Weak acids reaction with hydroxide

A base is any material that produces hydroxide ions when it is dissolved in water. The words alkaline, basic, and caustic are often used synonymously. Common bases include sodium hydroxide (lye), potassium hydroxide (potash lye), and calcium hydroxide (slaked lime). The concepts of strong versus weak bases, and concentrated versus dilute bases are exactly analogous to those for acids. Strong bases such as sodium hydroxide dissociate completely while weak bases such as the amines dissociate only partially. As with acids, bases can be either inorganic or organic. Typical reactions of bases include neutralization of acids, reaction with metals, and reaction with salts ... 

The fact that part of the nonbasic fractions of the asphaltene or preasphaltene samples could be dissolved in aqueous sodium hydroxide was surprising, for when untreated samples are extracted with aqueous base, almost nothing is removed. Removal of the nitrogen bases evidently frees the acidic components for reaction with hydroxide, even though the bases are only weakly basic and should not be able to compete with hydroxide ion for the acidic components. Presumably this is a question of wetting, contact, or occlusion. 

BORIC ACID (10043-35-3) BH3O3 Aqueous boric acid is a weak acid incompatible with alkali carbonates hydroxides strong reducing agents, including metal hydrides, nitrides, sulfides, and alkali metals. Violent reaction with potassium metal. Contact with acetic anhydride forms a heat-sensitive explosive. On small fires, use water fog. 

The benzyl group has been widely used for the protection of hydroxyl functions in carbohydrate and nucleotide chemistry (C.M. McCloskey, 1957 C.B. Reese, 1965 B.E. Griffin, 1966). A common benzylation procedure involves heating with neat benzyl chloride and strong bases. A milder procedure is the reaction in DMF solution at room temperatiue with the aid of silver oxide (E. Reinefeld, 1971). Benzyl ethers are not affected by hydroxides and are stable towards oxidants (e.g. periodate, lead tetraacetate), LiAIH, amd weak acids. They are, however, readily cleaved in neutral solution at room temperature by palladium-catalyzed bydrogenolysis (S. Tejima, 1963) or by sodium in liquid ammonia or alcohols (E.J. Rcist, 1964). 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cycHzed mbber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenoHc stmcture renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxyHc acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubiHty is controUed by chemical and polarity differences rather than molecular size. 

Iron Reduction. The reduction of nitrophenols with iron filings or turnings takes place in weakly acidic solution or suspension (30). The aminophenol formed is converted to the water soluble sodium aminopheno1 ate by adding sodium hydroxide before the iron-iron oxide sludge is separated from the reaction mixture (31). Adjustment of the solution pH leads to the precipitation of aminophenols, a procedure performed in the absence of air because the salts are very susceptible to oxidation in aqueous solution. 

Anhydrous gaseous or Hquid hydrogen sulfide is practically nonacidic, but aqueous solutions are weakly acid. The for the first hydrogen is 9.1 X 10 at 18°C for the second, is 1.2 x 10 . Reaction of hydrogen sulfide with one molar equivalent of sodium hydroxide gives sodium hydrosulfide with two molar equivalents of sodium hydroxide, sodium sulfide forms. Hydrogen sulfide reacts with sodium carbonate to produce sodium hydrosulfide... 

This reaction is useful in the preparation of anionic derivatives from the chlorides when the nucleophilic displacement route is unsatisfactory. Even weak acids, eg, phenols, mercaptans, and cycHc nitrogen compounds, can be made to undergo reaction with triorganotin hydroxides or bisoxides if the water of reaction is removed a2eotropicaHy as it forms. 

A typical weak acid-strong base titration is that of acetic acid with sodium hydroxide. The net ionic equation for the reaction is... 

Neutralisation reactions, or addimetry and alkalimetry. These include the titration of free bases, or those formed from salts of weak acids by hydrolysis, with a standard acid (addimetry), and the titration of free acids, or those formed by the hydrolysis of salts of weak bases, with a standard base (alkalimetry). The reactions involve the combination of hydrogen and hydroxide ions to form water. 

C04-0032. Carbonic acid, H2 CO3 (molecular model shown below), is a weak oxoacid that forms when carbon dioxide dissolves in water. Carbonic acid contains two acidic hydrogen atoms. Write the net ionic reaction that occurs when carbonic acid reacts with an excess of hydroxide ions. Draw a molecular picture of the process. 

As long as the buffer solution contains acetic acid as a major species, a small amount of hydroxide ion added to the solution will be neutralized completely. Figure 18-1 shows two hydroxide ions added to a portion of a buffer solution. When a hydroxide ion collides with a molecule of weak acid, proton transfer forms a water molecule and the conjugate base of the weak acid. As long as there are more weak acid molecules in the solution than the number of added hydroxide ions, the proton transfer reaction goes virtually to completion. Weak acid molecules change into conjugate base anions as they mop up added hydroxide. 

