Acidity increase

The acid, if monobasic, can usually be distilled directly from the reaction mixture. If this procedure is not possible, the reaction mixture is poured into excess of crushed ice, and the acid is isolated by ether extraction or by other suitable means. The acid is then characterised (Section 111,85). The addition of hydrochloric acid (as sodium chloride say 5 per cent, of the weight of sulphuric acid) increases the rate of the reaction. 

An alternative drivirg force could involve a donor - acceptor interaction. The electron-poor pyridine ring that is coordinated to the copper cation can act as electron acceptor with respect to the aromatic ring of the -amino acid. The fact that donating substituents on the amino acid increase the efficiency... 

The addition of sulphuric acid increased the rate of nitration of benzene, and under the influence of this additive the rate became proportional to the first powers of the concentrations of aromatic, acetyl nitrate and sulphuric acid. Sulphuric acid markedly catalysed the zeroth-order nitration and acetoxylation of o-xylene without affecting the kinetic form of the reaction. ... 

In the nitration and acetoxylation of o-xylene the addition of acetic acid increased the rate in proportion to its concentration, the presence of 3-0 mol 1" accelerating the rate by a factor of 30. In the presence of a substantial concentration (2-2 mol 1 ) of acetic acid the rate of reaction obeyed the following kinetic expression... 

Step 2 Protonation of the carboxylic acid increases the positive character of its... 

All other things being equal, the strength of a weak acid increases if it is placed in a solvent that is more basic than water, whereas the strength of a weak base increases if it is placed in a solvent that is more acidic than water. In some cases, however, the opposite effect is observed. For example, the pKb for ammonia is 4.76 in water and 6.40 in the more acidic glacial acetic acid. In contradiction to our expectations, ammonia is a weaker base in the more acidic solvent. A full description of the solvent s effect on a weak acid s piQ or on the pKb of a weak base is beyond the scope of this text. You should be aware, however, that titrations that are not feasible in water may be feasible in a different solvent. 

Aldehydes are important products at all pressures, but at low pressures, acids are not. Carbon monoxide is an important low pressure product and declines with increasing pressure as acids increase. This is evidence for competition between reaction sequence 18—20 and reaction 21. Increasing pressure favors retention of the parent carbon skeleton, in concordance with the reversibiUty of reaction 2. Propylene becomes an insignificant product as the pressure is increased and the temperature is lowered. Both acetone and isopropyl alcohol initially increase as pressure is raised, but acetone passes through a maximum. This increase in the alcohoLcarbonyl ratio is similar to the response of the methanoLformaldehyde ratio when pressure is increased in methane oxidation. 

Acetic anhydride and acetic acid increase the solubiUty of the two phases in each other, and they are employed for the commercial N-nitration of hexamethylenetetramine [100-97-0] (11) to form cyclotrimethylenetrinitramine [121-82-4] (RDX), (CH2)3(NN02)3. Renewed consideration has been given to replacing H2SO4 with an improved soHd catalyst to reduce the environmental problems of disposal or reconcentration of the waste acid and to increase production of desired nitrated isomers. For example, a catalyst with suitable pore size might increase the production of 4-MNT and reduce that of 3-MNT when toluene is nitrated. 

Chlorine may initially convert the selenium in solution to the hexavalent state, but as the hydrochloric acidity increases, reduction to the tetravalent state occurs spontaneously. 

Stannous Sulfate. Stannous sulfate (tin(Il) sulfate), mol wt 214.75, SnSO, is a white crystalline powder which decomposes above 360°C. Because of internal redox reactions and a residue of acid moisture, the commercial product tends to discolor and degrade at ca 60°C. It is soluble in concentrated sulfuric acid and in water (330 g/L at 25°C). The solubihty in sulfuric acid solutions decreases as the concentration of free sulfuric acid increases. Stannous sulfate can be prepared from the reaction of excess sulfuric acid (specific gravity 1.53) and granulated tin for several days at 100°C until the reaction has ceased. Stannous sulfate is extracted with water and the aqueous solution evaporates in vacuo. Methanol is used to remove excess acid. It is also prepared by reaction of stannous oxide and sulfuric acid and by the direct electrolysis of high grade tin metal in sulfuric acid solutions of moderate strength in cells with anion-exchange membranes (36). 

Polytungsta.tes, An important and characteristic feature of the tungstate ion is its abiUty to form condensed complex ions of isopolytungstates in acid solution (38). As the acidity increases, the molecular weight of the isopolyanions increases until tungstic acid precipitates. However, the extensive investigations on these systems have been hampered by lack of weU-defined soHd derivatives. 

High molecular weight primary, secondary, and tertiary amines can be employed as extractants for zirconium and hafnium in hydrochloric acid (49—51). With similar aqueous-phase conditions, the selectivity is in the order tertiary > secondary > primary amines. The addition of small amounts of nitric acid increases the separation of zirconium and hafnium but decreases the zirconium yield. Good extraction of zirconium and hafnium from ca 1 Af sulfuric acid has been effected with tertiary amines (52—54), with separation factors of 10 or more. A system of this type, using trioctylarnine in kerosene as the organic solvent, is used by Nippon Mining of Japan in the production of zirconium (55). 

Unsaturation in a fatty acid increases its solubihty in organic solvents, and the differences in solubiHties between saturated and unsaturated acids can be used to separate these acids (Table 9). 

