Electrical phenomena accompanying the formation of new surfaces, and their role in adhesion and cohesion

Upon tearing off polymer films from metals and glasses phenomena are observed which testify to the apparition of high differences of potentials between the interfaces formed. In particular, if the film is stripped under vacuum, electron emission is observed with electron velocities of the order of kilovolts. These phenomena are due to division upon stripping of the double electric layer, formed upon close contact between the polymer and the substrate, and to retardation of its discharge. The same retardation of the discharge of the double layer may explain quantitatively both the high value of the work spent on tearing off the film, the dependence of the latter on the speed of stripping and on the pressure of surrounding gas. Similar phenomena were found to take place during the destruction of many crystalline (but not amorphous) solids and are explained by the formation and division of an alternating-sign double layer of mosaic structure.     

Modifying action of carbon dioxide in catalytic oxidation of ethylene on silver

Carbon dioxide exerts a strong inhibitory effect on oxygen adsorption and complete oxidation of ethylene on silver but has little effect on the rate of ethylene oxidation to ethylene oxide.

---

.

     

Anthocyanins of Hibiscus cannabinus

Conclusions Two anthocyanin glycosides have been isolated from the flowers ofHibiscus cannabinus var. simplex. One of them is a new glycoside, which has been called cannabinin, and the second is the known glycoside myrtillin, this being the first time that it has been isolated from the flowers of Kenaf hemp.Scientific-Research Institute for the Chemistry and Technology of Cotton Cellulose, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 723–727, November–December, 1971.     

Oxidative coupling of 5-membered heterocycles catalyzed by a Pd(II)-heteropolyacid system in dimethylformamide

Oxidative coupling of thiophene and 2-methylfuran to the corresponding dihetaryls in DMFA medium occurs in the presence of the homogeneous catalytic system Pd(II)-molybdovanodophosphoric heteropolyacid (HPA). The data obtained show that HPA may act as a reversible oxidant in polar aprotic media.

---

, Pd(II)- 2- . , .

     

The remote effect of vicinal large groups on the anomeric equilibrium: 2-methoxy-cis- and -trans-5,6-dimethyltetrahydropyrans

The anomeric equilibrium of 2-methoxy-trans-5,6-dimethyltetrahydropyran was found to have an enhanced fraction of axial methoxyl compared to 2-methoxy-4- or 6-methyltetrahydropyran. The 2-methoxy-cis-5,6-dimethyltetrahydropyran did not. The enhanced anomeric effect is attributed to a steric repulsion between the trans vicinal Me groups. A similar effect is postulated for methyl glucoside and glucose pentaacetate.     

Studies of dynamic properties of heterogeneous catalytic reactions in a closed isothermal gradientless system over biographically inhomogeneous catalyst surface

The dynamics of a closed isothermal system of constant volume consisting of an ideal gaseous mixture and particles adsorbed over the biographically inhomogeneous catalyst surface, has been studied. The existence, uniqueness and asymptotic stability of the point of detailed equilibrium in each positive reaction simplex has been proved.

---

, , . , , .

     

Racemization of chiral amino alcohols III: Effect of Mg or Ca addition on the activity and stability of the Co/γ-Al2O3 catalyst

The racemization of R-(-)-2-amino-1-butanol in a reaction using Co/γ-Al₂O₃ catalysts and catalysts modified by Mg or Ca was investigated in this paper. Complete racemization was achieved with a yield of over 83% at using the Mg modified Co/γ-Al₂O₃ catalyst under optimized reaction conditions of 170°C and 2.5 MPa of H₂. The catalysts were thoroughly characterized by XRD, XPS, TPR, SEM and TEM. The addition of Mg and Ca may be advantageous for dispersing and stabilizing the active species of the Co/γ-Al₂O₃ catalyst, protecting from sintering, significantly improving its catalytic activity and stability.     

EPR study of the nature of active sites and the type of their deactivation in CO hydrogenation on (Ni+Ti)/SiO2 catalysts

As shown by EPR, upon supporting Ni(-C₃H₅)₂ on Ti/SiO₂, the Ni complex is coordinated to Ti³⁺ ions. Deactivation of (Ni+Ti)/SiO₂ catalysts so obtained during CO hydrogenation is due to the oxidation of Ti³⁺ ions and metallic nickel particles by reaction products.

---

, Ni(-C₃H₅)₂ Ti/SiO₂ Ni Ti³⁺. , (Ni+Ti)/SiO₂ CO Ti³⁺ .

     

Triterpene glycosides ofAstragalus and their genins. XXII. Cycloorbicoside A fromAstragalus orbiculatus

The quantitatively main glycoside — cycloorbicoside A — has been isolated from the epigeal parts of the plantAstragalus orbiculatus, and on the basis of chemical transformations and spectral characteristics its structure has been established as (23R,24S)-16,23:16,24-diepoxycycloartane-3,7,25-triol 3-0--D-xylopyranoside.Institute of the Chemistry of Plant Substances Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 719–726, November–December, 1986.