Strong Organic Bases Research Articles

Racemization of (S)-Profen Thioesters by Strong Neutral Bases in Nonpolar Organic Solvents: Implication for Ion-Pair Kinetic Basicity

The racemization of (S)-profen 2,2,2-trifluoroethyl thioesters in isooctane with trioctylamine as base was carried out, in which the Hammett equation log(k(int)) = 3.584sigma - 3.745 was successfully applied to describe the electron-withdrawing effect of the substituents to the alpha-phenyl moiety of the thioesters. A combination of neutral strong organic bases with different nonpolar solvents was employed to determine the second-order interconversion constants for the racemization of (S)-naproxen 2,2,2-trifluoroethyl thioester, in which solvent hydrophobicity was found to have less effect on the racemization. Implication for ion-pair kinetic basicity scale for the neutral strong bases in isooctane was further discussed.

On the Problem of the Tetrafluoroborate Ion State in Complexes with Nitrogen-Containing Organic Bases

Using a number of Cu(II), Zn(II), and Cd(II) tetrafluoroborate complexes with nitrogen-containing organic bases as examples, the possible existence of two states of the BF4– ion, namely, the "half-coordination" and counter-ion states, was studied. It was found that in [ML2(BF4)2] complexes with strong organic bases (L), the "half-coordination" of the anion exists. As the electron-donating ability of the ligand increases, the interaction between the tetrafluoroborate ion and the metal atom becomes more efficient.

Gas-phase structural (internal) effects in strong organic nitrogen bases

Gas-phase basicities (GB) of strong organic bases containing the imino group were re-examined in the light of the re-evaluated GB values for the reference bases given in a recent compilation of Hunter and Lias. Structural (internal) effects which influence the basicity are discussed and general relations for the GB prediction are proposed for simple alkyl amidines and guanidines. These relations were used for estimation of cyclization and intramolecular H-bonding effects. Copyright © 2000 John Wiley & Sons, Ltd.

Chemo-and Stereoselectivity of Nucleophilic Substitution in Mixed Phosphorus-Carboxylic Anhydrides

Miwed phosphorus-carboxylic anhydrides have demonstrated both acylating and phosphorylating properties.[1] Here we report the reactivity of O,O-diethyl(O-2,4,6-trimethylbenzoyl) phosphates (1), and O-methyl (O-2,4,6-trimetyIbenzoyl) dimethylphosphonates (2)with nucleophiles in the presence of different strong organic bases (DBU, DMAP).

PTC and organic bases–LiCl assisted alkylation of imidazolidinone–glycine iminic derivatives for the asymmetric synthesis of α-amino acids

Iminic derivatives of (4 R,5 S)-1,5-dimethyl-4-phenylimidazolidin-2-one and glycine 4 have been highly diastereoselectively alkylated with activated alkyl halides or electrophilic olefins either under PTC conditions or in the presence of the strong organic bases DBU or BEMP at −20°C in the presence of LiCl. Hydrolysis of the alkylated imino imides gave ( S)-α-amino acids with recovery of the imidazolidinone chiral auxiliary.

Toward engineering of very strong organic bases: pronounced proton affinity of molecules possessing imino structural and electronic motif

The absolute proton affinity of a group of compounds involving AN imino group is examined by employing the MP2(fc)/6-311+G ∗∗ // HF/6-31G ∗ + ZPVE(HF/6-31G ∗ ) theoretical model. It appears that these systems exhibit high proton affinity thus representing good candidates for efficient proton sponges. Their heavily substituted derivatives, involving bulky alkyl groups, which protect the reactive double bonds, should possess even higher proton affinity being at the same time apt to chemical synthesis.

Superbase catalysis of oxazolidin-2-one ring formation from carbon dioxide and prop-2-yn-1-amines under homogeneous or heterogenous conditions

N-alkyl-substituted prop-2-yn-1-amines and N-tri-, tetra- and penta-alkyl-substituted guanidines or other strong organic bases assemble under the action of carbon dioxide to afford carbamates, from which methyleneoxazolidinones 2 are formed by ring closure. If alkyl or cycloalkyl chains of appropriate length are present in the guanidines the reaction readily occurs under heterogenous conditions without solvent.

