Role of chain transfer in heterogeneous polymerization of ethylene

The role of chain transfer was studied for the radiation-induced polymerization of ethylene in precipitating media, namely n-butyl alcohol, tert-butyl alcohol and their mixtures. The affinities of those solvents for polyethylene are similar, but the chain-transfer coefficient of n-butyl alcohol is larger than that of tert-butyl alcohol. The polymerizations were carried out in a reactor of 100 ml under a pressure of 300 kg/cm², at 60°C, dose rate of 3.07 × 10⁴–1.75 × 10⁵ rad/hr in the presence of 50 ml of solvents. The polymerization in tert-butyl alcohol shows the kinetic behavior characteristic of a heterogeneous polymerization, such as rate acceleration, high dose rate dependence of polymerization rate, and low dose rate dependence of polymer molecular weight, whereas the polymerization in n-butyl alcohol does not exhibit such behavior and gives polymer having a molecular weight much lower than that of polymer obtained in tert-butyl alcohol. The polymer formed in tert-butyl alcohol exhibits a bimodal molecular weight distribution measured by gel permeation chromatography. In mixed tert-butyl alcohol and n-butyl alcohol solvent, with increasing fraction of n-butyl alcohol, the two peaks not only shift to lower molecular weight but the higher molecular weight peak becomes relatively small. Eventually, the polymer formed in n-butyl alcohol exhibits a unimodal distribution. Those results are well explained on the basis of the proposed scheme for heterogeneous polymerization.     

Measuring the Relative Hydrogen‐Bonding Strengths of Alcohols in Aprotic Organic Solvents

Voltammetric experiments with 9,10‐anthraquinone and 1,4‐benzoquinone performed under controlled moisture conditions indicate that the hydrogen‐bond strengths of alcohols in aprotic organic solvents can be differentiated by the electrochemical parameter ΔE_p^red=|E_p^red(1)?E_p^red(2)|, which is the potential separation between the two one‐electron reduction processes. This electrochemical parameter is inversely related to the strength of the interactions and can be used to differentiate between primary, secondary, tertiary alcohols, and even diols, as it is sensitive to both their steric and electronic properties. The results are highly reproducible across two solvents with substantially different hydrogen‐bonding properties (CH₃CN and CH₂Cl₂) and are supported by density functional theory calculations. This indicates that the numerous solvent–alcohol interactions are less significant than the quinone–alcohol hydrogen‐bonding interactions. The utility of ΔE_p^red was illustrated by comparisons between 1) 3,3,3‐trifluoro‐n‐propanol and 1,3‐difluoroisopropanol and 2) ethylene glycol and 2,2,2‐trifluoroethanol.     

Sorption of aliphatic alcohols from aqueous solutions by starch cryotextures

Capillary GLC was applied to study the sorption ofn-butanol,n-hexanol,n-octanol, and linalood from aqueous solutions by com starch cryotextures. The concentrations of alcohols in aqueous solutions were varied from 0.5 to 15 mmol L⁻¹. The sorption of alcohols by crytotextures formed of sols containing these alcohols and the coefficients of their. distribution depend on the initial concentration and structure of the alcohols.n-Butanol is not sorbed by the corn starch cryotextures over the range of 0.5–80 mmol L⁻¹. The sorption of other alcohols increases with increasing length of the alkyl substituent and the concentration of the alcohol. The highest sorption capacity of the cryotexture (88%) was observed forn-octanol. The sorption of linalool decreases due to the double bonds and branching in its molecules. Translated fromIzestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 734–737, April, 1999.     

Solvent effect on the complex formation of distally dialkylated calix[4]arenes with 1-chloro-4-(trifluoromethyl)benzene

The complexation behavior of the distally dialkylated calix[4]arenes and 4-tert-butylcalix[4]arenes (hosts) with 1-chloro-4-(trifluoromethyl)benzene (guest) was examined in four different alcohols (MeOH, EtOH, n-PrOH, n-BuOH) as solvents. The complex stability constants (K_s) and the complexation energy of the host-guest complexes were determined. Fair ‘by group’ linear correlations between each log K series determined in the same solvent and the complex stabilization energies were found. As a consequence, the solvents having high permittivities result in less stability of the host-guest complex in these particular cases examined.     

