Monobasic solutes

Very recently (51), nonequivalence has been found in a variety of additional monobasic solutes whose configurational analysis was thought earlier to lie outside the scope of the CSA technique. 2-Butanol, for example, when dissolved in benzene saturated with TFAE, shows nonequivalence in both methyl resonances. A variety of other chiral and prochiral compounds such as 2-propanol, methyl 2-propyl sulfide, 2-aminobutane, and 2-methyl-1-butanol show nonequivalence for their enantiotopic methyl groups under these conditions. The magnitudes of nonequivalence in these instances are small (0.02-0.03 ppm) but, as illustrated in Figure 4 for enriched 2-butanol,... 

Monobasic solutes that have no carbinyl hydrogens may also show nonequivalence. 3-Methyl-2-butanone, 4-methyl-2-pentanone, 2-methylpropanal, methyl 2-methylbutyrate, 2,2,6,6-tetramethyl-piperidine, methyldiisopropylcarbinol, and methylethyl-n-butyl-carbinol in TFAE-saturated benzene all show nonequivalence of sufficient magnitude (0.01-0,03 ppm) to allow nonequivalence sense determination at 220 MHz. An especially striking example is that provided by pyrazolines 26. With only a severalfold excess of (S)-TFAE, 3(5),5(S)-enriched samples of these compounds show nonequivalence in their methyl resonances (downfield sense for the singlets and upfield sense for the triplets) sufficient for enantiomeric purity determination at 90 MHz (52). 

SIL CN column (5 pm particle size, 150 mm x 4.6 mm I.D.) and a mobile phase of 0.05M aqueous potassium phosphate (monobasic) solution containing 0.05% (v/v) triethylamine (pH 4.0) acetonitrile (75 25). The separation is achieved at ambient temperature using a flow rate of 1.0 mL/minute. UV absorbance detection is accomplished at a wavelength of 236 nm. The standard and sample solutions are prepared in a diluent of acetonitrile and 20 pL are injected onto the column. The retention time of diltiazem is approximately 13 minutes while that of the potential degradation product, desacetyl diltiazem, is 9 minutes. The analysis is completed within 17 minutes and allows quantitation of both components. A typical HPLC chromatogram is shown in Figure 14. 

Store the monobasic solution, the dibasic solution, and the pH 6.0 phosphate buffer at room temperature. 

Hypophosphorous acid, H3PO2, H2P(0)0H. A monobasic acid. Ba(H2P02)2 is formed when white phosphorus is dissolved in Ba(OH)2 solution. H3PO2 and its salts are strong reducing agents. 

Boron trioxide is not particularly soluble in water but it slowly dissolves to form both dioxo(HB02)(meta) and trioxo(H3B03) (ortho) boric acids. It is a dimorphous oxide and exists as either a glassy or a crystalline solid. Boron trioxide is an acidic oxide and combines with metal oxides and hydroxides to form borates, some of which have characteristic colours—a fact utilised in analysis as the "borax bead test , cf alumina p. 150. Boric acid. H3BO3. properly called trioxoboric acid, may be prepared by adding excess hydrochloric or sulphuric acid to a hot saturated solution of borax, sodium heptaoxotetraborate, Na2B407, when the only moderately soluble boric acid separates as white flaky crystals on cooling. Boric acid is a very weak monobasic acid it is, in fact, a Lewis acid since its acidity is due to an initial acceptance of a lone pair of electrons from water rather than direct proton donation as in the case of Lowry-Bronsted acids, i.e. 

It is important that the solution of the sodium salt be faintly acid in order that the formation of coloured by-products in the subsequent reaction may be prevented. If the molecular weight of the monobasic acid is known, it is desirable to employ a slight excess of the sodium salt, since excess of the latter is more easily removed than the unchanged reagent. 

