- Recycling method of beta,beta-iminodipropionitrile and application
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The invention provides a recycling method of beta,beta-iminodipropionitrile and application, and relates to the technical field of waste recycling. According to the recycling method, by adopting a specific reaction synthesis route, the beta,beta-iminodipropionitrile finally generates calcium pantothenate with wide application, and the recycling method not only reduces hazardous waste emission and treatment and lowers the hazardous waste treatment cost, but also realizes the purpose of turning waste into wealth from beta,beta-iminodipropionitrile, and the utilization value of beta,beta-iminodipropionitrile is greatly improved. The invention further provides application of the recycling method of the beta,beta-iminodipropionitrile, and in view of the advantages of the recycling method of the beta,beta-iminodipropionitrile, a new process route is provided for preparing calcium pantothenate.
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Paragraph 0093-0095; 0100-0124; 0129-0130
(2021/05/26)
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- Methods for synthesizing Beta-calcium aminopropionate and D-calcium pantothenate
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The invention relates to the field of biochemical engineering, and discloses methods for synthesizing Beta-calcium aminopropionate and D-calcium pantothenate. According to the methods, acrylonitrile is utilized to react with liquid ammonia to prepare Beta-aminopropionitrile; nitrilase is utilized to catalyze to hydrolyze the Beta-aminopropionitrile to generate Beta-aminopropionic acid, afterwards,the Beta-aminopropionic acid reacts with a calcifying agent to synthesize the Beta-calcium aminopropionate, then the Beta-calcium aminopropionate generates an acylation reaction with D-pantolactone,and the D-calcium pantothenate is obtained by filtration and drying. The synthesis methods provided by the invention do not need to use a strong base to hydrolyze the Beta-aminopropionitrile, also donot need to use ion exchange resin to extract the Beta-aminopropionic acid, are used for effectively reducing the generation of a by-product salt, is easily amplified, is used for realizing continuousproduction, and has a quite good industrial application prospect, and a technique is simple, convenient, easy and feasible.
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Paragraph 0030; 0031; 0032; 0033; 0034; 0035
(2018/06/26)
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- Method for preparing 3-aminopropionitrile under supercritical condition
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The invention discloses a method for preparing 3-aminopropionitrile under a supercritical condition. According to the method, liquid ammonia and acrylonitrile are used as raw materials which are subjected to direct addition reaction in a pipeline reactor without adding a catalyst and a solvent to obtain 3-aminopropionitrile. The reaction according to the invention is carried out under a supercritical condition of the liquid ammonia, thus avoiding the use of a catalysts and a solvent when the liquid ammonia is used in reports in the past; a product can be obtained through continuous rectification; unreacted raw materials can be directly used; the process is safe and environmentally friendly, substances of non-reactive raw materials are not introduced, and the method accords with a concept of green chemistry. The conversion rate of acrylonitrile can reach 99.5-100.0%, and the selectivity can reach 85.5-95.8%, so that the acrylonitrile has a high industrial application value.
