Showing papers by "Indian Association for the Cultivation of Science published in 1968"

Thermal Conductivity of Argon-Carbondioxide and Nitrogen-Carbondioxide Gas Mixtures

Abstract: The thermal conductivity of the binary gas mixtures A–CO 2 and N 2 –CO 2 has been measured over temperature range 0° to 200°C by the hot-wire method. An attempt has been made to interpret the data in terms of the recent theories of heat conductivity of polyatomic gas mixtures.

Mode of termination in the copolymerization of vinyl acetate–isobutyl methacrylate and methyl methacrylate–methyl acrylate at 60°C

Abstract: The mode of termination in the vinyl acetate–isobutyl methacrylate (VA–IBMA) and methyl methacrylate–methyl acrylate (MMA–MA) copolymerization systems has been investigated at 60°C. by using the dye-interaction technique for functional endgroup estimation. The results show that pairs of poly(vinyl acetate) radicals interact almost exclusively through a disproportionation mechanism. In the homopolymerization of methyl methacrylate and methyl acrylate, about 1.16 and 1.22 carboxyl-containing endgroups per polymer molecule have been estimated, which shows the predominance of disproportionation over combination in these termination reactions. In poly(isobutyl methacrylate) about 1.55 tagged initiator fragments per chain indicate that 29% of the total radicals terminate through the disproportionation mechanism. Cross termination in the (VA-IBMA) copolymerization system occurs almost entirely through combination for monomer feeds richer in isobutyl methacrylate content while for the MMA-MA system, combination is more important at intermediate monomer feed ratios. These results have been discussed in the light of different explanations for the reaction mechanism.

Kinetics and mechanism of dissociation of metal chelates. V. Dissociation of tris‐acetylacetonato‐chromium(III). With 4 figures

Abstract: From spectral observations it has been shown that in acid (HClO4) media tris-acetyl-acetonato-chromium(III), Cr(acac)3, appears to undergo dissociation in stages forming [Cr(acac)2(OH2)2]+, [Cr(acac)(OH2)4]2+ and [Cr(OH2)6]3+. The rate of dissociation of the tris- to the bis- complex has been investigated. The dissociation occurs by two concurrent paths in accordance with the following rate law: Rate = k′[Complex] + k″[Complex][H+]. It has been suggested that the H+ independent path involves a slow one-ended solvent assisted dissociation of a Cr(III)–Ligand chelate ring followed by a very much more rapid dissociation of the other Cr(III)–Ligand bond leading to the loss of the ligand. The H+ dependent path involves a similar set of changes of the protonated complex (the conjugated acid) formed in a rapid pre-equilibrium step. Values of the activation parameters ΔH≠ and ΔS≠ corresponding to the rate constants k′ and k″ are in agreement with the assigned mechanisms. The highly negative ΔS≠ values further suggest that, in addition to solvent participation of the type already mentioned, considerable solvation of the ligand being released must also be important. Increase in ionic strength of the medium under otherwise identical conditions increases k″ without affecting k′ as expected. Die Dissoziation von Chrom(III)-tris-acetylacetonat, Cr(acac)3, in saurem wasrigem Medium entsprechend den Stufen [Cr(acac)2(OH2)2]+, [Cr(acac) (OH2)4]2+, [Cr(OH2)6]3+ wurde spektrophotometrisch verfolgt. Die Kinetik der Dissoziation zum Bis-Komplex last auf zwei Reaktionswege schliesen, von denen der eine H+-unabhangig und der andere uber den protonierten Tris-Komplex ablauft. Die jeweiligen Aktivierungsenthalpien und -entropien wurden ermittelt und in bezug auf Solvatationseffekte ausgewertet.

Determination of chain transfer of alcohols by end group estimation

Abstract: Chain transfers of methyl alcohol, ethyl alcohol, n-propyl alcohol, and isopropyl alcohol in methyl methacrylate polymerization at 100°C have been evaluated from estimation of hydroxyl end group in the polymer. The results agree fairly well with the values obtained by the conventional method. The mechanism of the transfer reaction has also been discussed in the light of the results obtained from end group determination and it is inferred that the transfer reaction takes place mainly by the rupture of CH bond. Das Ausmas der Kettenubertragung durch Methyl-, Athyl-, n-Propyl- und Isopropylalkohol wahrend der Polymerisation von Methacrylsauremethylester bei 100°C wurde aus der Bestimmung der Hydroxylendgruppen im Polymeren berechnet. Die Ergebnisse stimmen mit den durch die konventionellen Methoden erhaltenen Werten gut uberein. Unter Berucksichtigung der aus der Endgruppenbestimmung erhaltenen Ergebnisse wird auch der Mechanismus der Ubertragungsreaktion erortert, und es wird geschlossen, das die Ubertragungsreaktion hauptsachlich durch Bruch der CH-Bindung erfolgt.

Studies in some new initiator systems for vinyl polymerization. III. Amine–halogen systems as redox initiators

Abstract: Amine–halogen redox systems are very efficient initiators of polymerization of a number of vinyl monomers in benzene media and are rather inefficient initiators in aqueous media. A large number of aliphatic amines and a few aromatic amines have been used. Among the halogens, chlorine and bromine are very effective. Iodine initiates with a few amines only. Endgroups incorporated are halogen and amine totalling an average of nearly one per chain in the case of polymerization in benzene media and 0.5-0.7 per chain in polymerization in aqueous media. In the light of endgroup results, a mechanism of initiation through halogen and amine radicals has been suggested.

