Base anhydrides

The metallic properties increase down any column and towards the left in any row on the periodic table. One important metallic property is that metal oxides are base anhydrides. A base anhydride will produce a base in water. These are not oxidation-reduction reactions. Many metal oxides are too insoluble for them to produce any significant amount of base. However, most metal oxides, even those that are not soluble in water, will behave as bases to acids. A few metal oxides, and their hydroxides, are amphoteric. Amphoteric means they may behave either as a base or as an acid. Amphoterism is important for aluminum, beryllium, and zinc. Complications occur whenever the oxidation number of the metal exceeds +4 as in the oxides that tend to be acidic. 

Basic oxides, also called base anhydrides, are ionic and are formed by metals on the left side of the periodic table. Water-soluble basic oxides, such as Na20, dissolve by reacting with water to produce OH- ions ... 

Poly(dimercuryimmonium hydroxide) ( Millon s base anhydride ) [12529-66-7]... 

Carbonates, acid salts, and acid and base anhydrides are similar to acids and bases in some of their chemical properties. 

Oxides of Group I and II metals are base anhydrides, obtained by removing water from the corresponding hydroxides. Calcium oxide, CaO, is the base anhydride of calcium hydroxide, Ca(OH)2- The removal of water from Ca(OH)2 is the reverse of the addition of water to the oxide ... 

The base anhydride of NaOH is Na20. Oxides of metals in the middle groups of the periodic table (III through V) lie on the border between ionic and covalent behavior and are frequently amphoteric. An example is aluminum oxide (AI2O3), which dissolves to only a limited extent in water but much more readily in either acids or bases ... 

Although oxoacids and hydroxides are Arrhenius acids and bases (they release or OYi (aq) into aqueous solution), acid and base anhydrides do not fall into this classification because they contain neither nor OH. Acid anhydrides are acids in the Lewis sense, (they accept electron pairs), and base anhydrides are bases in the Lewis sense, (their ions donate electron pairs). The reaction between an acid anhydride and a base anhydride is then a Lewis acid-base reaction. An example of such a reaction is... 

Here, the Lewis base CaO donates an electron pair (one of the lone pairs of the oxygen atom) to the Lewis acid (CO2) to form a coordinate covalent bond in the CO ion. Similar Lewis acid-base reactions can be written for other acid-base anhydride pairs. Sulfur trioxide, for example, reacts with metal oxides to form sulfates ... 

Identify each of the following oxides as an acid or base anhydride. Write the chemical formula and give the name of the acid or base formed upon reaction with water. 

Submicroscopic Behavior of Bases Other Acids and Bases Anhydrides The Macroscopic-Submicroscopic Acid-Base Connection MiniLab 14.1 What do acids do ... 

Acid chlorides are useful precursors to anhydrides, including both symmetrical and mixed (unsymmetrical) anhydrides. In one experiment, heptanoyl chloride (50) reacted with heptanoic acid (51), with benzene as a solvent and in the presence of pyridine (53), to give the symmetrical heptanoic anhydride (53) in 83% isolated yield. Unsymmetrical anhydrides are prepared by choosing which half of the anhydride comes from the acid chloride and which comes from the carboxylic acid. This choice allows one to control formation of the mixed anhydride. If heptanoyl chloride (50) and butanoic acid (7) react in the presence of triethylamine as the base, anhydride 54 is formed. Anhydride 54 can also be prepared by the reaction of butanoyl chloride with hexanoic acid, but the easiest to obtain and cheapest combination is usually used. 

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