Mechanism of Difluoroamine Deaminations

An alternative explanation of the reductive deamination with difluoroamine is suggested which does not involve the originally proposed formation of nitrogen monofluoride and Wolff-Kishner cleavage.The reductive deamination of amines by difluoroamine has been discussed in terms of intermediate formation of nitrogen monofluoride [1, 2]. Some steps in the proposed mechanism seem questionable and hence an alternative view of the reaction is presented.Bumgardner put forward a five step reaction scheme. The initial step was a proton transfer between difluoroamine and a more basic primary amine to form a salt with the difluoronitrogen (I) anion. This salt decomposed in a rate determining step to produce nitrogen monofluoride which inserted rapidly into the N-H bond of HNF₂. The product eliminated hydrogen fluoride with further amine to form a di-imine, which then extruded dinitrogen and left the alkane. The overall stoichiometry accords with.3RNH₂ + HNF₂ = RN = NH + 2RN₃⁺ F^- (1)There is only indirect evidence for the intermediacy of a fluoronitrene (NF) in reactions, based mainly on reaction products and their stereochemistry. Le Noble [3] inferred such an intermediate in the alkaline decomposition of HNF₂ from a large positive volume of activation obtained from the pressure variation of rate. The suggested rate determining step wasNF₂^-aq → NFg + F^- aqEven if this were the only explanation of a larger transition state, one has to transfer a mechanism obtained using a fully dissociated base in an aqueous medium to a relatively weak base in a non-aqueous medium.     

Some approaches to the synthesis of fluorinated alcohols and esters. III. Synthesis of 2-(F-alkyl)ethanols from 2-(F-alkyl)-1-iodoethanes and amides.

1-Iodo-2-(F-alkyl)ethanes, R_FCH₂CH₂I, when heated with a large excess of N-methylformamide (NMF) give in high yield, mixtures of predominately R_FCH₂CH₂OH, some formate ester and a little R_FCHCH₂. In a study of this process, significant variables were examined, including solvent, reactant ratio, effect of water, and alternative amide reactants. The coproduct from NMF is the amidine salt, [MeNHCH(NHMe)]⁺I⁻. By contrast, R_FCH₂CH₂I with N,N-dimethylformamide (DMF) and water (one or two mols) gives chiefly the formate ester; the coproduct is Me₂NH₂⁺I⁻. A mechanistic scheme is proposed: in the first step, an alkyl imidate salt, e.g., [HC(NH Me)OCH₂CH₂R_F]⁺I⁻ is formed by O-alkylation of NMF; reaction of the imidate with more NMF gives a tetrahedral intermediate that breaks down rapidly to R_FCH₂CH₂OH, and HC(NHMe)NMeCHO⁺I⁻. The formate ester is derived from the alcohol and this N-formyl acylating agent, in a subsequent step. Analogously, the alkyl imidate salt from DMF and R_FCH₂CH₂I reacts with water as nucleophile (but not with DMF) to give a tetrahedral intermediate that cleaves under stereoelectronic control to formate ester and amine salt, but not to alcohol. Quantitative isolation of amine salt and amidine salt, and observed rates of reaction give solid support to this proposed mechanism.     

Effect of amines on the ceric ion-initiated polymerization of vinyl monomers. II. Polymerization of acrylonitrile by ceric ion in presence of various substituted amines

The effect of various substituted amines on the polymerization of acrylonitrile initiated by ceric ammonium sulfate has been studied in aqueous solution at 30°C. It was found that the secondary and tertiary amines considerably increased the rate of polymerization, whereas the primary amines seemed to have no effect at all. From the kinetic studies it was found that the overall polymerization rate R_p is independent of ceric ion concentration and can be expressed by the equation: R_p = k₁ [amine] [monomer] + k₂[monomer]², where k₁ and k₂ are constants (involving different rate constants). The accelerating effect of the amines was attributed to a redox reaction between the ceric ion and the amine involving a single electron transfer, the relative activity of the different amines being thus dependent on the relative electron-donating tendency of the substituents present in the amine. The mechanism of the polymerization is discussed on the basis of these results, and various kinetic constants are evaluated.     

