Step reaction

Reaction databases additionally contain information on chemical reactions, giving the reaction participants and reaction conditions of both single- and multi-step reactions. 

CASREACT The CASREACT Eile (The Chemical Absiracts Reaction Search Service) is a chemical reaction database with reaction inlormatioii derived from journal documients from 1974 to the present and from patent documeiiis from 1982 to date. Thie document-based file conlains both 3 million single-step and 3.0 million multi-step reactions (Pcbiniaiy, 2003). 

CASREACT (Chemical Abstracts Reaction Search Service) is a reaction database started in 1985 with more than 6.7 million reactions (3 million single-step and 3.7 million multi-step reactions) (March, 2003) derived from 400 000 documents (journals, patents, etc.). The records contain the following information ... 

Chemln- formRX FIZ CHEMIE GmbH, Germany chemical reactions reaction, biblio., struc- ture 1.0 mio substances, 113859 records, 689029 single-step reactions, 377491 multi-step reactions 250 journals FIZ commercial online quarterly www.mdli.com... 

Short of determining an entire reaction coordinate, there are a number of structures and their energies that are important to defining a reaction mechanism. For the simplest single-step reaction, there would be five such structures ... 

All the techniques discussed in this chapter are applicable to single-step reaction mechanism. For multiple-step mechanisms, it is necessary to work through this process for each step in the reaction. 

The expression template reaction indicates mostly a reaction in which a complexed me) ion holds reactive groups in the correct orientation to allow selective multi-step reactions. T1 template effect of the metal is twofold (i) polymerization reactions are suppressed, since th local concentration of reactants around the metal ion is very high (ii) multi-step reactions are possible, since the metal holds the reactants together. In the following one-step synthesis eleven molecules (three ethylenediamine — en , six formaldehyde, and two ammonia molecules) react with each other to form one single compound in a reported yield of 95%. It is ob vious that such a reaction is dictated by the organizing power of the metal ion (I.I. Creasei 1977),... 

An efficient carboannulation proceeds by the reaction of vinylcyclopropane (135) or vinylcyclobutane with aryl halides. The multi-step reaction is explained by insertion of alkene, ring opening, diene formation, formation of the TT-allylpalladium 136 by the readdition of H—Pd—I, and its intramolecular reaction with the nucleophile to give the cyclized product 137[I08]. 

Allenes also react with aryl and alkenyl halides, or triflates, and the 7r-allyl-palladium intermediates are trapped with carbon nucleophiles. The formation of 283 with malonate is an example[186]. The steroid skeleton 287 has been constructed by two-step reactions of allene with the enol trillate 284, followed by trapping with 2-methyl-l,3-cyclopentanedione (285) to give 286[187]. The inter- and intramolecular reactions of dimethyl 2,3-butenylmalonate (288) with iodobenzene afford the 3-cyclopentenedicarboxylate 289 as a main product) 188]. 

The reaction of l,4-bis(trimethylsilyl)-l,3-butadiyne (174) with disilanes, followed by treatment with methylmagnesium bromide, produces i,l,4,4-tetra(-trimethylsilyl)-l,2,3-butatriene (175) as a major product[96]. The reaction of octaethyltetrasilylane (176) with DMAD proceeds by ring insertion to give the six-membered ring compounds 177 and 178[97], The l-sila-4-stannacyclohexa-2,5-diene 181 was obtained by a two-step reaction of two alkynes with the disilanylstannane 179 via the l-sila-2-stannacyclobutane 180[98],... 

The Diels-Alder cycloaddition is one example of a pencyclic reaction, which is a one step reaction that proceeds through a cyclic transition state Bond formation occurs at both ends of the diene system and the Diels-Alder transition state involves a cyclic array of six carbons and six tt electrons The diene must adopt the s cis conformation m the transition state... 

These full color transparencies of illustrations from the text include reproductions of spectra orbital diagrams key tables computer generated molecular models and step by step reaction mechanisms... 

The steps (reactions) by which normal ions fragment are important pieces of information that are lacking in a normal mass spectrum. These fragmentation reactions can be deduced by observations on metastable ions to obtain important data on molecular structure, the complexities of mixtures, and the presence of trace impurities. 

Diester/Ether Diol of Tetrabromophthalic Anhydride. This material [77098-07-8] is prepared from TBPA in a two-step reaction. First TBPA reacts with diethylene glycol to produce an acid ester. The acid ester and propylene oxide then react to give a diester. The final product, a triol having two primary and one secondary hydroxyl group, is used exclusively as a flame retardant for rigid polyurethane foam (53,54). 

Step Reaction AH25 AH325 AGjs AG325... 

