The Oxidation Of(Perhydroxyl)Cucurbituril And Their Nitration/Nitrolysis

Cucurbit[6]uril(CB[6]) is a cage-like macrocyclic compound composed of 6 units of glycoluril linked by 12 methylene bridges. It is a highly symmetrically rigid and very stable molecule. They have been used in many fields such as drug delivery, supramolecular polymers, molecular machines and catalytic reaction. In recent years, many researchers pay more attentions on cucurbituril. There are two major defects on the studies of cucurbituril, one is relative lower solubility of cucurbituril and another one is that it is difficult to get cucurbituril derivatives directly. Based on the structural characteristics of cucurbituril composed of urea, bridging methylene, the waist methenyl, and hydrolysis of urea carbonyl and amine nitration, functionalization of sp3 C-H bond, cucurbituril maybe be derivatived, so the two above shortcomings of cucurbituril would be improved. Supported by the 086 project, this paper will study the oxidation and nitration or nitrolysis of cucurbituril. The specific conclusions and innovative achievements are shown as follows:(1) The solubility of cucurbit[n]uril(n = 5, 6, 7, 8) in pure water and different concentration of hydrochloric acid aqueous solution were first investigated between 273.15 K and 323.15 K at atmospheric pressure by using the UV-vis spectrophotometer method. The solubility of CB[n] increased with the gradually increase of temperature, but the increase rate was not the same. The solubilities of CB[6] and CB[8] were increased with the increasing concentration of acid, and the solubility of CB[7] was changed complicatedly with the changing concentration of acid. The solubility of CB[5] in pure water was lower than that in hydrochloric acid aqueous solution when the temperature was below room temperature. It should be worth noting that the solubility in water was higher than that in hydrochloric acid aqueous solution when the temperature was above temperature, this new phenomenon will be benefit for the purification of CB[5].(2) The perhydroxycucurbituril was prepared from cucurbituril with the persulfate as oxidant other than HNO3, H2O2, O2. The improved condition was that the reaction solution was heated to 70 oC to make cucurbituril dissolve and then the solution was cooled to 50 oC. The optimal parameters were that the amount of oxidant was 1.2 times of the equivalent of the waist C-H, the reaction time was 16 h under 50 oC. The separation and purification of persulfate oxidation product of cucurbituril were improved as follow, the precipitation of crude product was from dilution solution of the reaction mixture by acetone, then the solid was soluted in dimethyl sulfoxide and the solution was mixed with acetone to precipitate hydroxycucurbituril.In the studies on the improvement of perhydroxycucurbituril synthetic conditions, oxalic acid was obtained by the deep oxidation from cucurbituril(CB[5], CB[6], CB[7], CB[8]) and hydroxyl derivatives, and this is the first time to discover that both cucurbituril and its hydroxyl derivatives could be collapsed into small molecular compound. The oxalic acid was characterized by IR, MS, NMR, and confirmed by single crystal X-ray diffraction.(3) Perhydroxycucurbituril was nitrated by a series of nitric reagents such as HNO3, HNO3-H2SO4, HNO3-Ac2 O, NO2+BF4-, etc. A yellow acicular solid, which had the detonation characteristic, was afforded from the nitration of perhydroxycucurbit [6]uril in the mixture of nitric acid and acetic anhydride, and its structure was characterized by IR, MS, and single crystal X-ray diffraction to give nitroform. Nitroform was also obtained by the nitration of other cucurbiturils and perhydroxycucurbituril with HNO3-Ac2 O, and this is the first time to discover that nitroform was provided by the nitration of cucurbituril and perhydroxycucurbituril. The nitrolysis of isotopic labeled CB[n] showed that the carbon atom of nitroform was originated from the waist methylene group. It’s amazing to find that the Na atom of nitroformate is coordinated with eight O atoms of five different nitroform molecular, the coordination of two nitro is equivalent of each nitroform, and the coordination of another nitro is different. Such coordination makes the crystal structure of nitroform sodium salt have optical rotation, and the three-dimensional structure of nitroform carbanion is plane rather than tetrahedral configuration(general configuration of negative carbon ion).In addition, acetic anhydride-nitric acid mixture was replaced by trifluoroacetic anhydride(TFAA)-nitric acid for the nitration of perhydroxycucurbituril, unexpectedly TFAA was decomposed into CF3 OK, and when using NO2+BF4-, a six-membered ring material with nitro groups was obtained.