Kinetics and Mechanism of the Reactions of N-Pentafluorocarbonimidoyl Dihalides with Aliphatic Amines in Acetonitrile

A mechanism is proposed for the substitution of the first halogen atom in N-pentafluorophenylcarbonimidoyl dihalides (Ar_FN=CX₂, X = Cl, Br) by aliphatic amines and includes a tetrahedral intermediate (T _E ). In the case of the reactions of primary and secondary amines the rate-limiting stage is the formation of the intermediate, and in the case of tertiary amines it is stereomutation of the intermediate (T _E ) to the thermodynamically more stable configuration (T _Z ). In the case of all the amines the final product (the Z isomer) is formed from the configuration (T _Z ).     

Double addition d'organometalliques sur des nitriles α-oxygenes R CN. Obtention d'amines primaires de type (RRR')CNH2

Synthesis of the amines (R¹RR')CNH₂ (I) was carried out by the action of two organometallic compounds RM and R'M' on the α-oxygenated nitriles R¹ CN. Aliphatic and unhindered organolithium or α-ethylenic organomagnesium compounds must be used in the second addition. The nature of the two metallic atoms of the aminate (R¹RR')CN(MM'), precursor of the amine I, has an influence on the yield of this amine. If M = M' = Li an elimination reaction occurs and the amine I is obtained in low yields (2—34%). If M = Mg and M' = Li, the intermediate aminate is more stable, and the amine I is formed in good yields (48—75%). A mechanism explaining these results and the formation of by-products is proposed.     

Double addition d'organometalliques sur des nitriles α-oxygenes R1 CN. Obtention d'amines primaires de type (R1RR')CNH2

Synthesis of the amines (R¹RR')CNH₂ (I) was carried out by the action of two organometallic compounds RM and R'M' on the α-oxygenated nitriles R¹ CN. Aliphatic and unhindered organolithium or α-ethylenic organomagnesium compounds must be used in the second addition. The nature of the two metallic atoms of the aminate (R¹RR')CN(MM'), precursor of the amine I, has an influence on the yield of this amine. If M = M' = Li an elimination reaction occurs and the amine I is obtained in low yields (2—34%). If M = Mg and M' = Li, the intermediate aminate is more stable, and the amine I is formed in good yields (48—75%). A mechanism explaining these results and the formation of by-products is proposed.     

Reaction of halogenated hydrocarbon solvents with tertiary amines: Spectrophotometric and conductimetric study

Halogenated hydrocarbon solvents, SolvCl, (dichloromethane, chloroform, and 1,2‐dichloroethane) react with various types of tertiary amines, A, such as tri‐n‐buthylamine, tropane derivatives (tropine and atropine) and quinine generating a quaternary ammonium salt, N‐halogenalkylammonium chloride (SolvA⁺Cl^?). Some tertiary amines, as well as secondary and primary amines, cannot react with these solvents. This reaction has been detected and studied by both conductivity and visible spectrophotometry measures—the latter after adding a small quantity of a dye, such as bromocresol green (BCGH₂), bromophenol blue (BPBH₂), or tetrabromophenolphthaleinethyl ester (TBPEH). Both study methods permit the determination of the kinetic parameters, and they are in good agreement. The monoprotic TBPEH is the dye of the simplest mechanism, useful to study kinetics of amines of uncertain behavior as quinine, while BPBH₂ is the best dye for quantitative determinations. Kinetics for this reaction are of first order for both amine, A, and solvent, SolvCl; activation energy, E_a, and frequency factor are also determined. Rate constants increase with the amine basicity and with a reduction in the number of the halogen atoms present in the solvent. This reaction is slow but not negligible and must be considered a side reaction of these universally used solvents. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:500–509, 2004     

Using Me3Si–F–Al(ORF)3 and Me3Si–Cl as Methylating Agents – Synthesis and Characterization of SeMeCl2[F{Al(ORF)3}2]

