Carbamate Anion Research Articles

Isocyanates from primary amines and carbon dioxide: ‘dehydration’ of carbamate anions

Carbamate anions, derived from primary amines CO2 and an added base (e.g. NEt3), undergo rapid reaction with electrophilic ‘dehydrating agents’(e.g. POCl3, P4O10) to give the corresponding isocyanates in excellent yields.

Highly selective generation of urethanes from amines, carbon dioxide and alkyl chlorides

Generation of carbamate anions from either a primary or secondary amine, carbon dioxide and a stoichiometric amount of a pentaalkylguanidine followed by the addition of alkyl chlorides gives high yields of urethanes.

Diffusion-reaction of urea through multimembrane containing urease — Effects of microenvironments around urease and asymmetry of the membrane

Diffusion-reactions through enzyme membranes were studied by using a multimembrane, consisting of an enzyme layer sandwiched between films. The multimembrane was shown to possess the following characteristics: (1) the microenvironments around the enzyme can be altered arbitrarily by adding polymers etc., and (2) the asymmetries of the multimembranes can be controlled easily by using various films. Diffusion-reactions of urea through symmetric and asymmetric multimembranes having a urease layer were studied by measuring total fluxes J p T and flux ratios — J p I/ J p II of one of the products (NH 4 + ion) into a donor and an acceptor compartment. By adding sodium alginate NaAlg to the urease layer, the pH showing the maximum J p T shifted towards the alkaline pH region by 0.6 pH unit, and the maximum J p T increased. From the value of the pH shift, the electrostatic potentialψ α around the active site of the urease was calculated to be − 0.0343 V. The values of J p I/ J p II through the symmetric multimembrane were in the range 1.2–1.7, and those for the asymmetric multimembrane were in the range 0.2–0.3. In the diffusion-reaction through the latter membrane, carbamate anions were found to play an important role. Diffusionreaction through the multimembranes was analyzed by assuming that the reactions in the enzyme layer obey a first order reaction.

Nitrogen- and oxygen-bonded urethane: hydrolysis and linkage isomerization of [(NH3)5Co(NH2CO2C2H5)]3+ and [(NH3)5CoOC(NH2)OCH2CH3]3+

Coordination of ethyl carbamate via N rather than O to the pentaamminecobalt(III) moiety results in activation toward ligand hydrolysis. The carbonyl oxygen of the carbamate anion and of its ethyl ester (urethane) are preferentially coordinated in kinetically controlled syntheses. Noncoordinating bases facilitate the thermal rearrangement of the O-bound urethane complex in solution to the N-bonded linkage isomer, which has been isolated as its unreactive deprotonated form [(NH 3 ) 5 CoNHCO 2 C 2 H 5 ] 2+ . Similarly, the N-bound carbamate complex, previously believed to be an intermediate in the acid-induced conversion of [(NH 3 ) 5 CoNCO] 2+ to [(NH 3 ) 6 Co] 3+ and CO 2 , has been detected for the first time in this reaction

Novel Synthesis of Carbamate Ester from Carbon Dioxide, Amines, and Alkyl Halides

Abstract A novel synthesis of carbamate ester using carbon dioxide as a direct material is reported in this article. The direct reaction of carbon dioxide, aliphatic amines, and alkyl halides was found to give the corresponding alkyl carbamate esters in good yields. Reactions using secondary alkyl bromides gave carbamate esters in higher yields than those using primary or tertiary alkyl bromides. The carbamate ester yields increased with the addition of N,N-dimethylformamide to the reaction system of carbon dioxide, amines and, alkyl halides. This reaction is considered to proceed by an SN2 displacement reaction of the alkyl halide by the carbamate anion formed from the reaction of carbon dioxide and the amine.

The E1cB mechanism for thiocarbamate ester hydrolysis: equilibrium and kinetic studies

The alkaline hydrolyses of a series of S-aryl thiocarbamate esters have been measured and the mechanism confirmed to be dissociative. Equilibrium constants for the synthesis of thiocarbamates from thiol and isocyanic acid have been obtained for aqueous media using both kinetic and analytical techniques. Hammett and Brønsted parameters for the equilibrium reaction indicate that there is less positive effective charge on the sulphur in the thiocarbamate compared with that on the oxygen in the oxygen analogue. Theoretical arguments are advanced to show that the dissociative reactions of simple carbamate anions involve a planar geometry of the participating atoms.

Reactivity of N-phenacyloxycarbamates and related systems in the presence of bases: study of a new [1,2] anionic rearrangement

N-Phenacyloxycarbamates and other systems containing a CH2–O–N framework, in the presence of bases, undergo a CH2–O–N→ CH(OH)–N rearrangement. The mechanism of this reaction has been studied kinetically and through crossover and capture experiments. The bulk of the data favours an intermolecular ionic mechanism which occurs by removal of a proton from the methylene group in the rate-determining step, followed by interaction between a glyoxal molecule and a carbamate anion in the fast step of the reaction.