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Paragraph 0039; 0040; 0044; 0045
(2018/06/15)
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- Amido Complexes of Iridium with a PNP Pincer Ligand: Reactivity toward Alkynes and Hydroamination Catalysis
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The pincer ligand HN(CH2CH2PPh2)2 (1; PNHP) reacted with [{Ir(μ-X)(cod)}2] (X = Cl, OMe), affording complexes [fac-(PNHP)Ir(cod)]Cl (2) and [fac-(PNP)Ir(cod)] (3), respectively. The X-ray molecular structure of 2 showed that the PNP ligand coordinates in a facial fashion, with the N atom in an axial site and both P atoms coordinated in the equatorial plane. Compound 1 is able to protonate the hydroxo bridges in the complex [{Ir(μ-OH)(coe)2}2] forming the new amido complex [mer-(PNP)Ir(coe)] (4). Complex 4 is an extremely air sensitive compound, as confirmed by the isolation of the oxo complex [mer-(PNP)Ir(σ2-O2)] (8) from its interaction with air. Protonation of 4 with HBF4 afforded the corresponding amino complex [mer-(PNHP)Ir(coe)]BF4 (5), whose molecular structure enlightened by X-ray crystallography confirmed the PNP ligand to be coordinated in a meridional fashion. The coe ligand in 4 is tightly bonded to iridium; however, under an atmosphere of ethylene at 60 °C or with acrylonitrile at 70 °C complex 4 exchanges the olefin, affording compounds [mer-(PNP)Ir(σ2-C2H4)] (6) and [mer-(PNP)Ir(σ2-C2H3CN)] (7), respectively. Interaction of 4 with alkynes depends on the nature of the substrate; therefore, methyl phenylpropiolate reacted with 4, affording the adduct [mer-(PNP)Ir(σ2-PhCCC(O)OMe)] (9), while the parent acetylene undergoes a double C-H activation, affording the Ir(III) complex [fac-(PNHP)IrH(Ca‰?CH)2] (10). A DFT theoretical analysis of this transformation supports a metal-ligand cooperation mechanism. The reaction starts by deprotonation of an alkyne moiety by the PNP ligand followed by oxidative addition of the C-H bond to the metal of a second alkyne molecule. Additionally, we have tested complex 4 as a catalyst for the addition of gaseous ammonia to activated unsaturated substrates. A DFT theoretical analysis disclosed the operative mechanism on these organic transformations, which starts with a nucleophilic attack of ammonia to the bound alkyne, hydrogen migration to the metal, and reductive elimination steps.
- Hermosilla, Pablo,López, Pablo,García-Ordunìa, Pilar,Lahoz, Fernando J.,Polo, Víctor,Casado, Miguel A.
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p. 2618 - 2629
(2018/08/21)
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- Parent-amido (NH2) palladium(II) complexes: Synthesis, reactions, and catalytic hydroamination
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The treatment of [PdL3(NH3)](OTf)n (n = 1; L3 = (PEt3)2(Ph), (2,6-(Cy2PCH2)2C6H3), n = 2; L3 = (dppe)(NH3)) with NaNH2 in tetrahydrofuran at ambient temperature or -78 °C afforded the dimeric and monomeric parent-amido palladium(II) complexes anti-[Pd(PEt3)(Ph)(μ-NH2)]2 (1), [Pd(dppe)(μ-NH2)]2(OTf)2 (2), and Pd(2,6-(Cy2PCH2)2C6H3)(NH2) (3), respectively. The molecular structures of the amido-bridged (μ-NH2) dimeric complexes 1 and 2 were determined by single-crystal X-ray crystallography. The monomeric amido complex 3 reacted with trace amounts of water to give a hydroxo complex, Pd(2,6-(Cy2PCH2)2C6H3)(OH) (4). Exposing complex 3 to an excess of water resulted in the complete conversion of the complex into two species [Pd(2,6-(Cy2PCH2)2C6H3)(OH2)]+ and [Pd(2,6-(Cy2PCH2)2C6H3)(NH3)]+. Complex 3 reacted with diphenyliodonium triflate ([Ph2I]OTf) to give the aniline complex [Pd(2,6-(Cy2PCH2)2C6H3)(NH2Ph)]OTf. The reaction of 3 with phenylacetylene (HCCPh) yielded a palladium(II) acetylenide Pd(2,6-(Cy2PCH2)2C6H3)(CCPh) (5), quantitatively, along with the liberation of ammonia. The reaction of 3 with dialkyl acetylenedicarboxylate yielded diastereospecific palladium(II) vinyl derivatives (Z)-Pd(2,6-(Cy2PCH2)2C6H3)(CRCR(NH2)) (R = CO2Me (6a), CO2Et (6b)). The reaction of complexes 6a and 6b with p-nitrophenol produced Pd(2,6-(Cy2PCH2)2C6H3)(OC6H4-p-NO2) (7) and cis-CHRCR(NH2), exclusively. Reactions of 3 with either dialkyl maleate (cis-(CO2R)CHCH(CO2R)) (R = CH3, CH2CH3) or cis-stilbene (cis-CHPhCHPh) did not result in any addition product. Instead, isomerization of the cis-isomers to the trans-isomers occurred in the presence of catalytic amounts of 3. Complex 3 reacted with a stoichiometric amount of acrylonitrile (CH2CHCN) to generate a metastable insertion product, Pd(2,6-(Cy2PCH2)2C6H3)(CH(CN)CH2NH2). On the other hand, the reaction of 3 with an excess of acrylonitrile slowly produced polymeric species of acrylonitrile. The catalytic hydroamination of olefins with NH3 was examined in the presence of Pd(2,6-(Cy2PCH2)2C6H3)(OTf), producing a range of hydroaminated products of primary, secondary, and tertiary amines with different molar ratios of more than 99% overall yield. A mechanistic feature for the observed catalytic hydroamination is described with regard to the aminated derivatives of palladium(II).
