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Conditions of reaction

The choice of catalyst and the conditions of reaction can be critical in the performance of the process because of the resulting influence on selectivity. [Pg.48]

In contrast to its effect upon the general mechanism of nitration by the nitronium ion, nitrous acid catalyses the nitration of phenol, aniline, and related compounds. Some of these compounds are oxidised under the conditions of reaction and the consequent formation of more nitrous acids leads to autocatalysis. [Pg.57]

The catalysed nitration of phenol gives chiefly 0- and />-nitrophenol, (< 0-1% of w-nitrophenol is formed), with small quantities of dinitrated compound and condensed products. The ortho para ratio is very dependent on the conditions of reaction and the concentration of nitrous acid. Thus, in aqueous solution containing sulphuric acid (i 75 mol 1 ) and nitric acid (0-5 mol 1 ), the proportion of oriha-substitution decreases from 73 % to 9 % as the concentration of nitrous acid is varied from o-i mol l i. However, when acetic acid is the solvent the proportion of ortAo-substitution changes from 44 % to 74 % on the introduction of dinitrogen tetroxide (4-5 mol 1 ). [Pg.57]

The orientation of substitution into phenol was strongly dependent on the conditions of reaction (see below). [Pg.91]

Pectin lyase (PNL) activity was measured spectrophotometrically by the increase in absorbance at 235 nm of the 4,5-unsaturated reaction products. Reaction mixtures containing 0.25 ml of culture filtrate, 0.25 ml of distilled water and 2.0 ml of 0.24% pectin from apple (Fluka) in 0.05M tris-HCl buffer (pH 8.0) with ImM CaCl2, were incubated at 37 C for 10 minutes. One unit of enzyme is defined as the amount of enzyme which forms Ipmol of 4,5-unsaturated product per minute under the conditions of the assay. The molar extinction coefficients of the unsaturated products is 5550 M cm [25]. Also viscosity measurements were made using Cannon-Fenske viscometers or Ostwald micro-viscosimeter, at 37°C. Reaction mixtures consisted of enzyme solution and 0.75% pectin in 0.05 M tris-HCl buffer (pH 8.0) with 0.5 mM CaCl2. One unit is defined as the amount of enzyme required to change the inverse specific viscosity by 0.001 min under the conditions of reaction. Specific viscosity (n p) is (t/to)-l, where t is the flow time (sec) of the reaction mixture and t is the flow time of the buffer. The inverse pecific viscosity (n p ) is proportional to the incubation time and the amount of enzyme used [26]. Units of enzyme activity were determined for 10 min of reaction. [Pg.749]

A mechanism proposed 87) for the alkaline hydrolysis of tetraethyl pyrophosphate, which is markedly accelerated by HPO e ions, has been substantiated by isotopic labeling 88). The nucleophilic attack by HPOJp on the symmetrical pyrophosphate 131 is considered to lead initially to the unsymmetrical P P1-diethyl pyrophosphate dianion 132 which decomposes spontaneously under the conditions of reaction to give the diethyl phosphate anion and POf 102. The latter reacts with water to form inorganic phosphate and with alcohols suclj as methanol and ethylene glycol to produce alkyl phosphates. [Pg.102]

Three approaches have been tested, as already described above for inorganic supports. The first attempts concern the direct reaction of transition metal carbonyls with unmodified organic polymers like poly-2-vinyl-pyridine.61 62 However, this kind of anchoring is restricted to only a few complexes. Various polymers have been functionalized with donor groups 63-72 ligand displacement reactions using these afforded the corresponding immobilized complexes. Finally, tests with modified complexes and unmodified polymers are scarce because of the low stability of these complexes under the conditions of reactions. [Pg.451]

At atmospheric pressure the Diels-Alder adducts of 1,4-benzoquinones are often not stable under the conditions of reaction and undergo an isomerization leading to the corresponding hydroquinones (Scheme 4). Due to the acceleration at high pressure the temperature of reaction can be lowered so that the secondary isomerization does not proceed and the primary Diels-Alder adduct can be isolated in good yields. The diastereoselectivity at high pressure induced by a chiral auxiliary, however, is with a diastereomeric excess of d.e. = 36%, only moderate. [Pg.564]

Compound R Conditions of reaction Yields (%) (related to the turnover of the azulene) 28 29 Reference... [Pg.573]

The same report23 describes the generation of C-P bonds using red phosphorus under acidic conditions. The intermediate reactive species under these conditions is hypophosphorous acid.25 Using aqueous HI (57%) with dioxane, a 25% (purified) yield of benzylphos-phonic acid could be isolated from the reaction involving benzalde-hyde (Figure 2.8). Under the conditions of reaction, aqueous HI with... [Pg.29]

In this section, we compare the effect of order of reaction n on cAlcAo = 1 - fA for various conditions of reaction, using the model reaction... [Pg.75]

Cleavage of cyclobutane rings can occur easily. As indicated in the introductory section, the strain of the four-membered ring, the substituents on the ring, the nature of the reagents as well as the conditions of reaction are all responsible for the ease of cleavage of cyclobutanes 3). The substituents on the ring constitute one of the... [Pg.115]

N)4 = (en)2 system the most stable under the basic conditions of reaction with amines. [Pg.354]

When heated with chlorine, bromine or iodine vapors arsenic forms the corresponding trihalides however, with fluorine, arsenic pentafluoride, AsFs is produced. With sulfur it forms mixtures of sulfides, AS2S3, AS2S2 and AS2S5 in vitreous forms and varying proportions depending on the conditions of reactions. [Pg.63]

