Influence of alkyl chain length of alpha olefin sulfonates on surface and interfacial properties

Alpha olefin sulfonates (AOS) with various alkyl chain lengths have been used to investigate the influence of alkyl chain length on the interfacial properties at air–water, liquid paraffin–water, and parafilm–water interfaces. It was found that the critical micelle concentration decreased with increasing alkyl chain length, while the efficiency of reducing surface tension was inverse relationship with alkyl chain length. The diffusion coefficient obviously reduced with an increase of surfactant concentration and alkyl chain length. The C_14-16AOS shows better wettability and emulsification than C_16-18AOS and C_20-24AOS. For foaming properties, the foamability and foam stability dramatically decreased with increasing alkyl chain length.     

Efficient preparation of dichloromethyl alkyl ethers and their application in the formylation of aromatic compounds: Scope and limitations

Practical preparations of dichloromethyl alkyl ethers are described, based on the reaction of alkyl formates with oxalyl chloride in the presence of N-methylformanilide. The method involves a simple procedure that does not require the use of harmful reagents. Dichloromethyl propyl and dichloromethyl butyl ethers represent secure synthetic equivalents to dichloromethyl methyl ether. Formylations of both electron-deficient and electron-rich aromatics with these dichloromethyl alkyl ethers in the presence of AlCl₃, FeCl₃, or TiCl₄ have been systematically investigated. A plausible mechanism of formylation is discussed.     

Selectivity studies on branched and linear alkyl bonded stationary phases in reversed-phase liquid chromatography

Summary Reversed-phase liquid chromatographic retention characteristics for the sixteen acyclic C₁−C₅ N-alkylbenzamide congeners were measured on various branched and linear, alkyl bonded hydrocarbon stationary phases. Retention factors, k′, were determined in acetonitrile-water mobile phase compositions on ethyl, n-octyl, n-dodecyl, n-octadecyl, 1-ethyladamantyl, 4-butyloctyl, and 2,4,4-trimethylpentyl stationary phases. Statistical analysis of the two main effects investigated — type of stationary phase and percentage of organic modifier (acetonitrile) in the mobile phase — described greater than ninety percent of the variability in the data for most of the comparisons. Selectivity effects due to variation in the mobile phase dominated the results.     

A density functional theory study of alkyl group migration in RMn(CO)5 complexes

The kinetics of alkyl group migration in RMn(CO)₅ complexes ( R=CH₃, C₂H₅ and C₃H₇) were studied. Isomers of CH₃Mn(CO)₅ with an agostic structure, an η¹ structure, and an η² structure were found to be local minima on the system's potential energy surface. Transition states for the inter-conversion of these species were also located. The activation free energy for this migration reaction was compared with experimental data and provides insights into the important steps in the overall reaction mechanism.     

An efficient and convenient synthesis of pentasubstituted pyrroles from alkyl acetoacetates,dialkyl acetylenedicarboxylates,and amines

A simple and efficient synthesis of pentasubstituted pyrroles has been developed using a one-pot, two-step reaction. The synthesis of a series of 4-hydroxypenta-1,3-diene-tricarboxylates from alkyl acetoacetates and dialkyl acetylenedicarboxylates in the presence of K₂CO₃, followed by cyclization with amines, gave the corresponding pyrroles in excellent yields.     

Semi‐micro reversed‐phase liquid chromatography for the separation of alkyl benzenes and proteins exploiting methacrylate‐ and polystyrene‐based monolithic columns

Monolithic columns were synthesized inside 1.02 mm internal diameter fused‐silica lined stainless‐steel tubing. Styrene and butyl, hexyl, lauryl, and glycidyl methacrylates were the functional monomers. Ethylene glycol dimethacrylate and divinylbenzene were the crosslinkers. The glycidyl methacrylate polymer was modified with gold nanoparticles and dodecanethiol (C₁₂). The separation of alkylbenzenes was investigated by isocratic elution in 60:40 v/v acetonitrile/water. The columns based on polystyrene‐co‐divinylbenzene and poly(glycidyl methacrylate)‐co‐ethylene glycol dimethacrylate modified with dodecanethiol did not provide any separation of alkyl benzenes. The poly(hexyl methacrylate)‐co‐ethylene glycol dimethacrylate and poly(lauryl methacrylate)‐co‐ethylene glycol dimethacrylate columns separated the alkyl benzenes with plate heights between 30 and 60 μm (50 μL min^?1 and 60°C). Similar efficiency was achieved in the poly(butyl methacrylate)‐co‐ethylene glycol dimethacrylate column, but only at 10 μL min^?1 (0.22 mm s^?1). Backpressures varied from 0.38 MPa in the hexyl methacrylate to 13.4 MPa in lauryl methacrylate columns (50 μL min^?1 and 60°C). Separation of proteins was achieved in all columns with different efficiencies. At 100 μL min^?1 and 60°C, the lauryl methacrylate columns provided the best separation, but their low permeability prevented high flow rates. Flow rates up to 500 μL min^?1 were possible in the styrene, butyl and hexyl methacrylate columns.     