Complexation in the System Paramagnetic Ion (Tm3 +)-Diamagnetic Ion (Mg2 +)-Carboxylic Acid

The dependence of the NMR chemical shift in the system containing complexes of a paramagnetic cation PL and PL₂ on the concentration of a diamagnetic salt was simulated. The complexation in the system paramagnetic ion (Tm^{3 +})-diamagnetic ion (Mg^{2 +})-carboxylic acid (acetic, propionic, n-butyric) was studied experimentally. The effect of the second cation on the calculated complexation constants was detected.     

Characterization and Semiquantitative Analysis of Volatile Compounds in Orange Juice by Use of Headspace-Solvent Microextraction and Gas Chromatography

By alternate use of two different extraction solvents, n-hexadecane and benzyl alcohol, a headspace-solvent microextraction (HSME)–GC–FID/MS method has been established for characterization of the volatile components of an orange juice beverage. The method avoids two disadvantages of conventional HSME—difficulty identifying components obscured by the solvent peak and inefficient extraction of some of the compounds if one solvent only is used. The optimum conditions (droplet volume, equilibration temperature and time, extraction time, and ionic strength) were determined by the factor-rotation method. The volatile components of the beverage were mainly terpenes, terpenols, fatty acids, and alcohols, for example limonene (114.71 mg L⁻¹), phellandrene (4.50 mg L⁻¹), terpineol (p-menth-1-en-8-ol; 3.12 mg L⁻¹), α-pinene (0.33 mg L⁻¹), n-hexadecanoic acid (0.28 mg L⁻¹), and terpinol (0.13 mg L⁻¹).     

Effects of alcohols on micellization and on the reaction methyl 4‐nitrobenzenesulfonate + Br− in cetyltrimethylammonium bromide aqueous micellar solutions

The effects of n‐hexanol, n‐pentanol, and n‐butanol on the critical micelle concentration (cmc), on the micellar ionization degree (α), and on the rate of the reaction methyl 4‐nitrobenzenesulfonate + Br^? have been investigated in cetyltrimethylammonium bromide (CTAB) aqueous solutions. An increase in the alcohol concentration present in the solution produces a decrease in the cmc and an increase in the micellar ionization degree. Kinetic data show that the observed rate constant decreases as alcohol concentration increases. This result was rationalized by considering variations in the equilibrium binding constant of the methyl 4‐nitrobenzenesulfonate molecules to the micelles, variations in the interfacial bromide ion concentration, and variations in the characteristics of the water–alcohol bulk phase provoked by the presence of alcohols. When these operative factors are considered, kinetic data in this and other works show that the second‐order rate constants in the micellar pseudophases of water–alcohol micellar solutions are quite similar to those estimated in the absence of alcohols. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 634–641, 2004     

Solvatochromism of the π* ← n transition of acetone by combined quantum mechanical—classical mechanical calculations

The solvent shift of the π* ← n transition of acetone in water, acetonitrile, and tetrachloromethane was calculated in a combined quantum mechanical—classical mechanical approach, using both dielectric continuum and explicit, polarizable molecular solvent models. The explicit modeling of solvent polarizability allows for a separate analysis of electrostatic, induction, and dispersion contributions to the shifts. The calculations confirm the qualitative theories about the mechanisms behind the blue shift in polar solvents and the red shift in nonpolar solvents, the solvation of the ground state due to electrostatic interactions being preferential in the former, and favorable dispersion interaction with the excited state, in the latter case. Good quantitative agreement for the solvent shift between experiment (+1,700, +400, and −350 cm⁻¹ in water, acetonitrile, and tetrachloromethane, respectively) and the explicit solvent model (+1,821, +922, and −381 cm⁻¹) was reached through a modest Monte Carlo sampling of the solvent degrees of freedom. A consistent treatment of the solvent could only be realized in the molecular solvent model. The dielectric-only model needs reparameterization for each solvent. © 1996 John Wiley & Sons, Inc.     

The triplet state of 4-nitro-N,N-dimethynaphthylamine

Nanosecond laser photolytic studies of 4-nitro-N,N-dimethylnaphthylamine (4-NDMNA) in nonpolar and polar solvents at room temperature show a transient species with an absorption maximum in the 500-510-nm range. This species is assigned to the lowest triplet excited state of 4-NDMNA. The absorption maximum of this state is independent of solvent polarity, and its lifetime is a function of the hydrogen donor efficiency of the solvent. In n-hexane the lifetime 1/k of the triplet state is 9.1 × 10^?6 sec, while in acetonitrile 1/k is 2.0 × 10^?7 sec. The hydrogen abstraction rate constant k_H of the triplet state with tributyl tin hydride (Bu₃SnH) in n-hexane is 1.7 × 10⁷M^?1·sec^?1, while in the case of isopropyl alcohol as hydrogen donor, k_H is 4.0 × 10⁷M^?1·sec^?1. The activation energy for the hydrogen abstraction by the triplet state from Bu₃SnH in deaerated n-hexane is 0.6 kcal/mol. The lack of spectral shift with increasing solvent polarity, and the appreciable hydrogen abstraction reactivity of the triplet state, also independent of solvent polarity, seem to indicate that this excited state is an n-π* state which retains its n-π* character even in polar media.     