Monofluorophosphoric Acid. Monofluorophosphoric acid (1) is a colorless, nonvolatile, viscous Hquid having practically no odor. On cooling it does not crystallize but sets to a rigid glass at —78°C. It has a density of = 1.818 g/mL. Little decomposition occurs up to 185°C under vacuum but it caimot be distilled. An aqueous solution shows the normal behavior of a dibasic acid the first neutralization point in 0.05 N solution is at pH 3.5 and the second at pH 8.5. Conductance measurements, however, indicate H2PO2F behaves as a monobasic acid in aqueous solution (59). The... 

A freshly made solution behaves as a strong monobasic acid. Neutralized solutions slowly become acidic because of hydrolysis to monofluorophosphoric acid and hydrofluoric acid. The anhydrous acid undergoes slow decomposition on distillation at atmospheric pressure, reacts with alcohols to give monofluorophosphoric acid esters, and is an alkylation (qv) and a polymerization catalyst. 

Hexamethylenetetramine. Pure hexamethylenetetramine [100-97-0] (also called hexamine and HMTA) is a colorless, odorless, crystalline sohd of adamantane-like stmcture (141). It sublimes with decomposition at >200° C but does not melt. Its solubiUty in water varies Htde with temperature, and at 25°C it is 46.5% in the saturated solution. It is a weak monobase aqueous solutions are in the pH 8—8.5 range (142). Hexamethylenetetramine is readily prepared by treating aqueous formaldehyde with ammonia followed by evaporation and crystallisation of the soHd product. The reaction is fast and essentially quantitative (142). 

The greatest industrial consumption of monobasic aluminum acetate has been as a solution in the preparation of red color lakes for the dyeing of cotton. Formation of a water-resistant coating on fabrics, paper, leather, or other materials is also an important appHcation. In this process, for example, cloth is dipped into a solution of water-soluble soap, then into the aluminum salt solution, forming an insoluble, water-resistant aluminum soap coating on the fiber surfaces (10). 

Monobasic aluminum acetate is dispensed as a 7% aqueous solution for the topical treatment of certain dermatological conditions, where a combination of detergent, antiseptic, astringent, and heat-dispersant effects are needed (12). The solution, diluted with 20—40 parts water, is appHed topically to the skin and mucous membranes as a wet dressing (13). Burrow s solution, prepared from aluminum subacetate solution by the addition of a specific amount of acetic acid, is also used as a topical wet dressing. Standards of purity and concentration have been estabHshed for both pharmaceutical aluminum acetate solutions (13). Each 100 mL of aluminum subacetate solution yields 2.30—2.60 g of aluminum oxide and 5.43—6.13 g of acetic acid upon hydrolysis. For the Burow s solution, each 100 mL yields 1.20—1.45 g of aluminum oxide and 4.25—5.12 g of acetic acid. Both solutions may be stabilized to hydrolysis by the addition of boric acid in amounts not to exceed 0.9% and 0.6% for the subacetate and Burow s solutions, respectively (13). 

Production of both monobasic aluminum diformate, (HO)Al(OOCH)2, and monobasic aluminum formoacetate, (HO)Al(OOCH) (OOCCH ), has declined. One reason could be the ready substitution of inexpensive aluminum formate solution (17—19) for soHd aluminum acetate in formoacetate in most of the common commercial appHcations. Monobasic aluminum formoacetate, mol wt 148.05, mp 350°C, is a fine crystalline powder, prepared from aluminum metal. It is used for fabric water repeUency and in the tanning of coUagen tape for surgical sutures (10). 

An inflection point in a pH-rate profile suggests a change in the nature of the reaction caused by a change in the pH of the medium. The usual reason for this behavior is an acid-base equilibrium of a reactant. Here we consider the simplest such system, in which the substrate is a monobasic acid (or monoacidic base). It is pertinent to consider the mathematical nature of the acid-base equilibrium. Let HS represent a weak acid. (The charge type is irrelevant.) The acid dissociation constant, = [H ][S ]/[HS], is taken to be appropriate to the conditions (temperature, ionic strength, solvent) of the kinetic experiments. The fractions of solute in the conjugate acid and base forms are given by... 