The intermediate HCIO2 is rapidly oxidized to chloric acid. Some chlorine dioxide may also be formed. Kinetic studies have shown that decomposition to O2 and chloric acid increase with concentration, temperature (88), and exposure to light (89—92), and are pH dependent (93). Decomposition to O2 is also accelerated by catalysts, and decomposition to chlorate is favored by the presence of other electrolytes, eg, sodium chloride (94—96). 

Resolution of racemic alcohols by acylation (Table 6) is as popular as that by hydrolysis. Because of the simplicity of reactions ia nonaqueous media, acylation routes are often preferred. As ia hydrolytic reactions, selectivity of esterification may depend on the stmcture of the acylatiag agent. Whereas Candida glindracea Upase-catalyzed acylation of racemic-cx-methylhenzyl alcohol [98-85-1] (59) with butyric acid has an enantiomeric value E of 20, acylation with dodecanoic acid increases the E value to 46 (16). Not only acids but also anhydrides are used as acylatiag agents. Pseudomonasfl. Upase (PFL), for example, catalyzed acylation of a-phenethanol [98-85-1] (59) with acetic anhydride ia 42% yield and 92% selectivity (74). 

Unsaturated Hydrocarbons. Olefins from ethylene through octene have been converted into esters via acid-catalyzed nucleophilic addition. With ethylene and propjiene, only a single ester is produced using acetic acid, ethyl acetate and isopropyl acetate, respectively. With the butylenes, two products are possible j -butyl esters result from 1- and 2-butylenes, whereas tert-huty esters are obtained from isobutjiene. The C5 olefins give rise to three j iC-amyl esters and one /-amyl ester. As the carbon chain is lengthened, the reactivity of the olefin with organic acids increases. 

If chlorides are present internally, acidity increases due to hydrolysis ... 

Aluminum corrodes at a fairly low rate between a pH of 5.5 and 8.5 at room temperature. At concentrations between 50% and 95%, sulfuric acid causes rapid attack below 10%, corrosion is much less. Hydrochloric acid is quite corrosive in all but dilute concentrations. The corrosion rate in hydrochloric acid increases 100-fold as temperature increases from 50°F (10°C) to 176°F (80°C) in a 10% hydrochloric acid solution. 

Decreasing values below 7.0 indicate increasing acidity increasing values above 7.0 indicate increasing basicity. 

Trimethylsilylimidazole, CCI4 or THF, rt. This is a powerful silylating agent for hydroxyl groups. Basic amines are not silylated with this reagent, but as the acidity increases silylation can occur. 

For some applications, such as for repulpable type PSAs, it may be advantageous to incorporate high levels of acrylic acid because this makes the polymer more hydrophilic. At the same time, high levels of acid also improve the water-dispersibility of the adhesive, especially at higher pH where the acid groups are converted to the more water-soluble neutralized salt form. Since the high level of acid increases the of the resulting polymer, a non-tacky material results. To make the adhesive pressure sensitive, the polymer can be softened with water-dispersible or soluble plasticizers, such as polyethers [68]. 

The proportion of ionized and unionized forms of a chemical compound can be readily calculated according to the above equation. It can be easily seen that pK is also a pH value at which 50% of the compound exists in ionized form. The ionization of weak acids increases as the pH increases, whereas the ionization of weak bases increases when the pH decreases. As the proportion of an ionized chemical increases, the diffusion of the chemical through the biological membranes is greatly impaired, and this attenuates toxicokinetic processes. For example, the common drug acetosalicylic acid (aspirin), a weak acid, is readily absorbed from the stomach because most of its dose is in an unionized form at the acidic pH of the stomach. 

The total yield of products from alkanecarboxyhc acids increases, in most cases, by addition of anhydrous hydrogen fluoride. The optimum hydrogen fluoride concentration is much higher than catalytic and is related to the basicity of a carbonyl group. A mechanism for the formation of both 1,1,1-trifluoroalkanes and bis(l,l-difluoroalkyl) ethers has been proposed [206] (equation 102)... 

The easy liberation of trifluoroethanol from 2,2,2-tnfluoroethyl hydrogen 3,6-di methylphthalate can be accounted for by nng closure to form 3,6 dimethylphthalic anhydride [57] (equation 56) The carboxylate anion is the intermediate needed for nng closure because the rate increases as the pH, while still acidic, increases... 

The acidity increases as carbon becomes more electronegative. Ionization of acetylene gives an anion in which the unshared electron pah occupies an orbital with 50% 5 character. 

B5H9 also acts as a weak Brpnsted acid and, from proton competition reactions with other boranes and borane anions, it has been established that acidity increases with increasing size of the borane cluster and that arachno-boranes are more acidic than nido-horancs ... 

The strengths of the monobasic acids increase rapidly with increase in oxidation state of the halogen in accordance with Pauling s rules (p. 50). For example, approximate values of pKa are HOCl 7.52, HOCIO 1.94, HOCIO2 - 3, HOCIO3 — 10. The pXa values of related acids increase in the sequence Cl < Br < I. 

In the 4-substituted 1,3-dimethylpyrazoles with ethynyl group fixed in position 5, the acidity increases with a change in the character of substituents in the series H = NH2 < C CPh < I < Br = Cl. 

Nitrating propane produces a complex mixture of nitro compounds ranging from nitromethane to nitropropanes. The presence of lower nitroparaffins is attributed to carbon-carbon bond fission occurring at the temperature used. Temperatures and pressures are in the range of 390°-440°C and 100-125 psig, respectively. Increasing the mole ratio of propane to nitric acid increases the yield of nitropropanes. Typical product composition for 25 1 propane/acid ratio is ... 

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