basic salt

Examples of basic salt in the following topics:

• Salts that Produce Basic Solutions

  • When dissolved in water, a basic salt yields a solution with pH greater than 7.0.
  • There are several varieties of salts, and in this section we will consider basic salts.
  • What makes a basic salt basic?
  • An example of a basic salt is sodium bicarbonate, NaHCO3.
  • Because it is capable of deprotonating water and yielding a basic solution, sodium bicarbonate is a basic salt.

• Overview of the Acid-Base Properties of Salt

  • As we have discussed, salts can form acidic or basic solutions if their cations and/or anions are hydrolyzable (able to react in water).
  • Basic salts form from the neutralization of a strong base and a weak acid; for instance, the reaction of sodium hydroxide (a strong base) with acetic acid (a weak acid) will yield water and sodium acetate.
  • Sodium acetate is a basic salt; the acetate ion is capable of deprotonating water, thereby raising the solution's pH.
  • Acid salts are the converse of basic salts; they are formed in the neutralization reaction between a strong acid and a weak base.
  • This video examines the hydrolysis of an acid salt, a basic salt, and a salt in which both ions hydrolyze.

• Salts that Produce Acidic Solutions

  • Salts with acidic protons in the cation are most commonly ammonium salts, or organic compounds that contain a protonated amine group.
  • Acid salts can also contain an acidic proton in the anion.
  • From the previous concept, we know that salts containing the bicarbonate ion (HCO3-) are basic, whereas salts containing bisulfate ion (HSO4-) are acidic.
  • We determine whether the hydrolyzable ion is acidic or basic by comparing the Ka and Kb values for the ion; if Ka > Kb, the ion will be acidic, whereas if Kb > Ka, the ion will be basic.
  • Anilinium chloride is an example of an acid salt.

• Synthesis of Amino Acids

  • A common method of resolving racemates is by diastereomeric salt formation with a pure chiral acid or base.
  • In the initial display, the carboxylic acid function contributes to diastereomeric salt formation.
  • The racemic amino acid is first converted to a benzamide derivative to remove the basic character of the amino group.
  • Next, an ammonium salt is formed by combining the carboxylic acid with an optically pure amine, such as brucine (a relative of strychnine).
  • Since amino acids are amphoteric, resolution could also be achieved by using the basic character of the amine function.

• Basic and Amphoteric Hydroxides

  • Now we will examine amphoteric hydroxides—that is, hydroxide salts that can act as either an acid or a base, depending on reaction conditions.
  • This is a classic acid-base neutralization reaction: the HCl completely protonates all three hydroxides per mole of Al(OH)3, yielding pure water and the salt AlCl3.
  • From what we know about the basic properties of hydroxides so far, this is exactly as we would expect—so how can a hydroxide act as an acid?
  • We will now consider aluminum hydroxide's reaction in a strongly basic solution:
  • In a basic solution, it forms a bond with an OH- ion, pulling it out of solution and lowering the solution's pH.

• Substitution and Elimination Reactions of Amines

  • Elimination reactions of 4º-ammonium salts are termed Hofmann eliminations.
  • Since the counter anion in most 4º-ammonium salts is halide, this is often replaced by the more basic hydroxide ion through reaction with silver hydroxide (or silver oxide).
  • The resulting hydroxide salt must then be heated (100 - 200 ºC) to effect the E2-like elimination of a 3º-amine.
  • First, it generates a 4º-ammonium halide salt in a manner different from exhaustive methylation.
  • Second, this salt is not converted to its hydroxide analog prior to elimination.

• Carbon Oxides and Carbonates

  • The most basic oxocarbons are carbon monoxide and carbon dioxide.
  • The salt of carbonic acids are called carbonates and are characterized by the carbonate ion, CO32-.
  • In strongly basic conditions, the carbonate ion predominates, while in weakly basic conditions, the bicarbonate ion predominates.
  • Sodium carbonate is basic when dissolved in water (meaning it results in a basic solution upon dissolution), and sodium bicarbonate is weakly basic.
  • Although the carbonate salts of most metals are insoluble in water, this is not true of the bicarbonate salts.

• Nucleophilicity of Sulfur Compounds

  • Although the basicity of ethers is roughly a hundred times greater than that of equivalent sulfides, the nucleophilicity of sulfur is much greater than that of oxygen, leading to a number of interesting and useful electrophilic substitutions of sulfur that are not normally observed for oxygen.
  • Sulfides, for example, react with alkyl halides to give ternary sulfonium salts (equation # 1) in the same manner that 3º-amines are alkylated to quaternary ammonium salts.
  • Although equivalent oxonium salts of ethers are known, they are only prepared under extreme conditions, and are exceptionally reactive.
  • Remarkably, sulfoxides (equation # 2), sulfinate salts (# 3) and sulfite anion (# 4) also alkylate on sulfur, despite the partial negative formal charge on oxygen and partial positive charge on sulfur.

• Important Reagent Bases

  • Most base reagents are alkoxide salts, amines or amide salts.
  • Since alcohols are much stronger acids than amines, their conjugate bases are weaker than amide bases, and fill the gap in base strength between amines and amide salts.
  • Its basicity and nucleophilicity may be modified by steric hindrance, as in the case of 2,6-dimethylpyridine (pKa=6.7), or resonance stabilization, as in the case of 4-dimethylaminopyridine (pKa=9.7).
  • An interesting group of neutral, highly basic compounds of nitrogen and phosphorus have been prepared, and are referred to as superbases.

• Salt Formation

  • Because of their enhanced acidity, carboxylic acids react with bases to form ionic salts, as shown in the following equations.
  • In the case of alkali metal hydroxides and simple amines (or ammonia) the resulting salts have pronounced ionic character and are usually soluble in water.
  • Heavy metals such as silver, mercury and lead form salts having more covalent character (3rd example), and the water solubility is reduced, especially for acids composed of four or more carbon atoms.
  • Carboxylic acids and salts having alkyl chains longer than six carbons exhibit unusual behavior in water due to the presence of both hydrophilic (CO2) and hydrophobic (alkyl) regions in the same molecule.