Orthoboric acid, B(OH)3, is the normal end product of hydrolysis of most boron compounds and is usually made ( 160 000 tonnes pa) by acidification of aqueous solutions of borax. Price depends on quality, being 805 per tonne for technical grade and about twice that for refined material (1990). It forms flaky, white, transparent crystals in which a planar array of BO3 units is joined by unsymmetrical H bonds as shown in Fig. 6.25. In contrast to the short O—H O distance of 272 pm within the plane, the distance between consecutive layers in the ciystal is 318 pm, thus accounting for the pronounced basal cleavage of the waxy, plate-like ciystals, and their low density (1.48 g cm ). B(OH)3 is a very weak monobasic acid and acts exclusively by hydroxyl-ion acceptance rather than proton donation ... 

Wittwer and Zollinger (1954) determined the neutralization curves of aqueous solutions of diazonium salts under standard conditions of ionic strength, etc., and found that the acidity depended on the degree of neutralization in a manner different to that expected for a dibasic acid. The curve obtained did not exhibit two steps with an intermediate region of a few pH units in which the monobasic acid is stable, as is the case, for instance, with oxalic acid (Fig. 5-1). On the contrary, there was only one step, but it extended over two equivalents of base per diazonium ion. 

Carboxylic acids with one acid group are known as monobasic acids while those with two acid groups are dibasic acids. All acids with more than one acid group are in the class of polybasic acids. The simplest organic acid, formic acid, is responsible for the irritation of bee and ant stings. Vinegar is a 5% solution of acetic acid in water. The acetic acid is responsible for the characteristic sour taste. Citric acid, found in citrus fruits and used in soft drinks, is a tribasic acid with three carboxylic acid groups. The dibasic acid, adipic acid, is a major component of nylon. 

Similarly, bases made from the metals of Group I on the periodic table, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH), are called monobasic because they release one hydroxide ion into solution. Bases made up of Group II metals, such as calcium hydroxide [Ca(OH)2] or magnesium hydroxide [Mg(OH)2], release two hydroxide ions and are therefore dibasic. Like acids, any base that is capable of releasing more than one hydroxide ion into solution is called polybasic. 

For example, a monobasic reagent HR dissociates in aqueous solution (dissociation constant ) and is distributed between the organic and aqueous phases (distribution coefficient/fDR). Thus... 

The diazeniumdiolate functional group is a monobasic acid (Scheme 3.13), which is also unstable in acidic solutions. This has created some difficulties in measuring its properties. The aromatic compounds (cupferron analogs) have pKa values between 3.5 and 4.4 in water solutions [146], while the piG values of aliphatic derivatives range from 5.1 for nitrosofungin [147] to 6.4 for fragin (20) [148]. N-Hydroxy-N-... 

Epon 812 (Polybed) Formvar Glutaraldehyde Ilford L-4 emulsion with appropriate safelight Osmium tetroxide Phosphate Dibasic Monobasic Propylene oxide Sodium thiosulfate fixing solution... 

A 0.01 M solution of an ester is passed through an ion exchange catalyst bed where it is decomposed into a monobasic acid and an alcohol. The amount of acid, mols/liter, produced at different flow rates, liters/hr, are tabulated. The quantity of resin catalyst was 120 kg, the bulk density was 1.10 and the true density was 1.25 g/cc. Confirm that the reaction is first order. 

Shortly after Perkin had produced the first commercially successful dyestuff, a discovery was made which led to what is now the dominant chemical class of dyestuffs, the azo dyes. This development stemmed from the work of Peter Griess, who in 1858 passed nitrous fumes (which correspond to the formula N203) into a cold alcoholic solution of 2-aminO 4,6 dinitrophenol (picramic acid) and isolated a cationic product, the properties of which showed it to be a member of a new class of compounds [1]. Griess extended his investigations to other primary aromatic amines and showed his reaction to be generally applicable. He named the products diazo compounds and the reaction came to be known as the diazotisation reaction. This reaction can be represented most simply by Scheme 4.1, in which HX stands for a strong monobasic acid and Ar is any aromatic or heteroaromatic nucleus. 

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