Lithium Perchlorate‐Catalyzed Boc Protection of Amines and Amine Derivatives

A new mild and chemoselective method for mono‐N‐protection of amines and amine derivatives as tert‐butoxycarbonyl derivatives is reported. The reaction proceeds with lithium perchlorate (20 mol %) and pyrocarbonates, and shows general applicability. The catalytic action of LiClO₄ is specific for the activation of Boc₂O, thus acid‐sensitive functionalities of the starting materials remain unchanged in the protection process. This procedure works well for sterically hindered primary amine as well as electron‐deficient primary arylamines, primary and secondary amino alcohols, α‐amino acid esters, hydroxylamines, hydrazines and sulfonamides.     

Removal of aldehydes by amino acids and their salts in ambient air

The removal of gaseous aldehydes by amino acids and by their sodium salts and hydrochlorides was studied in ambient air with the relative humidity of 30% at 25°C. Amino acid sodium salts, diamino acids, sodium p-aminobenzoate (PABANa), and o-aminobenzoate (OABANa), and p-aminobenzoic acid (PABA) on sepiolite, both having a carboxylato functionality (? COO^?) together with an amino (? NH₂) group, were highly reactive with aldehydes. In contrast, PABA which has free carboxylic acid functionality (? COOH: dimeric) was not so reactive with aldehydes. Normal amino acids and their hydrochlorides having ammonio (? NH₂⁺) and ? COO^? or ? COOH (dimeric) groups were less reactive with aldehydes. The reactivity was closely related to the degree of dissociation of carboxylate anion; as the degree of dissociation increases, the compound becomes more reactive. p-Aminobenzoic acid hydrochloride (PABA · HCl), having ? NH₃⁺ and ? COOH (monomeric) groups, was the most reactive (with ethanal) of all the amino acids and their salts examined. Amino acid sodium salts, diamino acid, PABANa, OABANa, and PABA on sepiolite are proved to be excellent removers of aldehydes in ambient air. Among them, PABA · HCl is particularly good for ethanal.     

CO2 absorption in aqueous solutions of hindered amines

Sterically hindered amines constitute a new class of chemicals which have recently come into industrial use in a variety of gas-treating processes: chemical solvents in both aqueous and non-aqueous solutions, rate promotion additives for the hot carbonate process, and chemical solvents for the selective removal of hydrogen sulfide. The scant published data on the behavior of hindered amines do not allow one to estimate the actual values of the apparent kinetic constants or equilibrium constants, and even less to establish the chemical steps involved.In this paper, the results of an investigation of the behavior of one particular amine, 2-amino-2-methyl-1-propanol (AMP), as a chemical solvent for CO₂ in aqueous solutions are reported. The equilibrium behavior of a hindered monoamine like AMP in aqueous solutions is dominated by the values of two equilibrium constants: the protonation constant K_p and the carbamate stability constant K_c. The value of K_p at infinite dilution has been determined experimentally, and is large enough to neglect formation of the carbonate ion. The value of K_c has been found experimentally to be significantly less than 10⁻¹ 1/gmol, as is expected for a hindered amine.A thermodynamic model has been developed and tested against experimental equilibrium data. Preliminary kinetic data seem to indicate that the reaction with CO₂ is first order with respect to both CO₂ and AMP. A first step in the elucidation of the chemical steps involved is presented.     

Highly Efficient Ligands for the Palladium‐Assisted Double N‐Arylation of Primary Amines for One‐Sep Construction of Carbazoles

A highly efficient one‐pot synthesis of carbazoles via palladium‐catalyzed double N‐arylation of primary amines with 2,2′‐dihalobiphenyls is described using a catalyst system comprised of tris(dibenzylideneacetone)dipalladium(0) (Pd₂dba₃) and the proazaphosphatrane P(i‐BuNCH₂CH₂)₃N ( 8 ) or its derivative (t‐Bu)₂PN P(i‐BuNCH₂CH₂)₃N ( 9a ) as the ligand. The process is effective for double N‐arylation of 2,2′‐biphenyl dibromide, diiodide, and even dichloride with a variety of primary amines including neutral, electron‐rich, electron‐deficient, and sterically hindered anilines as well as aliphatic amines.     

