Sulfamate , hydrolysis rate

Aqueous sulfamic acid solutions are quite stable at room temperature. At higher temperatures, however, acidic solutions and the ammonium salt hydroly2e to sulfates. Rates increase rapidly with temperature elevation, lower pH, and increased concentrations. These hydrolysis reactions are exothermic. Concentrated solutions heated in closed containers or in vessels having adequate venting can generate sufficient internal pressure to cause container mpture. An ammonium sulfamate, 60 wt % aqueous solution exhibits mnaway hydrolysis when heated to 200°C at pH 5 or to 130°C at pH 2. The danger is minimised in a weU-vented container, however, because the 60 wt % solution boils at 107°C (8,10). Hydrolysis reactions are ... 

Alkali metal sulfamates are stable in neutral or alkaline solutions even at boiling temperatures. Rates of hydrolysis for sulfamic acid in aqueous solutions have been measured at different conditions (Table 4) (8,10)-... 

Kinetic studies of the hydrolysis of V-methyl O-phenyl sulfamate (144) and NJ -dimethyl 0-phenyl sulfamate (144 Me for H) showed that the presence of an NH group in the former has a profound effect on its rate of hydrolysis compared to that of the latter. From data obtained at pH 5.9 and 513-552 K, the extrapolated rate of hydrolysis of the V,V-dimethyl compound was found to be 10 -fold less than that of the Af-methyl compound at 298 K. A comparison of the rate of hydrolysis of the V-methyl compound... 

The hydrolysis of neopentyl sulfamate (147) was studied with a view to estimating the catalytic efficiency of an S-N cleaving sulfamidase. Kinetic data were obtained at 473 K and pH 0-7, and, remarkably, it was concluded that there was no evidence for a pH neutral reaction, even in the alkaline region of the pH rate profile. This complicated efforts to determine eutrai(H20) and, therefore, directly estimate the catalytic rate acceleration of sulfamidase enzymes. The reader is invited to see the ingenious method the authors used to make a reasonable estimate. Suffice it to say that the acid-catalysed hydrolysis of neopentyl sulfamate (147) was unexceptional (Scheme 44) and was similar to that proposed previously for other alkyl sulfamates. 

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