Unstable in basic solutions

Tetrazolium salts are unstable in basic solutions yielding intense colors. This reaction is still little understood.233,234 In the reaction of 2,3,5-triphenyltetrazolium with hydroxide, it is postulated that a hydroxide ion is involved first as a counterion later leading to the hypothetical A-hydroxy-formazan (147).229 Weiner studied the kinetics of this reaction and identified 1,3,5-triphenylformazan in 10% yield. In concentrated alkaline solutions, the A-hydroxytetrazole (148) has been isolated from triphenyltetrazolium chloride (Scheme 19).235,236... 

All penicillins are susceptible to attack in acidic solution via intramolecular attack of the amide carbonyl oxygen on the (3-lactam carbonyl, leading to the complete destruction of the (3-lactam ring, and thus the antibacterial activity. Similarly, penicillins are unstable in basic solution because of (3-lactam ring opening by free basic nucleophiles. Thus, for the antibacterial activity, the stability of the (3-lactam functional group in penicillins is of paramount importance. 

The XRD patterns of PSM and AMM samples after treatment in NaOH solution (pH = 11) for 12 h are shown in Figure 5. Both AMM-1 and AMM-5 samples still exhibit well defined XRD patterns, showing good preservation of the textural uniformity of AMM samples in a strong basic solution. In contrast, no XRD peak is detected for PSM sample under the same treatment conditions, showing that the uniform mesoporous structure of PSM has been completely destroyed by NaOH solution in 12 h. This result is not surprising as it has been well reported that PSM was unstable in basic solution [4], The results of this investigation show that the chemical stability of MCM-41 material in basic solution can be substantially improved by the external introduction of Al species onto its surface. 

Despite the apparent simplicity of their structures, the chemistry of the nicotinamide ring in NAD+ and NADP+ is surprisingly complex.128 129 NAD+ is extremely unstable in basic solutions, whereas NADH is just as unstable in slightly acidic media. These properties, together with the ability of NAD+ to undergo condensation reactions with other compounds, have sometimes caused serious errors in interpretation of experiments and may be of significance to biological function. 

There are important differences between the behaviors of uni- and dipositive mercury in solution. Perhaps the most striking is the very feeble complexing ability of the mercurous ion. Only a handful of com-plexing agents (among them pyrophosphate, succinate, and oxalate) appear to form complexes with univalent mercury. Hg(I) is unstable in basic solutions, in ammoniacal solutions, and in the presence of sulfide or cyanide ions. It decomposes under such conditions to elemental mer-... 

The chemical reactivity of all of the compounds of this series is governed by the powerful, electron-withdrawing influence of the sulfonyl groups this renders the acyclic, saturated members liable to eliminations, and the acyclic, unsaturated members susceptible to attack at C-2 by nucleophiles, and makes both the cyclic and the acyclic members unstable in basic solutions. This last feature provides the main source of interest in these compounds, all of which are degraded by aqueous ammonia to diethyl-sulfonylmethane and the aldose derived from the parent sugar by loss of C-1. Treatment with hydrazine in methanol, followed by cleavage of the derived hydrazone, offers a satisfactory means for degrading the acetylated sulfone (148) to n-arabinose (yield, 73%). ... 

Comments Although some workers recommend preparing the reagent directly in alkaline buffer, Nirnura and Kinoshita [155] reported that the reagent was unstable in basic solution and recommended that the base be added immediately before the reaction. 

A considerable range and variety of thiols have been employed as nucleophiles. Some thiols are unstable in basic solution, but can be employed as their thiolate salts. Examples of this type of thiol include trifluoromethanethiol and pentafluorobenzenethiol. The trifluoromethane-thiolate anion readily loses fluoride in solution in an irreversible reaction , but the mercury derivative, Hg(SCFa)2, effectively acts as a source of... 

The Mn ion is so unstable that it scarcely exists in aqueous solution. In acidic aqueous solution, manganic compounds readily disproportionate to form Mn ions and hydrated manganese(IV) oxide, Mn02 2H20 in basic solution these compounds hydroly2e to hydrous manganese(III) oxide, MnO(OH). Sulfuric acid concentrations of about 400 450 g/L are required to stabilize the noncomplexed Mn ion in aqueous solutions. 