Upon reacting SeCl₄ with Me₃Si–F–Al(OR^F)₃, the selenonium salt SeMeCl₂[al‐f‐al] ( 1 ) {[al‐f‐al]^– = [F[Al(OC(CF₃)₃)₃]₂]^–} was obtained and characterized by NMR, IR, and Raman spectroscopy as well as single crystal XRD experiments. Despite the [SeX₃]⁺ (X = F, Cl, Br, I) and [SeR₃]⁺ salts (R = aliphatic organic residue) being well known and thoroughly studied, the mixed cations are scarce. The only previous example of a salt with the [SeMeCl₂]⁺ cation is SeMeCl₂[SbCl₆], which was never structurally characterized and is unstable in solution over hours. Only ¹H‐NMR studies and IR spectra of this compound are known. The unexpected use of Me₃Si–F–Al(OR^F)₃ as a methylating agent was investigated via DFT calculations and NMR experiments of the reaction solution. The reaction of SeCl₃[al‐f‐al] with Me₃Si‐Cl at room temperature in CH₂Cl₂ proved to yield the same product with Me₃Si–Cl acting as a methylating agent.     

Bildung,Kristallstruktur und absolute Konfiguration von (−)-N-(Chloromethyl)galanthaminium-chlorid

Formation, X-Ray Crystal Structure, and Absolute Configuration of (?)-N-(Chloromethyl)galanthaminium Chloride The acetylcholinesterase inhibitor galanthamine ( 1 ), main alkaloid of several Narcissus species, readily forms a quaternary ammonium salt by reaction with the solvent CH₂Cl₂. The structure and absolute configuration of (?)-N-(chloromethyl)galanthaminium chloride ( 2 ) were determined by X-ray diffraction (R = 0.075 for 2775 observed independent reflexions) and NMR spectroscopy. The tetragonal crystals (space group P4₃) contain two crystallographically independent cations which do not differ significantly from one another. The CH₂Cl group is attached to the quaternary N-atom in stereospecific (R)-configuration. In the crystal, the configurational position of the Me group at the N-atom of 2 differs from that of the crystalline free base 1 . Hydrogen bonding is observed from the OH group at C(3) of 2 to the Cl^? anion or to the Cl-atom of an adjacent cation.     

The syntheses of fluorinated alkanesulfonamides and poly-(fluorinated alkanesulfonamides)

In order to synthesize poly-(fluorinated alkanesulfonamides) a series of model experiments were carried out: (1) reactions of fluorinated alkanesulfonyl fluorides with amines, (2) reactions of fluorinated alkanesulfonyl chloride with amines and (3) reactions of sodium salts of fluorinated alkanesulfonamides with alkyl iodides of fluorinated alkanesulfonic acid esters. Seventeen new fluorinated alkanesulfonamides were prepared in good yields, namely: R_FO(CF₂)₂SO₂NR¹R² (1a-h), R¹R²NSO₂R_FSO₂NR¹R² (2a-h) and [Cl (CF₂)₄O(CF₂)₂SO₂NH(CH₂)₃]₂ (3). Reaction of R_FSO₂NH₂ with equivalent amount of NaOCH₃ and methyl iodide was shown to give both the N-mono- and N,N-di-substituted amides. Consequently the N-monosubstituted alkanesulfonamides were chosen as monomers for syntheses of the poly-(fluorinated alkanesulfonamides) and two new polymers were synthesized. The effect of the condition of the polycondensation on M?_n of the polymers were discussed and elemental composition, ¹⁹F NMR, IR, M?_n, Tg, tensile strength, thermal and chemical stabilities of the polymers were measured. Several new perfluoroalkanesulfonyl chlorides CISO₂R_FSO₂Cl (4a-c) and fluorinated alkanesulfonic acid esters (6a-d) were synthesized. However, reaction of CFCl₂CF₂O(CF₂)₂SO₂F with AlCl₃ was found to give Cl₃CCF₂O(CF₂)₂SO₂F (5) instead of the expected sulfonyl chloride.     

