Protonolysis is the cleavage of a chemical bond by acids. Many examples are found in organometallic chemistry since the reaction requires polar Mδ+-Rδ- bonds, where δ+ and δ- signify partial positive and negative charges associated with the bonding atoms. When compounds containing these bonds are treated with acid (HX), these bonds cleave:
- M-R + HX → M-X + H-R
Hydrolysis (X
− = OH
−) is a special case of protonolysis. Compounds susceptible to hydrolysis often undergo protonolysis.
Hydrides
The
borohydride Ion is susceptible to reaction with even weak acids, resulting protonolysis of one or more B-H bonds. Protonolysis of sodium borohydride with
acetic acid gives triacetoxyborohydride:
[Gordon W. Gribble, Ahmed F. Abdel-Magid, "Sodium Triacetoxyborohydride" Encyclopedia of Reagents for Organic Synthesis, 2007, John Wiley & Sons.]
- NaBH4 + 3 HO2CCH3 → NaBH(O2CCH3)3 + 3 H2
Related reactions occur for hydrides of other electropositive elements, e.g. lithium aluminium hydride.
Alkyls
The alkyl derivatives of many metals undergo protonolysis. For the alkyls of very electropositive metals (zinc, magnesium, and lithium), water is sufficiently acidic, in which case the reaction is called hydrolysis. Protonolysis with
Mineral acid is sometimes used to remove organic ligands from a metal center.
[Chu Sun, Masami Okabe, David L. Coffen, Jeffrey Schwartz "Conjugate Addition Of A Vinylzirconium Reagent: 3-(1-octen-1-yl)cyclopentanone".Org. Synth. 1993, 71, 83. .]
Nitrides, phosphides, silicides and related species
Inorganic materials with highly charged anions are often susceptible to protonolysis. Derivatives of nitride (N
3−), phosphides (P
3−), and silicides (Si
4−) hydrolyze to give
ammonia,
phosphine, and
silane. Analogous reactions occur with molecular compounds with M-NR
2, M-PR
2, and M-SiR
3 bonds.
[Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. .]
