Milon Sprecher

A Detailed Investigation of the Thermal Reactions of LiPF6 Solution in Organic Carbonates Using ARC and DSC

The thermal stability of 1 M LiPF 6 solutions in mixtures of ethylene carbonate, diethyl carbonate, and dimethyl carbonate in the temperature range of 40 to 350°C was studied by accelerating rate calorimeters (ARC) and differential scanning calorimeters (DSC). Nuclear magnetic resonance (NMR) was used to analyze the condensed reaction products at different reaction stages. Studies by DSC and pressure measurements during ARC experiments with LiPF 6 solutions detected a gas-releasing endothermic reaction starting at ∼170°C, involving diethyl carbonate which occurs before a number of exothermic reactions, which follow as the temperature increases. Fluoride ions are released and react with the alkyl carbonate molecules both as bases and as nucleophiles. The bulk analysis by NMR shows that HO-CH 2 -CH 2 -OH, FCH 2 CH 2 -OH, F-CH 2 CH 2 -F, and polymer are major products. Gas analysis by NMR and Fourier transform infrared spectroscopy shows PF 5 , CO 2 , CH 3 F, CH 3 CH 2 F, and H 2 O as major gaseous products of the thermal reaction of these solutions.

The use of accelerating rate calorimetry (ARC) for the study of the thermal reactions of Li-ion battery electrolyte solutions

The thermal stability of 1M LiPF6, LiClO4, LiN(SO2CF2CF3)2 (LiBETI) and LiPF3(CF2CF3)3 (LiFAP) solutions in mixtures of ethylene carbonate, diethyl carbonate and dimethyl carbonate in the temperature range 40–350 8C was studied by ARC and DSC. NMR was used to analyze the reaction products at different reaction stages. The least thermally stable are LiClO4 solutions. LiPF3(CF2CF3)3 solutions showed higher thermal stability than LiPF6 solutions. The highest thermal stability was found for LiN(SO2CF2CF3)2 solutions. Studies by DSC and pressure measurements during ARC experiments with LiPF6 and LiFAP solutions detected an endothermic reaction, which occurs before a number of exothermic reactions as the temperature increases. Fluoride ions are formed and react with the alkyl carbonate molecules both as bases and as nucleophiles. # 2003 Elsevier Science B.V. All rights reserved.

Cinnamic acid derived oxazolinium ions as novel cytotoxic agents.

Substituted cinnamoyl chlorides, 11, were converted into (2-hydroxyethyl)-oxazolinium chlorides 14, N,N-bis-(2-chloroethyl)amides 16 and (2-chloroethyl)-oxazolinium chlorides 17. Although derivatives 14 which possess electron-donating substituents (Me or MeO) were more potent than those substituted by electron-withdrawing groups (NO(2), Cl or CF(3)), the difference in cytotoxic actin was not significant. Modification of the lipophilic character in a series of alkoxy-substituted derivatives 14 led to more active compounds, where 14t that possesses a 4-octyloxy-phenyl-substituent was the most potent and displayed cytotoxic activity in the microM range. It is assumed that the oxazolinium salts act as alkylating agents, and undergo nucleophilic attack on the methylene adjacent to the ring oxygen where the oxazolinium ring parallels the aziridinium ring intermediate found in classical alkylating agents.

Steroid phosphate esters

Abstract Four phosphorylation procedures were used in the preparation and characterization of sundry steroid phosphate and phosphonate esters, as well as some P1,P2-disteroid pyrophosphates. An attempt to prepare cholest-3,5-dien-3-yl dialkyl phosphate by a vinylogous Perkow reaction from 6-bromocholest-4-en-3-one yielded only dienenones. As a model for P1,P2-disteroid pyrophosphate (and steroid phosphate) behavior in solution, the neutral crystalline complex 2,2′-bipyridine zinc P1,P2-bis(1-n-dodecyl)pyrophosphate was prepared and characterized.

