Similar Series Of Reactions Research Articles

Influence of intraparticle cross-linking on polymer diffusion in latex films prepared from secondary dispersions

In this work, we synthesized surfactant-free latex dispersions of nanoparticles (NPs) based upon emulsification of a preformed proprietary BASF polymer (MnGPC = 5000 g/mol, Ð = 3, denoted as Pol), in which the —COOH groups were partially neutralized by ammonia. To obtain useful coatings with polymers of such low molecular weight (MW), we approached this problem through the reaction of carboxylated polymer dispersions with neopentyl glycol diglycidyl ether (NGDE, 20 to 60 mol% based on carboxyl groups) to increase the MW and to introduce gel content. We employed AFM to monitor the influence of cross-link density on the surface roughness and found the presence of cross-links increases the resistance of particles to deformation. Fluorescence resonance energy transfer (FRET) measurements were carried out to determine the extent of polymer mixing upon film formation. Our most important finding is that the gel content substantially limited the extent of molecular mixing at long annealing times or in corresponding solvent-cast films. In parallel, we carried out a series of similar reactions on the secondary dispersion particles with a monoepoxide, consisting of a mixture of dodecyl and tetradecyl glycidyl ether. This reaction maintained the size and size distribution of the latex particles. These polymers had no gel content, but the reaction with the epoxide lowered the Tg of the polymer. FRET studies showed a pronounced influence of Tg on the rates of polymer diffusion in these films.

C(1)-Phenethyl Derivatives of [closo-1-CB11 H12 ]- and [closo-1-CB9 H10 ]- Anions: Difunctional Building Blocks for Molecular Materials.

C(1)-vinylation of [closo-1-CB9 H10 ]- (A) and [closo-1-CB11 H12 ]- (B) with 4-benzyloxystyryl iodide followed by hydrogenation of the double bond and reductive deprotection of the phenol functionality led to C(1)-(4-hydroxyphenethyl) derivatives. The phenol functionality was protected as the acetate. The esters were then treated with PhI(OAc)2 and the resulting isomers were separated kinetically (for derivatives of anion A) or by chromatography (for derivatives of anion B) giving the difunctionalized building blocks in overall yields of 9 % and 50 %, respectively. A similar series of reactions was performed starting with anions A and B and 4-methoxystyryl bromide and iodide. Significant differences in the reactivity of derivatives of the two carborane anions were rationalized with DFT computational results. Application of the difunctionalized carboranes as building blocks was demonstrated through preparation of two ionic liquid crystals. The extensive synthetic work is accompanied by single crystal XRD analysis of six derivatives.

On the possibility of a priori quantitative prediction of the quantum yield of a photochemical reaction

The possibility of performing predictive calculations of the kinetics and quantum yields of photochemical transformations of polyatomic molecules with satisfactory accuracy has been shown. Taking into account the physically grounded requirements imposed and rather stringent constraints on the prediction error (less than 50%), a satisfactory theoretical result has been obtained for all of the considered reactions of three chemically different types. In most cases (eight out of ten reactions), the deviation from the experimental data was less than 20%. Model parameters have high transferability in a series of similar reactions, thereby ensuring the predictive character of simulation of photochemical processes using the method developed earlier. In complicated cases, it is possible to a priori theoretically assess the type of the reaction of interest and its physicochemical characteristics.

Thermal Degradation Kinetics of Neoxanthin, Violaxanthin, and Antheraxanthin in Virgin Olive Oils

A first-order kinetic mechanism was appropriate for describing the thermal degradation of epoxy xanthophylls in virgin olive oil (VOO). Consecutive reactions that involve reorganization of 5,6-epoxide groups to 5,8-furanoxide groups and subsequent rupture of the polyene chain occurred in the degradation pathways. Thermal stability was significantly affected by changes in the chemical structure (epoxy to furanoid structure), being the greatest stability for neoxanthin. A true kinetic compensation effect was found in a series of similar reactions, that is, the degradation of 5,8-furanoxides into colorless products. An isokinetic study in different VOO matrices showed that the oily medium did not significantly affect the reaction mechanisms. Consequently, the kinetic parameters obtained as temperature functions according to the Arrhenius model can be used to develop a prediction mathematical model for 5,8-furanoxide xanthophylls in VOO over time. The potential usefulness of the parameter neoxanthin/neochrome ratio is discussed as a chemical marker of heat treatment in VOO.