A group of peptide derivatives such as peptide arginals and boronic acid peptide derivatives belong to another class of reversible thrombin inhibitors. One such inhibitor is PPACK (D-Phe-Pro-Arg chloromethyl ketone), which functions as a powerful irreversible thrombin inhibitor by alkylating the histidine residue at the catalytic site of thrombin (58). It, however, is unstable in neutral solution, as it undergoes cyclization and inactivation. However, the D-methyl derivative of D-Phe-Pro-Arg-H (D-Mephe-Pro-Arg-H) called efegatran, with a molecular mass of 515 Da, is a stable selective reversible inhibitor of thrombin with a K. of approximately 100 nM. The basic amino terminus in this compound is responsible for promoting the specificity toward thrombin (63). 

As a result, the products of reactions of halogens in basic solutions depend on pH, temperature, and the concentrations of the reactants. The acids are unstable compounds that decompose in two ways ... 

A report in 1977 (3) of an active system prepared from [Rh(CO)2CI]2, CH3CO2H, cone. HC1 and Nal in water demonstrated that a basic medium is not a necessary condition for WGSR catalysis. This result stimulated us to examine the potential activity of several simple metal carbonyls in acidic solution as well. Attempts with Fe(CO)5 and Iri (CO)12 (17), both active in alkaline and amine solutions, proved unfruitful. However Ru3(CO)12 in acidic (0.5 N H2SOtf) aqueous ethoxyethanol gave WGSR activity substantilly larger than found in basic solutions under otherwise analogous conditions (Pco=0.9 atm, T=100°C, [Ru]Total=0 036 mol/L) (15). This solution proved unstable and... 

Ozonolysis " of Am(OH)3 slurries in basic media or in the presence of HCO3 afforded solutions containing Am. This oxidation state is unstable in basic media, however, and reduction to Am occurs readily. 

In a series of papers almost a century ago, Wieland and coworkers described the synthesis of alkali and silver nitrosolates (M[RC(NO)2], M = metal, R = organic substituent) . These nitrosolates can be obtained from unstable Af,Af -dihydroxyamidines by disproportionation in ammonia (Scheme 7) or by oxidation (KIO4) in basic solution For R = H these procedures result in the formation of, e.g., potassium dinitrosomethanide, the simplest nitrosolate, when potassium hydroxide is used as base. 

Local anesthetics are unstable and insoluble in basic solution. If a local anesthetic lacks an amine, it is insoluble in water and is only used topically. 

Oxidation of green Bk(III) hydroxide as a suspension in 1 M NaOH to yellow Bk(IV) hydroxide was performed by bubbling ozone through the slurry (113). In basic solution, Bk(III) is unstable toward oxidation by radiolytically produced peroxide. This auto-oxidation had been previously observed in carbonate solution (95). Bk(III) can be stabilized in alkaline media by the presence of a reducing agent such as hydrazine hydrate (113). 

Disproportionation of this unstable species in basic solutions occurs as represented by the equation... 

The common oxidation states of iron are + 2 and + 3. The relative stability of the two oxidation states in acid aqueous solution is defined by the standard electrode potential of + 0.77 V for the Fe3+/Fe2+ couple.1 This potential is such that the hydrated Fe11 cation is thermodynamically unstable with respect to atmospheric oxidation (equation 1). The oxidation is even more favourable in basic solution (equation 2). It is apparent, therefore, that the chemistry of iron, including its... 

Vitamin is iasoluble ia water and is soluble ia 70% alcohol, cbloroform, petroleum ether, ben2ene, and hexane. Vitamin is stable in air but should be protected from light. Although unstable ia alkali, the vitamin is stable ia acidic medium. Its facile decomposition in basic solution forms the basis of the Dam-Karrer color test. 

Construct the Latimer diagram for manganese in basic solution (from values in Table F. I), and predict which oxidation states will be stable. Explain the source of instability for each unstable species. 

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