Relative reactivity of three and four membered rings ? the absence of charge effectElectronic supplementary information (ESI) available: Gaussian archive file. See http://www.rsc.org/suppdata/ob/b3/b314869f/

Radical (neutral) and electrophilic (cationic) ring opening reactions were studied computationally in order to probe the difference in reactivity between three and four membered rings. Using the Marcus equation we have shown that the activation energy for the four membered ring opening is close to the Marcus predicted barrier whereas three membered rings display much higher reactivity than that predicted by the Marcus equation. Thus, the reactivity of the three membered rings is enhanced, in addition to the strain release, by another factor which is not operative in the four membered rings. It is clear also that this factor is not charge dependent. The possible origin of this effect is discussed.

A facile entry into a stable functionalized bis(methylene)cyclobutene system

Abstract A parameter for the stabilization of the 3,4-bis(methylene)cyclobutene system has been identified. Appropriate functionalized derivatives, stable even in solution, have been conveniently prepared by tandem double [2,3]-sigmatropic rearrangement of conjugated dipropargylic sulfenates to diallenic disulfoxides and spontaneous cyclization of the latter. Stereochemical aspects are presented.

A novel borane effect on the C/O alkylation ratio in competing SRN1–SN2 reactions

The presence of Et3B in the reaction of 2-nitropropane anion (1) with p-nitrobenzyl bromide (5b) in tert-butyl alcohol results in an approximately three-fold increase in C-alkylation [yielding 1-(2-methyl-2-nitropropyl)-4-nitrobenzene (9) by an SRN1 mechanism] versus O-alkylation (by an SN2 mechanism, and leading thereafter to p-nitrobenzaldehyde). Dioxygen completely inhibits C-alkylation in the absence of Et3B, but is ineffective in its presence. p-Dinitrobenzene does not significantly affect the thermal reaction (30 °C) of 1 with 5b, but partially inhibits C-alkylation in reaction under photostimulation. However, p-dinitrobenzene catalyzes C-alkylation in the thermal reaction in the presence of Et3B. Rationalizations of these novel results are presented. Qualitatively similar results were obtained for the reaction of phenylnitromethane anion (16) with 5b. Copyright

The Preparation of Thiol Formates

Abstract A simple procedure for the preparation of sundry types of thiol formates is presented.

1,2-Rearrangement of protonated-heterosubstituents in ethyl radicals: a molecular orbital study

Abstract Ab initio self-consistent field (SCF) calculations in a Gaussian orbital basis set have been carried out on both the equilibrium “open” ( 3 ) and bridging ( 4 ) structures of various protonated β-substituted ethyl radicals (C 2 H 4 A + ′H; A′H = ClH, SH 2 , PH 3 ). In contrast to the findings for the unprotonated species ( 1 and 2 ), heteroatom protonation, which stabilizes both the “open” ( 3 ) and bridged ( 4 ) forms, results in paths for 1,2-A′H + migration whose energies are substantially below the energy of dissociation to [CH 2 CH 2 + A′H]· + · moieties. In the case of CH 2 CH 2 C l + H, intramolecular ClH + migration can proceed without significant barrier. This raises the possibility that apparent chlorine atom migrations to vicinal radical termini may in fact be ClH + migrations. It is found that protonation of the “open” structures 1b and 1c (A′ = SH, Cl) to give 3b and 3c (A′H = SH 2 , ClH) respectively, considerably enhances hyperconjugative interaction between the C α single electron orbital and the C β A bond orbitals. The contrasting result that protonation of 1a (A′= PH 2 ) to 3a (A′H = PH 3 ) does not enhance hyperconjugation has been rationalized on the basis of rehybridization of the heteroatom bonds.

Brominated vinyl ketene thioacetal, ene- and diene acetals; potential four-carbon synthons

Abstract A novel and convenient procedure for the preparation of conjugated vinyl ketene thioacetals is described: it involves addition of CBr4 to acrolein, followed by thioacetalization of the corresponding aldehyde 2 and double dehydrobromination of 3 under basic conditions For comparison, three O-acetals 4–6 were also prepared. In contrast to the reaction of dithioacetal 3, these acetals undergo either a single or double HBr elimination with formation of mono-olefins or cumulated diene, respectively. The mechanism of formation of the reaction products is discussed, and the reactivity of the novel per-functionalized tetrasubstituted 1,3-butadiene 1 with the strongly electrophilic dienophile PTAD is presented.