Tetrabutylammonium Cyanide Research Articles

Tetrabutylammonium Cyanide Catalyzed Aldol Self-Condensation of Ley’s Butane-2,3-diacetal (BDA) Protected Glyceraldehydes. Synthesis of Two New BDA-Protected Sugar-Derived Scaffolds

The self-aldol reaction of Ley’s protected BDA-(R)- and (S)-glyceraldehydes is described for the first time. The reaction is catalyzed by tetrabutylammonium cyanide.

Formation and Structure of Self-Assembled Monolayers of Octylthioacetates on Au(111) in Catalytic Tetrabutylammonium Cyanide Solution

The formation and structure of self-assembled monolayers (SAMs) by the adsorption of acetyl-protected octylthioacetate (OTA) on Au(111) in a catalytic tetrabutylammonium cyanide (TBACN) solution were examined by means of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). Molecular-scale STM imaging revealed that OTA molecules on Au(111) in a pure solvent form disordered SAMs, whereas they form well-ordered SAMs showing a c(4 × 2) structure in a catalytic TBACN solution. XPS and CV measurements also revealed that OTA SAMs on Au(111) formed in a TBACN solution have a stronger chemisorbed peak in the S 2p region at 162 eV and a higher blocking effect compared to OTA SAMs formed in a pure solvent. In this study, we clearly demonstrate that TBACN can be used as an effective deprotecting reagent for obtaining well-ordered SAMs of thioacetyl-protected molecules on gold.

Copper(I) Templated Synthesis of a 2,2´-Bipyridine Derived 2-Catenane: Synthetic, Modelling, and X-ray Studies

Following molecular modelling employing molecular mechanics and semi-empirical (PM3) calculations as an aid to ligand design, a new copper(i)-containing [2]-catenane has been prepared by the reaction of 6,6′-bis[(4″-formylphenoxy)methyl]-2,2′-bipyridyl with 1,6-hexanediamine in the presence of a copper(i) template, followed by in situ sodium borohydride reduction of the tetra-imine species generated. The corresponding [2]-catenane was obtained as a deep orange crystalline solid. The X-ray structure of this product along with that of the corresponding bis-dialdehyde precursor copper(i) complex have been determined. In the latter case, the structure is pre-organized for catenane formation. The new catenane appears to be the first example of a tetrahedral metal template product incorporating a bis-bipyridyl derivative core. Isolation of the metal-free [2]-catenane has also been achieved following treatment of the copper(i) catenane complex in dimethylsulfoxide with tetrabutylammonium cyanide.

Determining the Transition-State Structure for Different SN2 Reactions Using Experimental Nucleophile Carbon and Secondary α-Deuterium Kinetic Isotope Effects and Theory

Nucleophile (11)C/ (14)C [ k (11)/ k (14)] and secondary alpha-deuterium [( k H/ k D) alpha] kinetic isotope effects (KIEs) were measured for the S N2 reactions between tetrabutylammonium cyanide and ethyl iodide, bromide, chloride, and tosylate in anhydrous DMSO at 20 degrees C to determine whether these isotope effects can be used to determine the structure of S N2 transition states. Interpreting the experimental KIEs in the usual fashion (i.e., that a smaller nucleophile KIE indicates the Nu-C alpha transition state bond is shorter and a smaller ( k H/ k D) alpha is found when the Nu-LG distance in the transition state is shorter) suggests that the transition state is tighter with a slightly shorter NC-C alpha bond and a much shorter C alpha-LG bond when the substrate has a poorer halogen leaving group. Theoretical calculations at the B3LYP/aug-cc-pVDZ level of theory support this conclusion. The results show that the experimental nucleophile (11)C/ (14)C KIEs can be used to determine transition-state structure in different reactions and that the usual method of interpreting these KIEs is correct. The magnitude of the experimental secondary alpha-deuterium KIE is related to the nucleophile-leaving group distance in the S N2 transition state ( R TS) for reactions with a halogen leaving group. Unfortunately, the calculated and experimental ( k H/ k D) alpha's change oppositely with leaving group ability. However, the calculated ( k H/ k D) alpha's duplicate both the trend in the KIE with leaving group ability and the magnitude of the ( k H/ k D) alpha's for the ethyl halide reactions when different scale factors are used for the high and the low energy vibrations. This suggests it is critical that different scaling factors for the low and high energy vibrations be used if one wishes to duplicate experimental ( k H/ k D) alpha's. Finally, neither the experimental nor the theoretical secondary alpha-deuterium KIEs for the ethyl tosylate reaction fit the trend found for the reactions with a halogen leaving group. This presumably is found because of the bulky (sterically hindered) leaving group in the tosylate reaction. From every prospective, the tosylate reaction is too different from the halogen reactions to be compared.