Synthetic operations involving ozonolysis lead to formation of aldehydes, ketones or carboxylic acids, as shown in Scheme 16, or to various peroxide compounds, as depicted in Scheme 7 (Section V.B.5), depending on the nature of the R to R substituents and the prevalent conditions of reaction no effort is usually made to isolate either type of ozonide, but only the final products. This notwithstanding, intermediates 276 and 278 are prone to qualitative, quantitative and structural analysis. The appearance of a red-brown discoloration during ozonization of an olefin below — 180°C was postulated as due to formation of an olefin-ozone complex, in analogy to the jr-complexes formed with aromatic compounds however, this contention was contested (see also Section V1I.C.2). [Pg.717]

Figure 2 is a good representation of almost all the 112 runs made with 1-octanol. There was curvature on only a few runs, undoubtedly caused by experimental error since they could not be reproduced. This feature was checked carefully after mathematical analysis indicated reasons to expect curvature. The conditions of reactions and values of k0 have been tabulated (Tables I and II). Since k0 depends upon 1-octanol and TMAE, it is called the pseudo-first-order rate constant. [Pg.240]

The dehydration reactions initiated by eliminating a hydroxyl group from an enediol are discussed in the present article. The products (usually dicarbonyl compounds) of these eliminations are normally transient intermediates, and undergo further reaction. The final products formed are determined by the carbohydrate reacting, the conditions of reaction, and the character of the medium. Except for a Section on analytical methods (see p. 218), the subject matter is restricted to aqueous acids and bases. The presence of compounds other than the carbohydrate under study has only been considered where it has helped to elucidate the mechanism involved. The approach here is critical and interpretative, with emphasis on mechanism. An attempt has been made to demonstrate how similar reactions can logically lead to the various products from different carbohydrates a number of speculative mechanisms are proposed. It is hoped that this treatment will emphasize the broad functions of these reactions, an importance that is not fully recognized. No claim is made for a complete coverage of the literature instead, discussion of results in the articles that best illustrate the principles involved has been included. [Pg.162]

In the majority of dehydration reactions, heterocyclic compounds are formed, rather than carbocyclic compounds. Many possibilities for formation of carbocyclic compounds exist, but these are important only if (a) the heterocyclic or acyclic tautomers cannot undergo further elimination reactions, or (b) the conditions of reaction greatly favor the formation of an acyclic tautomer capable of affording only the carbocyclic compound. Both five- and six-membered carbocyclic compounds have been isolated, with reductic acid being the compound most frequently reported. Ring closure occurs by an inter-molecular, aldol reaction that involves the carbonyl group and an enolic structure. Many examples of these aldol reactions that lead to formation of carbocyclic rings have been studied.47 As both elimination and addition of a proton are involved, the reaction occurs in both acidic and basic solutions. As examples of the facility of this reaction, pyruvic acid condenses spontaneously to a dibasic acid at room temperature in dilute solution, and such 8-diketones as 29 readily cyclize to form cyclohexenones, presumably by way of 30, either in acid or base. [Pg.174]

With reaction (56) a competing process to form olefins occurs, in which the chemical bond R—O is broken, as outlined in scheme (11). The formation of olefins, as mentioned above, depends primarily on the character of the alkyl group and also on the conditions of reaction. [Pg.17]

It is possible to oxidize all the CH2OH groups to carboxylic groups, if the conditions of reaction are sufficiently severe, when the content of COOH may reach 25%. The product obtained in this way is a polyanhydroglucuronic add, known as carboxycellulose or celluronic acid. When half the CH2OH groups present in the cellulose are oxidized, a product with a 13% COOH content is obtained, soluble in dilute solutions of caustic soda, ammonia and sodium carbonate. Celluronic acid can form esters with nitric acid. The properties of these esters will be discussed later. [Pg.349]

The ionic character of catalysts prepared strongly depended on the experimental conditions used in surface reactions (1) and (2) and on the modes of the removal of the unreacted butyl lithium. As far as in reaction (1] an excess butyl lithium was used it was very important to remove unreacted butyl lithium by washing or extracting with n-hexane. In this way undesired reduction of PdCl under condition of reaction 12) could be prevented. [Pg.316]

The intermediate of complete oxidation (in our case, supposedly, acetaldehyde) would have been a product of partial oxidation if it had not undergone further oxidation. Thus, the difference between partial and complete oxidation is due not to the substantial difference in the nature of the primary act of oxygen addition, but to the difference in the capability of primary products for further oxidation under the conditions of reaction. It is evident that no hydrocarbons can be oxidized to C02 and HzO directly without intermediate steps. [Pg.234]


See other pages where Conditions of reaction is mentioned: [Pg.115]    [Pg.2313]    [Pg.1046]    [Pg.57]    [Pg.592]    [Pg.308]    [Pg.259]    [Pg.42]    [Pg.59]    [Pg.18]    [Pg.1151]    [Pg.147]    [Pg.113]    [Pg.95]    [Pg.128]    [Pg.261]    [Pg.300]    [Pg.171]    [Pg.750]    [Pg.515]    [Pg.303]    [Pg.604]    [Pg.291]    [Pg.417]    [Pg.289]    [Pg.112]   
See also in sourсe #XX -- [ Pg.169 , Pg.188 ]




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