Alkyltin Intermedia.tes, For the most part, organotin stabilizers are produced commercially from the respective alkyl tin chloride intermediates. There are several processes used to manufacture these intermediates. The desired ratio of monoalkyl tin trichloride to dialkyltin dichloride is generally achieved by a redistribution reaction involving a second-step reaction with stannic chloride (tin(IV) chloride). By far, the most easily synthesized alkyltin chloride intermediates are the methyltin chlorides because methyl chloride reacts directiy with tin metal in the presence of a catalyst to form dimethyl tin dichloride cleanly in high yields (21). Coaddition of stannic chloride to the reactor leads directiy to almost any desired mixture of mono- and dimethyl tin chloride intermediates ... 

Hydrazine as Nucleophile. Reaction of hydrazine and carbon dioxide or carbon disulfide gives, respectively, hydrazinecarboxyhc acid [471-31-8], NH2NHCOOH, and hydrazinecarbodithioic acid [471-32-9], NH2NHCSSH, in the form of the hydrazinium salts. These compounds are useful starting materials for further synthesis. For example, if carbon disulfide reacts with hydrazine in basic medium with an alkyl haUde, an alkyl dithiocarbazate ester is obtained in a one-step reaction ... 

Reaction measurement studies also show that the chemistry is often not a simple one-step reaction process (37). There are usually several key intermediates, and the reaction is better thought of as a network of series and parallel steps. Kinetic parameters for each of the steps can be derived from the data. The appearance of these intermediates can add to the time required to achieve a desired level of total breakdown to the simple, thermodynamically stable products, eg, CO2, H2O, or N2. 

The reaction between esterase and phosphorus inhibitor (109) is bimolecular, of the weU-known S 2 type, and represents the attack of a nucleophilic serine hydroxyl with a neighboring imida2ole ring of a histidine residue at the active site, on the electrophilic phosphorus atom, and mimics the normal three-step reaction that takes place between enzyme and substrate (reaction ). 

These reactions occur as low as 200°C. The exact temperature depends on the specific hydrocarbon that is nitrated, and reaction 8 is presumably the rate-controlling step. Reaction 9 is of minor importance in nitration with nitric acid, as indicated by kinetic information (32). 

Nitio olefins can be made in some cases by dehydration of the aromatic nitrohydroxy derivatives. Subsequent reduction yields the aromatic amine. The following three-step reaction yielding 2-amino-l-phenylbutane illustrates the synthesis of this class of valuable pharmaceutical compounds. 

The lactamate then initiates a two-step reaction which adds a molecule of the lactam to the polymer chain (50—52) ... 

Uses. AEyl chloride is industrially the most important aHyl compound among all the aHyl compounds (see Chlorocarbons and CHLOROHYDROCARBONS, ALLYL CHLORIDE). It is used mosdy as an intermediate compound for producing epichlorohydrin, which is consumed as a raw material for epoxy resins (qv). World production of AC is approximately 700,000 tons per year, the same as that of epichlorohydrin. Epichlorohydrin is produced in two steps reaction of AC with an aqueous chlorine solution to yield dichloropropanol (mixture of 1,3-dichloropropanol and 2,3-dichloropropanol) by chlorohydrination, and then saponification with a calcium hydroxide slurry to yield epichlorohydrin. 

Indirect Hydration. Indirect hydration is based on a two-step reaction of propylene and sulfuric acid. In the first step, mixed sulfate esters, primarily isopropyl hydrogen sulfate, but also diisopropyl sulfate, form. These are then hydrolyzed, forming the alcohol and sulfuric acid. 

Alternatively, radiohalogen-labeled compounds may be prepared by way of isotopic labeling from the unlabeled bromo or iodo derivatives by various two-step reaction sequences. Examples include the use of trialkylsilyl synthons as described in References 10—13, and the use of boronic acid synthons as described in References 14 and 15. 

Saponification can proceed direcdy as a one-step reaction as shown above, or it can be achieved indirectly by a two-step reaction where the intermediate step generates fatty acids through simple hydrolysis of the fats and oils and the finishing step forms soap through the neutralization of the fatty acid with caustic soda. There are practical considerations which must be addressed when performing this reaction on a commercial scale. 

Commercial-scale processes have been developed for the production of hydrogen sulfide from heavy fuel oils and sulfur as well as from methane, water vapor, and sulfur. The latter process can be carried out in two steps reaction of methane with sulfur to form carbon disulfide and hydrogen sulfide followed by hydrolysis of carbon disulfide (116). 