Mechanism of nucleophilic substitution in chromium(III) complexes. I. Some reactions of Isothiocyanato- and Nitrito-pentamminechromium(III) ions in solution

Abstract: The kinetics of replacement of SCN- by OH− in [Cr(NH3)5(NCS)]2+ and of NO by OH−, and CH3COO− in [Cr(NH3)5(ONO)]2+ have been investigated. Evidence has been obtained that in alkaline media [Cr(NH3)5(NCS)]2+ undergoes a reaction leading to the formation of [Cr(NH3)4(OH)2]+, concurrent with usual base hydrolysis leading to the formation of [Cr(NH3)5(OH)]2+ by both an OH− dependent path and through aquation. Arguments have been put forth that the OH− dependent path in this case involves an SN1 IP mechanism; evidence for ion-pair formation has been obtained from conductance measurements. Replacement of NO by OH− in [Cr(NH3)5(ONO)]2+ appears to proceed by a pseudo-substitution process without a rupture of the CrO bond. Replacement of NO in this complex by CH3COO− appears to occur by three independent paths involving (1) SN 1 dissociation of the CrONO bond followed by rapid addition of CH3COO− to the five-coordinated Cr(NH3) forming the product, (2) SN 1 dissociation of the protonated form [Cr(NH3)5ONOH]3+, followed by addition of CH3COO− to the Cr(NH3) as in (1), and (3) SN 2 displacement of (ONO)− by CH3COO−. The usual kinetic parameters, k, δLH≠ and δLS≠, have been evaluated. Der Austausch von SCN− gegen OH− in [Cr(NH3)5NCS]2+ und von NO gegen OH− und CH3COO− in [Cr(NH3)5ONO]2+ wurde an Hand der Reaktionskonstanten, Aktivierungsenthalpien und -entropien untersucht. [Cr(NH3)5NCS]2+ geht in alkalischen Medium OH−−abhangig und durch Hydratation in [Cr(NH3)5OH]2+ und [Cr(NH3)4(OH)2]+ uber, wobei der OH−−abhangige Weg wahrscheinlich nach einem SN 1-Ionenpaar-Mechanismus verlauft. Der Ersatz von NO in [Cr(NH3)5ONO]2+ durch OH− lauft wahrscheinlich als Pseudo-substitution ohne Spaltung der CrO-Bindung ab, wahrend der Austausch durch CH3COO− offenbar auf drei voneinander unabhangigen Reaktionswegen erfolgt.

Dilute solution properties of poly(m‐methyl styrene)

Abstract: Viscometric and osmometric studies have been carried out with fractions of poly(mmethyl styrene) in solutions of benzene, cyclohexane, and ethyl acetate at 30, 40, and 50°C. The values of K′ and ‘a’ in the KUHN-HOUWINK relation have been reported for the above polymer-solvent systems. The values of unperturbed dimension, (r/M)1/2, solvent polymer interaction constant (B) and conformational parameter (σ) have been computed applying the theories of FLORY-FOX-SCHAEFGEN, KURATA-STOCKMAYER-ROIG, and STOCK-MAYER-FIXMAN. The applicability of the theories of FLORY, KURATA et al., and PTITSYN has been critically analysed from the dependence of the expansion factor (α) on molecular weight. Values of thermodynamic parameters, Θ, Ψ1, x1, and X1, have also been calculated. Viskosimetrische und osmometrische Messungen an Fraktionen von Poly-m-methyl-styrol wurden in Benzol, Cyclohexan und Athylacetat bei 30, 40 und 50°C ausgefuhrt. Die K′- und a-Werte der KUHN-HOUWINK-Gleichung werden fur diese Losungsmittel an gegeben. Die Werte des Kettenendenabstandes (r/M)1/2, der Wechselwirkungskonstante B zwischen Losungsmittel und Polymerem und der Konformationsparameter σ werden unter Anwendung der Theorien von FLORY-FOX-SCHAEFGEN-ROIG und STOCKMAYER-FIXMAN berechnet. Die Anwendbarkeit der Theorien von FLORY, KURATA und Mitarb., sowie PTITSYN wurde in bezuG auf die Abhangigkeit des Expansionskoeffizienten α vom Molekulargewicht kritisch untersucht, ebenso werden die Werte der thermodynamischen Parameter Θ, Ψ1, x1 und X1 berechnet.

On the representation of the interaction energy between two polar molecules

Abstract: An attempt has been made to represent the interaction energy between two polar molecules by using an ‘effective’ relative orientation of the pair of the colliding molecules. Calculations made for gaseous ammonia show fairly satisfactory results.

Effect of chemical reaction on diffusion in the system N2O4 leftrightharpoons 2NO2

Abstract: The diffusion of krypton into the dissociating system N2O4 leftrightharpoons 2NO2 has been measured by the radioactive tracer technique. The results show that, as pointed out by Rai Dastidar and Barua, chemical reaction exerts a retarding influence on the diffusion process in reacting systems.