Polyfluoroalkyl <Emphasis Type="Italic">N</Emphasis>-(trifluoromethylsulfonyl)amidosulfites,number one stable NH-containing amidosulfites

We prepared for the first time NH-containing amidosulfites, polyfluoroalkyl N-(trifluoro-methylsulfonyl) amidosulfites CF₃SO₂NHS(O)OR_F, by reaction of N-sulfinyl-trifluoromethanesulfonamide CF₃SO₂N=S=O with alcohols R_FOH. Amidosulfites were formed also in reaction of chlorosulfites R_FOS(O)Cl with trifluoromethanesulfonamide, with its sodium salt, and N-trimethylsilyl derivative.     

Photoinitiated Reactions of Haloperfluorocarbons with Gold(I) Organometallic Complexes: Perfluoroalkyl Gold(I) and Gold(III) Complexes

The study of perfluoroalkyl metal complexes is key to understand and improve metal-promoted perfluoroalkylation reactions. Herein, we report the synthesis of the first gold complexes with primary or secondary perfluoroalkyl ligands by photoinitiated reactions between Au^I organometallic complexes and iodoperfluoroalkanes. Complexes of the types LAuR_F (L=PPh₃ or N,N-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; R_F=n-C₄F₉, n-C₆F₁₃, i-C₃F₇, c-C₆F₁₁) and [Au(R_F)(Ar)I(PPh₃)] (Ar=2,4,6-trimethylphenyl) have been isolated and characterized. Alkynes R_FC≡CR were formed by reaction of Ph₃PAuC≡CR (R=Ph, nHex) with IR_F (R_F=n-C₄F₉, i-C₃F₇). According to the evidences obtained, this transformation undergoes through a photoinitiated radical mechanism. Au^III complexes [Au(n-C₄F₉)(X)(Y)L] (X=Y=Cl, Br, I, Me; X=Me, Y=I) have been prepared or in situ generated, and their thermal or photochemical decomposition reactions have been studied.     

N‐Silylation of Amines Mediated by Et3SiH/KOtBu

Silylation of primary and secondary amines is reported, using triethylsilane as the silylating reagent in the presence of potassium tert‐butoxide (KO^tBu). The reaction proceeds well in the presence of 0.2 equiv. of KO^tBu. In competition experiments, aniline is selectively silylated over aliphatic amines. Computational studies support a catalytic mechanism which is initiated by KO^tBu interacting with the silane to form KH and silylated amine. The KH then takes over the role of base in the propagation of the cyclic mechanism and deprotonates the amine. This reacts with R₃SiH to afford the product R₃SiNR′R′′ and regenerate KH.     

The preparation of perfluorinated carboxylic esters and perfluoro carbonates

Aliphatic perfluorinated carboxylic esters have been prepared by two methods; (i) the reaction of the potassium salt of perfluoro 3-ethyl pent-3-ol, KOC(C₂F₅)₃, with perfluoro acid chlorides R_fCOCl, to yield perfluorinated esters of composition R_fCOOC(C₂F₅)₃, and (ii) the reaction of carbonyl chloride or thionyl chloride with a mixture of the potassium salt KOC(C₂F₅)₃ and perfluoro acid salts of the general formula KOCOR_f in a polar solvent. The product ester has the composition R_fCOOC(C₂F₅)₃, and in this instance carbon dioxide or sulphur dioxide is liberated during the reaction. A qualitative study of the thermal decomposition of a perfluoro ester has been made.A tertiary perfluoro carbonate of composition [(C₂F₅)₂CF₃CO]₂CO has been prepared by the reaction of phosgene with the potassium salt KOC(C₂F₅)₂CF₃ in a polar solvent. The intermediate acid chloride (C₂F₅)₂CF₃COCOCl can be isolated.     

