Alkali Metal Counterions Research Articles

Linewidth alternation, as a result of intramolecular cation migration, in the electron spin resonance spectrum of the 1,4-naphthoquinone radical anion

The radical anion of 1,4-naphthoquinone has been prepared by electrochemical reduction in dimethylformamide and by alkali-metal reduction in 1,2-dimethoxyethane. The e.s.r. spectrum of the radical anion in dimethylformamide can be readily interpreted in terms of three pairs of equivalent protons. However, in 1,2-dimethoxyethane, association of the alkali-metal counter-ion with one of the carbonyl groups removes the equivalence within each of these pairs. Linewidth alternation is observed in the e.s.r. spectrum when either Na+, K+ or Cs+ is the counter-ion as a result of intramolecular cation migration between equivalent sites adjacent to the two carbonyl groups. The rate of migration varies in the sequence Cs+ > K+ > Na+ > Li+, indicating that Li+ interacts more strongly with the radical anion than (say) Cs+. The disruption of the spin distribution within the radical anion, which is also greatest when Li+ is the counter-ion, supports this conclusion.

On the reaction of metallated acetylenes and allenes with carbon disulfide. Influence of the alkali metal counter-ion and the substituents in the acetylene and allene on the course of the reaction

Addition at low temperatures of carbon disulfide to a solution of the lithium compound ▪ (R 1 = CH 3, C 3H 7, Ph, OCH 3, SCH 3) results in the initial formation of an allenic carbodithioate H 2CCC(R 1)CSSLi, while for R 1 = t-C 4H 9 or SiMe 3 acetylenic carbodithioates R 1CCCH 2CSSLi are formed. The initial products undergo very rapid subsequent reactions. For R 1 = CH 3 or C 3H 7 the lithium compound adds (in the allenic form) in a conjugated fashion to the CCCS system of the allenic carbodithioate. The acetylenic dithioates are deprotonated to give the geminal dithiolates R 1CCCHC(SLi) 2. For R 1 = Ph, OCH 3 or SCH 3, subsequent deprotonation at the terminal carbon atom of the initial allenic dithioate gives enyne dithiolates HCCC(R 1)C(SCH 3) 2; this reaction proceeds more satisfactorily with the potassium compounds.

Transformation of oligodimethylsiloxanols in the presence of a strong base. Reactivity enhancement of the siloxane bond by the adjacent hydroxyl group

AbstractThe kinetics of the base catalysed disproportionation of polydimethylsiloxanes having silanol end groups was studied using the model systems 1,1,3,3,3‐pentamethyldisiloxane‐1‐ol (1) and 1,1,3,3,5,5,7,7,9,9,9‐undecamethylpentasiloxane‐1‐ol (5) in 2‐propanol in the presence of alkali metal 2‐propanolates and in THF containing 2 vol.‐% of water in the presence of NaOH. The results did not confirm our earlier mechanistic proposition. Silanone is not formed intermediately. The process proceeds according to the kinetic law for a bimolecular process and shows a high negative value of activation entropy. However, the reaction exhibits some features better explained by an elimination‐addition than by an SN2 mechanism. The hydroxyl group exerts a specific role making the cleavage of the adjacent siloxane bond much easier. The reaction is also accelerated by the assistance of the alkali metal counter ion and its rate seems to be little dependent on the basicity of the nucleophile. A mechanism combining elements of both the SN2 and the elimination‐addition pathways is proposed.

Acid–base equilibria in polyelectrolyte systems

Acid–base equilibria in carboxylic polyelectrolyte solutions and gels have been investigated by studying ion-exchange equilibria involving hydrogen and alkali ions. The investigations were carried out with solutions of poly(acrylic acid), poly(methacrylic acid), carboxymethyl cellulose and a carboxymethyl cellulose gel. The acid–base dissociation constants of the polyacids were determined, and acid strength was found to increase in the order poly(methacrylic acid), poly(acrylic acid), carboxymethyl cellulose. In the latter case a marked decrease of acid strength with increasing degree of substitution was observed, which was attributed to increased fluctuations in the concentration of carboxylic groups at high degrees of substitution. In the presence of simple salt the ionisation of the polyacids increased with increasing salt concentration. The effect is analogous to the increased ionisation of low-molar-mass weak acids, caused by the salt-induced depression of the ionic activity coefficients. However, the effect is more pronounced in polyelectrolytes and depends on the nature of the alkali-metal counterion, the ionisation being higher for K+ and Cs+ ions than for Na+ and Li+ ions.