- Kim, Youngwon,Park, Soonheum
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p. 614 - 629
(2016/06/01)
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- Common origins of RNA, protein and lipid precursors in a cyanosulfidic protometabolism
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A minimal cell can be thought of as comprising informational, compartment-forming and metabolic subsystems. To imagine the abiotic assembly of such an overall system, however, places great demands on hypothetical prebiotic chemistry. The perceived differences and incompatibilities between these subsystems have led to the widely held assumption that one or other subsystem must have preceded the others. Here we experimentally investigate the validity of this assumption by examining the assembly of various biomolecular building blocks from prebiotically plausible intermediates and one-carbon feedstock molecules. We show that precursors of ribonucleotides, amino acids and lipids can all be derived by the reductive homologation of hydrogen cyanide and some of its derivatives, and thus that all the cellular subsystems could have arisen simultaneously through common chemistry. The key reaction steps are driven by ultraviolet light, use hydrogen sulfide as the reductant and can be accelerated by Cu(I)-Cu(II) photoredox cycling.
- Patel, Bhavesh H.,Percivalle, Claudia,Ritson, Dougal J.,Duffy, Colm D.,Sutherland, John D.
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p. 301 - 307
(2015/04/14)
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- SPIROHYDANTOIN COMPOUNDS AND THEIR USE AS SELECTIVE ANDROGEN RECEPTOR MODULATORS
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The present invention relates to a compound of formula (1-1 ) in free form or in pharmaceutically acceptable salt form in which the substituents are as defined in the specification; to its preparation, to its use as a medicament and to medicaments comprising it. The present invention further provides a combination of pharmacologically active agents and a pharmaceutical composition.
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Page/Page column 84
(2013/09/12)
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- Novel synthesis of 3-aminopropionitriles by ring opening of 2-oxazolidinones with cyanide ion
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Nucleophilic attack of cyanide ion on the 5-position of 2-oxazolidinones in the presence of 18-crown-6 gave 3-aminopropionitriles.
