The Effect of the Substituents (Alkyl-groups) on the Thermal Dissociation of Carbaminic Acid Esters

Abstract

The rate constants of the thermal dissociation of carbaminic acid esters in fatty acids were determined. In the case of phenylcarbaminic acid alkylestees, the rates showed the following order. tert-Bu>>isoPr≥Me The relative rates may be considered to denote the ability of —OR groups as proton acceptors and the results of the experiment can be explained by the inductive effect of the substituted alkyl-groups. In the case of alkylcarbaminic acid phenyl-esters, the rates showed the following order. Acetyl>>isoPr>Me The relative rates may be considered to denote the ability of (Remark: Graphics omitted.) groups as proton donors. In acetylcarbaminic acid phenylester, because of the resonance effect of the (Remark: Graphics omitted.) and COOR groups, the intervening nitrogen aquires a positive potential. The phenomenon will make the hydrogen attached to nitrogen have more tendency to transfer, hence the reaction. That isopropylcarbaminic acid phenylester dissociates faster than methyl-carbaminic acid phenylester will be explained by the steric effect of alkyl-groups. The rates of the thermal dissociation of esters depend on the nature of the solvent acids.

<i>p</i>-Methoxy- and 2,4-Dimethoxybenzyl <i>N</i>-Acetylcarbamate Potassium Salts: Versatile Reagents for <i>N</i>-Alkylacetamide and <i>p</i>-Methoxy- and 2,4-Dimethoxybenzyl Carbamates

“…N-Acetylation using acetic anhydride and Amberlyst 15 afforded methyl N-acetylcarbamate (3). The initial attempt at thermal transesterification with p-methoxybenzyl alcohol in xylene 37,38) through acetyl isocyanate failed owing to the formation of di(p-methoxybenzyl) ether. 39) Significantly, the addition of a stoichiometric quantity of i-Pr 2 NEt suppressed the formation of the ethereal side product, and the desired p-methoxybenzyl N-acetylcarbamate (4a) was obtained in an excellent yield.…”

Reaction of Aryl Isocyanates With Cotton Cellulose

“…Mukaiyama et al have studied the thermal dissociation of N-substituted car-bamic acid esters to the corresponding isocyanate and alcohol or phenol [ 5,13 ] . For phenyl N-phenyl carbamate, the dissociation was first order with an activation energy of 33.3 kcal/mole.…”