The Pinner Reaction refers to the acid-catalyzed reaction of nitriles with alcohols to form imidate salts (alkyl imidate hydrochlorides), known as Pinner salts, which can further react with water or ammonia to yield esters or amidines. This reaction was first discovered in 1877 by Adolf Pinner and is named after him. It remains a classical and reliable method for synthesizing various amidines, and has been widely applied in organic synthesis.

• Reagents: Hydrogen chloride, water, ammonia

• Reactants: Nitrile, alcohol

• Products: Ester or amidine

Experimental Tips:

• The reaction is typically carried out in anhydrous solvents such as benzene or dioxane.

• Temperature control is crucial. Imidate hydrochlorides are thermodynamically unstable, and low temperatures help prevent their rearrangement into amides or alkyl chlorides.

• The term Pinner reaction specifically refers to the acid-catalyzed process, but base-catalyzed versions also exist. These two methods are often complementary; for instance, some nitriles that are unreactive under acidic conditions can undergo conversion under basic catalysis. The choice of method generally depends on the electron-rich or electron-deficient nature of the nitrile.

• Pinner salts themselves are highly reactive intermediates, and can undergo further nucleophilic additions to produce a variety of useful compounds. For example, they can react with:

  • Alcohols to give orthoesters

  • Hydrogen sulfide to form thioesters

Reaction Mechanism

(Include SN1/SN2 steps and proton transfers if needed – let me know if you'd like a mechanism diagram.)

Original Literature

• A. Pinner, F. Klein; Berichte der deutschen chemischen Gesellschaft 1887, 10(2), 1889–1897.

Key References:

• One-Pot Synthesis of 3-Carboxycoumarins via Consecutive Knoevenagel and Pinner Reactions in Water. Synthesis 2003, 15(31), 2331–2334.

• The Synthesis of a Selective PDE4/TNFα Inhibitor. Org. Process Res. Dev. 2001, 5(6), 587–592.