- Taniguchi, Tsuyoshi,Goto, Naoya,Ishibashi, Hiroyuki
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supporting information; experimental part
p. 4857 - 4858
(2009/10/26)
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- Efficient preparation of [1-15N]-3-cyano-4-methyl-1H-pyrrole by a Wittig-based strategy
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3-Cyano-4-methyl-1H-pyrrole (1) was prepared by a new Wittig procedure from simple, commercially available starting materials in four steps with an overall yield of 39%. Similarly, [1-15N]-3-cyano-4-methyl-1H-pyrrole (1a) was prepared starting from [15N]-phthalimide. In this synthesis, Wittig coupling was used to form the central C-C bond of intermediate 6, which has nitrile and methyl substituents. Upon deprotection and cyclization pyrrole 1 is obtained directly in one pot. This scheme also allows stable isotope incorporation at any position or a combination of positions. 3-Cyano-4-methyl-1H-pyrrole was converted into the novel 1-benzyl-3-cyano-4- methylpyrrole and the novel 4-methyl-1H-pyrrole-3-aldehyde. It is clear that this novel Wittig procedure has a wide scope that will allow the easy preparation of many new pyrrole systems. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Dawadi, Prativa B. S.,Lugtenburg, Johan
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experimental part
p. 2288 - 2292
(2009/04/05)
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- Chemoselective hydrogenation of α,β-unsaturated nitriles
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The chemoselective hydrogenation of cinnamonitrile to 3-phenylallylamine proceeds with up to 80% selectivity at conversions of > 90% with Raney cobalt and up to 60% selectivity with Raney nickel catalysts. Best results were obtained with a doped Raney cobalt catalyst (RaCo/Cr/Ni/Fe 2724) in ammonia saturated methanol at 100°C and 80 bar. Major problems are the formation of hydrocinnamonitrile and of secondary amines, and overreduction to 3-phenylpropylamine. Important parameters are the catalyst type and composition, the solvent type and the presence and concentration of ammonia. The catalytic system tolerates functional groups like OH, OMe, Cl, C=O, but not aromatic nitro groups. Preliminary experiments indicate that other unsaturated nitriles with di- or trisubstituted C=C bonds are also suitable substrates.
- Kukula, Pavel,Studer, Martin,Blaser, Hans-Ulrich
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p. 1487 - 1493
(2007/10/03)
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- Polynuclear branched tetrazole systems. 2*. New 2-(5-tetrazolyl) ethyl podands and their NH-acidity
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Nine new polynuclear 2-(5-tetrazolyl)ethyl podands have been obtained by the azidation of the corresponding nitriles. Using Bjerrum distribution functions, the values of pKa1, pKa 2, pKa3, and pKa4 have been determined by a potentiometric method for 14 polynuclear tetrazoles in aqueous and aqueous methanolic solution. The found values lie in the range from 3.5 to 7.5 pH units. The overall rules and the sequence of the ionization of the spatially separated tetrazole fragments in these podand systems are discussed.
- Zubarev,Bezklubnaya,Pyartman,Trifonov,Ostrovskii
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p. 1317 - 1325
(2007/10/03)
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- Aryl sulfonamides as selective PDE4 inhibitors
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A series of novel selective phosphodiesterase 4 (PDE4) inhibitors has been developed which displays activity both in vitro and in vivo. These compounds possess good selectivity for the catalytic site of PDE4 over the high affinity Rolipram binding site. In vivo studies demonstrate a reduced propensity to display the emetic side effects which are commonly observed with PDE4 inhibitors.
- Montana, John G.,Buckley, George M.,Cooper, Nicola,Dyke, Hazel J.,Gowers, Lewis,Gregory, Joanna P.,Hellewell, Paul G.,Kendall, Hannah J.,Lowe, Christopher,Maxey, Robert,Miotla, Jadwiga,Naylor, Robert J.,Runcie, Karen A.,Tuladhar, Bishwa,Warneck, Julie B. H.
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p. 2635 - 2640
(2007/10/03)
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- Amino disazo dyestuffs containing a fluoropyrimidinyl or a fluorotriazinyl reactive group
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Dyestuffs of the formula STR1 wherein X=--CH=CH2, --CH2 --CH2 OSO3 H, --CH=CHCl or --CH2 --CH2 Cl and Y=a fiber-reactive fluoropyrimidinyl or fluorotriazine radical and wherein u and v=H or SO3 H, where u~v. Such dyestuffs suitable for dyeing and printing diverse substrates, particularly cotton, to give products a high degree of dyestuff fixation.