Salts of alkyl hydrogen sulfates that are free of sulfuhc acid can be prepared from crude hydrogen sulfates containing ROSO H and sulfuhc acid in a two-step reaction. Eirst, the crude product reacts in aqueous solution with the hydroxide or carbonate of a metal whose sulfate is insoluble in water. After filtration of the insoluble metal sulfate, the necessary amount of a water-soluble metal sulfate is added to the filtrate, which precipitates the insoluble metal sulfate, leaving the desired salt of the alkyl hydrogen sulfate in solution. 

The Claus process converts hydrogen sulfide to elemental sulfur via a two-step reaction. The first step involves controUed combustion of the feed gas to convert approximately one-third of the hydrogen sulfide to sulfur dioxide (eq. 9) and noncatalytic reaction of unbumed hydrogen sulfide with sulfur dioxide (eq. 10). In the second step, the Claus reaction, the hydrogen sulfide and sulfur dioxide react over a catalyst to produce sulfur and water (eq. 10). The principal reactions are as foUow ... 

Another process involves a one-step reaction of isobutylene with formaldehyde and acetone under high temperature and pressure (eq. 2) (20). a-MethyUieptenone (2) (6-methyIhept-6-en-2-one [10408-15-8]) is the product, but it is easily catalyticaHy isomerized to P-methyUieptenone (21,22). Unconverted isobutylene and acetone can be recycled to the process, thus making it commercially viable (23,24). Variations of this process have also been described in the Hterature (25—28). 

The reaction of magnesium noncarbonate hardness with lime and with soda ash is a two step reaction since reaction 6 produces a reasonably soluble calcium salt that must react with in order to cause calcium precipitation ... 

Epichlorohydrin and Bisphenol A-Derived Resins. Liquid epoxy resins maybe synthesized by a two-step reaction of an excess of epichl orohydrin to bisphenol A in the presence of an alkaline catalyst. The reaction consists initially in the formation of the dichi orohydrin of bisphenol A and further reaction by dehydrohalogenation of the intermediate product with a stoichiometric quantity of alkaH. 

Oxidation of the hydrazone of 2-hydrazinopyrazole (226) with Pb(OAc)4 in CH2CI2 is a two-step reaction. The azine (227) was formed as an intermediate and this underwent ring closure to the 3H-pyrazolo[5,l-c][l,2,4]triazole (228) (79TL1567). A similar reaction applied to the benzal derivative of 2-hydrazinobenzothiazole (229) gave 3-phenyl-[l,2,4]triazolo[3,4-6]benzothiazole (230) together with a by-product (231) (72JCS(P1)1519). 

The mechanism of the reaction is unknown. The stereospecificity observed with (E)- and (Z)-l-methyl-2-phenylethylene points to a one-step reaction. The very low Hammett constant, -0.43, determined with phenylethylenes substituted in the benzene ring, excludes polar intermediates. Yields of only a few percent are obtained in the reaction of aliphatic alkenes with (52). In the reaction of cyclohexene with (52), further amination of the aziridine to aminoaziridine (99) is observed. Instead of diphenylazirine, diphenylacetonitrile (100) is formed from diphenylacetylene by NH uptake from (52) and phenyl migration. 

As seen in Figure 1, the example plant has three major processing steps Reaction, Compression, and Fractionation. There are four available feeds to the plant (FI, F2, F3, and F4). The desire is to use all of the available Feed 1. The model is inhibited from leaving any Feed 1 capacity unused by a large negative SPRICE as seen in the matrix. Feeds 2, 3, and 4 are given a choice of how much of the available material to use. However, Feeds 3 and 4 must be utilized in a 2 1 ratio as dictated by row MIX in the matrix. Feeds 1, 2, and 3 have a choice of 2 conversion levels, while Feed 4 has a choice of 3. 

Reaction coordinate for a two-step reaction Fig. 4.1. Potential energy diagrams for single-step and two-step reactions. 

Identification of the intermediates in a multistep reaction is a major objective of studies of reaction mechanisms. When the nature of each intermediate is fairly well understood, a great deal is known about the reaction mechanism. The amount of an intermediate present in a reacting system at any instant of time will depend on the rates of the steps by which it is formed and the rate of its subsequent reaction. A qualitative indication of the relationship between intermediate concentration and the kinetics of the reaction can be gained by considering a simple two-step reaction mechanism ... 

Specific acid catalysis is observed when a reaction proceeds through a protonated intermediate that is in equilibrium with its conjugate base. Because the position of this equilibrium is a function of the concentration of solvated protons, only a single acid-dependent term appears in the kinetic expression. For example, in a two-step reaction involving rate-determining reaction of one reagent with the conjugate acid of a second, the kinetic expression will be as follows ... 

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