Water Solvent Method for Esterification and Amide Formation between Acid Chlorides and Alcohols Promoted by Combined Catalytic Amines: Synergy between N‐Methylimidazole and N,N,N′,N′‐Tetramethylethylenediamine (TMEDA)

An efficient method for esterification between acid chlorides and alcohols in water as solvent has been developed by combining the catalytic amines, N‐methylimidazole and N,N,N′,N′‐tetramethylethylenediamine (TMEDA). The present Schotten–Baumann‐type reaction was performed by maintaining the pH at around 11.5 using a pH controller to prevent the decomposition of acid chlorides and/or esters and to facilitate the condensation. The choice of catalysts (0.1 equiv.) was crucial: the combined use of N‐methylimidazole and TMEDA exhibited a dramatic synergistic effect. The catalytic amines have two different roles: (i) N‐methylimidazole forms highly reactive ammonium intermediates with acid chlorides and (ii) TMEDA acts as an effective HCl binder. The production of these intermediates was rationally supported by a careful ¹H NMR monitoring study. Related amide formation was also achieved between acid chlorides and primary or secondary amines, including less nucleophilic or water‐soluble amines such as 2‐(or 4‐)chloroaniline, the Weinreb N‐methoxyamine, and 2,2‐dimethoxyethanamine.     

Dissolution characteristics of hectorite in inorganic acids

The effect of acid type (HCl, HNO₃ and H₂SO₄) and concentration on the dissolution rate of hectorite were monitored through chemical analyses and XRD. The rate of dissolution increased with increasing acid concentration during the first 2–4 h of contact. After that time, the correlation between acid concentration and the amounts of dissolved elements strongly decreased and often higher concentrations were found in 0.25 M solutions than in 1 M solutions. The monitoring of the amount of Si is somewhat more complex since it is the result of two processes: release from the mineral and reprecipitation as an amorphous end product. In the case of HCl, the behavior of Li, Mg and Fe differed from their behavior in the other acids, but further research is necessary to characterize the reactions that may occur. From the half times of dissolution, the dissolution curves and the XRD data, it could be concluded that the dissolution rate of hectorite decreased in the order H₂SO₄>HNO₃≥HCl at the same molar concentration, which is the reverse of what was found by other investigators. After 8 h, for example, the 1 M H₂SO₄ treatment dissolved more than 70% of all Li present in the hectorite, whereas equal molar HNO₃ and HCl dissolved 58% and 53%, respectively. Oriented XRD patterns only showed a background scatter after 6 h of contact with 0.25 M H₂SO₄ and after 4 h using a concentration of 1 M H₂SO₄. Treatments with 0.25 M HNO₃ and 0.25 M HCl still gave reflections after 6 h and even after 8 h, the d(001) XRD peak could still be observed. In 1 M HNO₃ and 1 M HCl, no more reflections could be seen after 4–6 h. At that time, XRD powder patterns showed that the crystal structure was still partly preserved in the a- and b-direction of the mineral. It must be stressed that absence or a decrease in intensity of the d(001) peaks may not be fully assigned to the breakdown of the mineral structure since the Si, extracted from the lattice reprecipitates as amorphous silica, which may disrupt the layer stacking and decrease the coherence of the reflections. For the comparison of the three acids on a normal basis, the quarter times of dissolution were found to be a more appropriate tool than the half times of dissolution. The results showed that the differences among the three acids were rather small and that the concentration of the acids was the main parameter affecting the dissolution rate of the hectorite, in particular, in the beginning of the treatment.     

The inhibitive effect of poly(p‐toluidine) on corrosion of iron in 1M HCL solutions

In recent years, polymer amines have been recognized as an excellent corrosion inhibitors for iron in acid solutions. In this work, the inhibitive effect of p‐toluidine and poly(p‐toluidine) on corrosion of iron in 1M HCl has been studied by the electrochemical methods such as impedance, linear polarization, Tafel polarization techniques. The effectiveness of poly(p‐toluidine) was found to be high in comparison with that of monomer. The results showed that p‐toluidine and poly(p‐toluidine) suppressed both cathodic and anodic processes of iron dissolution in 1M HCl. The inhibition efficiency of both p‐toluidine and poly(p‐toluidine) were found to increase with the inhibitor concentrations. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Premembranes for porogen-derived membranes and thermal decomposition of porogens

Various t-butyl and di-t-butyl esters, N-boc and di-N-boc amines, metal salts of N-boc amino acid, and glycerol–formic acid esters are potential porogens for porogen-derived membranes. Introduction of more than 20 such compounds into polysulfone or poly(vinyl chloride) films was studied. Transparency, IR spectra, changes in glass transition temperature, and differential scanning calorimetry were used to differentiate between molecular dispersion and formation of micro phases. The results show that for many of the studied additives more than 10% by weight can be practically molecularly dispersed in the polymers. The upper limit of porogen concentration in premembranes depends on characteristics of the polymer and of the porogen, on casting solvent composition, and on drying procedure. Metal salts of N-boc amino acids were found to be suitable heat-decomposable porogens. Their decomposition in premembranes proceeds in two stages, in the first of which 2 C₄H₈ + 2CO₂ are released per salt molecule. The metal complex formed goes through decarboxylation at a higher temperature. A heating procedure for completion of the first decomposition stage and for avoiding the second was determined.     