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- Coproduction of propanediamine and alkylated aminopropylamines
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This invention relates to a process for the coproduction of propanediamines and alkylated aminopropanediamines. The process contemplates an initial cyanoethylation of ammonia under conditions for producing aminopropionitrile and modest levels of iminobispropionitrile. After separation of the iminobispropionitrile from the aminopropionitrile, the process involves the catalytic reductive alkylation of the iminobispropionitrile by reaction with an aldehyde in the presence of hydrogen to form the alkylated iminobispropionitrile followed by the catalytic hydrogenation of the nitrile group in aminopropionnitrile and iminobispropionitrile to the amine.
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- Triazinyl reactive dyestuffs in which triazinyl group is further substituted with a beta-chloroethylsulfonyl- or vinylsulfonylbutyrylamino moiety
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Reactive dyes of the formula STR1 in which D is the radical of an organic dye of the monoazo, polyazo, metal complex azo, anthraquinone, phthalocyanine, formazan, azomethine, dioxazine, phenazine, stilbene, triphenylmethane, xanthene, thioxanthrone, nitroaryl, naphthoquinone, pyrenequinone or perylenetetracarbimide series, R is hydrogen or substituted or unsubstituted C1-4 -alkyl, X is a substituent which is detachable as an anion, B is a radical of the formula STR2 R1 and R2, independently of each other, are hydrogen or substituted or unsubstituted C1-4 -alkyl or phenyl, A is a substituted or unsubstituted aliphatic or aromatic bridge member, Y is a --CO--Z or --SO2 --Z radical, Z is an aliphatic, aromatic or heterocyclic reactive radical, and n is 1 or 2, are suitable for dyeing or printing cellulose-containing and nitrogen-containing materials and in high dyeing yield produce dyeings and prints having good fastness properties.
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- Iodide Reduction of Sulfilimines. 2. Evidence for Concurrent Stepwise and Concerted Mechanisms for the Decomposition of Sulfurane Intermediates
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The iodide reduction of N-(substituted ethyl or phenyl)-S,S-dimethylsulfilimmonium salts (aqueous solution, 25 deg C, μ = 1.0 with KCl) is first order in proton activity and iodide concentration in the pH range 0.5-5.The solvent deuterium isotope effects for the reduction reaction vary in the range kH/kD = 0.26-0.48 as the nitrogen substituent is changed from ethyl- to trifluoroethylamine.Electron-withdrawing groups in the leaving group decrease the rate of the reaction and give βl.g. values of ca. 0.7 for cyanoethyl- and trifluoroethylamine leaving groups and ca. 0.1 for the more basic ethylamine derivatives; a βl.g. of 0.58 is observed for aniline derivatives.General acid catalysis is observed in the reduction of the acidic ethylamine and aniline derivatives with Broensted α values of 0.59 and 0.39 for cyanoethyl- and trifluoroethylamine leaving groups, respectively; for anilines, the Broensted α values decreased from 0.67 to 0.50 as the leaving group is changed from 4-methyl- to 3-nitroaniline.The value of βl.g. decreases with decreasing strength of the catalyzing acid and the term pxy = (δβl.g./δpKaHA) = (δα/δKal.g.) ca. -0.06 to -0.1.The solvent deuterium isotope effect on the general catalyzed reduction reaction increases with increasing acid strength; for the cyanoethylamine derivative, kBH/kBD = 1.47-2.32 for acetic and chloroacetic acids, respectively.A mechanism is suggested involving concurrent stepwise and concerted mechanisms for the reduction reaction; the mechanism observed seems to depend on the nature of the catalyzing acid.
- Young, Paul R.,Huang, H. C.
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p. 1805 - 1809
(2007/10/02)
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- SPERMIDINE: AN INDIRECT PRECURSOR OF THE PYRROLIDINE RINGS OF NICOTINE AND NORNICOTINE IN NICOTIANA GLUTINOSA
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Spermidine, which was labeled asymmetrically in its four-carbon moiety (-1,5,10-triazadecane), was administered to Nicotiana glutinosa plants.After 7 days the plants were harvested, yielding radioactive nicotine (0.43 percent incorporation) and nornicotine (0.07 percent inc.).A systematic degradation of the alkaloids indicated that they were labelled equally at C-2' and C-5' of their pyrrolidine rings.These results are consistent with the hypothesis that spermidine is degraded to putrescine prior to its incorporation into the pyrrolidine rings of nicotine and nornicotine.Key Word Index - Nicotiana glutinosa; Solanaceae; biosynthesis; nicotine; nornicotine; spermidine; putrescine.