Negative ion mode electrospray ionization mass spectrometry study of ammonium-counter ion clusters

Electrospray ionization mass spectrometry (ESI-MS) was used to examine clusters of protonated amine salt solutions with chloride counter ions in the negative ion mode. These ions have the general formula [(RNH₃)_xCl_x+1]⁻. Primary amines generate a wide cluster distribution with clusters up to 14 mer for methylamine hydrochloride clusters. Secondary and quaternary amines only generate the monomer ion under identical conditions. Collision induced dissociation (CID) of the cluster ions generates cluster ions of lower m/z with the next lower cluster being the most abundant. The product ions from MeNH₃Cl₂⁻, Me₂NH₂Cl₂⁻ and (MeNH₃)₂Cl₃⁻ have low threshold appearance energies of 1. 24 to 2. 22 eV center-of-mass frame. Secondary amine monomer ions have lower threshold CID energies than primary amine monomer ions. The amine threshold CID energy decreases as the carbon chain length increases. As an electrospray solvent, isopropyl alcohol (IPA) promotes the formation of counter ions and clustering.     

Kinetic study of the reaction of chlorine atoms with CF3I and the reactions of CF3 radicals with O2, Cl2 and NO at 296 K

The kinetics of the gas-phase reaction of Cl atoms with CF₃I have been studied relative to the reaction of Cl atoms with CH₄ over the temperature range 271–363 K. Using k(Cl + CH₄) = 9.6 × 10^?12 exp(?2680/RT) cm³ molecule^?1 s^?1, we derive k(Cl + CF₃I) = 6.25 × 10^?11 exp(?2970/RT) in which E_a has units of cal mol^?1. CF₃ radicals are produced from the reaction of Cl with CF₃I in a yield which was indistinguishable from 100%. Other relative rate constant ratios measured at 296 K during these experiments were k(Cl + C₂F₅I)/k(Cl + CF₃I) = 11.0 ± 0.6 and k(Cl + C₂F₅I)/k(Cl + C₂H₅Cl) = 0.49 ± 0.02. The reaction of CF₃ radicals with Cl₂ was studied relative to that with O₂ at pressures from 4 to 700 torr of N₂ diluent. By using the published absolute rate constants for k(CF₃ + O₂) at 1–10 torr to calibrate the pressure dependence of these relative rate constants, values of the low- and high-pressure limiting rate constants have been determined at 296 K using a Troe expression: k₀(CF₃ + O₂) = (4.8 ± 1.2) × 10^?29 cm⁶ molecule^?2 s^?1; k_∞(CF₃ + O₂) = (3.95 ± 0.25) × 10^?12 cm³ molecule^?1 s^?1; F_c = 0.46. The value of the rate constant k(CF₃ + Cl₂) was determined to be (3.5 ± 0.4) × 10^?14 cm³ molecule^?1 s^?1 at 296 K. The reaction of Cl atoms with CF₃I is a convenient way to prepare CF₃ radicals for laboratory study. © 1995 John Wiley & Sons, Inc.     

Oxidation of primary amines by bromamine-B catalyzed by Osmium(VIII) in alkaline medium: A kinetic and mechanistic study

The kinetics of oxidation of the aliphatic primary amines, n-propylamine, n-butylamine, and isoamylamine, by N-sodio-N-bromobenznesulfonamide or bromamine-B (BAB), in the presence of osmium(VIII), has been studied in alkaline medium at 35°C. In the presence of the catalyst, the experimental rate law for the oxidation of the amine substrate (S) takes the form, rate=k[BAB][OsO₄][OH⁻]^x, which in the absence of the catalyst changes to the form, rate=k[BAB][S][OH⁻]^y, where x and y are less than unity. Additions of halide ions and the reduction product of BAB (benzenesulfonamide), and the variation of ionic strength of the solvent medium have no effect on the reaction rate. Activation parameters have been evaluated. The proposed mechanism assumes the formation of a complex intermediate between the active oxidant species, PhSO₂NBr⁻, and the catalyst, OsO₄, in the rate determining step. This complex then interacts with the substrate amine in fast steps to yield the end products. The average value for the deprotonation constant of monobromamine-B, forming PhSO₂NBr⁻, is evaluated for the Os(VIII) catalyzed reactions of the three amines in alkaline medium as 9.80×10³ at 35°C. The average value for the same constant for the uncatalyzed reactions is 1.02×10⁴ at 35°C. © 1997 John Wiley & Sons, Inc.     