Understanding Hydrogen Atom Transfer: From Bond Strengths to Marcus Theory

Hydrogen atom transfer (HAT), a key step in many chemical, environmental, and biological processes, is one of the fundamental chemical reactions: A-H + B → A + H-B. Traditional HAT involves p-block radicals such as tert-BuO(•) abstracting H(•) from organic molecules. More recently, the recognition that transition metal species undergo HAT has led to a broader perspective, with HAT viewed as a type of proton-coupled electron transfer (PCET). When transition metal complexes oxidize substrates by removing H(•) (e(-) + H(+)), typically the electron transfers to the metal and the proton to a ligand. Examples with iron-imidazolinate, vanadium-oxo, and many other complexes are discussed. Although these complexes may not "look like" main group radicals, they have the same pattern of reactivity. For instance, their HAT rate constants parallel the A-H bond strengths within a series of similar reactions. Like main group radicals, they abstract H(•) much faster from O-H bonds than from C-H bonds of the same strength, showing that driving force is not the only determinant of reactivity. This Account describes our development of a conceptual framework for HAT with a Marcus theory approach. In the simplest model, the cross relation uses the self-exchange rate constants (k(AH/A) for AH + A) and the equilibrium constant to predict the rate constant for AH + B: k(AH/B) = (k(AH/A)k(BH/B)K(eq)f)(1/2). For a variety of transition metal oxidants, k(AH/B) is predicted within one or two orders of magnitude with only a few exceptions. For 36 organic reactions of oxyl radicals, k(AH/B) is predicted with an average deviation of a factor of 3.8, and within a factor of 5 for all but six of the reactions. These reactions involve both O-H or C-H bonds, occur in either water or organic solvents, and occur over a range of 10(28) in K(eq) and 10(13) in k(AH/B). The treatment of organic reactions includes the well-established kinetic solvent effect on HAT reactions. This is one of a number of secondary effects that the simple cross relation does not include, such as hydrogen tunneling and the involvement of precursor and successor complexes. This Account includes a number of case studies to illustrate these and various other issues. The success of the cross relation, despite its simplicity, shows that the Marcus approach based on free energies and intrinsic barriers captures much of the essential chemistry of HAT reactions. Among the insights derived from the analysis is that reactions correlate with free energies, not with bond enthalpies. Moreover, the radical character or spin state of an oxidant is not a primary determinant of HAT abstracting ability. The intrinsic barriers for HAT reactions can be understood, at least in part, as Marcus-type inner-sphere reorganization energies. The intrinsic barriers for diverse cross reactions are accurately obtained from the HAT self-exchange rate constants, a remarkable and unprecedented result for any type of chemical reaction other than electron transfer. The Marcus cross relation thus provides a valuable new framework for understanding and predicting HAT reactivity.

Synthesis of Some Benzofuro Benzopyrones

7-Hydroxy-3-phenyl-[4H]-1-benzopyran-4-one 1a was condensed with 2-bromocyclohexanone to yield the corresponding ether 2a which on alkaline hydrolysis gave tetrahydrodibenzofuran derivative 3a the pyran ring being opened up during this reaction. Compound 3a was dehydrogenated with DDQ and the benzopyrone ring was constructed on dibenzofuran nucleus with sodium and ethyl formate to provide 3-phenyl-[4H]-benzofuro (3,2-g)-1-benzopyran-4-one 5a. Compound 5a was also synthesized by first converting 3a into corresponding [4H]-1-benzopyran-4-one 6a and then subjecting it to dehydrogenation. A similar series of reactions were employed for 7-hydroxy-8-methyl-3-phenyl-[4H]-1-benzopyran-4-one 1b and 7-hydroxy-2-methyl-3-phenyl-[4H]-1-benzopyran-4-one 1c to obtain 2-hydroxy-1-methyl-3-phenylacetyl dibenzofuran 4b and 2-methyl-3-phenyl-[4H]-benzofuro (3,2-g)-1-benzopyran-4-one 5c respectively.