Identify the major species in solution by assigning each of the points to one of the four characteristic regions of the titration curve. In the titration reaction, hydroxide ions react with molecules of weak acid ... 

In a weak acid or base, the backwards reaction (where ions join to form the acid or base) occurs more often than it does in a strong acid or base. Therefore, with a weak acid or base, some hydrogen and hydroxide ions are released, but there are many more molecules of intact acid or base than there would be with a strong acid or base. Most acids and bases are weak. They do not completely break down in water. 

Acetylene is sufficiently acidic to allow application of the gas-phase proton transfer equilibrium method described in equation l7. For ethylene, the equilibrium constant was determined from the kinetics of reaction in both directions with NH2-8. Since the acidity of ammonia is known accurately, that of ethylene can be determined. This method actually gives A f/ acid at the temperature of the measurement. Use of known entropies allows the calculation of A//ac d from AG = AH — TAS. The value of A//acij found for ethylene is 409.4 0.6 kcal mol 1. But hydrocarbons in general, and ethylene in particular, are so weakly acidic that such equilibria are generally not observable. From net proton transfers that are observed it is possible sometimes to put limits on the acidity range. Thus, ethylene is not deprotonated by hydroxide ion whereas allene and propene are9 consequently, ethylene is less acidic than water and allene and propene (undoubtedly the allylic proton) are more acidic. Unfortunately, the acidity of no other alkene is known as precisely as that of ethylene. 

Alternatively, some conclusions can be derived from the relative reactivities of car-banions. For example, DePuy and colleagues13 made use of a clever method involving reactions of silanes with hydroxide ion to deduce acidities of such weak acids as alkanes and ethylene. The silane reacts with hydroxide ion to form a pentacoordinate anion that ejects a carbanion held as a complex with the hydroxysilane rapid proton transfer gives the stable silanoxide ion and the carbon acid (equation 5). 

In the process of a weak acid or weak base neutralization titration, a mixture of a conjugate acid-base pair exists in the reaction flask in the time period of the experiment leading up to the inflection point. For example, during the titration of acetic acid with sodium hydroxide, a mixture of acetic acid and acetate ion exists in the reaction flask prior to the inflection point. In that portion of the titration curve, the pH of the solution does not change appreciably, even upon the addition of more sodium hydroxide. Thus this solution is a buffer solution, as we defined it at the beginning of this section. 

Each of the above liquid residues was tritrated against standard sodium hydroxide, using phenolphthalein as indicator. Identical titer values were obtained the same titer value was also given by the original solid residue of unreacted TBTA (0-1). Such an observation of identical titer Values should be expected if the conversion of TBTA, by reaction with sodium chloride, is solj.ly to TBTCl. However, any side reaction leading to TBT hydroxide or TBTO will result in lower titer values since these tin compounds, unlike TBTA or TBTCl cannot be titrated like weak acids. Clearly, the side reactions are not noticeable in these experiments. Hydrolysis is not competitive under the conditions of this study, probably because chloride concentration never drops below 10-1 whereas hydroxide concentration is always below 10 s. (It was noticed that the pH of the aqueous layer in each case had risen from 6.5 to 9.0.)... 

Mono-A-alkylation of the amides occurs under relatively mild liquiddiquid two-phase conditions (Table 5.10), using concentrated aqueous sodium or potassium hydroxide. Under soliddiquid conditions with sodium hydroxide-potassium carbonate or potassium hydroxide, or by using super-saturated aqueous potassium or sodium hydroxide, it is possible to control the reaction to obtain either the mono-or dialkylated derivatives f2-4]. Soliddiquid two-phase conditions also provide the most effective route to mono-AI-alkylalion of weakly acidic aliphatic amides, but it has been suggested that the procedure is not sufficiently selective for the monoalkylation of the more acidic amides [4],... 

If a salt consists of the cation of a strong base and the anion of a weak acid, such as NaCHsCOO, only the anion reacts significantly with water. The reaction produces hydroxide ions. Therefore, the solution will have a pH that is greater than 7. Salts of strong bases and weak acids dissolve in water and form basic solutions. 

The reaction of aminoguanidine bicarbonate (84) with sodium nitrite in the presence of excess acetic acid produces 1,3-ditetrazolyltriazine (89), another nitrogen-rich heterocycle (C2H3N11 = 85 % N) which readily forms explosive metal salts. The reaction of aminoguanidine bicarbonate (84) with sodium nitrite in the presence of mineral acid yields guanyl azide (90), of which, the perchlorate and picrate salts are primary explosives. Guanyl azide (90) reacts with sodium hydroxide to form sodium azide, whereas reaction with weak base or acid forms 5-aminotetrazole. ... 

However, attempts to make an aqueous solution of the base sodium amide would result in the formation of sodium hydroxide and ammonia. The amide ion is a strong base and abstracts a proton from water, a weak acid. The reverse reaction is not favoured, in that hydroxide is a weaker base than the amide ion, and ammonia is a weaker acid than water. Take care with the terminology amide the amide... 

---