The Benzil Rearrangement Reaction: Trapping of a Hitherto Minor Product and Its Application to the Development of a Selective Cyanide Anion Indicator

The isolation and characterization of an intermediate from the benzil-cyanide reaction is reported. The use of this trapping chemistry to produce a chemical indicator for the cyanide anion is described. It relies on the synthesis and reaction of a pi-extended analogue of benzil. Addition of tetrabutylammonium cyanide to organic solutions of this species, referred to as compound 3 in the text, gives rise to a dramatic change in both color and fluorescence properties.

A New Insight into Using Chlorine Leaving Group and Nucleophile Carbon Kinetic Isotope Effects To Determine Substituent Effects on the Structure of SN2 Transition States

Chlorine leaving group k(35)/k(37), nucleophile carbon k(11)/k(14), and secondary alpha-deuterium [(kH/kD)alpha] kinetic isotope effects (KIEs) have been measured for the SN2 reactions between para-substituted benzyl chlorides and tetrabutylammonium cyanide in tetrahydrofuran at 20 degrees C to determine whether these isotope effects can be used to determine the substituent effect on the structure of the transition state. The secondary alpha-deuterium KIEs indicate that the transition states for these reactions are unsymmetric. The theoretical calculations at the B3LYP/aug-cc-pVDZ level of theory support this conclusion; i.e., they suggest that the transition states for these reactions are unsymmetric with a long NC-C(alpha) and reasonably short C(alpha)-Cl bonds. The chlorine isotope effects suggest that these KIEs can be used to determine the substituent effects on transition state structure with the KIE decreasing when a more electron-withdrawing para-substituent is present. This conclusion is supported by theoretical calculations. The nucleophile carbon k(11)/k(14) KIEs for these reactions, however, do not change significantly with substituent and, therefore, do not appear to be useful for determining how the NC-C(alpha) transition-state bond changes with substituent. The theoretical calculations indicate that the NC-C(alpha) bond also shortens as a more electron-withdrawing substituent is placed on the benzene ring of the substrate but that the changes in the NC-C(alpha) transition-state bond with substituent are very small and may not be measurable. The results also show that using leaving group and nucleophile carbon KIEs to determine the substituent effect on transition-state structure is more complicated than previously thought. The implication of using both chlorine leaving group and nucleophile carbon KIEs to determine the substituent effect on transition-state structure is discussed.

New Solvents for Cellulose: Dimethyl Sulfoxide/Ammonium Fluorides

New solvents based on DMSO in combination with alkylammonium fluorides, in particular TBAF . 3H(2)O and BTMAF . H(2)O, were established as media for homogeneous functionalization of cellulose. Even DMSO in combination with freshly prepared, anhydrous TBAF, obtained by the reaction of tetrabutylammonium cyanide and hexafluorobenzene, dissolves cellulose. In contrast, a mixture of DMSO and tetramethylammonium fluoride does not dissolve cellulose. The solvents were characterized by capillary viscosity, which showed that a cellulose solution of DMSO/BTMAF . H(2)O possesses a lower viscosity at comparable cellulose concentrations compared with DMSO/TBAF . 3H(2)O. The determination of the degree of polymerization of the starting cellulose (microcrystalline cellulose, spruce sulfite pulp, and cotton linters), and of the regenerated samples, shows that degradation of the polymer depends on the dissolution time, temperature and on the ammonium fluoride used. The results of different homogeneous reactions including acylation and carbanilation of cellulose in the solvents were compared with those of the most-commonly-applied solvent N,N-dimethylacetamide/LiCl. The products were characterized by elemental analysis, (1)H- and (13)C NMR spectroscopy (additionally after perpropionylation) and FTIR spectroscopy.

Aliphatic Thioacetate Deprotection Using Catalytic Tetrabutylammonium Cyanide.