The effect of steric hindrance on physical properties in an amine-cured epoxy

A pair of aliphatic amines were synthesized in order to study the effect steric hindrance has on the physical properties of an amine-cured epoxy resin. The hindered amine (TMSiDA) has NH₂ groups that are obstructed by the presence of adjacent methyl groups while the unhindered amine (SiDA) does not contain any NH₂ steric hindrance. DGEBA cured with TMSiDA is less dense, absorbs less moisture, and has a higher T_g than does SiDA/DGEBA. Torsional pendulum results show that TMSiDA/DGEBA has a slightly higher rubbery modulus and a secondary transition at a lower temperature than DGEBA cured with SiDA. Activation energies for the secondary transition were determined for TMSiDA/DGEBA and SiDA/DGEBA and are 19 and 14 kcal/mol, respectively.     

Reaction kinetics for hindered amine/epoxides by DSC

The rate constants for the reaction of two aliphatic hindered amines with phenylglycidyl ether (PGE) and the diglycidyl ether of bisphenol A (DER 332) were determined by differential scanning calorimetry (DSC). The two exothermic peaks which are present in the DSC data result from the consecutive reactions of the primary and secondary amine hydrogens and allow k₁ and k₂ to be determined. The resulting k₁/k₂ ratios obtained for these hindered amine systems are larger than the ratios previously reported for unhindered amine/epoxides.     

PALLADIUM WITH TRIOCTYLMETHYLAMMONIUM CHLORIDE SOLVENT EXTRACTION OF PALLADIUM(II) WITH TRIOCTYLMETHYLAMMONIUM CHLORIDE

Equilibrium distribution of palladium(II) was investigated in the solvent extraction with tri-octylmethylammonium chloride (QC1) in toluene from hydrochloric acid solutions at 303 K. The title extracting reagent extracted hydrochloric acid as the species of the types, QC1(HC1) (_n(n= 1,2), according to the similar extraction reactions as observed in the extraction of organic acids such as acetic acid and phenol with high-molecular-weight amines in the previous works. From the concentration dependencies of the reactant species on the distribution ratio and from the result of loading test, it was elucidated that palladium(II) is extracted as a mononuclear ion pair complex of the type, Q⁺;[PdCl]₃ (HCl)] in the very high concentration region of hydrochloric acid. The equilibrium constant of the extraction reaction was evaluated.     

Activation and reactivity of epoxides on solid acid catalysts

The aminolysis of epoxides over novel solid catalysts (Brönsted-acidic SBA-15 functionalized with propylsulfonic acid and Lewis-acidic Ti-MCM-41) is reported. The acidic properties of these catalysts were determined by FTIR spectroscopy and temperature-programmed desorption of pyridine and NH₃, respectively. The mesoporous solid acids of the present study are reusable and exhibit significantly higher catalytic activities than known catalysts for opening of the oxirane ring with nitrogen (aromatic and aliphatic amines)-containing and oxygen (alcohols)-containing nucleophiles. A range of β-amino alcohols with high regioselectivity and stereoselectivity were synthesized. Adsorption studies as well as the sigmoid shape of the conversion-versus-time plots show that the epoxide and amine compete for adsorption on the acidic sites (SO₃H or Ti⁴⁺) on the catalyst surface. Epoxide adsorption and activation on acid sites are the more critical processes. Catalytic activity decreases with increasing basicity of the amines and/or the alcohol, as well as the dielectric constant of the solvent.     

CO2 Absorption into Aqueous Solutions of a Polyamine (PZEA), a Sterically Hindered Amine (AMP), and their Blends

Among numerous techniques existing for reducing CO₂ emissions, CO₂ capture by absorption in aqueous alkanolamine solutions was specifically studied in this work. For the choice of the adequate amine solution, two major criteria must be taken into account: absorption performances (higher with primary and secondary amines) and energy costs for solvent regeneration (more interesting with tertiary and sterically hindered amines). The different types of amines can also be mixed in order to combine the specific advantages of each type of amines, an activation phenomenon being observed. Aqueous solutions of (piperazinyl‐1)‐2‐ethylamine (PZEA, a polyamine known as absorption activator) and 1‐amino‐2‐propanol (AMP, a sterically hindered amine), pure or mixed with other amines, are experimentally compared with respect to CO₂ removal performances by means of absorption test runs achieved in a special gas‐liquid contactor at 25 °C. The positive impact of addition of PZEA to monoethanolamine (MEA), N‐methyldiethanolamine (MDEA), and AMP solutions was clearly highlighted. The absorption performances have also been satisfactorily simulated with coherent physicochemical data.     