Polarizability and inductive effect contributions to solvent–cation binding observed in electrospray ionization mass spectrometry

Electrospray ionization (ESI) mass spectrometry (MS) has been used in conjunction with computer modeling to investigate binding tendencies of alkali metal cations to low molecular weight solvents. Intensities of peaks in ESI mass spectra corresponding to solvent-bound alkali metal cations were found to decrease with increasing ionic radii (Li⁺ > Na⁺ > K⁺ > Cs⁺) in either dimethylacetamide (DMAc) or dimethylformamide (DMF). When a lithium or sodium salt was added to an equimolar mixture of DMF, DMAc, and dimethylpropionamide (DMP), the intensities of gas-phase [solvent + alkali cation]⁺ peaks observed in ESI mass spectra decreased in the order DMP > DMAc ≫ DMF. A parallel ranking was obtained for alkali metal cation affinities in ESI-MS/MS experiments employing the kinetic method. These trends have been attributed to a combination of at least three factors. An inductive effect exhibited by the alkyl group adjacent to the carbonyl function on each solvent contributes through-bond electron donation to stabilize the alkali metal cation attached to the carbonyl oxygen. The shift in the partial negative charge at the oxygen binding site with increasing n-alkyl chain length (evaluated via computer modeling), however, cannot fully account for the mass spectrometric data. The increasing polarizability and the augmented ability to dissipate thermal energy with increasing size of the solvent molecule are postulated to act in conjunction with the inductive effect. Further evidence of these contributions to solvent–cation binding in ESI-MS is given by the relative intensities of [solvent + Li]⁺ peaks in mixtures containing equimolar quantities of alcohols, indicating preferential solvation of Li⁺ in the order n-propanol > ethanol > methanol. These experiments suggest a combined role of polarizability, the inductive effect, and solvent molecule size in determining relative intensities of solvated cation peaks in ESI mass spectra of equimolar mixtures of homologous solvents.     

Effect of alcohols on the gamma-radiation-induced polymerization of ethylene

Gamma-radiation-induced polymerization of ethylene in alcohols such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, and n-pentyl alcohols was carried out under a pressure of 400 kg./cm.²at 30°C. at a dose rate of 1.4 × 10⁵ rad/hr. in a batch reactor of 100 ml. capacity. The yield and molecular weight of polymer formed in the alcohols (except tert-butyl alcohol) were much lower than those of the bulk polymerization under the same conditions, whereas the addition of tert-butyl alcohol increased the yield and reduced the molecular weight. From the infrared spectra of the polymers and those of the bromination products it was concluded that only primary OH exists in the polymer formed in methyl alcohol and that both primary and secondary OH are in the polymer formed in other primary alcohols. Both secondary and tertiary OH were observed in the polymer when the secondary alcohols were used, and only tertiary OH in the case of tert-butyl alcohol. These polymers were found to contain small amounts of vinylidene unsaturation and methyl group. On the basis of these results the roles of the alcohols in the polymerization are discussed.     

NH2 stretching vibration absorption and association mechanism of methylamine in n-hexane and carbon tetrachloride

Hydrogen bonding of methylamine in n-hexane is studied by recording the NH₂ stretching vibration absorption as a function of temperature and concentration and comparing it to the absorption in carbon tetrachloride. A continuous or quasi-continuous shift of the symmetric NH₂ stretching vibration on association in hexane and a discontinuous shift by about the same total amount together with an intensity change between a monomeric and an associated band in carbon tetrachloride suggest different association mechanisms in the two solvents. These are related to the enhancement of the proton donor or acceptor ability of the amine resulting from complexation with the solvent in carbon tetrachloride and to a similar influence of the added amine molecules, corresponding to the concept of hydrogen bond cooperativity, in hexane. Differences of 3–5 kJ mol⁻¹ between the mean association energy of methylamine in hexane and of methylamine or its homologues in carbon tetrachloride can be attributed to the energy needed for disruption of the complexes with the chlorine solvent and therefore support the assumption of the complex formation. Further results concern the chain-length dependence of the amine association, the association degrees in the two solvents and the intensity behaviour of the symmetric vibration of the neat compound in i.r. and Raman spectra.     

