic solutions of the chlorides were measured and acidity constants of the [MCl(CH(3)OH)(5)](+) ions and NGlc were determined in this solvent. Addition of NGlc to the salt solutions resulted in lowering their pH. Raising the methyloxonium ion concentration in the solutions resulted in rapid increase in the rate of mutarotation in the presence of MCl(2). It is suggested that in solutions of NGlc and MCl(2), the CH(3)OH(2)(+) ions are generated by solvolysis of the salts and additionally by dissociation of the hydroxyl group at C-6 of the glucosylamine molecule taking place during complexation of the metal ions. A scheme has been derived for interaction of deprotonated NGlc molecules with the transition metal ions.
Smiataczowa
Kazimiera
K
Faculty of Chemistry, University of Gdańsk, Sobieskiego 18, PL-80-952 Gdańsk, Poland.
Kosmalski
Jarosław
J
Widernik
Teresa
T
Warnke
Zygmunt
Z
D002236:Carbohydrate Conformation; D002384:Catalysis; D005944:Glucosamine / Q000031:analogs & derivatives* / Q000737:chemistry*; D007700:Kinetics; D008670:Metals / Q000737:chemistry*; D000432:Methanol / Q000737:chemistry*; D015394:Molecular Structure
D008670:Metals; C480089:N-(4-chlorophenyl)glucopyranosylamine; C075822:glucopyranosylamine; D005944:Glucosamine; D000432:Methanol