ChemInform Abstract: HETEROPOLYATOMIC ANIONS OF THE POST TRANSITION METALS. SYNTHESIS AND STRUCTURE OF THE DILEADDIANTIMONIDE(2‐) ANION, PB2SB22‐

AbstractDie Komplexierung der Alkalimetallgegenionen mit Crypt (4.7.13.16.2l.24‐Hexaoxa‐l.lO‐diazabicyclo[8.8.8]hexacosan) stabilisiert Zintl‐Anionen enthaltende Salze.

Raman spectroscopic and X-ray diffraction studies of electrode-solution interfaces

Surface-enhanced Raman scattering (SERS) of adsorbed water species has been obtained at roughened silver electrodes; these species are always coadsorbed with anions. The spectra obtained with adsorbed cyanide and iodide ions are used to illustrate this behaviour. For the latter system it is shown that the water molecules seen by SERS are in the solvation shells of the alkali metal counterions. The spectra due to coadsorbed water, chloride and pyridine are reinterpreted and it is shown that the potential dependence of the spectra correlate with changes in the differential capacitance; preliminary data for SERS on palladium electrodes are also given. It is shown that whereas Raman spectra give information about the short-range order and environment of species adsorbed at electrode-solution interfaces, in situ X-ray diffraction measurements (INSEX) give information about the longer-range order. Measurements are illustrated by the UPD of lead on silver and it is shown that here again the change in structure of the solvent in the interface may be observed.

ChemInform Abstract: THE CHEMISTRY OF ANIONS DERIVED FROM TETRACYANODIPHENOQUINODIMETHANE (TCNDQ)

AbstractDie Dihydro‐Titelverbindung (IV) wurde dargestellt (siehe Schema) und durch Behandlung mit MOH in Wasser bzw. MH in Acetonitril (M: Na, K) in das Di‐Na‐ bzw. Di‐K‐Salz übergeführt.

The chemistry of anions derived from tetracyanodiphenoquinodimethane (TCNDQ)

Dihydro-TCNDQ was prepared from biphenyl. The dianion salts of TCNDQ with alkali metal and tetraalkylammonium counter ions were prepared and characterized by their nmr and uv-visible spectra. Solutions of these dianions undergo two one-electron oxidations at −0.31 and −0.15 V in DMF. The electrochemistry is complicated by a second chemical process involving the monoanion [Formula: see text]. This was postulated to involve a dimerization of [Formula: see text] and this process was also implicated in the analysis of the uv-visible spectra of this anion. The [Formula: see text] anion has a solution esr spectrum of over 25 lines which have been analyzed by a computer simulation of the spectrum.

Dilatometric study of monovalent counter-ion association with carboxylates

Volume changes accompanying the protonation of mono-, di- and poly-carboxylates in water were measured at 25° using the circulation dilatometer. The carboxylates include alkali metal and tetra-alkylammonium (TAA) salts of acetic, pivalic, glutaric acid and samples of poly(methacrylic acid) (PMA) having various molecular weights and degrees of stereoregularity. It was found that TAA counter-cation exerts specific influence on the differential molar volume change on protonation of the pivalate and PMA in contrast to the absence of such specificity in the corresponding alkali metal salts. These results were interpreted by the proposed association of the hydrophobic ammonium cation with the carboxylate anions. Volume contraction is accompanied by the association. It was also proposed, on the basis of these findings, that alkali metal counter-ion is not likely to be ‘site bound’ by the respective charges of PMA. PMA configuration has a minor effect on the volume change.