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Aliphatic thioacetate deprotection using catalytic tetrabutylammonium cyanide

A series of thiol-functionalized organic compounds were selected to analyze the scope and efficiency of a new thioacetate deprotection method using catalytic tetrabutylammonium cyanide (TBACN) to effect the transformation of a thioacetate group to a free thiol in the presence of a protic solvent. Particularly attractive are the mild reaction and workup conditions, reduced byproduct formation typically seen using literature methods and yields of greater than 80% for the free aliphatic thiols. This method is effective on aliphatic thiols with trityl, benzyl, p-halo-benzyl, phenethyl, phenoxyethyl, and cyclohexylethyl structural moieties, but it is not effective with thiophenols.

Organocatalytic Ring Expansion of β-Lactams to γ-Lactams through a Novel N1−C4 Bond Cleavage. Direct Synthesis of Enantiopure Succinimide Derivatives

Tetrabutylammonium cyanide (20 mol %) catalyzes ring expansion of 4-(arylimino)methylazetidin-2-ones 2 to 5-aryliminopyrrolidin-2-ones 3 through a novel N1-C4 bond cleavage of the beta-lactam nucleus. New, efficient one-pot protocols to enantiopure succinimide derivatives 3 and 4 from beta-lactam aldehydes 1 have also been developed. [reaction: see text]

Anhydrous Tetrabutylammonium Fluoride

Tetrabutylammonium fluoride (TBAF) is prepared at low temperature by nucleophilic aromatic substitution of hexafluorobenzene with tetrabutylammonium cyanide. Adventitious water is scavenged during this synthesis by the generated hexacyanobenzene, which readily adds water under basic conditions. Contrary to expectations, TBAF is stable to Hofmann elimination in polar aprotic solvents under anhydrous conditions. Added hydroxylic solvents are shown to catalyze the decomposition of TBAF and to catalyze proton exchange with DMSO. The synthetic utility of this salt is described briefly.

Tetrabutylammonium cyanide catalyzed diasteroselective cyanosilylation of chiral α-hydroxyketones

Tetrabutylammonium cyanide has been used as non-metallic catalyst for the diastereoselective cyanosilylation of α-hydroxyketones derived from the chiral pool. This affords α-substituted-α,β-dihydroxynitriles with high levels of asymmetric induction.

Tetrabutylammonium cyanide catalyzes the addition of TMSCN to aldehydes and ketones

The catalytic effect of Bu4NCN on the addition of TMSCN to the carbonyl group of spiroepoxycyclohexadienones and to some other representative carbonyl compounds has been considered.

Experimental and theoretical multiple kinetic isotope effects for an SN2 reaction. An attempt to determine transition-state structure and the ability of theoretical methods to predict experimental kinetic isotope effects.

The secondary alpha-deuterium, the secondary beta-deuterium, the chlorine leaving-group, the nucleophile secondary nitrogen, the nucleophile (12)C/(13)C carbon, and the (11)C/(14)C alpha-carbon kinetic isotope effects (KIEs) and activation parameters have been measured for the S(N)2 reaction between tetrabutylammonium cyanide and ethyl chloride in DMSO at 30 degrees C. Then, thirty-nine readily available different theoretical methods, both including and excluding solvent, were used to calculate the structure of the transition state, the activation energy, and the kinetic isotope effects for the reaction. A comparison of the experimental and theoretical results by using semiempirical, ab initio, and density functional theory methods has shown that the density functional methods are most successful in calculating the experimental isotope effects. With two exceptions, including solvent in the calculation does not improve the fit with the experimental KIEs. Finally, none of the transition states and force constants obtained from the theoretical methods was able to predict all six of the KIEs found by experiment. Moreover, none of the calculated transition structures, which are all early and loose, agree with the late (product-like) transition-state structure suggested by interpreting the experimental KIEs.

Mechanistic insight from activation parameters for the reaction between co-enzyme B12 and cyanide: further evidence that heterolytic Co–C bond cleavage is solvent-assistedElectronic supplementary information (ESI) available: NMR and kinetic data. See http://www.rsc.org/suppdata/dt/b2/b210068a/