Basicities of thiazole heterocyclic compounds and the reaction of 3-methyl-2-methylimino-Δ4-thiazolines with ethyl bromoacetate and 2-bromoacetophenone

The pKa′s of several thiazole heterocyclic compounds have been determined and represent products with significantly high values. Because of their high basicities, sometimes these compounds were able to act as not only nucleophiles but also strong organic bases. 4-Substituted-3-methyl-2-methylimino-Δ4-thiazolines 5a-d reacted with ethyl bromoacetate in refluxing benzene, giving the corresponding N-alkylated salts 8a-d, while the products obtained from the reaction with 2-bromoacetophenone in the presence of base were pyrrolothiazines 10b-d.

Base-catalysed direct introduction of carbon dioxide into acetylenic amines

N-Alkylprop-2-ynylamines readily react with carbon dioxide in the presence of catalytic amounts of strong organic bases and undergo intramolecular cyclization to 5-methylene-1.3-oxazolidin-2-ones in good yields.

Novel, highly deactivated reversed-phase for basic compounds

Silica has proven invaluable as a support material for reversed-phase high-performance liquid chromatography. However, contributions of residual acidic silanols lead to poor chromatography of basic compounds. This paper demonstrates the utility of a new, highly deactivated silica-based reversed-phase packing material for the study of a series of weak and strong organic bases. Correlation between retention times on the column and octanol-water partition coefficients at pH 7.0 is demonstrated. Also shown are the results of further experiments in which we investigated the retention characteristics of basic, acidic and neutral compounds by the new deactivated phase.

Lineare Oligophosphaalkane, XXIV Synthese und strukturelle Charakterisierung von Cu8‐Mehrkernkomplexen mit Elektronenmangel‐Phosphidobrücken

Linear Oligophosphaalkanes, XXIV. – Syntheses and Structural Characterisation of Cu8 Complexes with Electron‐Deficient Phosphido BridgesReaction of silylphosphanes (Me3Si)RP–CH2–PR(SiMe3) (R = iPr, tBu, 2,4,6,‐Me3C6H2) with four equivalents of copper(1) halides CuX (X = Cl, Br) or a mixture of two equivalents of CuCl and Cul in the presence of pyridine as an auxiliary ligand affords octanuclear copper(1) complexes of composition Cu8X4(RP–CH2–PR)2(Py)n(CH3CN)m (n = 5, m = 0; n = 4, m = 1; X = Cl, Br, I). Multinuclear compounds of this type may also be obtained by deprotonation of the disecondary phosphanes HRP–CH2–PRH (R = iPr, Ph, 2,4,6‐Me3C6H2) with strong organic bases (DBU) in the presence of CuCl and pyridine. The X‐ray structural analysis of Cu8Cl4(iPr–P–CH2–PiPr)2(Py)5 (3a) (space group P21/c) reveals a Cu4(P–C–P)2 skeleton to which four CuCl(Py)n units (n = 1, 2) are coordinated by Cu–Cl and Cu–P bridges. The phosphorus atoms of the electron‐deficient μ3–PRR′ bridges formed thereby show a distorted trigonal bipyramidal coordination with almost planar PCu3 units. Due to the multiple bridging of the Cu(I) ions in 3a the Cu ⃛Cu distances in the Cu8 complex are relatively short (247.1–276.5 pm).

Use of ?-2-cyanoethyl tert-butoxycarbonylaspartate as an intermediate for synthesis of ?-esters

The use of α-2-cyanoethyl Boc-aspartate is proposed for the first time for the synthesis of β-esters of Boc-aspartic acid. The α-2-cyanoethyl protective group is selectively split out by strong organic bases under hydrolytic conditions without the β-ester bond being affected. Using the α-2-cyanoethyl derivative, β-cyclohexyl, β-benzyl, and β-tert-butyl Boc-aspartates have been synthesized in good yields.

