Solution basicity

Dipping solution Basic lead(II) acetate solution (lead content 17.5—19%). Storage... 

This technique provides quantitative information about tautomeric equilibria in the gas phase. The results are often complementary to those obtained by mass spectrometry (Section VII,E). In principle, gas-phase proton affinities, as determined by ICR, should provide quantitative data on tautomeric equilibria. The problem is the need to correct the measured values for the model compounds, generally methyl derivatives, by the so-called N-, 0-, or S-methylation effect. Since the difference in stability between tautomers is generally not too large (otherwise determination of the most stable tautomer is trivial) and since the methylation effects are difficult to calculate, the result is that proton affinity measurements allow only semi-quantitative estimates of individual tautomer stabilities. This is a problem similar to but more severe than that encountered in the method using solution basicities (76AHCS1, p. 20). 

It is not necessary that the intermediate be separated from the reaction medium in the preparation of the end product. Instead, the reaction mixture, after cooling, is treated with 200 ml of water acidified with 42 ml 10% hydrochloric acid solution, and filtered. To the clear, light yellow filtrate is added dropwise a solution of 9.B g (0.07 mol) 5-nltro-2-furaldehyde in 100 ml ethyl alcohol. An orange solution of the hydrochloride results. The free base is precipitated asyellow plates by making the solution basic with saturated sodium carbonate solution. 14 g of the compound is filtered off by suction, washed with alcohol, and dried. The yield, MP 204°C to 205°C (dec.), is 53% of theoretical based on 3-(N-morpholinyl)-1,2-epoxy-propane. Recrystallization from 95% alcohol (75% recovery) raises the melting point to 206°C (dec.). 

You are probably familiar with a variety of aqueous solutions that are either acidic or basic (Figure 4.6). Acidic solutions have a sour taste and affect the color of certain organic dyes known as acid-base indicators. For example, litmus turns from blue to red in acidic solution. Basic solutions have a slippery feeling and change the colors of indicators (e.g., red to blue for litmus). 

The OH- ions formed make the solution basic. A 0.10 M solution of sodium fluoride, NaF, has a pH of about 8.1. 

As pointed out in Section 13.5, anions that are the conjugate bases of weak acids act themselves as weak bases in water They accept a proton from a water molecule, leaving an Oil ion that makes the solution basic. The reactions of the fluoride and carbonate ions are typical ... 

To a solution of 0.18 g (1 mmol) of /V-benzylideneaniline in F.t,0 is added 0.194 g (1.1 mmol) of 9-(2-butenyl)-9-borabicyclo[3.3.1]nonane (crotyl-9-BBN) at — 78 °C. The reaction is quenched at O C with several drops of coned [ICl. The mixture is stirred overnight at r.t.. and a 3 N aq soln of NaOH is added at 0°C to make the solution basic. The mixture is extracted twice with ht20. dried, condensed, and filtered through a short column of silica gel (hexane/Et20 10 1) to remove the 9-BBN residue. 

An aqueous solution of a soluble salt contains cations and anions. These ions often have acid-base properties. Anions that are conjugate bases of weak acids make a solution basic. For example, sodium fluoride dissolves in water to give Na, F, and H2 O as major species. The fluoride anion is the conjugate base of the weak acid HF. This anion establishes a proton transfer equilibrium with water ... 

Acidic solution + Basic solution = Salt+Solvent... 

The acidity of a solution is determined by the hydronium ion concentration of the solution. The greater [H,0+], the more acidic the solution the lower [H,0+], the more basic the solution. Other substances, for example, OH, affect the acidity of a solution by affecting the concentration of H, 0+. The presence of OH in water in greater concentration than H30+ makes the solution basic. If the relative concentrations are reversed, the solution is acidic. 

Some of the OH reacts with the H,0 present in water. The excess OH makes the solution basic. 

Keeping the solution basic prevents the extraction into the tetralin of acidic products which are highly colored saturating the solution with sodium chloride makes the extraction more rapid. 

The solution basicities in water at 25 °C of ortho-, meta- and para-substituted primary, secondary and tertiary anilines have been widely discussed by Smith1. Preliminary gas-phase data were reported by Bohme2. Subsequently, the gas-phase basicities (proton... 

If the PCA scores are used in subsequent methods as uncorrelated new variables, the optimum number of PCs can be estimated by several techniques. The strategies applied use different criteria and usually give different solutions. Basics are the variances of the PCA scores, for instance, plotted versus the PC number (Figure 3.5, left). According to the definition, the PCI must have the largest variance, and the variances decrease with increasing PC number. For many data sets, the plot shows a steep descent after a few components because most of the variance is covered by the first components. In the example, one may conclude that the data structure is mainly influenced by two driving factors, represented by PCI and PC2. The other... 

Cation derived from a strong base Reaction with water neither ion Solution neutral Examples NaCl, K2SO4, Ca(N03)2 Reaction with water only the anion Solution basic Examples NaCHsCOO, KF, Mg(HS04)2... 

Cr + forms a precipitate when a solution of NH3 is added. (Making the solution basic has the same effect as adding OH. ) Ag+ also forms a precipitate in a basic solution. 

Learning what makes a solution basic and the compounds that can make it so... 

Burgess, J. (1988) Ions in solution Basic principles of chemical interactions. Ellis Horwood, Chichester... 

J. Burgess, Ions in Solution Basic Principles of Chemical Interactions (Ellis-Horwood Ltd, Chichester, UK 1988). 

The use of aqueous citric acid avoids the formation of insoluble gelatinous precipitates, which result when aqueous hydrochloric acid is employed. Sulfuric acid is a suitable alternative to citric acid but must be used in substantial excess to prevent precipitation. 2,2,6,6-Tetramethylpiperidine may be recovered from the citric acid extract by making the aqueous solution basic and extracting with ethyl ether. 

Basicity in the gas phase is measured by the proton affinity (PA) of the electron donor and in solution by the pAj,. A solution basicity scale for aldehydes and ketones based on hydrogen bond acceptor ability has also been established [186]. Nucleophilicity could be measured in a similar manner, in the gas phase by the affinity for a particular Lewis acid (e.g., BF3) and in solution by the equilibrium constant for the complexation reaction. In Table 8.1 are collected the available data for a number of oxygen systems. It is clear from the data in Table 8.1 that the basicities of ethers and carbonyl compounds, as measured by PA and p , are similar. However, the nucleophilicity, as measured by the BF3 affinity, of ethers is greater than that of carbonyl compounds, the latter values being depressed by steric interactions. 

Sulfates. Lead sulfate CAS 7446-l4-2. PbSOj. white precipitate, formed by reaction of soluble lead salt solution and sulfuric acid or sodium sulfate solution basic lead sulfate, "sublimed white lead." white solid, formed 11 > by reaction ol lead sulfate and lead hydroxide in waler Islow reaction , and t2i by roasting galenite in a ennem of air. 

The oxygen and sulfur bases are weaker than the nitrogen bases, and accurate solution basicities are not available. Arnett s heat of protonation studies indicate that the order of decreasing basicity is ROR > ROH > HaO,98 a result that is in agreement with gas-phase measurements.99 Hydrogen sulfide in the gas phase has basicity comparable to that of water (Table 3.18), and substitution of H by alkyl produces stronger gas-phase bases just as does similar substitution on oxygen. 

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