Enrichment of eicosenoic and docosadienoic acids fromLimnanthes oil

The long chain (>C₁₈) monoene and diene acids ofLimnanthes oil are useful in synthesizing diene and tetraene wax ester intermediates for prospective lubricant additives and PVC plasticizers. Low-temperature crystallization of theL. alba acids (61% eicosenoic, 19% docosadienoic, and 20% others) in acetone (initial concentration=0.05 g/ml) at −50 C enriches eicosenoic acid (74%) in the precipitated fraction while concentrating docosadienoic (70%) in the supernatant fraction. This simple and efficient process is well suited for large-scale laboratory separations.     

A simple method for the synthesis of ceramides and radiolabeled analogues

A simple method has been developed for the coupling of amines to carboxylic acids.N-Fatty-acyl-sphingosine, cerebroside, and GM₃, as well as their respective [¹⁴C] analogues, were synthesized using diethylphosphoryl cyanide as a potent coupling agent in the presence of triethylamine. The reaction procedure is rapid, racemization-free, and utilizes acids without derivatization. The desired ceramide products were obtained in 85–90% yield within one hour. The facile method presented here can also be used to synthesize [³H]-N-acyl-labeled, as well as [¹⁴C] [³H] double-labeled, ceramides.     

CO2 removal by single and mixed amines in a hollow‐fiber membrane module—investigation of contactor performance

This work investigates CO₂ removal by single and blended amines in a hollow‐fiber membrane contactor (HFMC) under gas‐filled and partially liquid‐filled membrane pores conditions via a two‐scale, nonisothermal, steady‐state model accounting for CO₂ diffusion in gas‐filled pores, CO₂ and amines diffusion/reaction within liquid‐filled pores and CO₂ and amines diffusion/reaction in liquid boundary layer. Model predictions were compared with CO₂ absorption data under various experimental conditions. The model was used to analyze the effects of liquid and gas velocity, CO₂ partial pressure, single (primary, secondary, tertiary, and sterically hindered alkanolamines) and mixed amines solution type, membrane wetting, and cocurrent/countercurrent flow orientation on the HFMC performance. An insignificant difference between the absorption in cocurrent and countercurrent flow was observed in this study. The membrane wetting decreases significantly the performance of hollow‐fiber membrane module. The nonisothermal simulations reveal that the hollow‐fiber membrane module operation can be considered as nearly isothermal. © 2014 American Institute of Chemical Engineers AIChE J, 61: 955–971, 2015     

Fatty acid-specific, regiospecific, and stereospecific hydroxylation by cytochrome P450 (CYP152B1) from Sphingomonas paucimobilis: Substrate structure required for α-hydroxylation

Fatty acid α-hydroxylase from Sphingomonas paucimobilis is an unusual cytochrome P450 enzyme that hydroxylates the α-carbon of fatty acids in the presence of H₂O₂. Herein, we describe our investigation concerning the utilization of various substrates and the optical configuration of the α-hydroxyl product using a recombinant form of this enzyme. This enzyme can metabolize saturated fatty acids with carbon chain lengths of more than 10. The K _m value for pentadecanoic acid (C₁₅) was the smallest among the saturated fatty acids tested (C₁₀–C₁₈) and that for myristic acid (C₁₄) showed similar enzyme kinetics to those seen for C₁₅. As shorter or longer carbon chain lengths were used, K _m values increased. The turnover numbers for fatty acids with carbon chain lengths of more than 11 were of the same order of magnitude (10³ min⁻¹), but the turnover number for undecanoic acid (C₁₁) was less. Dicarboxylic fatty acids and methyl myristate were not metabolized, but monomethyl hexadecanedioate and ω-hydroxypalmitic acid were metabolized, though with lower turnover values. Arachidonic acid was a good substrate, comparable to C₁₄ or C₁₅. The metabolite of arachidonic acid was only α-hydroxyarachidonic acid. Alkanes, fatty alcohols, and fatty aldehydes were not utilized as substrates. Analysis of the optical configurations of the α-hydroxylated products demonstrated that the products were S-enantiomers (more than 98% enantiomerically pure). These results suggested that this P450 enzyme is strictly responsible for fatty acids and catalyzes highly stereo- and regioselective hydroxylation, where structure of ω-carbon and carboxyl carbon as well as carbon chain length of fatty acids are important for substrate-enzyme interaction.     