ACID BASE PHENOMENA IN DISTILLATE FUEL STABILITY

ABSTRACT Carboxylic and organic sulfonic acids, added to distillate fuel blends containing catalytically cracked stock, Increase deposit formation, sometimes very dramatically. The carboxylic acids data fitted into a unified treatment in relationship to hydrogen ion concentration calculated from pKa values for aqueous solutions. These acids enhance deposit formation by catalytic action and are not Incorporated into the deposit. Organic sulfonic acids may fit into the unified acid catalysis pattern but await resolution of ionization phenomena in non-aqueous solution. A tertiary aliphatic amine stabilizer was effective for reducing deposit amounts from fuel blends containing acids. This amine acts on a stoichiometric basis to counteract strong acids in the fuels. For weak acids, the amine stabilizer exhibited an effect slightly more than that for a 1:1 basis with the amount of acid in the fuel. Other amines exerted favorable behavior only if they were strong organic bases.

Studies on the oxidation of hydrazones with iodine and with phenylselenenyl bromide in the presence of strong organic bases; an improved procedure for the synthesis of vinyl iodides and phenyl-vinyl selenides

The oxidation of hydrazones by iodine in the presence of strong organic bases (guanidines) has been studied. Improved yields of vinyl iodides can be obtained by inverse addition using dry solvents and with a final heating period where appropriate. The reaction has been extended to various dihydrazones with interesting results. In complementary studies hydrazones have been oxidized by phenylselenenyl bromide in the presence of strong organic bases to give the corresponding phenyl vinyl selenides in good yield.

The interaction of organic cations with the mitochondrial membrane.

Weak and strong organic bases behave in an opposite manner in respect to several mitochondrial functions. The former induce a catalytic exchange with K+ in valinomycon-treated, respiratory-inhibited mitochondria, and act as uncouplers in respiring mitochondria. The latter induce a stoicheometric exchange with K+ and are actively taken up by respiring mitochondria.

Sulfur Vulcanization of Vinyl-Substituted Polysiloxanes

Abstract The vinyl content of the polysiloxane polymer affects the rate of vulcanization in such a way that the vulcanization time varies inversely with the vinyl concentration raised to a power less than 1. Furthermore, this power appears to be dependent upon the vinyl concentration, so that a stationary value cannot be quoted. Sulfur alone crosslinks only polysiloxane polymers of high vinyl content. A 4 mole per cent vinyl-containing polymer exhibited no vulcanization after 3 hours at 160° C with sulfur alone. Vulcanization times in the same range as those found with sulfur-vulcanizing organic polymers were obtained in this polysiloxane system by the proper choice of accelerators. Starting with the most active, compounds for accelerating or activating this vinyl-containing polysiloxane-sulfur system were: strong organic bases (TEPA), DPG, thiuram disulfides (TMTD), magnesium oxide, bivalent metal dithiocarbamates, thiazoles (MBT), weak organic bases (aniline), calcium oxide. Zinc oxide and litharge are inhibitors in this system to varying extents, depending on the accelerator present. Organic acids such as stearic acid inhibit vulcanization in this system. For recipes void of elemental sulfur, the following conclusions may be made: Accelerators that vulcanize vinyl-containing polysiloxanes without the aid of elemental sulfur follow very closely the list of compounds capable of vulcanizing organic polymers. (D.P.)c data indicated that two vinyl groups are involved in each cross link.

Sulfur Vulcanization of Vinyl-Substituted Polysiloxanes

Abstract The vinyl content of the polysiloxane polymer affects the rate of vulcanization in such a way that the vulcanization time varies inversely with the vinyl concentration raised to a power less than 1. Furthermore, this power appears to be dependent upon the vinyl concentration, so that a stationary value cannot be quoted. Sulfur alone crosslinks only polysiloxane polymers of high vinyl content. A 4 mole per cent vinyl-containing polymer exhibited no vulcanization after 3 hours at 160° C with sulfur alone. Vulcanization times in the same range as those found with sulfur-vulcanizing organic polymers were obtained in this polysiloxane system by the proper choice of accelerators. Starting with the most active, compounds for accelerating or activating this vinyl-containing polysiloxane-sulfur system were: strong organic bases (TEPA), DPG, thiuram disulfides (TMTD), magnesium oxide, bivalent metal dithiocarbamates, thiazoles (MBT), weak organic bases (aniline), calcium oxide. Zinc oxide and litharge are ...