- Leete, Edward
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p. 957 - 960
(2007/10/02)
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- Irreducible Analogues of Mevaldic Acid Coenzyme A Hemithioacetal as Potential Inhibitors of HMG-CoA Reductase. Synthesis of a Carbon-Sulfur Interchanged Analogue of Mevaldic Acid Pantetheine Hemithioacetal
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Synthesis of (3,5)-threo- and (3,5)-erythro-6-propanamido>methyl>thio>-3,5-dihydroxy-3-methylhexanoic acid, threo- and erythro-7d, as well as the corresponding δ-lactones, cis- and trans-13a, is described.The key step in the syntheses is the selective amidomethylation of the sulfhydryl in cis- or trans-4-hydroxy-6-(mercaptomethyl)-4-methyl-3,4,5,6-tetrahydro-2H-pyran-2-one, cis- or trans-13d, with N-(hydroxymethyl)pantothenamide, 23.The target compounds are the first in a class being explored as potential inhibitors of HMG-CoA reductase, the key regulated enzyme in cholesterol biosynthesis.They are structurally identical with mevaldic acid pantetheine hemithioacetal, 2b (a known substrate for the enzyme and an analogue of the enzyme-bound intermediate 2a), but they are unable to be reduced by the enzyme because the labile C-S bond in 2b has been replaced with a stable C-C bond in 7d by interchanging a carbon and a sulfur atom.
- Fischer, Gordon C.,Turakhia, Rajesh H.,Morrow, Cary J.
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p. 2011 - 2019
(2007/10/02)
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- INTRAMOLECULAR GENERAL-BASE CATALYSIS OF SCHIFF-BASED HYDROLYSIS BY TERTIARY AMINO GROUPS.
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Hydrolysis of a series of Schiff bases derived from benzophenone and various amines has been studied kineticlly in aqueous solution. A linear correlation of the log of the rate constants for the water reaction with the Schiff base pK//a (slope minus 0. 70) shows large positive deviations for Schiff bases derived from (2-aminoethyl)diethylamine, N-(2-aminoethyl)morpholine, N-(2-aminoethyl)piperazine and 2-(aminomethyl)pyridine (1i) but small deviations for Schiff bases from N-(3-aminopropyl)morpholine and 2-(2-aminoethyl)pyridine. The deviations found are attributed to intramolecular general-base catalysis of the water reaction by the internal tertiary amino groups. Magnitudes of the rate enhancement are correlated well with pK//a//l of the internal catalyst ( beta equals 0. 49). Effective concentrations of the internal bases are estimated to range from 340 (1e) to 40 M.
- Okuyama,Shibuya,Fueno
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p. 730 - 736
(2007/10/02)
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- The Chemical Reactivity of Penicillins and Other β-Lactam Antibiotics
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The rates of the acid catalysed hydrolysis of penicillins and cephalosporins are linear in Ho and, unlike other amides, show no rate maximum with increasing acidity.Electron-withdrawing substituents at C-6 in penicillins decrease the rate of hydrolysis with a ρI of ca. 4 and they decrease the rate when attached to the amine leaving group.The acylamido-group at C-6 in penicillins, but not at C-7 in cephalosporins, exhibits neighbouring group participation with a rate enhancement of ca. 103.The absence of penicillenic acid formation from benzylpenicillin in acidic solution is not due to the ionisation of the carboxy-group.These observations are rationalised by a scheme involving N-protonation and formation of an acylium ion intermediate.The alkaline hydrolysis of penicillins proceeds 102 faster than a β-lactam after correction for substituent effects.There is no evidence for substantial inhibition of amide resonance in the bicyclic β-lactam antibiotics, little evidence to indicate extra strain in these systems and no evidence that expulsion of the leaving group at C-3 in cephalosporins occurs in the transition state.