Isolation of Dithio Carbamate Anions as Salts of Benzoylacetonato Biscyclopentadienyl Titanium(IV) and Zirconium (IV) Chelates

Abstract A series of [Cp2ML]dtc− compounds where M=Ti or Zr, L is the conjugate base of benzoylacetone and dtc− = Me2NCS1 2; Et2Ncs− 2; 1-Pr2 NCS− 2 Me, cyhxNCS− 2; and 1-Pr, chyhxNCS− 2 have been prepared by adding the sodium salt of the apporopriate dithiocarbamate (Nadtc) to an aqueous solution of [cp2ML]+cl−. Conductivity measurement in nitrobenzene for all the compounds indicate that these are 1:1 electrolytes. IR and 1H NMR spectra indicate that ligand L is chelating in all these complexes and the meal atom M is essentially tetracoordinated.

ChemInform Abstract: MECHANISM OF CLEAVAGE OF CARBAMATE ANIONS

Chemischer InformationsdienstVolume 11, Issue 30 Preparative Organic Chemistry ChemInform Abstract: MECHANISM OF CLEAVAGE OF CARBAMATE ANIONS S. P. EWING, S. P. EWINGSearch for more papers by this authorD. LOCKSHON, D. LOCKSHONSearch for more papers by this authorW. P. JENCKS, W. P. JENCKSSearch for more papers by this author S. P. EWING, S. P. EWINGSearch for more papers by this authorD. LOCKSHON, D. LOCKSHONSearch for more papers by this authorW. P. JENCKS, W. P. JENCKSSearch for more papers by this author First published: July 29, 1980 https://doi.org/10.1002/chin.198030105AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume11, Issue30July 29, 1980 RelatedInformation

Mechanism of cleavage of carbamate anions

Mechanism of cleavage of carbamate anions

ChemInform Abstract: MECHANISMS OF HYDROLYSIS OF SALICYLANILIDE N‐METHYLCARBAMATES

AbstractEs wird der Mechanismus der basenkatalysierten Hydrolyse von Sa1icylanilid‐N‐methylcarbamaten und analogen Verbindungen in 50% Äthanol untersucht.

Mechanisms of Hydrolysis of Salicylanilide N-Methylcarbamates

The facile hydroxide-ion-catalyzed hydrolysis of the carbamoyl group in salicylanilide N-methylcarbamate (I) and analogs unsubstituted on the anilide nitrogen proceeds by a reaction mechanism involving anchimeric assistance by the o-carboxanilide group. Substitution of an alkyl or aryl group for the anilide proton greatly reduces the hydrolysis rate; the reaction rate constant for I is ˜7 × 102 times that for N-methylsalicylanilide N-methylcarbamate (II). To characterize the mechanism for II, comparative parameters of activation were determined for I and II. The entropy of activation (ΔS) for II was 8.6 eu more negative than that for I, suggesting steric hindrance in the transition state for II. The observed reaction rate constant for II was consistent with estimates based on the electronic ortho-substituent effect of the carboxanilide group. It is concluded that II is hydrolyzed via the established mechanism for simple aryl N-monosubstituted carbamates (rapid proton extraction followed by a rate-determining conversion of the carbamate anion to an isocyanate) rather than by the mechanism followed by I.

Elimination–addition mechanism for the hydrolysis of carbamates. Trapping of an isocyanate intermediate by an o-amino-group

The hydrolytic conversion of aryl carbamates to amines is base catalysed and evidence is presented that the process involves an E1cB elimination with the formation of isocyanate intermediates. Substituents in the leaving group (O-aryl ring) have a larger effect (ρ=+3·17) on the observed rate of hydrolysis than those in the N-aryl ring (ρ=+0·64) where the effects of a substituent are compensatory. Using N-(p-nitrophenyl)carbamates, it was possible to measure both the acidity of the carbamate (Ka1) and the rate of reaction of the carbamate anion (k2); k2 was sensitive to substituent effects (ρ=+2·90) for aryl carbamates indicating a high degree of acyl–oxygen bond cleavage in the transition state. A change in mechanism from E1cB to BAC2 attack by hydroxide ion was noted for poorer leaving groups. The pH profile for the conversion of p-nitrophenyl N-(o-aminophenyl)carbamates to o-phenyleneurea was interpreted to show that the o-amino-group traps an isocyanate intermediate after the rate determining E1cB elimination. Substituent effects for NN-disubstituted carbamates which hydrolyse via a BAC2 mechanism are also discussed.