Cationic Exciplexes: Role of Hydrogen Bonding in Deactivation and Electronic Coupling

Emissive properties for the cationic exciplex (A⁺*/D→A^.D^.+) of an isoquinolinium cation tethered to a substituted arene ( 1⁺ ) are strongly affected by hydrogen bonding solvents. At equal dielectric constant (ϵ), the ground-to-excited state energy gaps (ΔG) and solvent reorganization energies (λ_s) decrease from nitriles to aliphatic alcohols. The corresponding decrease from aliphatic alcohols to high hydrogen bond acidity solvents is ∼3 times larger. The exciplex decay (k_Ex), largely determined by unfolding of the exciplex to a stretched conformer, changes in a complex way depending on the strength of the hydrogen bond ability of these solvents. In contrast, the electronic couplings between the exciplex ground, excited, and charge transfer states do not show a solvent functionality dependence.     

Separation of iron(III) and gold(III) by paper chromatography using mixed solvents containing diisopropyl ether

The separation of iron(III) and gold(III) by partition paper chromatography has been investigated employing a mixture of diisopropyl ether (IPE) and n-alcohol saturated with hydrochloric acid (initial acid concentration 5.0 M) as solvent. Methyl, ethyl, n-propyl, n-butyl, and n-pentyl alcohols were used as components of the solvent. The content of n-alcohol in the initial organic phase was varied. It was found that the R_f values for both of the metals increased with an increase in the carbon-to-oxygen ratio in the alcohol (except in the case or iron(III) and n-pentyl alcohol), and with an increase in the alcohol content in the initial organic phase (except in the case of iron(III) and n-propyl alcohol). The best separation results were obtained by using the systems: hydrochloric acid (5.0 M)-IPE-n-propyl alcohol (50:35:15) gDR_f = 0.56, hydrochloric acid (5.0 M)-IPE-ethyl alcohol (50:15:35) ΔR_f = 0.51, and hydrochloric acid (5.0 M)-IPE-n-pentyl alcohol (50:35:15) ΔR_f = 0.37.     

Catalytic action of metallic salts in autoxidation and polymerization. IX. Polymerization of methyl methacrylate with sodium hexanitrocobaltate(III) in mixed solvent of acetone and water

Polymerization of methyl methacrylate with some cobalt (III) complexes was carried out in various solvents and in mixed solvents of acetone and water or alcohols. Sodium hexanitrocobaltate(III) was found to be an effective initiator in mixed solvent of water and acetone. The kinetic study on the polymerization of methyl methacrylate with Na₃[Co(NO₂)₆] in a water-acetone mixed solvent gave the following over-all rate equation: R_p = 8.04 × 10⁴ exp{ ?13,500/RT} [I]^1/2[M]² (mol/1.?sec). The effects of various additives on polymerization rate and the copolymerization curve with styrene suggest that polymerization proceeds via a radical mechanism. The dependence of the polymerization rate on the square of monomer concentration and the spectroscopic data were indicative of the formation of a complex between initiator and monomer.     

Effect of the substituent position at the heterocycle on proton transfer from alcohols to the excited molecules of 1,2-dihydroquinolines

A novel compound 1,2,2,3-tetramethyl-1,2-dihydroquinoline (1223TMDQ) was synthesized, and the products of its steady-state photolysis in water, MeOH, EtOH, trifluoroethanol (TFE), PrⁿOH, and BuiOH were analyzed by ¹H NMR and mass-spectrometry. The corresponding adducts with water and alcohols were identified. The presence of the adducts for alcohols with a number of carbon atoms n > 1 distinguishes 1223TMDQ from 2,2,4-trimethyl-1,2-dihydroquinolines with methyl-, alkoxy-, and hydroxy-substituents at positions 1, 6, and 8, for which the formation of adducts was observed only in the presence of water and MeOH. The results were interpreted in terms of the effect of steric hindrance caused by substituents in the heterocycle and increasing size of the alkyl group of alcohol on proton transfer from a solvent to the molecule of 1,2-dihydroquinoline, which occurs in the complex between the solvent and the dihydroquinoline molecule in the excited singlet state. It was shown that the main steric hindrance for the photoinduced proton transfer in 2,2,4-substituted 1,2-dihydroquinolines is the substituent at position C(4) of the heterocycle.     

