Oxonium hydroxide

The strikingly good solubility in water of PEGs is due to the formation of hydrate complexes. By analogy with the formation of ammonium hydroxide when ammonia is dissolved in water, the process involved in adding water to the ether oxygen of PEGs is referred to as oxonium hydroxide formation. Unlike the aqueous solution of ammonia, however, the PEG solutions react neutrally. 

There is no published mechanistic study on the Auwers flavone synthesis. The mechanism may involve the nucleophilic addition of oxonium 7, derived from 1, with hydroxide to give 8. Base-promoted ring opening of 8 could provide the putative intermediate 9, which then could undergo an intramolecular Michael addition to form 10. Expulsion of bromide ion from 10 would then give flavonol 2. 

The H2S+ ion is generally termed a lyonium ion and the S" ion is termed a lyate ion. The symbol H2S+ (for example H30+, CH3COOH2+, etc.) refers only to a proton solvated by a suitable solvent and does not express either the degree of solvation (solvation number) or the structure. For example, two water molecules form the lyonium ion H30+, termed the oxonium (formerly hydronium or hydroxonium) ion, and the lyate ion OH", termed the hydroxide ion. 

Next, we come to the question what is the role of histidine-57 We are observing an example of general acid-base catalysis catalysis not just by hydroxide ions and oxonium ions, but by all the bases and conjugate acids that are present, each contributing according to its concentration and its acid or base strength. 

Salts of ammonium, oxonium, sulfonium, etc., are placed under the formula of the corresponding hydroxide. (C6H5)2lCl is found under C12H11OI. Diazo-nium compounds are handled in the same manner, under the corresponding amine. 

Triethyltin hydroxide in the crystal forms zig-zag Sn-0(H)-Sn-0(H) chains with rSnO 215.6 and 222.4 pm, and SnOSn 145.5°. Hydrolysis of Et3Sn+ B(C6F5)4 gives the oxonium salt 12-6 in which the SnO bond is long (212 pm) and the tetrahedra about the tin are flattened, indicating a pronounced stannylium character (see Section 7.2).31... 

General acid catalysis occurs when the rate law includes a concentration term due to added acid (rate = AhaIHA]). Specific acid catalysis involves a rate law with only the oxonium ion (rate = itHlHjOq). Similar definitions apply to general base and specific base catalysis involving base and hydroxide ion respectively. 

These equations factor all the acid-base types in a series to that where p = = 1. For example, if triethylamine and diaminoethane monocation are to be interpreted in the same correlation they need corrections because the former has p = 1 and q = 1 whereas the latter has p = 2 and q = 1. The assignment of p and q is not satisfactory for acid-base pairs with uncertain structures (such as H3O and HO ) or species with multiple centres of differing reactivity hydronium and hydroxide ions almost always show anomalous reactivities in corrected Bronsted correlations, but these are partly due to solvation effects. The protons attached to a single atom such as ammonium (R-NHj or oxonium ion (R-OH2 ) are regarded as having p = 1 rather than the number of identical protons. A similar convention selects the q value for hydroxide ion as unity even though there are three lone pairs free to accept a proton. The statistical... 

The fit to an Eigen equation of the proton transfer step to the carbon base (CN") indicates that the 2 step is not rate limiting and the cyanide ion behaves as if it were a heteroatom base. The anomalously large values of the rate constants for oxonium and hydroxide ions are consistent with their faster diffusion rates resulting from Grotthus translational-type effects. 

At a = 0.1 some 98% of the total reaction flux is taken by the solvent water acting as the acid at a = 1.0 the oxonium ion takes 99.8% of the total reaction flux. At intermediate a values the general acid takes a substantial proportion of the reaction flux. The consequences of these results are that extreme values of a are more difficult to measure because the solvent species take most of the reaction, resulting in only small changes in rate constant for variation in general acid concentration. Similar arguments can be advanced for general base catalysis in competition with water or hydroxide ion. 

