Some reactions

Organotin compounds are particularly useful for such purposes as the preparation of vinyl-lithium (from viny Sn+PhLi), of phenylboron chlorides (from 4BCI3 +1 or 2 Ph4Sn), and of fluorocarbon derivatives, e.g. 

These hydrides are occasionally used to prepare hydrides of other elements, particularly those which might prove reactive towards, or difficult to separate from, polar reagents or solvents. Thus trimethylsilane and gallium trichloride give gallium dichloride hydride and trimethyl-chlorosilane  

The by-product McsSiCl is volatile enough to be distilled without difficulty from the reaction mixture. Reactions of various trimethylsilyl derivatives MejSiX, particularly where X = H, NRj, OR, SR or pseudohalide, with covalent chlorides or bromides are frequently convenient methods of preparing such derivatives of other elements, e.g. 

Organotin hydrides add to alkenes and alkynes by both polar and radical mechanisms, frequently concurrently, according to the conditions. Such additions when carried out between dienes and dihydrides R2SnH2 lead to polymers incorporating tin in the polymer backbone 

The products of addition of tin hydrides to groups such as C=0 or C=N have tin attached to the hetero atom, and are themselves susceptible to further reaction with tin hydrides, forming tin-tin bonds, e.g. 

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Some reactions are carried out in the liquid phase in a solvent. If this is the case, then the solvent is separated and recycled in arrangements similar to that shown in Fig. 4.5. 

L,2-propadiene, allene, CH2=C = CH2, CjH4. Colourless gas prepared by the electrolysis of potassium itaeonate, or by the action of zinc and alcohol on 1,3-dibromopropane. It is easily isomerized to propyne (methylacetyl-ene), and is produced as a mixture with this substance from some reactions. 

It is a gas at room temperature with a boiling point of 128 K. It is a strong oxidising agent, some reactions occurring with explosive violence. Water hydrolyses it slowly at room temperature, but the reaction evolving oxygen is rapid in the presence of a base, and explosive with steam ... 

When is a compound to be considered as a starting material, and when as a reagent There is certainly some arbitrariness involved in such a distinction, because both a starting material and a reagent might contribute atoms to the reaction products. Some reaction databases consider a compound to be a starting material when... 

Some reactions require the bonds being broken or made in a reaction to be aligned with other parts ti- or free electrons) of a molecule. These requirements are called stereoelectronic effects. Figure 3-6f shows that the bromide ion has to open a bro-monium ion by an anti attack in order that the new bond is formed concomitantly with the breaking of one bond of the three-membered ring. 

The second most important reaction scheme is the next higher homolog to that shown in Figure 3-13, involving the breaking and making of three bonds. Figure 3-15 shows this reaction scheme and some reaction types that follow it. 

Figure 3-19. Reaction center of the dataset of 120 reactions (reacting bonds are indicated by broken lines), and some reaction instances of this dataset.

Figure 3-21. Some reactions that proceed under stereochemical control.

Consider the fact that some reactions have no barrier. You might also be making incorrect assumptions about the reaction mechanism. Consider these possibilities and start over. 

Some reactions, such as ion-molecule association reactions, have no energy barrier. These reactions cannot be described well by the Arrhenius equation or... 

Some reactions in liquid ammonia can be, or have to be, carried out very... 

Phosphites, such as triisopropyl and triphenyl phosphite, are weaker electron donors than the corresponding phosphines, but they are used in some reactions because of their greater rr-accepting ability. The cyclic phosphite trimethylol-propane phosphite (TMPP) or 4-ethyl-2,6,7-trioxa-l-phosphabicyclo[2.2.2]oc-tane (8), which has a small cone angle and small steric hindrance, shows high catalytic activity in some reactions It is not commercially available, but can be prepared easily[27]. 

Propargylic (or 2-alkynyl) compounds are derivatives of alkynes. However, Pd-catalyzed reactions of propargylic derivatives, particularly esters and halides, are very different mechanistically from those of simple alkynes, except in a few cases. Therefore, the reactions of propargylic esters and halides are treated in this section separately from those of other alkynes. However, some reactions of propargylic alcohols, which behave similarly to simple alkynes, are treated in Section 6. 

This genera] scheme could be used to explain hydrogen exchange in the 5-position, providing a new alternative for the reaction (466). This leads us also to ask whether some reactions described as typically electrophilic cannot also be rationalized by a preliminary hydration of the C2=N bond. The nitration reaction of 2-dialkylaminothiazoles could occur, for example, on the enamine-like intermediate (229) (Scheme 141). This scheme would explain why alkyl groups on the exocyclic nitrogen may drastically change the reaction pathway (see Section rV.l.A). Kinetic studies and careful analysis of by-products would enable a check of this hypothesis. 

