Two step reaction

In the Wittig reaction, the sacrificial reagents are triphenylphosphine and potassium t-butoxide. The formation of the triphenylphosphonium bromide is 100% atom economical. 

The overall transformation is substitution of a hydroxyl group for a hydrogen atom. The sacrificial reagents are sodium hydride, carbon disulfide, and iodomethane in the first step to prepare the xan-thate ester. The source of the hydrogen atom in the product is tri-n-butyltin hydride. 

In this transformation, one of the tri-n-butyltin hydride molecules is acting as a sacrificial reagent in donating a hydrogen atom to the departing phenoxyl radical. 

Sodium periodate acts as a sacrificial oxidant in the first step and in the second step trimethyl-phosphite electronically improves the leaving group ability of the departing group. 

In the Stork enamine synthesis, the pyrrolidine acts as a sacrificial reagent to electronically facilitate the alpha-carbon alkylation. The formation of the enamine is 100% atom economical. 

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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],... 

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). 

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 ... 

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). 

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 ... 

The Diels-Alder adduct isolated from the reaction with 2,3-dimethylbuta-l, 3-diene at elevated temperatures [200] is in fact the product of a two step reaction a 1,3-cycloaddition followed by a 3,2-sigmatropic rearrangement [199] (equaPon 49)... 

When Jencks reacted hydroxylamine with p-nitrophenyl acetate, p-nitrophenolate ion was released at a rate faster than that at which acetohydroxamic acid was formed. This burst effect is evidence for a two-step reaction. In this case the intermediate is O-acetylhydroxylamine, which subsequently reacts with hydroxylamine to form the hydroxamic acid. 

We will demonstrate the treatment with the two-step reaction system shown in Scheme III. 

The reaction is known to be complex, proceeding through a tetrahedral intermediate called a carbinolamine. Generalizing to the reactions of amines with carbonyls, the two-step reaction sequence is... 

A bell-shaped pH-rate profile can also be produced in a two-step reaction involving a single ionizable group if the rate-determining step changes when the pH is altered. An example, the oximation of acetone, is shown in Fig. 5-12. 

Much evidence suggests that electrophilic aromatic substitution takes place in a two-step reaction with the formation of a benzenonium ion intermediate. 

Fig. 20.19 (a) Analogy showing how ihe rate at which a car can travel from /I to C is determined by the narrow controlled road BC (the r.d.s.). (b) Standard free energy of activation against distance for a two-step reaction since the activation energy required to produce the activated state B is and that to produce A is only AG°, the former is the r.d.s.,... 

Figure 10 shows typical examples of burst kinetics observed for the reactions of 29-Zn2+ and 38c-Zn2+ ion complexes under the conditions of excess substrate over ligand. Such burst kinetics can be accounted for a two-step reaction involving an acylated intermediate as in Scheme 4, and the rate constants, ka and kd, can be obtained based on Eqs. 8-11 38,39), where A is the slope of the steady-state line and B is the intercept obtained by extrapolating the steady-state line to time = 0. The ka should be the same with the kc in Table 5. 

Problem 5.13 Sketch an energy diagram for a two-step reaction with an endergonic first step and an exergonic second step. Label the parts of the diagram corresponding to reactant, product, and intermediate. 

Weak acid-strong base. When a strong base such as NaOH is added to a solution of a weak acid, HB, a two-step reaction occurs. The first step is the ionization of the HB molecule to H+ and B ions the second is the neutralization of the H+ ions produced in the first step by the OH- ions of the NaOH solution. 

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