Uncatalyzed reaction

Keywords cyanoacetamide, malodinitril, methyl cyanoacetate, aromatic aldehyde, Knoevenagel condensation, solid-solid reaction, base catalysis, melt reaction, uncatalyzed, cinnamamide, cinnamonitril, methyl cinnamate... 

A detailed reexamination of the thermal rearrangement of 1-methyl-imidazole originally reported by Wallach has been extended to encompass a wide range of 1-substituted imidazoles. The reaction appears to be of potential synthetic utility since it leads easily to 2-alkyl- and 2-arylimidazoles. It is an irreversible reaction, uncatalyzed, intramolecular, and does not involve radicals [l,5]-sigmatropic shifts, as shown in Scheme 40, are probably implicated. The major product is the 2-substituted imidazole (134), but small amounts of the 4- (or 5-) isomer (135) are also formed. A 1-allyl substituent migrates with equal facility to both 2- and 4(or 5)-positions, suggesting that a Cope-type rearrangement may also be involved for this substituent. ... 

Reactions of amines with substituted phenyl acetates are subject to a change in pathway as a function of basicity of the leaving phenoxide group. In the ammonolysis, hydrazinolysis, and imidazole-catalyzed hydrolysis of substituted phenyl acetates, both first- and second-order terms in amine are observed (Bruice and Mayahi, 1960 Bruice and Benkovic, 1964). Out of five phenyl acetate derivatives (p-NOg, m-N02, p-H, p-Cl, and p-CHs) the general-base term kz is observed with only the least acidic leaving groups, that is p-CHs, p-H, and p-Cl in the case of ammonolysis and hydrazinolysis, and p-CHj in the case of the imidazole reaction. Uncatalyzed k terms are observed with all... 

Type of reaction uncatalyzed, ligand exchange, chemiluminescence, photochemical inhibition. AAS, atomic absorption spectrometry FIA, flow injection analysis NAA, neutron activation analysis. 

Type of reaction uncatalyzed chemiluminescence "TS, 3,3, 5-triiodo-L-thyronine T4, 3,3 5,5 -tetraiodo-L-thyronine (i-Thyroxine) CAR, continuous-addition-of-reagent technique LC, liquid chromatography. 

It is possible to prepare 1-acetoxy-4-chloro-2-alkenes from conjugated dienes with high selectivity. In the presence of stoichiometric amounts of LiOAc and LiCl, l-acetoxy-4-chloro-2-hutene (358) is obtained from butadiene[307], and cw-l-acetoxy-4-chloro-2-cyclohexene (360) is obtained from 1.3-cyclohexa-diene with 99% selectivity[308]. Neither the 1.4-dichloride nor 1.4-diacetate is formed. Good stereocontrol is also observed with acyclic diene.s[309]. The chloride and acetoxy groups have different reactivities. The Pd-catalyzed selective displacement of the chloride in 358 with diethylamine gives 359 without attacking allylic acetate, and the chloride in 360 is displaced with malonate with retention of the stereochemistry to give 361, while the uncatalyzed reaction affords the inversion product 362. 

The allyl-substituted cyclopentadiene 122 was prepared by the reaction of cyclopentadiene anion with allylic acetates[83], Allyl chloride reacts with carbon nucleophiles without Pd catalyst, but sometimes Pd catalyst accelerates the reaction of allylic chlorides and gives higher selectivity. As an example, allylation of the anion of 6,6-dimethylfulvene 123 with allyl chloride proceeded regioselectively at the methyl group, yielding 124[84]. The uncatalyzed reaction was not selective. 

Equation 11 predominates in uncatalyzed vapor-phase decomposition and photo-chemicaHy initiated reactions. In catalytic reactions, and especially in solution, the nature of the reactants determines which reaction is predominant. 

The hydroxyl number can be deterrnined in a number of ways such as acetylation, phthalation, reaction with phenyl isocyanate, and ir and nmr methods. An imidazole-catalyzed phthalation has been used to measure the hydroxyl number for a number of commercial polyether polyols and compared (favorably) to ASTM D2849 (uncatalyzed phthalation) (99). The uncatalyzed method requires two hours at 98°C compared to 15 minutes at the same temperature. 