TABLE 1-61. PHYSICOCHEMICAL DATA FOR SOME REACTIONS OF THIAZOLE AND PYRIDINE... 

With an atomic number of 28 nickel has the electron conflguration [Ar]4s 3c (ten valence electrons) The 18 electron rule is satisfied by adding to these ten the eight elec Irons from four carbon monoxide ligands A useful point to remember about the 18 electron rule when we discuss some reactions of transition metal complexes is that if the number is less than 18 the metal is considered coordinatively unsaturated and can accept additional ligands... 

As we saw m Chapter 20 thioesters are more reactive than ordinary esters toward nucleophilic acyl substitution They also contain a greater proportion of enol at equilib rmm Both properties are apparent m the properties of acetyl coenzyme A In some reactions it is the carbonyl group of acetyl coenzyme A that reacts m others it is the a carbon atom... 

Equation (5.47) is of considerable practical utility in view of the commercial importance of three-dimensional polymer networks. Some reactions of the sort we have considered are carried out on a very large scale Imagine the consequences of having a polymer preparation solidify in a large and expensive reaction vessel because the polymerization reaction went a little too far Considering this kind of application, we might actually be relieved to know that Eq. (5.47) errs in the direction of underestimating the extent of reaction at... 

Termination. By some reaction, generally involving two polymers containing active centers, the growth center is deactivated, resulting in dead polymer ... 

To deal with the case of termination by combination, it is convenient to write some reactions by which an n-mer might be formed. Table 6.5 lists several specific chemical reactions and the corresponding rate expressions as well as the general form for the combination of an (n - m)-mer and an m-mer. On the assumption that all kj values are the same, we can write the total rate of change of [M -] ... 

The monomer recovery process may vary ia commercial practice. A less desirable sequence is to filter or centrifuge the slurry to recover the polymer and then pass the filtrate through a conventional distillation tower to recover the unreacted monomer. The need for monomer recovery may be minimized by usiag two-stage filtration with filtrate recycle after the first stage. Nonvolatile monomers, such as sodium styrene sulfonate, can be partially recovered ia this manner. This often makes process control more difficult because some reaction by-products can affect the rate of polymerization and often the composition may vary. When recycle is used it is often done to control discharges iato the environment rather than to reduce monomer losses. 

Hydrogen atoms ate thought to play a principal role in the mechanistic steps of many reactions, including hydrocarbon thermolysis (119). Some reactions of atomic hydrogen with olefins and paraffins ate the following (120—122) ... 

Other perturbations have been demonstrated. The pressure,, jump, similar to the T-jump in principle, is attractive for organic reactions where Joule heating may be impractical both because of the solvent being used and because concentrations might have to be measured by conductivity. Large (10 —10 kPa) pressures are needed to perturb equiUbrium constants. One approach involves pressurizing a Hquid solution until a membrane mptures and drops the pressure to ambient. Electric field perturbations affect some reactions and have also been used (2), but infrequentiy. 

The fate of the ion pair iatermediate depends on the stmcture of the amine and the reaction conditions. Certain tertiary amines, eg, dimethylaruline (DMA), react with specific diacyl peroxides such as diben2oyl peroxide (BPO) to generate free radicals at ca 20°C. Some reactions, eg, DMA—BPO, are explosive when neat reactants are mixed. Primary and secondary amines do not yield free radicals. 

Sulfur monochloride can act as a chlorinating agent in some reactions. For example, 0,0-diaLkyl phosphorodithioic acids [756-80-9] are converted to 0,0-diaLkylphosphorochloridothioate ... 

Other components in the feed gas may react with and degrade the amine solution. Many of these latter reactions can be reversed by appHcation of heat, as in a reclaimer. Some reaction products cannot be reclaimed, however. Thus to keep the concentration of these materials at an acceptable level, the solution must be purged and fresh amine added periodically. The principal sources of degradation products are the reactions with carbon dioxide, carbonyl sulfide, and carbon disulfide. In refineries, sour gas streams from vacuum distillation or from fluidized catalytic cracking (FCC) units can contain oxygen or sulfur dioxide which form heat-stable salts with the amine solution (see Fluidization Petroleum). 

Coenzymes such as adenosine diphosphate (ADP), adenosine SGtriphosphate (ATP), nicotinamide adenine dinucleotide (NAD), and nicotinamide adenine dinucleotide, reduced (NADH), are involved in some reactions (4). 

Carbon disulfide is essentially unreactive with water at room temperature, but above about 150°C in the vapor phase some reaction occurs forming carbonyl sulfide (carbon oxysulfide) [463-58-1] and hydrogen sulfide [7783-06-4]. Carbonyl sulfide is an intermediate in the hydrolysis reaction ... 

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