The potential involvement of the solvent in heterolytic Co–C bond cleavage for vitamin B12 derivatives has been probed by measuring for the first time activation parameters for heterolytic Co–C bond cleavage. If a water molecule is part of the transition state, negative entropies and volumes of activation should be observed. Conversely, if Co–C bond cleavage is a purely dissociative process, these parameters will be positive. Activation parameters have been determined for the reactions of co-enzyme B12 (5′-deoxyadenosylcobalamin, AdoCbl) and the corresponding cobinamide, 5′-deoxyadenosylcobinamide (AdoCbi+), with cyanide, since previous studies have shown that these reactions proceed at convenient rates, Co–C heterolytic bond cleavage is rate-determining and the reaction proceeds cleanly (that is, negligible homolytic cleavage). In addition, the kinetics of the reaction of AdoCbl with cyanide in aqueous solution were re-investigated at high concentrations of sodium cyanide (up to 3.00 M) at pH 11.0 and I = 5.0 M (NaClO4) using UV-visible and 1H NMR spectroscopy. A significant kinetic saturation was obtained at high CN− concentrations and the limiting rate constant at 25.0 °C was found to be (2.21 ± 0.04) × 10−2 s−1, with an overall formation constant for the (β-Ado)(α-CN)Cbl− intermediate, KCN/KCo, of 0.259 ± 0.007 M−1. ΔH≠, ΔS≠ and ΔV≠ under these conditions were found to be 55 ± 1 kJ mol−1, −98 ± 3 J K−1 mol−1 and −5.7 ± 0.3 cm3 mol−1, respectively. ΔV≠ for the reaction of AdoCbi+ and CN− at pH 11.0 and 35.0 °C was found to be −4.5 ± 0.4 cm3 mol−1, while ΔV≠ for the reaction of AdoCbl and AdoCbi+ with tetrabutylammonium cyanide in 92%DMF–8%D2O at 35 °C was found to be −8.2 ± 0.3 and −8.8 ± 0.7 cm3 mol−1, respectively. The activation parameters data obtained in the present study support the earlier suggestion that the rate determining step for the reaction of AdoCbl and AdoCbi+ with CN− which involves heterolytic cleavage of the Co–C bond of the (β-Ado)(α-CN)Cbl− and (β-Ado)(α-CN)Cbi intermediates, respectively, is a solvent-assisted, β-elimination process, in which the solvent partially protonates the ribosyl oxygen of the intermediate.

Synthesis of the first amine–cyanocarboxyboranes, isoelectronic analogues of α-cyanocarboxylic acids

The first amine–cyanocarboxyboranes and their esters are synthesized from trimethylamine–bromo(methoxycarbonyl)boranes with tetrabutylammonium cyanide, followed by amine exchange reactions and acidic hydrolysis; pKa values of “boracyanocarboxylic acids” are determined and their stability in acidic medium examined.

Studies on the mechanism of the reaction between 5′-deoxyadenosylcobinamide and cyanide

The reaction between 5′-deoxyadenosylcobinamide (AdoCbi+OH−) and cyanide (NaCN or tetrabutylammonium cyanide) to form dicyanocobinamide, adenine and 1-cyano-D-erythro-2,3-dihydroxy-4-pentenol has been studied by 1H NMR and UV-visible spectroscopies in aqueous solution at pH (pD) 11.0 and in 92% N,N-dimethylformamide (DMF)–8% D2O. Saturation kinetics are observed by UV-visible spectroscopy at high cyanide concentrations and data were fitted to a mechanism involving rapid formation of an (β-adenosyl)(α-cyano)cobinamide intermediate, (β-Ado)(α-CN)Cbi (KCN = 5.6 (H2O) and 6.9 M−1 (D2O), 25.0 °C, I = 1.0 M (NaClO4); KCN = 4.6 (H2O) and 3.8 M−1 (D2O), 25.0 °C, I = 2.0 M (NaClO4), KCN = 2.8 × 103 M−1, 25.0 °C, I = 0.50 M ((TBA)ClO4)), followed by solvent-assisted, rate-determining cleavage of the Co–Ado bond of (β-Ado)(α-CN)Cbi (102k2 = 2.91 (H2O) and 2.17 s−1 (D2O), 25.0 °C, I = 1.0 M (NaClO4); 102k2 = 2.55 (H2O) and 2.45 s−1 (D2O), 25.0 °C, I = 2.0 M (NaClO4), 105k2 = 6.7 s−1, 92% DMF–8% D2O, 25.0 °C, I = 0.50 M ((TBA)ClO4)). Deviations in the plots of the observed rate constant versus cyanide concentration in aqueous solution at high cyanide concentrations is attributed to medium effects, and only CN−, not HCN, reacts with AdoCbiOH. Evidence for rapid formation of (β-adenosyl)(α-cyano)cobinamide from AdoCbiOH plus cyanide is also obtained by investigating the 1H NMR chemical shifts of the signals in the aromatic region immediately after mixing AdoCbiOH and cyanide as a function of cyanide concentration (D2O, 25.0 °C; KCN′ = 5.7 and 3.3 M−1 at I = 1.0 (NaClO4) and 2.0 M (NaClO4), respectively). A comparison of rate and equilibria constants for the reaction between AdoCbiOH and 5′-deoxyadenosylcobalamin is made.