ChemInform Abstract: Synthesis of Some Benzofuro-benzopyrones

7-Hydroxy-3-phenyl-[4H]-1-benzopyran-4-one 1a was condensed with 2-bromocyclohexanone to yield the corresponding ether 2a which on alkaline hydrolysis gave tetrahydrodibenzofuran derivative 3a the pyran ring being opened up during this reaction. Compound 3a was dehydrogenated with DDQ and the benzopyrone ring was constructed on dibenzofuran nucleus with sodium and ethyl formate to provide 3-phenyl-[4H]-benzofuro (3,2-g)-1-benzopyran-4-one 5a. Compound 5a was also synthesized by first converting 3a into corresponding [4H]-1-benzopyran-4-one 6a and then subjecting it to dehydrogenation. A similar series of reactions were employed for 7-hydroxy-8-methyl-3-phenyl-[4H]-1-benzopyran-4-one 1b and 7-hydroxy-2-methyl-3-phenyl-[4H]-1-benzopyran-4-one 1c to obtain 2-hydroxy-1-methyl-3-phenylacetyl dibenzofuran 4b and 2-methyl-3-phenyl-[4H]-benzofuro (3,2-g)-1-benzopyran-4-one 5c respectively.

Sugar-pendant diamines.

A set of 1,3-propanediamine derivatives connected to carbohydrates (5) has been prepared in four steps from peracetylated sugar and 1,3-dibromo-2-propanol in 60-73% yields. D-Glucose, D-mannose, D-galactose, D-xylose, D-ribose, and maltose are utilized as sugar molecules in this work. The diamine moiety was connected to the C1 carbon of the glycopyranose ring via an O-glycoside bond. All of the anomeric configurations and sugar puckering conformations, except in the D-maltose derivative, were determined by X-ray crystallography of the diazido or dibromo precursors. While glycosidation of peracetylated galactopyranose with 1,3-dibromo-2-propanol in the presence of boron trifluoride afforded both anomers, the neighboring group participation of the 2-acetoxy group yielded a single anomer for the other substrates. This method has been used to synthesize a library of sugar-pendant diamines including an OH-protected derivative (6), and an N,N'-diisopropyl-substituted derivative (7). A similar series of reactions using 2,3-dibromo-1-propanol gave ethylenediamine-type derivatives (11), and bis(bromomethyl)bis(hydroxymethyl)methane (12) gave bisglucose-pendant derivatives (16).

Cationic, arylbismuth(III) complexes of the form [BiR2L2]+ and [BiRL4]2+ where L is a neutral two-electron donor ligand

Synthetic and structural studies have been made for a range of cationic, ten-electron, four-co-ordinate, diarylbis(ligand)bismuth(III) complexes. Reactions between BiPh2Br, AgBF4 and 2 equivalents of a two-electron donor ligand L afforded the ionic complexes [BiPh2L2][BF4][L = OPPh3 or pyridine (py)]. The first was characterised by X-ray crystallography and comprises [BiPh2(OPPh3)2]+ cations, tetrafluoroborate anions and CH2Cl2 molecules of crystallisation. The bismuth centre is four-co-ordinate with a disphenoidal geometry in which the aryl groups are in equatorial positions with the ligands in axial sites. A long interaction is present between the bismuth centre and one of the fluorines of the BF4 group. A series of similar reactions were also carried out between BiR2Br (R = aryl), TlPF6 and 2 equivalents of L affording the ionic complexes [BiR2L2][PF6][R = Ph, L = OP(NMe2)3 or py; R = 4-MeC6H4, L = OP(NMe2)3; R = 2,4,6-Me3C6H2, L = OP(NMe2)3 or OPPh3]. Two of the complexes have also been characterised by X-ray crystallography, the cations having similar structures to that found in [BiPh2(OPPh3)2][BF4]. The reaction between BiPhBr2, 1 equivalent of TlPF6 and an excess of OP(NMe2)3 afforded the ionic complex [BiPh{OP(NMe2)3}4][PF6]2. The crystal structure of the dication comprises a square-based pyramidal bismuth centre with an apical phenyl group and four basal OP(NMe2)3 ligands. Examples of some dihalogenobismuth cations have also been obtained and their structures are described and compared with those of previously reported examples.

