Strong carbon-hydrogen acids

Two structures are possible for the interaction of aromatic hydrocarbons with acids.270 In the a-structures a covalent bond is established between the acidic reagent and a particular carbon atom of the benzene ring. The a-structures are essentially classical carbonium ions. In the -structures a non-classical bond is established, not to any particular atom, but to the -electron cloud in general. It is quite likely that both types of structure are represented by actual examples. Thus m-xylene interacts more strongly with hydrogen chloride than does o-xylene, but the difference between the two hydrocarbons is much more pronounced when their interactions with a boron trifluoride-hydrogen fluoride mixture are compared. This is readily understandable... 

The hydrogen (known as an a-hydrogen) bonded to a carbon adjacent to a carbonyl carbon (called an a-carbon) is acidic enough to be removed by a strong base, usually NaOH, to form an enolate anion. The enolate anion adds to the carbonyl carbon of a second molecule of aldehyde or ketone via nucleophilic addition reaction. 

Acids and bases react according to the rules in Section 8.3, but their reactions are so common that further details need to be learned. The double substitution reaction of an acid with a base is called a neutralization reaction. The products are water and a salt. Strong acids react with water completely to form ions, and weak acids react with water only slightly, but both kinds of acids react with bases to form salts. Substances that react with water to form acids or bases are called anhydrides. Acids containing more than one ionizable hydrogen atom can be partially neutralized, forming acid salts. Carbonates and acid carbonates react similarly to bases (Section 8.4). 

Shilov chemistry, developed from 1970, employs [Pt(II)CLt] salts to oxidize alkanes RH to ROH or RCl with modest efficiency. Pt(IV) is an efficient (but economically impractical) primary oxidant that makes the process catalytic. This discovery strongly contributed to the continuing activity in CH activation. Periana developed a related and much more efficient system for methane oxidation to methanol using 2,2 -bipyrimidine ligands and sulfuric acid as solvent. In this case, the sulfuric acid is the primary oxidant and the methanol formed is protected by being converted in situ to MeOSOsH, an ester that strongly resists further oxidation. This area is more fully described under the entry Alkane Carbon-Hydrogen Bond Activation. 

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