Darstellung und EPR-spektroskopie m-phenylen-verknuepfter biradikalischer bistetracyclon-metallketyle

The synthesis of several substituted bistetracyclones bridged by phenyl rings at meta positions is described. From the corresponding metal ketyls—obtained by alkali metal reduction—EPR triplet powder spectra have been recorded. The spectra can be interpreted in terms of electron-electron dipolar coupling between the unpaired spins of randomly oriented molecules. The influences of substitution, concentration of the paramagnetic species and of the nature of the alkali metal counter ion on the magnitude of the zero field splitting parameters are investigated. Assuming two different conformations of the bis-tetracyclone ketyl biradicals ( cis cis and cis trans—referred to the position of the oxygen atoms) the EPR data can be explained satisfactorily.

Polymérisation anionique de l'isoprène: Nature de la paire d'ions et stéréospécificité

AbstractWith accumulated HR‐NMR spectra of anionic polyisoprenes, it has been possible to study the influence of the nature of the propagating species on the microstructure of the obtained polymers If free ions are responsible for the propagation, the microstructure (1,4‐: 25%, 1,2‐: 33%, 3,4‐: 42%) does not depend on the nature of the cations. But with contact ion pairs, the different addition modes are governed by the size of the alkali metal counterions. Mechanisms of anionic propagations via diene–cation coordination are proposed.

Stability of colloidal silica: II. Ion exchange

The stabilities of the colloidal silicas, Ludox HS and Ludox AM, in the presence of various electrolytes have been systematically investigated by turbidity measurements. Complete “electrolyte concentration-pH” domains giving coagulation and stability regions have been determined for salts with cations of +1, +2, and +3 charge. By means of a titration technique, the amount of exchange of positive ions for silanolic hydrogens on the surface of the silica sols has been measured as a function of pH at various electrolyte concentrations. At low pH cation exchange on silica surfaces would appear to obey the mass action law. At pH > 6 the observed amount of exchange is considerably less than predicted on the basis of a simple equilibrium. It was established that the stability of colloidal silica can be related to ion exchange. For a given pH the minimum amount of cation exchange on a silanol surface necessary for coagulation was the same for all the alkali metal counterions studied regardless of the critical coagulation concentration. Up to pH 8 the relationship between ion exchange and the critical coagulation concentrations for calcium and lanthanum ions was the same as for the series of monovalent cations.

Studies on the anionic oligomerization of methacrylonitrile by alkali metal alkoxides

The bulk anionic oligomerization of methacrylonitrile (MAN) by RO/ROH solutions was studied at constant temperature. The disappearance of monomer and of alcohol, and the formation of the different oligomers up to n = 3 (trimers) were followed quantitatively by gas chromatography, and the change of DP of the oligomers with conversion was determined. The effects of the type of alcohol, [MAN]/[ROH] ratio, initiator concentration, and the nature of the alkali metal counterion were investigated. DP decreased in the order methanol > ethanol > isopropanol, and the rate of conversion vice versa. Increase of the [MAN]/[ROH] ratio and of initiator concentration increased DP . While the same behaviour was observed with sodium and potassium alkoxides, with the corresponding lithium alkoxides practically no oligomerization occurred even under more drastic conditions. Under the investigated conditions, the formation of the addition product, RO—MAN ( n=1) was reversible, contrary to the formation of the higher oligomers. The Koq of the reversible reaction, [MAN][ROH]/[RO—MAN] was determined from reactions using excess ROH; for methanol it was 55 mole/1., and for ethanol 7·8 mole/1. Some of the rate constants of the various steps of the oligomerization reactions for methanol and ethanol were estimated taking into account the reversibility of the initiation reaction, and assuming steady state conditions in the concentration of the various anions present in the system. The rate constant of the initiation reaction was greater than the rate constants of propagation; the rate constant of propagation of M 1 − (formation of dimer anion) was greater than that of M 2 −. The rate constants of termination of the various oligomer anions by ROH were only 2–4 times greater than the corresponding propagation rate constants. The steady state concentrations of M 1 −, M 2 − and M 3 − were estimated, and in some cases were relatively high so that their sum was as much as 90 per cent of the initial concentration of the alkoxide initiator. The initiation rate constant with C 2H 5O −/C 2H 5OH was about 4–5 times greater than that with CH 3O −/CH 3OH, and the corresponding termination rate constants were smaller by a factor of 4–5, which is in accordance with the acidity of the alcohols.