A regiocontrolled and stereocontrolled synthesis of allylsilanes from β-silyl enolates

The α-lithiated diphenylphosphine oxides 3 react with methyl iodide to give the phosphine oxides 4 and 5 in a ratio of 3–4 : 1. The corresponding reaction with aldehydes gives all four diastereoisomeric alcohols 7–10, which are not suitable for the synthesis of allylsilanes by a Wittig–Horner reaction. The β-dimethyl(phenyl)silyl enolates 13–15 and 25–28 react with aldehydes to give aldol products with high diastereoselectivity. The benzyl and allyl ester groups can be cleaved from these aldols to give the acids 16–18 and 29–32. The acids, in turn, can be induced to undergo decarboxylative elimination stereospecifically either in a syn or an anti sense to give the allylsilanes 19, 20, 23, 24, 33, 34 and 39–41. A similar series of reactions can be carried out with the β-trimethylsilyl enolates 45 and 46 giving the allylsilanes 49, 50, 53 and 54.

Microcanonical variational theory of radical recombination by inversion of interpolated partition function. Part 2.—CX3+ O2(X = H, F, Cl)

The title theory (MVIPF) has been applied to the recombinations of O2 with the radicals CH3, CF3, CF2Cl, CFCl2 and CCl3 and compared, with generally good results, to experimental data which are available for all radicals but one (CF2Cl). In particular, MVIPF, which is based on minimum information and uses an adjustable parameter (c) in a Gaussian-type switching function, correctly reproduces the fact that the recombination CH3+ O2 has a positive temperature coefficient, while all the other radical recombinations have a negative temperature coefficient. Consolidated results by MVIPF for the nine recombination reactions for which experimental data are available (the title reactions, plus CH3+ H, CH3+ CH3, CH2Cl + CH2Cl, CHCl2+ CHCl2, CCl3+ CCl3), yield a linear relation for a function of the logarithm of c, which in principle allows one to predict a recombination rate constant in a series of similar reactions within a factor of two.

A new route to chiral hydroxypyrrolidines from D-erythrose via intramolecular 1,3-cycloaddition

2,3-O-Isopropylidene-D-erythrose (1) reacted with ethoxycarbonylmethylene(triphenyl)phosphorane in refluxing benzene to give the E and Z alkene esters (2a) and (2b). The ester (2a) was converted, via the 6-triflate (7a) and 6-azide (3a), into the dihydrotriazole (8) by 1,3-cycloaddition. Ring opening of compound (8) with sodium ethoxide gave the pyrrolidine diazo ester (9) which on hydrogenolysis gave (2R,3S,4R)-ethyl (3,4-isopropylidenedioxypyrrolidin-2-yl)acetate (5). A similar series of reactions from the Z-ester (2b) gave the pyrrolidine ester (6), the 2S-isomer of (5). Thermolysis of the diazo ester (10), the 2S-isomer of (9), gave(Z)-(3S,4R)-ethyl (3,4-isopropylidenedioxypyrrolidin-2-ylidene) acetate (12) which was reduced with sodium cyanoborohydride to give the ester (5). The esters (2a) and (2b) undergo rapid and quantitative cyclisation in the presence of ethoxide ion. Kinetically the β-isomer (18) is preferred [100% from (2b), 86% from (2a)]; at equilibrium the α-isomer (19) is favoured (82%).