Efficient syntheses of beta-cyanosugars using glycosyl iodides derived from per-O-silylated mono- and disaccharides.

[reaction: see text] Reported herein is a general method for the efficient syntheses of a variety of beta-cyano glycosides through the activation of per-O-trimethylsilyl glycosides with TMSI to form alpha-glycosyl iodides, which undergo S(N)2-type displacement when treated with tetrabutylammonium cyanide. The cyanoglycosides were reduced under mild conditions using NaBH(4) in the presence of catalytic CoCl(2)(H(2)O)(6) in THF/H(2)O to give the corresponding aminomethyl glycosides.

Adsorption of CN at the Pt(111)/Liquid Interface by Dissociation of Acetonitrile and the Potentiality of CO Contamination: A Sum-Frequency Generation Study

The adsorption of cyanide, CN, on the Pt(111) surface by dissociation of acetonitrile, CH3CN, has been investigated by sum-frequency generation (SFG) as surface vibrational spectroscopy and by cyclic voltammetry. The adsorption procedure involved cooling of the flame-annealed Pt crystal above a dilute aqueous solution of acetonitrile (0.1 M HClO4 + 0.025 M CH3CN), followed by immersion of the sample into the electrolyte. The adsorbed species is identified as cyanide by the characteristic potential dependence of the stretching frequency, which increased from 2087 cm-1 at 0.1 V to 2136 cm-1 at 0.95 V, as well as by cyclic voltammetry. Comparison with the voltammogram in a 1 × 10-3 M solution of CH3CN indicates that the dissociation takes place in the gas phase above the solution. A second band in our spectra with a frequency near 2155 cm-1 is tentatively assigned to a Pt−cyano surface complex. We also report on experiments in which the same annealing/cooling procedure has been applied using neat liquid acetonitrile. Bands near 1860 and 2073 cm-1 in SFG spectra of these samples are shown to originate from adsorbed CO, most likely produced by oxidation of CH3CN vapor at the hot Pt crystal. CN adsorption at the Pt(111)/liquid acetonitrile interface, performed by deposition of cyanide ions from solutions of tetrabutylammonium cyanide in acetonitrile, is characterized by a single band near 2110 cm-1.

Studies on the mechanism of the reaction between coenzyme B12 and cyanide: direct 1H NMR spectroscopic evidence for a (beta-5'-deoxyadenosyl)(alpha-cyano)cobalamin intermediate.

The reaction between coenzyme B12 (5'-deoxyadenosylcobalamin, AdoCbl) and tetrabutylammonium cyanide to give dicyanocobalamin, adenine, and 1-cyano-D-erythro-2,3-dihydroxy-4-pentenol has been examined in 92% N,N-dimethylformamide (DMF)/8% D2O. Under these conditions rate-determining Co-C heterolytic cleavage is preceded by rapid addition of cyanide to AdoCbl to form an intermediate, (beta-5'-deoxyadenosyl)(alpha-cyano)cobalamin ((beta-Ado)(alpha-CN)Cbl-), identified by 1H NMR spectroscopy. Rate constants have been determined by both 1H NMR and visible spectroscopies, with the latter showing saturation kinetics. The observed rate constant is pH-independent in the pH region studied, and replacing D2O by H2O increases it by ca. 10%. Increasing the percentage of D2O in the DMF/D2O solvent mixture also increases the reaction rate, and for D2O > or = 50% there is a change in the rate-determining step, with formation of the (beta-Ado)(alpha-CN)Cbl- intermediate becoming rate-determining. A mechanism in 92% DMF/8% D2O is proposed which involves rapid reversible formation of (beta-Ado)(alpha-CN)Cbl- from base-off AdoCbl plus cyanide, followed by rate-determining solvent-assisted cleavage of the Co-C bond of the intermediate and subsequent rapid addition of a second cyanide to give the products.