Gunnar Aksnes

Interpretation of chemical structural changes by target-projection analysis of infrared profiles

Abstract Infrared profiles are used as structural descriptors for a range of chemical systems, embracing samples from process analysis, geochemistry and physical chemistry. Structural mapping by infrared profiling accompanied by target-projection analysis is shown to be a powerful tool for interpretation of the variation pattern in chemical systems. In most of the applications the interpretation complies with the understanding of the chemical changes taking place in the system discussed. For some applications, the target-projection analysis brings new insight by highlighting the changes in the multivariate infrared descriptors.

Photooxidation of diphenylmethane and 1,2,3,4-tetrahydronaphthalene as liquid film on water

Abstract The rate and product composition are analysed during photooxidation of diphenylmethane and tetralin (1,2,3,4-tetrahydronaphthalene) spread as liquid film on water. The data obtained from various reaction conditions (varying light, temperature, sensitizer and inhibitor) seem to conform the assumption that the photooxidation of these compounds is primarily initiated through a photoexcited hydrocarbon/oxygen collision complex.

STUDY OF THE ALKALINE CLEAVAGE OF THE P[sbnd]C BOND IN PHOSPHINE OXIDES AND DERIVATIVES OF TRICHLOROMETHANEPHOSPHONATE

Abstract A study of alkaline decomposition of several aromatic phosphine oxides containing p- and o-nitrobenzyl, and trichloromethyl as leaving groups, is reported. The property of the trichloromethyl group as leaving group, and the CCl− 3-groups further decomposition in the hydrolysis of diethyl and disodium trichloromethanephosphonates, have also been investigated.

Investigation Of The Reaction Between Dialkylphosphine Oxides And Carbontetrachloride

Abstract The time dependent formation of intermediates and end products in the reaction between Et2P(O)H and CCI4 is analysed using 31P-NMR technique. The various reaction steps are studied separately in order to elucidate the overall mechanism. A key step is the disproportionation of Et2P(O)H catalysed by Et2PCl and Et2P(O)Cl, in a cyclic process, the latter being produced initially by the reaction between Et2P(O)H and CCl4. The diethylphosphine formed during disproportionation reacts immediately with CCl4, driving the reaction through the intermediates. Et2PCl and Et2, PCCl3 which react with Et2P(O)OH producing Et2P(O)Cl, (Et2PO)2O, and Et2P(O)CHCl2, as end products. The influence of the substituents on rate and product yields was studied with n-propyl, n-butyl, noctyl, and allyl as substituents in the dialkylphosphine oxide.

TEMPERATURE AND SOLVENT EFFECTS IN WITTIG REACTIONS

Abstract The rates of the Wittig reactions between 4-nitrobenzaldehyde and five stabilized phosphoranes, Ph3P=CHC(O)R, where R = OMe, OPh, NPh2, Me, and Ph, are studied in benzene, dimethyl formamid (DMF), and methanol, at 25, 35, and 45°C. The activation energies, E, when plotted as function of the corresponding activation entropies, ΔS∗, are found in two different regions in the E – ΔS∗ diagram, approximately described by two parallel lines, one belonging to the reactions in benzene and DMF, the other to the reactions in methanol. The differences in the activation parameters in aprotic and protic solvents are most likely a consequence of strong H-bonding in protic solvents. Reaction mechanisms in aprotic and protic solvents are discussed.

KINETICS, MEDIUM, AND DEUTERIUM ISOTOPE EFFECTS IN THE ALKALINE DECOMPOSITION OF QUATERNARY PHOSPHONIUM SALTS III1 Tetraphenylphosphonium Chloride in Dimethylsulphoxide-Water Mixtures

Abstract The reaction between tetraphenylphosphonium chloride and hydroxide or deuteroxide anions was studied kinetically in a series of dimethylsulphoxide-water mixtures at several temperatures. The rate is first-order in the phosphonium cation and second-order in the hydroxide or deuteroxide anions. The reaction shows a dramatic increase in rate, up to about 1010 times, as the DMSO content is increased. The rate enhancement is attributed to a considerable drop in activation energy affected not only through an increased desolvation of reactant anions, but also through an increase in solvation of the transition state, brought about by gradual addition of DMSO. The kinetic solvent deuterium isotope effect in 60% DMSO-40% D2O is strongly dependent on temperature. The rate constant in the latter solvent mixture is represented by k i = 11.9 e −12700/RT l 2 mole−2 sec−1 as compared to k i = 19.0 e −22500/RT l 2 mole−2 sec−1 in the corresponding 60% DMSO-H2O mixture. The thermodynamic parameters of activation s...

THE EFFECT OF THE PHOSPHORYL SUBSTITUENTS ON THE STEREOCHEMISTRY OF THE HORNER REACTION

Abstract The stereochemistry of the olefin forming reaction of various phosphoryl stabilized carbanions and aldehydes in ethanol is reported. The aromatic aldehydes react with acyclic phosphoryl stabilized carbanions yielding the trans isomers stereoselectively, whereas the 5- and 6-membered cyclic phosphonates (II and III) resulted in high yields of cis isomeric olefins. The aliphatic aldehydes give rise to considerable amounts of cis olefins also, decreasing in the series phosphonates, phosphinates and phosphine oxides, respectively. The stereochemical results are discussed in terms of pentacoordinated reaction intermediates.

SOLVOLYSIS OF PHOSPHONIUM COMPOUNDS CONTAINING A THIOPHENOXY GROUP LINKED TO PHOSPHORUS

Abstract A kinetic study of the solvolysis of six alkylphenyl thiophenoxyphosphonium chlorides in 50% water/methanol is reported. The rates of solvolysis, where thiophenol and phosphine oxides are formed, are little influenced by the substituents linked to phosphorus. The present findings are in sharp contrast to the 104 higher rate of the alkaline decomposition of tetraphenyl as compared to tialkylphenyl phosphonium salts, where phenyl is the leaving group. Further, the rate of solvolysis of the cyclic phenyl thiophenoxyphospholanium salt, is nearly identical to the rate of the corresponding dialkylphenyl thiophenoxyphosphonium compound. Calculation of the activation parameters of the solvolysis of thiophenoxyphosphonium compounds shows that the underlying reaction forces, expressed as activation energies and entropies, are strongly influenced by the substituents. The results suggest that the thiophenoxy group is expelled from the pentacovalent, trigonal bipyramidal reaction intermediate, before pseudoro...

OXYPHOSPHORANE ANIONS AS NUCLEOPHILES IN INTRAMOLECULAR DISPLACEMENT REACTIONS

Abstract The present paper reports a kinetic study of alkaline decomposition of four bromoalkytriphenyl phosphonium bromides with the bromo-substituent in 3-, 4-, 5, and 6-positions, respectively (hereafter designated 3Br-P, 4Br-P, 5Br-P, and 6Br-P), together with the alkaline decomposition of 1,1,4,4-tetrabenzyl-1,4-diphosphoniocyclohexane dibromide (designated 2P). The very high rates of decomposition of 3Br-P and 2P are in accordance with an easy formation of five-membered oxaphospholane ring intermediates through participation of oxyphosphorane anions in intramolecular displacement reactions, with carbon in 3Br-P, and with phosphorus in the neighbouring phosphonium cation of 2P.

The Influence of the Structure of Water on Chemical Reactions

It is well known that water undergoes structural changes with rise of temperature. It is therefore to be expected that thermodynamic parameters of equilibrium reactions, and activation parameters of kinetic reactions in water will be influenced by these structural changes of water in the reaction mixture. If the water structure changes monotonously with rise of temperature, the reaction parameters would also be expected to result in correspondingly smooth temperature dependent courses.