Several carbamate esters were synthesized from amines, carbon dioxide, and alkyl chlorides. The effect of added hase on the yield and selectivity of carbamate ester formation was found to be highly important with the use of sterically hindered guanidine bases giving the best results. Relative rate studies were carried out giving the following order of reactivity between carbamate anions in acetonitrile with benzyl chloride giving carbamate esters:Rate studies were carried out with the diethyl, s-butyl, phenyl, and rc-butyl carbamates and activation parameters were determined to be Et2NC02~, AH* = 11.8 kcal/mol, AS* = -33 eu; s-BuNHC02", AH* = 12.8 kcal/mol, AS* --33 eu; PhNHC02-, AH* = 14.3 kcal/mol, AS* = -28 eu; rc-BuNHC02~, AH* = 23.4 kcal/mol, AS* = -3 eu. The unusual results obtained from the use of 7i-BuNHC02~prompted further studies which showed that the rate of reaction was inversely dependent on carbon dioxide pressure (20 psig C02, k = 4.84 x 10~4 M_1 s_1; 120 psig C02, k = 1.83 x 10-4 M-1 s_1). Nitrogen NMR spectroscopy indicated, via a labeling study with 15N amines and 13C enriched carbon dioxide, the formation of a doubly inserted product from the addition of two carbon dioxides to ethylamine in acetonitrile.

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Carbamate anions, derived from primary amines COP and an added base (e.g. NEt,), undergo electrophilic 'dehydrating agents' (e.g. P0Cl3, P4Ol0) t o give the corresponding isocyanates in 957 of Carbamate rapid reaction with excellent yields.