Atom-water reactions

SI, Ge, Sn and Pb metal atoms initially reacted with water on cocondensation to form the metal atom-water molecule adduct as has been generally observed for metal atom-water reactions ( ). The shift in the water bending mode frequency on adduct formation decreases with increasing atomic number as illustrated in Table I. Using the results obtained from theoretical studies ( 3, 5), it is believed that the water bending mode shift might serve as a relative measure of the extent of interaction between the water molecule and the metal atom, for metals within a particular group. 

Matrix Isolation IR Studies of Metal Atom-Water Reactions... 

Hauge, R.H., Kauffman, J.W., Fredln, L., and Margrave, J.L., "Matrix Isolation Infrared Studies of Metal Atom-Water Reactions", 181st National ACS Meeting, Atlanta, 1981, and references therein. 

The reaction of a tertiary alcohol with HX takes place by an Sf l mechanism when acid protonates the hydroxyl oxygen atom, water is expelled to generate... 

Potassium permanganate does not oxidize the sulfur atom in dibenzo[ft,/]thiepin (1), rather attacking the C —C double bond, which is very similar in reactivity to that in (Z)-stilbene, to provide various oxidation products, formed from ring opening or ring contraction, depending upon the acetone or water reaction medium.20... 

The above examples should suffice to show how ion-molecule, dissociative recombination, and neutral-neutral reactions combine to form a variety of small species. Once neutral species are produced, they are destroyed by ion-molecule and neutral-neutral reactions. Stable species such as water and ammonia are depleted only via ion-molecule reactions. The dominant reactive ions in model calculations are the species HCO+, H3, H30+, He+, C+, and H+ many of then-reactions have been studied in the laboratory.41 Radicals such as OH can also be depleted via neutral-neutral reactions with atoms (see reactions 13, 15, 16) and, according to recent measurements, by selected reactions with stable species as well.18 Another loss mechanism in interstellar clouds is adsorption onto dust particles. Still another is photodestruction caused by ultraviolet photons produced when secondary electrons from cosmic ray-induced ionization excite H2, which subsequently fluoresces.42... 

The question of the constitution of hydrocyanic acid has already been considered (p. 139). Here it need only be remarked that the isonitriles are converted by hydrolysis into primary amines and formic acid no carbon monoxide is produced, although from the formula this might be expected. The reason for this is to be sought in the fact that the first stage in the reaction consists in the addition of water to the two free valencies of the carbon atom. The reaction must therefore be formulated thus ... 

If the same criteria are applied to the analysis of the H2-air results in Figs. 4.1H12, some initially surprising conclusions are reached. At best, it can be concluded that the flame thickness is approximately 0.5 mm. At most, if any preheat zone exists, it is only 0.1 mm. In essence, then, because of the formation of large H atom concentrations, there is extensive upstream H atom diffusion that causes the sharp rise in H02. This H02 reacts with the H2 fuel to form H atoms and H202, which immediately dissociates into OH radicals. Furthermore, even at these low temperatures, the OH reacts with the H2 to form water and an abundance of H atoms. This reaction is about 50kJ exothermic. What appears as a rise in the 02 is indeed only a rise in mole fraction and not in mass. 

The associative mechanism resembles a conventional radical (hydrogen atom) substitution reaction where the 7T-bonded benzene molecule is attacked by a hydrogen atom formed by the dissociative adsorption of water or hydrogen gas. The activation energy in this process is essentially due to the partial localization of one tt electron in the transition complex 21, 31). The transition state differs, however, from conventional substitution reactions by being 77-bonded to the catalyst surface ... 

When halogenation of alkenes is carried out in aqueous solvent, a vicinal halohydrm is obtained. The reaction is regioselective, and follows the Markovnikov rule. The halide adds to the less substituted carbon atom via a bridged halonium ion intermediate, and the hydroxyl adds to the more substituted carbon atom. The reaction mechanism is similar to the halogenation of alkenes, except that instead of the halide nucleophile, the water attacks as a nucleophile. 

For the production of hydrogen on an industrial scale, CO oxidation is considered to be a participant in the water gas shift process, acting as an intermediate to react with adsorbed oxygen atoms [259]. Reactions in the water gas shift process are shown in Scheme 8.32. 

The SO 3 is readily converted to sulfuric acid in the presence of water vapor [6,7], An experiment employing 1803 provided evidence for acyclic adduct formation as originally proposed by Martinez et al. [127]. The ratio /c55//c54 was calculated to be (4.9 2.0) x 10 15 cm3 molecule. At any rate, the reaction of CH200 with S02 does not appear to be a simple bimolecular O-atom transfer reaction. 

Alcohols, water and even acetic acid are useful solvents for some radical reactions. However, they cannot be employed with organometallics that are basic. Conversely, halocarbon solvents are popular for many types of ionic reactions but they are not generally useful for radical reactions. Chloroform and carbon tetrachloride (and to a lesser extent, dichloromethane) can interfere by donating either hydrogen or halogen atoms to intermediate radicals and they are used only in atom transfer reactions where the solvent is also a reagent. 

This atom economic reaction, in which only water occurs as a by-product, is very attractive for forming various amines. Hydroaminomethylation includes three different mechanisms due to the three reactions involved. The mechanism of hydroaminomethylation is shown in Scheme 17. The first catalytic cycle is similar to hydroformylation, which is described above. 

As was demonstrated by addition of epoxide under reaction conditions, the epoxide is not the precursor of the cis diol. The cis dihydroxylation is probably a two-step reaction, first with addition of a H202-derived oxygen atom to the double bond, followed by insertion of a Mn-coordinated oxygen atom (water or OH-). It is clear that the availability of free coordination sites in cis positions on the Mn (4b) is important for understanding the formation of cis dihydroxylated products. This is the first example of a cis dihydroxylation that is catalytic and uses Mn the route is therefore an alternative to stoichiometric permanganate reactions or to catalytic methods with more... 

Remarkably, most reactions do not take place at the unsaturated part of the molecule, presumably because of the steric shielding of the Si=Si double bond by the bulky t-Bu3Si groups, but rather proceed through substitution of the iodine atoms. The reaction of 150 with water affords the product 160, whereas that with methanol furnishes compound 158 with retention of the tetrasilacyclobutene skeleton. On treatment of 150 with NaR the tetrahedro-tetrasilane 149 — the starting material for the preparation of 150 — is reformed. Finally, the reaction with BI3 proceeds with abstraction of an iodide ion to form the ionic compound 159140. 

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