The tendency of the AUPR3+ cations to form oxonium species in the reactions that would be expected to lead to the hydrate, [Au(OH2)(PR3)]+, hydroxide [Au(OH)(PR3)] or oxide [0(AuPR3)2] suggest the existence of structural factors enhancing the stability of the [0(AuPR3)3j+ ion compared to the above complexes, which are not known in the monomeric state. Such a factor could easily be the existence of inter- and intramolecular interactions of gold atoms. 

Ethers are generally spoken of as inert compounds. What is really meant is that they do not react with metals, alkalies, and most acids at ordinary temperatures with appreciable velocity. As pointed out, the properties of the olefinated hydrogen afford an explanation. The same holds true for tertiary amines. It has already been pointed out that a difference is shown in the stability, or better, the reactions of the olefinated hydrogen depending upon the other substances present. Thus, in the presence of chlorides, such as zinc chloride, etc., ethyl iodide reacts less rapidly than the chloride. The same relative order was observed with ammonium chloride, bromide, iodide, and hydroxide. The decomposition of ethers by heating with hydrogen iodide, a method used for the determination of the amount of ether groups present in compounds, may be explained on the same basis. They are simple displacement reactions. The existence of the intermediate addition compounds (oxonium salts) has been proven ... 

The name ethane hexamercarbide for Hofmann s base, C2Hg (OH)2, has been shown to be a misnomer since the compound is a methane derivative formed by condensation from C(HgOH)4, i.e. it is the hydroxide of a polymeric oxonium ion C—Hg—(OH)+—Hg—C the structural determination involved reaction of the base with trifluoroacetic or acetic acid to give the corresponding methane derivatives C(Hg-02CR)4 (R = CFs or Me), which were subjected to X-ray analysis. Cobalt tristrifluoroacetate has been prepared from equilibration of the OH-bridged compound [(AcO)2Co(OH)2(OAc)2] in trifluoroacetic acid ion-pair dissociation of (CF3 -C02)sCo in CFs OOsH accounts for it being a powerful electron-transfer oxidant e.g. PhH - -CFs OOsPh (95%)]. 

Acid-Base Disproportionation of Water Finally, we will take a look at the acid-base disproportionation of water. It has already been demonstrated that amphoteric water can function as an acid as well as a base. For this reason, proton transfer between the water molecules can take place where oxonium and hydroxide ions are formed even when there are no other acids or bases present ... 

This process bears the respectable name of "self-dissociation of water and is pre-smned to be an equihbrium reaction, because it concludes when the species indicated on the left and right side of this chemical equation (reactants and products) are present at the same time. This means the order of the reactants and products in the above chemical equation could even be reversed. The reaction itself is also called reversible. In pure water, the same amounts of hydrogen (H+) ions and hydroxide ions (OH ) form. The notation used for hydrogen ion is still a matter of debate in today s science. Some experts stubbornly stick to the notation HjO which is called oxonium or hydroxonium ion (—> 4.10). It is difficult to formulate justice here, as reality itself is much more complex than any single chemical formula could express. But as far as notations go, using the simpler one seems... well, simpler. 

Fig. 18.7. Schematic illustration of water layers which can be formed on an oxide or hydroxide surface or when oxonium ions are present.

The gas phase structures of the OH radical, the hydroxide ion, and the oxonium ion H3O+ have all been determined by spectroscopic methods. Bond distances and valence angles are listed in Table 17.3. The near-constant length of the OH bonds is striking. 

The deep-orange 3-methyl-2,4-diphenylthiazolium 5-thiolate (154) forms yellow solutions in acids, presumably owing to protonation of the exocyclic sulphur. Its oxidation by hydrogen peroxide in acetic-formic acids produces the 5-sulphonate (155) (91%) subsequent treatment with concentrated hydrochloric acid yields 2,4-diphenylthiazole (156). Anhydro-5-hydroxy-3-methyl-2-phenylthiazolium hydroxide (157) resists alkylation by conventional reagents, but is readily 0-alkylated by triethyl-oxonium fluoroborate, yielding 5-ethoxy-3-methyl-2-phenylthiazolium fluoroborate (158). In this respect, it resembles related mesionic systems based on 1,3,4- and 1,2,3-thiadiazoles (c/. Chapter 15). 

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