Nitrobenzotrichloride is also obtained in high yield with no significant hydrolysis when nitration with a mixture of nitric and sulfuric acids is carried out below 30°C (31). 2,4-Dihydroxybenzophenone [131 -56-6] is formed in 90% yield by the uncatalyzed reaction of benzotrichloride with resorcinol in hydroxyHc solvents (32) or in benzene containing methanol or ethanol (33). Benzophenone derivatives are formed from a variety of aromatic compounds by reaction with benzotrichloride in aqueous or alcohoHc hydrofluoric acid (34). 

The characteristics of enzymes are their catalytic efficiency and their specificity. Enzymes increase the reaction velocities by factors of at least one million compared to the uncatalyzed reaction. Enzymes are highly specific, and consequendy a vast number exist. An enzyme usually catalyzes only one reaction involving only certain substrates. For instance, most enzymes acting on carbohydrates are so specific that even the slightest change in the stereochemical configuration is sufficient to make the enzyme incompatible and unable to effect hydrolysis. 

A. K. Galwey, Reactions in the Sohd State, in Bamford and Tipper, eds.. Comprehensive Chemical Kinetics, vol. 22, Elsevier, 1980. Galwey, A. K., Chemistry of Solids, Chapman and Hall, 1967. Sohn, H. Y, and W. E. Wadsworth, eds.. Rate Frocesses of Extractive Metallurgy, Plenum Press, 1979. Szekely, J., J. W. Evans, and H. Y. Sohn, Gas-Solid Reactions, Academic Press, 1976. Uhmann, ed., Enzyklopaedie der technischen Chemie, Uncatalyzed Reactions with Solids, vol.. 3, 4th ed., Verlag Chemie, 1973, pp. 395-464. 

Oxidation of trimethylene sulfide catalyzed by tungstic acid is preferred to the uncatalyzed reaction Yields are better and the reaction time... 

Molecular chlorine is believed to be the active electrophile in uncatalyzed chlorination of aromatic compounds. Simple second-order kinetics are observed in acetic acid. The reaction is much slower in nonpolar solvents such as dichloromethane and carbon tetrachloride. Chlorination in nonpolar solvents is catalyzed by added acid. The catalysis by acids is probably the result of assistance by proton transfer during the cleavage of the Cl-Cl bond. ... 

Molecular bromine is believed to be the reactive brominating agent in uncatalyzed brominations. The brominations of benzene and toluene are first-order in both bromine and the aromatic substrate in trifluoroacetic acid solution, but the rate expressions become more complicated when these reactions take place in the presence of water. " The bromination of benzene in aqueous acetic acid exhibits a first-order dependence on bromine concentration when bromide ion is present. The observed rate is dependent on bromide ion concentration, decreasing with increasing bromide ion concentration. The detailed kinetics are consistent with a rate-determining formation of the n-complex when bromide ion concentration is low, but with a shift to reversible formation of the n-complex... 

Bromination is catalyzed by Lewis acids, and a study of the kinetics of bromination of benzene and toluene in the presence of aluminum chloride has been reported. Toluene is found to be about 35 times more reactive than benzene under these conditions. The catalyzed reaction thus shows a good deal less substrate selectivity than the uncatalyzed reaction, as would be expected on the basis of the greater reactivity of the aluminum chloride-bromine complex. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials No reaction Stability During Transport Stable when inhibited Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Undergoes uncatalyzed polymerization reaction around 200°C. Light promotes polymerization Inhibitor of Polymerization Hydroquinone 0.10 to 0.25 %. 

The use of a catalyst affects the rate of reaction by enabling the products to form by an alternative route. Each stage has lower activation energy than the uncatalyzed reaction. 

Thus, if Ca and Cb can both be measured as functions of time, a plot of v/ca vs. Cb allows the rate constants to be estimated. (If it is known that B is also consumed in the first-order reaction, mass balance allows cb to be easily expressed in terms of Ca-) The rate v(Ca) is the tangent to the curve Ca = f(t) at concentration Ca-This can be determined graphically, analytically, or with computer processing of the concentration-time data. Mata-Perez and Perez-Benito show an example of this treatment for parallel uncatalyzed and autocatalyzed reactions. 

A catalyst is a substance that makes available a reaction path with a lower free energy of activation than is available in its absence. (The catalyst does not lower AG the uncatalyzed reaction path remains available.)... 

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