Selection of quaternary ammonium groups for optimizing properties of water‐soluble,photosensitive phenolic resins and study of their postcuring mechanism

This article deals with the selection of quaternary ammonium groups for synthesis of water‐soluble, photosensitive phenolic resins, containing acrylate and different quaternary ammonium salt groups (AQSPRs), via ring‐opening reactions of epoxy phenolic resin (EPR) with acrylic acid and with different tertiary amine‐protonic acid salts. Conversion of epoxy groups, solubility, photosensitive properties, and thermal decomposition of the different AQSPRs were compared. Modification of AQSPR with methanol solution of KOH to form phenolic resin containing both quaternary ammonium hydroxide groups and acrylate groups (AQHPR) was also studied. Characterization by IR spectrum, DSC, and thermal gravimetric analysis was carried out. The results showed that in the synthesis of AQSPRs containing different quaternary ammonium salt groups, the efficiency of ring‐opening reaction of epoxy phenolic resin with tertiary amine salt in terms of conversion of epoxy groups decreases in the following order: for the tertiary amine, N,N‐dimethyl benzylamine (DMBA) > triethylamine (TEA) > trimethylamine (TMA) > N,N‐dimethyl aniline (DMA) > triethanolamine (TENA) > tri(n‐butylamine) (TBA); for the protonic acid, HCl > HBr > HCOOH > HI > NaHSO₃ > Cl₃CCOOH > HClO₄ > HBF₄. All the AQSPRs except that from HClO₄ can be dissolved in water, methanol, DMF, or DMSO. The gel content formed during UV exposure decreases in the following order of acids used in forming quaternary ammonium salt groups: HCl > HCOOH > NaHSO₃ > Cl₃CCOOH; or decreases in the following order of tertiary amines or hydrohalic acids used in forming the quaternary ammonium groups: TMA. > TEA > DBMA; HCl > HBr > HI. During thermal decomposition of EPR with about half epoxy groups of EPR ring‐opened with tertiary amine salt at 160°C for 0.5 h, water‐insoluble product was formed. The insoluble content and the % decrease of epoxy groups or halide ions increase in the following order: TMA < TEA < DMBA; HCl < HBr < HI. The % decrease of epoxy groups for the insoluble residue is nearly equal to the % decrease of halide ions. A crosslinking reaction mechanism occurred in the thermal decomposition was thus proposed. During the modification of AQSPR with KOH, conversion of quaternary ammonium chloride groups can reach above 90%. The decomposition temperature of the quaternary ammonium groups was lowered from 204 to 120°C after modification of AQSPR with KOH. The photosensitive properties of the resin after modification became lower. It is better to react DMBA · HCl with EPR so as to obtain a product with higher conversion of epoxy groups, good water solubility, moderate photosensitivity, lower decomposition temperature, and better postcuring. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2914–2922, 2004     

Synthesis of N‐Alkoxy Amines via Catalytic Oxidation of Hydrocarbons

Sterically hindered N‐alkoxy amines 3 are synthesized in good yields by coupling nitroxides 2 with hydrocarbyl radicals generated in situ by t‐BuOOH hydrogen abstraction from hydrocarbons. The reaction is catalyzed by copper halides as well as by onium iodides.     

Formations and controls of HCl and PAHs by different additives during waste incineration

This study employed a laboratory-scale fluidized bed incinerator to investigate the formations and controls of hydrogen chloride (HCl) and polycyclic aromatic hydrocarbons (PAHs) by adding different additives in the feedstock during waste incineration. The effects of different organic and inorganic chlorides on the formation and control of HCl and PAHs were also studied. Additionally, the thermodynamic equilibrium modeling was also carried out to interpret and compare with the experimental results.Experimental results showed that the formation of HCl was related to the potential of chlorine released from the combustion of different chlorides. Organic chloride PVC had greater potential to form HCl than inorganic chloride NaCl. The performances of additives were affected by incineration temperature. Increasing temperature decreased the control efficiency of additives because the emission yields of HCl and Cl₂ were increased with temperature. The control efficiencies for HCl and Cl₂ by calcium based additives (Ca(OH)₂, CaO, CaCO₃) were better than that by magnesium based additive (Mg(OH)₂) and CaO was the best additive. The control efficiencies of PAHs by adding CaO in the feedstock were not apparent because the fluidization quality in the fluidized bed incinerator was decreased.