Proportions Of Reactants Research Articles

Self-heating and spontaneous ignition in the combustion of gaseous methylhydrazine

The exothermic oxidation of gaseous monomethylhydrazine (CH3NHNH2) has been investigated in the gas phase over a temperature range 370–510°C in a 1-litre vessel. Critical conditions of pressure, temperature and reactant proportions for spontaneous ignition, and the effects of inert diluents have been examined. CH3NHNH2+ 2.5 O2→N2+ CO2+ 3 H2O; ΔH=– 1340 kJ mol–1(–320 kcal mol–1) Temperature changes have been followed by means of very fine thermocouples (13 µm diam. Pt–Pt/Rh) coated to prevent surface catalysis. The reactant is always hotter than the vessel, and the temperature excess is greatest at the centre, in accord with conductive theory. Uncommonly among gas-phase oxidations, the combustion of methylhydrazine is dominated by thermal effects. As was previously found for hydrazine, large central temperature excesses (about 80 and 100°C) are common and have to be exceeded for ignition to occur.The critical temperature excesses are consistent with the effective activation energy (ca. 80 kJ mol–1 or 19 kcal mol–1) derived from critical pressure limits and taken together indicate that the critical increment in average temperature is between 1.1 and 1.2 RT2a/E. These values do not provide support for the theoretical treatment by Adler and Enig, which requires stable temperature excesses greater than 2.41 RT2a/E to be realisable for a second order reaction; they are consistent, however, with our recent analytical and computational predictions on the stability of such systems.

Reactivity ratios for copolymerization of vinyl chloride with 2‐methylpentyl vinyl brassylate by computerized linearization

AbstractA computerized version of the Fineman‐Ross linearization procedure was used to determine reactivity ratios for copolymerization of vinyl chloride (monomer 1) and 2‐methylpentyl vinyl brassylate (monomer 2). From differential refractometry data for the products of low‐conversion copolymerization, the procedure gave r1 = 1.06 and r2 = 0.234. The ratios computed from chlorine contents of the same products were r1 = 1.10 and r2 = 0.239. The polarity factor (e2) and general monomer reactivity (Q2) calculated for monomer 2 from these ratios were, respectively, −0.95 to −0.98 and 0.032–0.033. The interquartile range for the copolymerization of a mixture of 60% monomer 1 and 40% monomer 2 was 1.4%. These values suggest that from suitable proportions of reactants, sufficiently homogeneous distribution of monomers can be achieved in copolymers of vinyl chloride and 2‐methylpentyl vinyl brassylate to offer the possibility of effective internal plasticization.

Synthesis of poltalkylenearyls Communication 6. Effect of the relative amounts of reactants on the course of the copolycondensation of benzene and chlorobenzene with 1, 2-dichloroethane

1. The effect of the original proportions of reactants on the course of the copolycondensation of 1,2-dichloroethane with benzene and chlorobenzene was studied. 2. The relative activity of chlorobenzene was determined (the activity of benzene being taken as unity), and it was shown that the relative activities of these aromatic compounds do not depend on their concentrations in the original mixture. 3. An empirical equation was found for the composition of the copolymer as a function of its yield and the relative amounts of aromatic compounds in the original mixture. 4. Increase in the dichloroethane content of the reaction mixture results in reduced yield of copolymer.

SYNTHESIS OF GUANIDINE FROM UREA, AMMONIUM BENZENESULPHONATE, AND AMMONIUM SULPHAMATE

Guanidine benzenesulphonate has been obtained in yields exceeding 70% by heating urea, ammonium sulphamate, and ammonium benzenesulphonate in respective molar ratios of 1:1:0.75. The effects of temperature, proportion of reactants, and reaction time were studied batchwise. Then the process was operated on a continuous basis in a four-flask cascade reactor at temperatures between 240° and 260 °C.

A study of sensitized explosions - X. The kinetics of decomposition of chloropicrin and of the hydrogen-oxygen and hydrogen-chlorine reactions sensitized by chloropicrin

A kinetic scheme is suggested for the decomposition of chloropicrin which is shown to be in agreement with the results of the work of Smith & Steacie (1938 a, b ), and which provides an explanation of the sensitizing action of chloropicrin on the hydrogen-oxygen and hydrogen-chlorine reactions described in parts VIII and IX (Ashmore & Norrish 1950 a, b ): CCl 3 NO 2 → Cl + ... k 1 CCl 3 NO 2 → COCl 2 + NOCl... k 2 Cl + NOCl → Cl 2 + NO... k 3 Cl + CCl 3 NO 2 → remove Cl... k 4 Estimates of the relative concentrations of chlorine atoms at various stages of the decomposition at different temperatures are made. The concentration of chlorine atoms passes through a maximum, and at temperatures above 340°C this maximum is probably reached within 1 msec. It occurs earlier, and is greater in magnitude, the higher the chloropicrin pressure at a given temperature or the higher the temperature for a given concentration of chloropicrin. These variations are shown to provide a direct explanation of the results for the range 340 to 400°C described in part IX, and to enable the results of part VIII to be explained by a modification of the scheme proposed by Dainton & Norrish (1941) for the nitrosyl chloride-hydrogen-oxygen reaction. This modification consists of an allowance for the variation in the initial number of chain-centres arriving in the reaction vessel, the variation being due to changes in the precise location within the entry tube of the maximum concentration of the chlorine atoms which initiate the chains. Kinetic schemes are suggested for the hydrogen-chlorine-chloropicrin reaction in the temperature region 100 to 200°C. A straight chain scheme, with chains initiated from reaction k 1 , is combined with a thermal condition for ignition to give a satisfactory account of the variation of the ignition limits with concentration of chloropicrin, with proportion of reactants, and with temperature, and also to account for the course of the slow reaction below the ignition limit. A branched chain mechanism is also discussed and is shown to account for the results only if the branching reaction is of the form H+Cl 2 +CCl 3 NO 2 →HCl+Cl+Cl+NO+COCl 2 . The experimental results do not allow a decision to be made between these possible schemes.

Specific Precipitation

Summary A complete solution is obtained for the equilibrium between bivalent antigen and bivalent antibody in a system restricted to the formation of linear chains. Some typical results of antigen titrations are tabulated, showing the effects of variation in bond-strength, steric interaction, relative proportion of reactants, and volume, on the maximal degree of aggregation possible. The principal conclusion is that surprisingly little aggregation can occur by specific means unless the reactions are of irreversible character. This conclusion, logically extended to systems of higher valence, emphasizes the importance of the structural effects of ring closure to the application of the lattice hypothesis. The problem of ring closure and its effect on the equilibrium is discussed, and a general method of approach is indicated. No explicit treatment is attempted at this time, except for the limiting case of perfectly flexible chains. A general treatment leading from equilibrium to statistical expressions for the structure of linear polymers is appended. Certain inferences, applicable to real precipitates, concerning the relation between the structure of aggregates and the properties of individual bonds, are drawn from the study of the simpler system. In immune precipitates, structural effects are probably far more important in determining the properties of the aggregate than is the intrinsic strength of the bond itself. It is for this reason that the composition of the precipitate, which is intimately connected with the initial equilibrium between specific bond-forming groups, is easier to predict than the amount of precipitate, which is largely determined by structural factors. It follows also that immune reactions may differ considerably depending on the physical character of the antigen, independently of the nature of the combining groups.