Study of intermolecular interactions in the equilibrium catalytic transesterification of esters

The interaction of alcohols ROH with esters PhCOOR (R = Me,n-Bu,n-C₇H₁₅) in binary mixtures and in solutions in non-polar solvents (CCl₄, cyclohexane) was studied over a wide temperature range by Fourier IR spectroscopy. Even with a great excess of alcohol (up to 3000-fold molar excess), two bands are observed in the region ofv(CO) vibrations. The low-frequency band, which is down-shifted by 15–20 cm^–1 with respect to thev(CO) band in the absence of alcohol, corresponds to ester molecules bonded by hydrogen bonds of the C=O...HO type. The high-frequency band is up-shifted by 3–5 cm^–1 with respect to the esterv(CO) band. The discreteness of the shift, which is confirmed by the appearance of an isobestic point, indicates that an H-complex of yet another type is formed between the alcohol and the ester. The analysis of the data available allows one to conclude that complex formation involves the alkoxyl oxygen atom of the ester. The enthalpies of formation were determined forn-BuOH H-bonds with the esters and with the transesterification catalysts, i.e., As(OBu)₃, B(OBu)₃, and Ti(OBu)₄.Part 3 — see ref.1Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 709–713, April, 1993.     

Magnesium-25 NMR studies of magnesium salts and complexes in nonaqueous solvents

Magnesium-25 NMR measurements were carried out on aqueous and non-aqueous solutions of magnesium salts. In the former case the²⁵Mg resonance frequency was independent of the concentration or of the counterion. In nonaqueous solvents, however, the resonance frequency was dependent on the solvent, the concentration, and on the nature of the counterion, indicating some cation-anion interactions. Measurements on Mg²⁺—phosphonoacetic acid mixtures in aqueous solutions gave strong indications of complexation. Only inconclusive evidence was obtained on the complexation of Mg²⁺ by macro-bicyclic cryptand C211 in methanol solutions, and no evidence of complexation was obtained with macrocycle 12-crown-4 in dimethylformamide solutions.     

Reactivity of Water and Alcohols toward Carbocations Generated in the Photolysis of 2,2,4,6-Tetramethyl-1,2-dihydroquinoline

The rate constants of the decay of carbocation generated in the photolysis of 2,2,4,6-tetramethyl-1,2-dihydroquinoline and the composition of reaction products were studied as a function of solvent composition in the mixtures H₂O–ROH and MeOH–ROH (R = Et, n-Pr, and i-Pr). The rate constants of carbocation decay in alcohols are more than 20 times higher than the corresponding rate constants in water. As follows from the composition of the products obtained in the photolysis in the alcohol–water mixtures, MeOH is only 1.4 times more reactive than water, and EtOH and n-PrOH are even less active than water. The inconsistency in the product composition in the mixtures and the values of the observed rate constants in these solvents was explained by the two-step mechanism of the reaction: the reversible formation of an adduct of the carbocation with the solvent components and subsequent proton transfer to the solvent to form the final product, with the first step determining the product composition and the second step determining the rate of carbocation decay. The relative rate constants of alcohols and water were determined for the two steps. The preferred solvation of the carbocation with water also contributes significantly to the reaction kinetics and the product composition in the water–alcohol solutions.     

Organic cluster ions from continuous-flow fast atom bombardment

Cluster ions from fast atom bombardment of liquid alcohols and nitriles were examined using a continuous-flow technique. Protonated molecular M_nH⁺ species are the dominant cluster ions observed in molecules of formula M. The abundances of the M_nH⁺ cluster ions decrease monotonically with increasing n, and within a homologous series the M_nH⁺ abundance diminishes more rapidly for higher molecular mass compounds. Reaction products (ROH)_n(H₂O)H⁺ and (ROH)_n(ROR)H⁺ are observed also in the case of alcohols, and the ion abundances decrease with increasing n. Radiation damage yields fragment ions and ionic alkyl reaction products which are captured in solvent clusters. Semi-empirical molecular orbital methods were used to examine the energetics of cluster ion formation and decomposition pathways. Metastable decomposition processes exhibit only evaporative loss of monomers, with the probability of loss increasing sharply with n. The evaporative ensemble model of Klots was used to predict the cluster size-dependent trends of metastable dissociation processes observed for alcohol and nitrile cluster ions.