Pseudo-base anions

Thus quaternized thiazoles (170) consume two equivalents of OH on titration because the pseudo bases (171) ring open to (172), which form anions (173). Quaternized oxazoles (174) are readily attacked by hydroxide to give open-chain products such as (175) (74AHC(17)99), and quaternized 1,3,4-oxadiazoles behave similarly. Quaternary isothiazoles (e.g. 176) are cleaved by hydroxide (72AHC(l4)l), as are 1,2,4-thiadiazolium salts (177 178). 

First, mention should be made of the metathetical reaction, replacing an anion of a pyrylium salt by another-, when the solubility of the latter salt is lower than that of the former, the conversion is easy. In the opposite case, one has to find a solvent in which the solubilities are reversed (perchlorates are less soluble in water than chloroferrates or iodides, but in concentrated hydrochloric or hydroidic acids, respectively, the situation is reversed For preparing chlorides which are usually readily soluble salts, one can treat the less soluble chloroferrates with hydrogen sulfide or hydroxylamine. Another method is to obtain the pseudo base in an organic solvent and to treat it with an anhydrous acid. 

In many respects the chlorine oxyfluorides resemble the chlorine fluorides. For example, they exhibit little or no self-ionization, but are amphoteric. With strong Lewis acids or bases they can form stable adducts. The tendency to form adducts was found (64) not to be so much a function of the relative acidity of the parent chlorine oxyfluoride but rather to depend on the structure of the amphoteric molecule and of that of the anion or the cation formed. The preferred structures are the energetically favored tetrahedron and octahedron. Consequently, a trigonal bipyramidal molecule, such as CIF3O (64), exhibits a pronounced tendency to form either a stable pseudotetrahedral cation or a pseudo-octahedral anion ... 

So-called pseudocyanides , analogous to pseudo-bases, are formed by reaction of cyanide anions with benzopyridinium cations. Quite often, different isomeric pseudocyanides are formed depending on the temperature. Thus, at — 70 to — 30°C (kinetic control), 1-methylquinolinium ion gives only the 2-cyanoadduct (309), whereas at 20°C (thermodynamic control) exclusively the 4-isomer (310) is observed in the NMR spectrum (80ZOR671). 

The term pseudo-base has been used less widely and less consistently than pseudo-acid. Logically it should be applied to a species which undergoes a change of structure when it adds on a proton. This would include the anions of the pseudo-acids discussed above, and a few uncharged species such as coloring matters (e.g., anthocyanins and flavones) derived from 7-pyrone, where the addition of a proton involves the reaction... 

The UV and H NMR spectral properties of 1-methylquinoxalinium iodide suggest that at pH 9-12, the pseudo base 10 is in equilibrium with the covalent hydrate 11 formed by addition of a molecule of water across the C-3, N-4 bond. At higher pH the anion 12 is formed, and this is less susceptible to covalent hydration across the C-3, N-4 bond. ... 

The description pseudo-base could logically have been applied to bases which undergo a structural change on the addition of a proton and are therefore the conjugate bases of pseudo-acids. Examples would be the anions of nitroparaffins, or derivatives of y-pyrone, which acts as a base in the following way ... 

The catechins, and probably the leuco-anthocyanins (whose structure is not completely known) are derived from a reduced flavone, i.e., a flavan molecule catechins, e.g., catechin (VII), being flavan-3-ols. Anthocyanins, in the colored anionic form in which they usually occur, are flavylium salts e.g., cyanidin, VTII). The anthocyanins may, however, occur in a colorless form, known as a pseudo base, possibly (IX),... 

Se3Bri3- < > SeCls , TeClj-, TeCle ", etc.< > The anion structures are much as expected with the Se species featuring square planar (pseudo-octahedral) units, and the trinuclear Se " anions as in the tellurium analogue above. See also p. 776. There are, in addition, a fascinating series of bromoselenate(II) dianions based on fused planar SeBr4 units, e.g. Se3Brg ", Se4Bri4 ,... 

A particularly interesting system for the epoxidation of propylene to propylene oxide, working under pseudo-heterogeneous conditions, was reported by Zuwei and coworkers [61]. The catalyst, which was based on the Venturello anion combined with long-chained alkylpyridinium cations, showed unique solubility properties. I11 the presence of hydrogen peroxide the catalyst was fully soluble in the solvent, a 4 3 mixture of toluene and tributyl phosphate, but when no more oxidant was left, the tungsten catalyst precipitated and could simply be removed from the... 

In 2004, Bolm et al. reported the use of chiral iridium complexes with chelating phosphinyl-imidazolylidene ligands in asymmetric hydrogenation of functionalized and simple alkenes with up to 89% ee [17]. These complexes were synthesized from the planar chiral [2.2]paracyclophane-based imida-zolium salts 74a-c with an imidazolylidenyl and a diphenylphosphino substituent in pseudo ortho positions of the [2.2]paracyclophane (Scheme 48). Treatment of 74a-c with t-BuOLi or t-BuOK in THF and subsequent reaction of the in situ formed carbenes with [Ir(cod)Cl]2 followed by anion exchange with NaBARF afforded complexes (Rp)-75a-c in 54-91% yield. The chela-... 

Figure 1. Hydrolysis pH-rate profiles of phenyl acetate (lower) and a substituted 2-phenyl-l,3-dioxane (HND). Phenyl acetate profile constructed from data of Mabey and Mill (32), HND profile from data of Bender and Silver (33). Phenyl acetate reacts via specific-acid catalyzed, neutral, and base-catalyzed transformation pathways. The pseudo-first-order rate constant is given by Kobs = K(h+) [H+] + Kn + K(qh-) [0H—]. HND hydrolyzes only via an acid-catalyzed pathway the phenolate anion is some 867 times more reactive than its conjugate acid.

Kinetics show that the reaction is pseudo-first order in the RX concentration and that there is a linear correlation in the rate of consumption of RX with the concentration of the catalyst. The need for a high rate of stirring indicates that, as discussed in Chapter 1, the base-initiated formation of the cobalt tetracarbonyl anion results from an interfacial exchange process. It is significant that, when preformed NaCo(CO)4 is used, the extractability of the anion by benzyltriethylammonium cation into diisopropyl ether is three times less efficient than it is into benzene or dichloromethane, but kinetic studies show that, in spite of the lower concentration of the anion in the ether, the rate of reaction with RX in that solvent is generally higher [3]. 

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