Synthesis of novel zirconium complexes bearing mono‐Cp and tridentate Schiff base [ONO] ligands and their catalytic activities for olefin polymerization

A series of novel zirconium complexes {R²Cp[2‐R¹‐6‐(2‐CH₃OC₆H₄N?CH)C₆H₃O]ZrCl₂ ( 1 , R¹ = H, R² = H, 2 : R¹ = CH₃, R² = H; 3 , R¹ = ^tBu, R² = H; 4 , R¹ = H, R² = CH₃; 5 , R¹ = H, R² = n‐Bu)} bearing mono‐Cp and tridentate Schiff base [ONO] ligands are prepared by the reaction of corresponding lithium salt of Schiff base ligands with R²CpZrCl₃·DME. All complexes were well characterized by ¹H NMR, MS, IR and elemental analysis. The molecular structure of complex 1 was further confirmed by X‐ray diffraction study, where the bond angle of Cl? Zr? Cl is extremely wide [151.71(3)°]. A nine‐membered zirconoxacycle complex Cp(O? 2? C₆H₄N?CHC₆H₄‐2? O)ZrCl₂ ( 6 ) can be obtained by an intramolecular elimination of CH₃Cl from complex 1 or by the reaction of CpZrCl₃·DME with dilithium salt of ligand. When activated by excess methylaluminoxane (MAO), complexes 1–6 exhibit high catalytic activities for ethylene polymerization. The influence of polymerization temperature on the activities of ethylene polymerization is investigated, and these complexes show high thermal stability. Complex 6 is also active for the copolymerization of ethylene and 1‐hexene with low 1‐hexene incorporation ability (1.10%). Copyright © 2006 John Wiley & Sons, Ltd.     

Mechanistic studies of carbonate macrocyclization

The kinetics of phenylchloroformate (PCF) reactions have been used to model some of the key chemical events in carbonate macrocyclization. Three reactions have been studied using stopped-flow FT-IR spectroscopy: formation of acyl ammonium salt from PCF and three different trialkylamines, the conversion of acyl ammonium salt to urethane, and the condensation reaction between acyl ammonium salt and 4-isopropylphenol. The rate dependence was studied for triethylamine (TEA), diethylmethylamine (DEMA) and tri-n-butylamine (TBA) at 0°C in anhydrous CH₂Cl₂. The reactivity order for acyl ammonium salt formation for TBA: TEA: DEMA is 1 : 2.7 : >444. By contrast, condensation and urethane formation are not sensitive to the structure of the amine. The rate of condensation is comparable to the rate of acyl ammonium salt formation for TEA and TBA, while the rate of urethane formation is the slowest process for all three amines. These results are consistent with the view that the yield of macrocyclic polycarbonates is related to the concentration of the acyl ammonium salt. The optimum amine concentration for obtaining high yields of cyclics varies with the amine structure and parallels the difference in the rates of acyl ammonium salt formation. © 1994 John & Sons, Inc.     

Formation and Stability of Difluoromethylene Phospho-Raiies,R3P=CF2

Abstract

Carbonyl compounds react with CBr₂F₂ in the presence of phosphanes, RP (R = Ph, NR;), and metals (M = Zn, Cd, Pb) forming geminal difluoroolefins (eq. 1)¹.

R′CHO + CBr₂F₂ + R₃P + M → R′CH=CF₂ + MBr₂ + R₃PO (1)

Without any doubt this reaction has to occur via the intermediate formation of difluoromethylene phosphoranes, which then undergo the Wittig reaction with carbonyl compounds (eq. 2). R₃P=CF₂ + R′CHO → R₃PO + R′CH=CF₂ (2).