Reactions of the electrochemically generated dianion of [60]fullerene with bulky secondary alky bromides

Reactions of the electrochemically generated dianion of [60]fullerene (C₆₀^2?) with bulky secondary alkyl bromides exhibit different reaction behaviors. Reaction of C₆₀^2? with diphenylbromomethane gives rise to 1,2-C₆₀HR or 1,4-C₆₀R₂ (R?=?CHPh₂) adducts, while reaction of C₆₀^2? with diethyl 2-bromomalonate unexpectedly affords methanofullerene C₆₀?>?CR₂ (R?=?CO₂Et). Plausible reaction mechanisms have been proposed to explain the formation of the observed products.     

Evaluation and comparison of n‐alkyl chain and polar ligand bonded stationary phases for protein separation in reversed‐phase liquid chromatography

Protein retention is very sensitive to the change of solvent composition in reversed‐phase liquid chromatography for so called “on–off” mechanism, leading to difficulty in mobile phase optimization. In this study, a novel 3‐chloropropyl trichlorosilane ligand bonded column was prepared for protein separation. The differences in retention characteristics between the 3‐chloropropyl trichlorosilane ligand bonded column and n‐alkyl chain modified (C₂, C₄, C₈) stationary phases were elucidated by the retention equation . Retention parameters (a and c) of nine standard proteins with different molecular weights were calculated by using homemade software. Results showed that retention times of nine proteins were similar on four columns, but the 3‐chloropropyl trichlorosilane ligand bonded column obtained the lowest retention parameter values of larger proteins. It meant that their retention behavior affected by acetonitrile concentration would be different due to lower |c| values. More specifically, protein elution windows were broader, and retentions were less sensitive to the change of acetonitrile concentration on the 3‐chloropropyl trichlorosilane ligand bonded column than that on other columns. Meanwhile, the 3‐chloropropyl trichlorosilane ligand bonded column displayed distinctive selectivity for some proteins. Our results indicated that stationary phase with polar ligand provided potential solutions to the “on–off” problem and optimization in protein separation.     

“Constrained geometry” catalysts of the rare-earth metals for the hydrosilylation of olefins

A series of yttrium and lutetium alkyl complexes [Ln(η⁵-C₅Me₄ZNR′-κN)(CH₂SiMe₃)(THF)_n] (Ln = Y, Lu) was prepared by reacting the tris(trimethylsilylmethyl) precursor [Ln(CH₂SiMe₃)₃(THF)₂] with different linked amino-cyclopentadienes of the type (C₅Me₄H)ZNHR′ (Z = SiMe₂, CH₂SiMe₂; R′ = tBu, Ph, C₆H₄-tBu-4, C₆H₄-nBu-4). The catalytic activity of these alkyl complexes in the hydrosilylation of 1-decene and styrene using PhSiH₃ as reagent was examined under standard conditions. A significant influence of the ligand structure on the catalytic property (turnover frequency, regioselectivity) was observed with the yttrium complex [Y(η⁵-C₅Me₄CH₂SiMe₂NtBu-κN)(CH₂SiMe₃)(THF)] being the most active for 1-decene hydrosilylation.     

A Novel Alkene(alkyl)(aqua)(aryl)platinum(II) Complex – [Pt{CH(CH2C6F5)CH2CH2CH=CH2}(C6F5)(OH2)]

From the reaction of PtCl₂(hex) (hex = hexa‐1,5‐diene) with LiC₆F₅ in diethyl ether, the complex [Pt{CH(CH₂C₆F₅)CH₂CH₂CH=CH₂}(C₆F₅)(OH₂)] ( 1 ) was isolated. The crystal structure (monoclinic, C2/c (no. 15), Z = 8, a = 15.241(3), b = 16.579(2), c = 16.225(2) Å, β = 111.12(2)°) shows a complex with square planar coordination around platinum with a template formed 1‐pentafluorophenylhex‐5‐en‐2‐yl ligand, and C₆F₅ and aqua ligands trans to the double bond and alkyl carbon, respectively.     