- Proctor, Philip,Gensmantel, Nigel P.,Page, Michael I.
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p. 1185 - 1192
(2007/10/02)
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- The Timing of the Proton-Transfer Process in Carbonyl Additions and Related Reactions. General-Acid-Catalyzed Hydrolysis of Imines and N-Acylimines of Benzophenone
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Observed general-acid-catalyzed hydrolysis of benzophenone imines, Ph2C=NR, or the kinetically equivalent general-base-catalyzed hydrolysis of the conjugate acids Ph2C=N+HR, corresponds mechanistically to general-base-catalyzed amine expulsion from the conjugate acid (T+) of the tetrhedral intermediate from water addition to Ph2C=NR.Broensted β values for this catalysis by carboxylate and cacodylate ions are 0.96 (for R = H), 0.93 (for R = C2H4CN), and 0.76 (for R = CH2CN).These results, combined with calculations that suggest that amine expulsion from the zwitterionic intermediate, T+/-, from ammonia is slower than diffusion processes involving T+/- and catalyst, are consistent with a mechanism in which a simple proton transfer process is not rate determining.Because of the stability of T+/- it is likely that catalysis in this system is "enforced" by the lifetime of this intermediate.We suggest that catalysis of these reactions is observed because hydrogen bonding of T+/- to the conjugate acid of the catalyst provides an energetic advantage by stabilizing both T+/- and the transition state for amine expulsion from this species.Hydrolysis of N-acyl benzophenone imines, Ph2C=NC(O)CH2X (X = H, OCH3, or Cl), involves a rapid, favorable equilibrium for addition of water across the C=N bond, followed by amide expulsion from the carbinolamide.The latter process, analogous to amine expulsion from carbinolamines, is subject to weak general acid catalysis with Broensted α values of 0.5-0.6.This catalysis probably corresponds mechanistically either to (1) bifunctional or "one-encounter" catalysis in which one or both of the proton-transfer processes is "concerted" with C-N cleavage, or (2) general base catalysis of the expulsion of the O-protonated amide from Ph2C(OH)N+HC(OH)CH2X.For uncatalyzed carbinolamide cleavage a cyclic transition state with intramolecular proton transfer to the acyl oxygen is suggested to explain the observed insensitivity to substituents, X, of amide expulsion from the neutral carbinolamides, Ph2C(OH)NHC(O)CH2X.
- Sayer, J. M.,Conlon, Patrick
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p. 3592 - 3600
(2007/10/02)
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- Mechanism of Cleavage of Carbamate Anions
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Carbamates and monothiocarbamates of basic aliphatic amines undergo rate-determining C-N cleavage after a rapid equilibrium protonation step, as shown most directly by inverse solvent deuterium isotope effects of kD/kH = 3.6-4.8 for O,O- and O,S-N-n-butylcarbamates and by rapid acid-catalyzed exchange of the NH proton of n-BuNHCOS- with kexch = 5 107 M-1 s-1.The lifetimes of substituted N-protonated carbamates have been estimated to range down to -10 s.It is concluded that general acid catalysis of the cleavage of carbamates of weakly basic anilines (α = 0.84) occurs through an enforced preassociation mechanism with hydrogen bonding to the leaving protonated nitrogen atom and C-N cleavage in the rate-determining step.There is more proton transfer in the transition state (larger α) and a smaller β1g with more basic amines and upon substitution of sulfur for oxygen.The low pKa values of N-protonated carbamates and monothiocarbamates illustrate the strong electron-accepting ability of -COO- and -COS-.
- Ewing, Sheila P.,Lockshon, Daniel,Jencks, William P.
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p. 3072 - 3084
(2007/10/02)
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