Grafting of polypeptides on polyhydroxy polymers

The homogeneous graft polymerization of γ-benzyl- l-glutamate NCA (N-carboxy anhydride) and ε-carbobenzoxy- l-lysine NCA on cellulose acetate alkoxide was studied to discover the mechanism of the graft polymerization. It was found that the initiation reaction was that of a direct addition of the alkoxide to carbonyl no. 5 of the NCA, and proof was obtained for the existence of an ester linkage between the polypeptide side chain and the cellulose acetate backbone. The polypeptide side chains had the amino group as the characteristic end group, as determined from titration and Van Slyke determination, and their DP n was equal to [NCA] o/[alkoxide] o( A/ I). A linear relationship was found between log [η] of graft polymer vs. log A/ I, showing that DP▾ of the polypeptide side chains was proportional to A/ I. The DP w found on the cleaved polypeptide side chains was higher than A/ I, and the ratio DP w / DP n was between 9 and 23. This high ratio was due to the fact that only 4–9 per cent of the alkoxide used initiated graft polymerization of the high molecular weight polypeptide side chains, the rest of the initiator leading to grafting of amino-acid units instead of the high polypeptide chains. The effects of the solvent, the alkali metal counterion and the concentrations of reactants on the intrinsic viscosity of the graft polymers was explained by the existence of propagation through a dissociated carbamate ion-pair as postulated by Idelson and Blout. The effect of both the polymeric backbone and the grafted side chains on the viscosity of the graft polymers was investigated and correlated with the conformation of the polypeptide side chains.

Kinetics of the anionic polymerization of styrene in benzene. Effect of the alkali-metal counter-ion

The propagation reaction in the anionic polymerization of styrene has been studied with the counter-ions, Na, K, Rb and Cs. In the range of active-centre concentration between 10–3 and 10–5M, with sodium the ion-pairs are entirely associated, with caesium the ion-pairs are not associated, while potassium shows intermediate behaviour. Absolute ion-pair propagation constants could be measured for polystyryl potassium, rubidium and caesium. The equilibrium constant for association of ion-pairs was determined for polystyryl potassium, together with the heat and entropy of association.

Anionic homogeneous and heterogeneous polymerizations of acrylonitrile by alkali metal alkoxides

The homogeneous (in dimethylformamide) and heterogeneous (in petroleum ether) polymerizations of acrylonitrile by methanolic solutions of alkali metal methoxides were compared. In the homogeneous system termination of polymerization was by chain transfer to monomer and degree of polymerization (DP) was constant, while in the heterogeneous system termination was by the acidic hydrogen of the alcohol and DP increased with monomer concentration according to the equation DP = Kp[M]/Kt[ROH]. Decrease in temperature led to increase in molecular weight in the heterogeneous polymerization but not in the homogeneous. The positive counterion influenced the molecular weight only under the heterogeneous conditions; the more electropositive potassium gave smaller molecular weights than the sodium catalyst. Owing to the high dielectric constant of dimethylformamide and its high solvating power, the growing ion pairs C−Li+, C−Na+, and C−K+ in this solvent were fully dissociated and showed their “limiting anionic behavior,” leading to the molecular weights' being constant irrespective of polymerization temperature and alkali metal counterions. Because of the high ionic character of the C−K+ bond, the potassium catalyst shows its “limiting anionic behavior” even under heterogeneous conditions, leading to molecular weights of the same order in both the homogeneous and the heterogeneous systems.