Mixed-mode liquid chromatography of aliphatic anionic surfactants with a naphthalenetrisulfonate mobile phase

Summary Separation of three classes of anionic surfactants (alkyl sulfates, alkanesulfonates, and alkyl phosphates) are achieved on a mixed-mode reversed phase (RP) phenyl/-anion exchange column using a naphthalenetrisulfonate (NTS)-acetonitrile (ACN) mobile phase via indirect photometric, indirect fluorometric, direct or indirect conductivity detection. Mixtures of C₅–C₁₈ sulfates, C₆–C₁₈ sulfonates, and C₁–C₄ phosphates (mono- and di-ester) can be separated in less than 20, 24, and 20 min respectively. Although hydrophobic effects are more pronounced in mixed-mode chromatography, equivalent-per-equivalent exchange of analysis and eluent ion is still required for sensitive indirect photometric, fluorometric, or conductivity detection. The detection limits of alkyl sulfates and alkanesulfonates are in the range of 3–15 pmoles which are at least an order of magnitude better than suppressed conductivity detection. The determination of surfactants in a variety of real samples is also presented.     

Coenzyme B12 model studies: An HSAB approach to the equilibria and kinetics of axial ligation of alkyl(aquo)-cobaloximes by imidazole and cyanide

Kinetics and equilibria of the axial ligation of alkyl(aquo)cobaloximes by imidazole and cyanide have been measured spectrophotometrically in aqueous solutions of ionic strength 1.0 M at 25°C as a function of pH. Comparison of K_IMD and K_CN- of CH₃, C₂H₅ and BrCH₂cobaloximes indicates that their stability is in the order BrCH₂>CH₃>C₂H₂. As the electron-withdrawing capacity of the alkyl grouptrans to water increases, the electron density of the cobalt(III) decreases and thus it becomes a stronger Lewis acid and binds more strongly to imidazole and cyanide. The association and dissociation rate constants are better correlated to the relative softness of the ligand showing that cyanide binds 30 times faster than imidazole. These complexes are isolated and are characterized by IR and¹H NMR spectra.     

Incorporation of D-glucosamine alkyi glucopyranosides into the bilayer of small unilamellar vesicles of egg phosphatidyl choline

Alkyl 2-acetamido-2-deoxy-β-d-glucopyranosides were incorporated into the phospholipid bilayer of small unilamellar vesicles. Depending on the lengths of the alkyl aglycone group (C₈–C₁₄), the carbohydrate was either found in the form of micelles (C₈) or was effectively incorporated in the bilayer (C₁₄). The use of radiolabelled lipids and/or carbohydrates enabled the quantitative determination of the amounts of lipid and carbohydrate recovered into the vesicles. An enzymatic assay has been carried out to evaluate the outer and inner distribution of the carbohydrate moieties on the liposomes.     

Ion chromatographic separation of alkylsulphonic acids with conductivity detection

Summary An ion chromatographic (IC) method has been developed for the separation of alkylsulphonic acid. Two different stationary phases, silica-based and polymer-based ion-exchange resins, were studied using pure ion exchange and/or hydrophobic interaction mechanisms. Correlations between analyte hydrophobicity and eluent polarity were made in order to investigate the possibility of changing the dominant separation mechanism by varying the eluent composition. The alkyl chain lengths of the sulphonic acids analysed ranged from C₁ to C₉. Detection limits in the submicromolar range were obtained by suppressed conductivity detection.     

Electrochemical NiH-Catalyzed C(sp3)−C(sp3) Coupling of Alkyl Halides and Alkyl Alkenes

Herein, an electrochemically driven NiH-catalyzed reductive coupling of alkyl halides and alkyl alkenes for the construction of Csp³−Csp³ bonds is firstly reported. Notably, alkyl halides serve dual function as coupling substrates and as hydrogen sources to generate NiH species under electrochemical conditions. The tunable nature of this reaction is realized by introducing an intramolecular coordinating group to the substrate, where the product can be easily adjusted to give the desired branched products. The method proceeds under mild conditions, exhibits a broad substrate scope, and affords moderate to excellent yields with over 70 examples, including late-stage modification of natural products and drug derivatives. Mechanistic insights offer evidence for an electrochemically driven coupling process. The sp³-carbon-halogen bonds can be activated through single electron transfer (SET) by the nickel catalyst in its low valence state, generated by cathodic reduction, and the generation of NiH species from alkyl halides is pivotal to this transformation.     

