Water with strong bases

Pyrrohdine [123-75-1] (tetrahydropyrrole) (19) is a water-soluble strong base with the usual properties of a secondary amine. An important synthesis of pyrrohdines is the reaction of reduced furans with excess amine or ammonia over an alumina catalyst in the vapor phase at 400°C. However, if labde substituents are present on the tetrahydrofurans, pyrroles may form (30). 

Cyclic carbonates and cyclic boronates have also found considerable use as protective groups. In contrast to most acetals and ketals the carbonates are cleaved with strong base and sterically unencumbered boronates are readily cleaved by water. 

Bicarbonate alkalinity The presence in a solution of hydroxyl (OH-) ions resulting from the hydrolysis of carbonates or bicarbonates. When these salts react with water, a strong base and a weak acid are produced, and the solution is alkaline. 

The two most common elimination reactions arc dehydroUalogenalion—the loss of HX from an alkyl halide—and dehydration—(he loss of water from an alcohol. Dehydrohalogenation usually occurs by reaction of an alkyl halide with strong base such as potassium hydroxide. For example, bromocvclohexane yields cyclohexene when treated with KOH in ethanol solution. 

Discussion. The hydroxides of sodium, potassium, and barium are generally employed for the preparation of solutions of standard alkalis they are water-soluble strong bases. Solutions made from aqueous ammonia are undesirable, because they tend to lose ammonia, especially if the concentration exceeds 0.5M moreover, it is a weak base, and difficulties arise in titrations with weak acids (compare Section 10.15). Sodium hydroxide is most commonly used because of its cheapness. None of these solid hydroxides can be obtained pure, so that a standard solution cannot be prepared by dissolving a known weight in a definite volume of water. Both sodium hydroxide and potassium hydroxide are extremely hygroscopic a certain amount of alkali carbonate and water are always present. Exact results cannot be obtained in the presence of carbonate with some indicators, and it is therefore necessary to discuss methods for the preparation of carbonate-free alkali solutions. For many purposes sodium hydroxide (which contains 1-2 per cent of sodium carbonate) is sufficiently pure. 

The whole range of carboxylic acids and alcohols can be reacted to form esters. They are found in a large number of natural and synthetic scents and perfumes because of their pleasant odor. Many are used as solvents for paints and resins. Esters are converted back into the original acids and alcohols hy reaction with strong bases in water in a process called saponification (soap formation). 

C04-0144. Vitamin C (also called ascorbic acid) is an acid whose formula is HCg H7 Og. When treated with strong base, it undergoes the following reaction HCg H7 0(5 + OH H7 Og + H2 O A pharmacist suspects that the vitamin C tablets received in a recent shipment are not pure. When a single 500.0-mg tablet is dissolved in 200.0 mL of water and titrated with a standard base that is 0.1045 M, it takes 24.45 mL to reach the stoichiometric point. Are the tablets pure If not, what is the mass percentage of impurities (Assume no impurity is either an acid or a base.)... 

C18-0103. When a solution of leucine (an amino acid) in water is titrated with strong base, the pH before titration is 1.85, the pH at the midpoint of the titration is 2.36, and the pH at the stoichiometric point is 6.00. Determine the value of K. for leucine. 

Castaneda Hernandez, H. R. et al Chem. Abs., 1987,107, 78274 Acrylonitrile polymerises violently in contact with strong bases, whether stabilised or unstabilised [1]. Alkaline hydrolysis of acrylonitrile is exothermic and violent, especially when the temperature is above 60° C, the pressure is above atmospheric, and when heating at 60°C is prolonged above 10 mins. Polymerisation does not induce a violent reaction at 40-50°C at a concentration of 3% of sodium hydroxide in water [2],... 

KOH is a water-soluble strong base, not an acid. As a strong base it will react with an acid. Iron(II) hydroxide, Fe(OH)2, is insoluble and will precipitate. 

Siloxane bonds are opened readily with strong bases. Nucleophilic attack at the silicon atoms is involved in the reaction mechanism. Attempts at complete hydrolysis of the siloxane bonds on the surface of Aerosil by Boehm and Schneider 267) met with limited success. Partial hydrolysis was achieved with cold water over long periods, with boiling water in limited time, and by the action of ammoniacal pyrocatechol solutions. However, the number of silanol groups never exceeded 3.3OH/100A. Ashasbeenshownonpage228, avalueof ca. 5OH/100A would be expected from theoretical considerations. 

Carbazole is a weak acid and will form salts with strong bases by loss of the iV-hydrogen. These salts provide the usual means for the introduction of substituents onto the nitrogen atom (see Section II,B). The pK of carbazole is 17.1 (extrapolated value in water) or 19.9 in dimethyl sulfoxide. This... 

Strong acids react with strong bases to form a salt and water Strong bases react with strong acids to form a salt and water... 

In a solvent with weak acidity, the solvent molecule cannot easily release a proton. Thus, the pH region is wider on the basic side than in water some strong bases, whose strengths are leveled in water, are differentiated some very weak acids, which cannot be determined by neutralization titration in water, can be determined. In contrast, in a solvent with strong acidity, a proton is easily released from the solvent molecule. Thus, the pH region is narrow on the basic side strong bases are easily leveled neutralization titrations of very weak acids are impossible. 

Saponification of fats and oils by boiling with strong base yields glycerol and the sodium salts of fatty acids. The latter are soaps. Soaps contain a long carbon chain that is lipophilic and a terminal polar group that is hydrophilic. Soap molecules aggregate in water to form micelles, which help emulsify droplets of oil or grease. 

Nitroethane forms a colorless to oily liquid with a pleasant odor. It has a melting point of -50 Celsius, and a boiling point of 115 Celsius. Nitroethane is only very slightly soluble in water, but miscible in alcohol, and ether. It is also soluble in chloroform. Nitroethane forms explosive salts when treated with strong bases. It can be made by reacting ethyl bromide with sodium nitrite. 

The addition-elimination mechanism for nucleophilic aromatic substitution requires strong electron-withdrawing substituents on the aromatic ring. Under extreme conditions, however, unactivated halobenzenes react with strong bases. For example, a commercial synthesis of phenol (the Dow process ) involves treatment of chlorobenzene with sodium hydroxide and a small amount of water in a pressurized reactor at 350 °C ... 

Reactions (i) to (iv) represent dissociations of acids, reaction (v) is the common reaction, called neutralization , of strong acids with strong bases, reaction (vi) describes the neutralization reaction between acetic acid and ammonia which takes place in the absence of water, reactions (vii) to (ix) represent hydrolysis reactions, while reaction (x), which is the same as reaction (v) but in the opposite direction, describes the dissociation (or, more properly, the autoprotolysis) of water. Some of these reactions will be discussed in more detail in subsequent chapters. 

Weak acids and weak bases react with water to a small extent but they react with strong bases or acids essentially completely ... 

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