[3251-23-8] · CuN2O6 · Copper(II) Nitrate-K10 Bentonite Clay · (MW 187.55)
Alternate Name: claycop.
Solubility: insol water and organic solvents.
Handling, Storage, and Precautions: no loss of activity is observed on standing for several weeks.1a Nitrates are potentially dangerous compounds. Scaling-up should be attempted only after appropriate safety tests. Avoid breathing dust; use in a fume hood. Store below 50 °C.
Claycop as a source of NO+ ion effects the coupling of thiophenol into diphenyl disulfide (eq 1).1a This quantitative reaction serves as a reactivity test (see also Iron(III) Nitrate-K10 Montmorillonite Clay (clayfen)).6
Thioacetals are used in organic syntheses for protection or umpolung of the reactivity of a carbonyl group.7 S,S-Diethyl acetals, 1,3-dithianes, and 1,3-dithiolanes (eq 2) are cleaved into aldehydes and ketones by claycop under very mild conditions.2 No external source of water is needed; it is provided by the internal structure of the clay. Although a wide variety of reagents (e.g. t-BuSNO, Ph3
Claycop has been utilized for the cleavage of selenoacetals (eq 3),9 but higher yields can be obtained by the use of clayfen (97%)9 or Copper(II) Chloride-Copper(II) Oxide (99%).10
Thiocarbonyl to carbonyl transformation is promoted by NO+ ion (see also Nitrosonium Tetrafluoroborate).11 Clayfen gives excellent results with aromatic substrates while claycop is less reactive and is limited in use to aliphatics (eq 4).12
1,4-Dihydropyridinedicarboxylates are aromatized smoothly at ambient temperature by claycop (eq 5).3 4-Arylpyridines are formed in 80-93% yields. Sonication greatly reduces the reaction time (from hours to 5-10 min).13a Pyridinium Chlorochromate adsorbed on Montmorillonite K10 exhibits similar activity.13b
Halobenzenes, deactivated for electrophilic aromatic substitution, are mononitrated by means of claycop in the presence of Ac2O.4 The proportion of para product is the largest for fluorobenzene (eq 6) and the smallest for iodobenzene. The para preference can be further improved: lowering the temperature to 0 °C increases the para:ortho ratio to 35:1. The para preference is modest under classical nitration procedures (e.g. 10.8:1 by Nitronium Tetrafluoroborate/sulfolane).14
Quantitative mononitration of toluene can be performed by claycop under Menke conditions with high para selectivity (eq 7).5 Acetyl nitrate is the likely nitrating species. The process is catalytic using Nitric Acid as reagent.5c Similar results are achieved by Benzoyl Nitrate-zeolite catalyst.15 Highly selective nitrating agents are obtained by complexation of NO2BF4 or Bu4NNO3 with crown ethers.16a,b
For further discussion on the use of clays in synthesis, see Montmorillonite K10.
Chinoin Pharmaceutical and Chemical Works, Budapest, Hungary