Ion chromatographic separation of alkylsulphonic acids with conductivity detection

Summary An ion chromatographic (IC) method has been developed for the separation of alkylsulphonic acid. Two different stationary phases, silica-based and polymer-based ion-exchange resins, were studied using pure ion exchange and/or hydrophobic interaction mechanisms. Correlations between analyte hydrophobicity and eluent polarity were made in order to investigate the possibility of changing the dominant separation mechanism by varying the eluent composition. The alkyl chain lengths of the sulphonic acids analysed ranged from C₁ to C₉. Detection limits in the submicromolar range were obtained by suppressed conductivity detection.     

An efficient synthesis of vinylogous carbamates from alkyl azides

An efficient one-pot synthesis of vinylogous carbamates is reported starting from alkyl azides by using NH₄Cl/Zn dust.     

Stereocontrolled palladium(0)-catalyzed preparation of unsaturated azidosugars: an easy access to 2- and 4-aminoglycosides

The palladium-catalyzed substitution of alkyl 4,6-di-O-acetyl-α-d-erythro-hex-2-eno-pyranosides using NaN₃ as the nucleophile gave predominantly the corresponding alkyl 2-azido-2,3,4-trideoxy-α-d-threo-hex-2-enopyranosides in the presence of Pd(PPh₃)₄. However, alkyl 6-O-acetyl-4-azido-2,3,4-trideoxy-α-d-erythro-hex-2-enopyranosides were obtained as the major products using Pd(PPh₃)₄ as the catalyst in the presence of dppb as the added ligand. Conversely, alkyl 6-O-(tert-butyldimethylsilyl)-4-O-methoxycarbonyl-2,3-dideoxy-α-d-hex-2-enopyranosides gave exclusively alkyl 4-azido-6-O-(tert-butyldimethylsilyl)-2,3,4-trideoxy-α-d-erythro-hex-2-enopyranosides in the presence of Pd₂(dba)₃/PPh₃ as the catalyst and Me₃SiN₃ as the nucleophile. The bis-hydroxylation followed by hydrogenation of ethyl 4-azido-2,3,4-trideoxy-α-d-erythro-hex-2-enopyranoside afforded the corresponding 4-amino-α-d-mannopyranoside, when propyl 2-azido-2,3,4-trideoxy-α-d-threo-hex-3-enopyranoside gave the 2-amino-α-d-altropyranoside under the same conditions.     

A Modified Water-Gas Shift Reaction. The Decomposition of Alkyl Formate in the Presence of Water Using a Ruthenium Carbonyl

Alkyl formates in the presence of water were rapidly decomposed to H₂, CO₂ and the corresponding alcohols using Ru₃(CO)₁₂ and KOAc as catalyst. Based on the hydrogen gas produced, a turnover rate as fast as 8446/h for ethyl formate at 140°C was observed. The catalyst system was also active for the decomposition of other alkyl formates. The rate of decomposition increased both with increasing amount of KOAc and with decreasing number of carbon atom in the alkyl group of the formate. In addition to Ru₃(CO)₁₂, several other transition metal complexes RuCl₃, RuCl₂(PPh₃)₃, Os₃(CO)₁₂, H₂Os₃(CO)₁₀, RhCl₃, and RhCl(PPh₃)₃, were active in the catalytic decomposition of alkyl formates, although their activities varied greatly. The Ru₃(CO)₁₂-KOAc system also catalyzed the reduction of nitrobenzene by HCOOEt-H₂O to aniline in EtOH and to a mixture of N-phenylformamide and N-methyl-N-phenylformamide in HCOOEt. Under coditions the same as for the hydrogenation of nitrobenzene, ethylene styrene and cyclohexenone were reduced to the corresponding alkanes, whereas 1-hexene and 1-octene were isomerized to the corresponding 2-alkene products.     

2-Hydroxy-N,N,N-tributylethanaminium thiocyanate as solvent and reagent for the preparation of alkyl thiocyanates

2-Hydroxy-N,N,N-tributylethanaminium thiocyanate was utilized as both solvent and reagent for the conversion of alkyl halides to the corresponding alkyl thiocyanates in good yields under mild conditions.