An Improved Synthesis of Carbamates

Investigations on the synthesis and chemiluminescence of novel 2-coumaranones - II

“…Since the intramolecular back-transfer has higher yields, the difference in the quantum yields between the 2-coumaranones can be explained by the selectivity of the electron back-transfer pathway: the more the mechanism is shifted to an intramolecular reaction, the higher the quantum yields. We are, however, not convinced that the electron-donating has to occur via a ressonance pathway, since electron-donation over the space has been observed with high emission quantum yields, 22 and may be a better suitable explanation for the efficient emission of coumaranones. However, it seems that the CIEEL mechanism is a good model for the chemiluminescent emission of those compounds.…”

O-Carbamates

“…Marshall [25] and others [26,27] described a method whereby tertiary alcohols reacting in situ generated cyanic acid from a mixture of anhydrous sodium cyanate in trichloroacetic acid. Loev [28] recently reported that modifying Marshall's procedure by using trifluoroacetic acid affords ί-butyl carbamates in over 90% yields. The beneficial effect of trifluoroacetic acid does not appear to be solely related to increased acid strength as hydrochloric acid or methanesulfonic acid gives only traces of carbamate when used in place of trifluoroacetic acid under similar conditions.…”

“…The Loev [28] procedure appears applicable to the synthesis of carb amates from primary, secondary, and tertiary alcohols (2 hr reaction time affords 60-90% yields), cyclic and acyclic 1,3-diols, phenols, oximes, aldoximes, and ketoximes, and primary, secondary, and tertiary mercaptans. The reason for this drastic effect is not known at this time.…”

Solvent-free preparation of primary carbamates using silica sulfuric acid as an efficient reagent

“…Synthesis of N-unsubstituted carbamates 1 from alcohols has been also accomplished by several-pot reaction methods such as; trichloroacetyl isocyanate, Loev and coworkers reported the synthesis of N-unsubstituted carbamates from alcohols by treatment with sodium cyanate and trifluoroacetic acid in certain organic solvents such as benzene, methylene chloride and carbon tetrachloride without any spectral data such as IR and NMR. 15 These solvents are toxic and are not eco-friendly. In addition, trifluoroacetic acid is very expensive.…”