GAS-SOLID REACTIONS WITH NITROGEN-DIOXIDE

Numerous gas/solid reactions of nitrogen dioxide with organic substrates are investigated preparatively and mechanistically. Gaseous NO2 reacts with crystalline stable free radicals (nitroxyls 1, verdazyl 6) by electron transfer. The nitrite ions formed are irreversibly oxidized by NO2 via oxygen atom transfer. Solid cation nitrates are formed quantitatively. Thione bonds of thiohydantoins 8 are transformed to carbonyl bonds with formation of sulfur and NO presumably via nitrites as intermediates. Hydantoin 13 oxygenates at its free 5-methylene group via C-H abstraction and nitrite or it undergoes N-1 nitration via N-H abstraction depending on the conditions. Both reactions proceed quantitatively. 1,3-Oxazolidin-2-one (15) gives N-nitration and N-nitrosation with the NO produced. Nonenolized crystalline barbituric acids 17 are quantitatively nitrated (C-N bond formation with radicals) at their methylene groups. 4-Hydroxybenzaldehyde (19) and vanilline (22) give quantitative aromatic nitration (C-N bond formation with arenes) without melting. All possible regioisomers are formed. Solid 9-methylanthracene (26) gives a quantitative yield of its 10-nitro derivative 27. Crystalline anthracene (28) and gaseous NO2 yield 3 primary products 29 (cis; trans) and the new dimeric product 30 as well as the stable secondary products 31 and 32. The gas/solid tetranitration of tetraphenylethylene (33) is severely hindered by the water of reaction. However, a 95% yield of pure tetrakis(p-nitrophenyl)ethylene is obtained if the drying agent MgSO4 . 2H(2)O is admired and the product 34 extracted. The gas/solid procedures avoid solvents and fuming nitric acid. They give pure products without necessity for recrystallization in most cases and they avoid wastes. Atomic force microscopy (AFM) measurements on prominent faces of single crystals of 1a, 11a, 28, and 33 reveal phase rebuildings with well-directed long-range molecular transports. Nanoliquids were only present on (110) of 28. The characteristic AFM features are correlated with known X-ray crystal structure data and compared with previous results. The shape of the features depends on the molecular packing in the crystal bulk and on the molecular shapes. Molecular interpretations of the AFM features are given.