Reconstruction of ring A of 3,4-dinor-2,5-seco steroids

Methods for the reconversion of 3,4-dinor-2,5-seco steroids into the parent 4-en-3-one systems are discussed. In an efficient route, reaction of 17β-acetoxy-5,5-ethylenedioxy-3,4-dinor-2,5-secoandros-tan-2-al with ethoxyvinyl-lithium led to the corresponding 2ξ-hydroxy-3-one. Acetylation followed by treatment with zinc dust in acetic acid then gave testosterone acetate. A similar series of reactions was performed in the progesterone series.

Ruthenium carbonyl complexes. I. Synthesis of [Ru(CO)2(bidentate)2]2+ complexes

The complexes RU(CO)2Cl2L [L = 1,l0-phenanthroline (phen) or 2,2'-bipyridyl (bpy)] react with silver carboxylates to yield Ru(CO)2(OCOR)2L derivatives (R = Me or CF3). Reactions of Ru(CO)2(OAc)2L and Ru(CO)2(OAc)2(phen) with trifluoroacetic and trifluoromethanesulfonic acid give Ru(CO)2(OCOCF3)2L and Ru(CO)2(OSO2CF3)2(phen) respectively. In acetonitrile, Ru(CO)2(OAC)2L complexes react with trifluoromethanesulfonic acid to give [Ru(CO)2(MeCN)2L] (O3SCF3)2. The complexes [RU(CO)2L2]2+, [Ru(CO)2(phen)(bpy)]2+, and [Ru(C02(phen)(tmp)]2+ (tmp = 3,4,7,8-tetramethyl-1,l0-phenanthroline) have been prepared by reaction of [Ru(CO)2- (MeCN)2L]2+ and/or Ru(CO)2(OSO2CF3)2 phen with an excess of the appropriate bidentate ligand. A similar series of reactions has yielded Ru(C0)2(OAc)2(py)2, [Ru(CO)2(MeCN)2(py)2] (O3SCF3)2, and [RU(CO)2(py)2L]2+ from Ru(CO)2Cl2(py)2. Stereochemical assignments have been made for all complexes.

Inversion of configuration at C-8 in the olivanic acids: conversion into the thienamycins and other novel derivatives

The inversion of stereochemistry at C-8 in the olivanic acids, MM 22383 (7) and MM 22381 (6), is described. The reaction of p-nitrobenzyl (5R,6S)-3-[(E)-2-acetamidovinylthio]-6-[(S)-1-hydroxyethyl]-7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylate (8) with diethyl azodicarboxylate, triphenylphosphine, and formic acid afforded the 6-[(R)-1-formyloxyethyl] derivative (17), which upon alkaline hydrolysis gave the 6-[(R)-1-hydroxyethyl] derivative (18). Hydrogenolysis of the p-nitrobenzyl ester (18) furnished the sodium salt of N-acetyldehydrothienamycin (15), the (8R)-epimer of the olivanic acid MM 22383 (7). The 3-(2-acetamidoethylthio)-analogue, MM 22381 (6), was converted into N-acetylthienamycin (14) by performing a similar series of reactions on its p-nitrobenzyl ester (10). The transformation of the ester (18) to bis-protected thienamycin (22), via the C-3 thiol (21), is also described. Reaction of the olivanic acid esters (8) and (10) with diethyl azodicarboxylate, triphenylphosphine and hydrazoic acid resulted in the formation of the 6-[(R)-1-azidoethyl] derivatives (27) and (28). Subsequent hydrogenolysis provided (5R,6R)-3-[(E)-2-acetamidovinylthio]-6-[(R)-1-aminoethyl]-7-oxo1-azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid (29) and the 3-(2-acetamidoethylthio)-analogue (30).

Purines, pyrimidines, and imidazoles. Part 56. Some aminoimidazole-carboxamidines and derived adenines

5-Amino-4-cyano-1-cyclohexylimidazole, prepared from aminomalononitrile, triethyl orthoformate, and cyclohexylamine with methanolic hydrogen chloride, produced methyl 5-amino-1-cyclohexylimidazole-4-carboximidate, which with ammonia gave 5-amino-1-cyclohexylimidazole-4-carboxamidine, formylation of which gave 9-cyclohexyl-N6-formyladenine, which was also prepared by formylation of 9-cyclohexyladenine. 9-(2,3-Dihydroxypropyl)-N6-formyladenine was produced in a similar series of reactions and the reaction of 5-aminoimidazole-4-carboxamidine with formic acetic anhydride has also been shown to produce not, as previously thought, the formylamidine, but N6-formyladenine which could also be obtained by formylation of adenine, whereas adenosine was not N-formylated under the same conditions.

Hammett ϱ values

Abstract The reactivity-selectivity principle states that reactivity and selectivity amongst a series of similar reactions should correlate inversely. Yet this is rarely found to be the case when the selectivity index is the Hammett ϱ value for a reaction series. This observation then calls into question the practice of using ϱ as an index of transition state character insofar as “early” vs “late” transition states are concerned. Or, if ϱ is considered as a transition state index, the practice of assigning progressively later (more product-like) transition states to slower reactions must be questioned, despite a multitude of non-LFER observations to the contrary. In resolving this paradox, we focus attention on differences in efficiency of charge transmission from reaction centre to substituent between similar reaction series. For a few reactions where sufficient data are available, it is found that once raw ϱ values are corrected for variation in transmission efficiency, they indeed follow the order predicted by the reactivity-selectivity principle.

ChemInform Abstract: CYCLOPHANES. VII. NAPHTHALENE AND PHENANTHRENE CYCLOPHANES FOR THE SYNTHESIS OF CORONENE

AbstractDie Kupplung des Phenanthrens (I) mit dem Dithiol (II) liefert das Cyclophan (IIIa).

Cyclophanes. VII. Naphthalene and phenanthrene cyclophanes for the synthesis of coronene

A coupling reaction between 3,6-bis(bromomethyl)phenanthrene and p- xylene-α,α?-dithiol gave 2,11-dithia[3,3](3,6)phenanthroparacyclophane (4). Ring-contraction of the sulphonium salt (5)proceeded in low yield. However, a corresponding dimethyl cyclophane (12) reacted efficiently togive the desired ring-contracted [2,2]cyclophane (13). Wittig rearrangement of the cyclophane (4) gave a high yield of compound (7) which in turn was oxidized to the disulphoxide (8). Thermal elimination of methylsulphenic acid produced the diene (9) which could be photochemically cyclized to coronene. A similar series of reactions with 2,13-dithia[3,3](2,7)naphthalenophane (14) was effected. Oxidation, halogenation and photochemical reactions of both the naphthalene- and phenanthrene-based cyclophanes are reported.

Pyrazolopyrimidine nucleosides. Part III. Synthesis of 1- and 2-(β-D-ribofuranosyl)pyrazolo[3,4-d]pyrimidines from pyrazole nucleo-side derivatives

The trimethylsilyl derivative (6) of 3-(3,3-dimethyl-1-triazeno)pyrazole-4-carboxamide (4) was condensed with 2,3,5-tri-O-acetyl-D-ribofuranosyl bromide (7) to give a mixture of nucleosides that were subsequently established as isomers rather than anomers. Removal of the blocking groups from one of the isomers furnished 5-(3,3-di-methyl-1-triazeno)-1-(β-D-ribofuranosyl)pyrazole-4-carboxamide (12) which was catalytically hydrogenated to afford the pyrazole analogue, 5-amino-1-(β-D-ribofuranosyl)pyrazole-4-carboxamide (13), of AICA riboside. Ring closure of (13) with formic acid-acetic anhydride followed by treatment with base furnished a mixture of nucleosides which were separated and characterized as 1-(β-D-ribofuranosyl)pyrazolo[3,4-d]pyrimidin-4-one (16; allopurinol riboside) and 6-methyl-1-(β-D-ribofuranosyl)pyrazolo[3,4-d]pyrimidin-4-one (17). The other isomer (8) furnished 3-(3,3-dimethyl-1-triazeno)-1-(β-D-ribofuranosyl)pyrazole-4-carboxamide (11) which was converted by a similar series of reactions into 2-(β-D-ribofuranosyl)pyrazolo[3,4-d]pyrimidin-4-one (15).