Preparation with Olah

Dinitration to obtain 1,2,4-fluorodinitrobenzene was described by Holleman and Beekman [47] who nitrated p- fluoronitrobenzene. Zahn and A. Wurz [48] prepared the same dinitrocompound by nitrating fluorobenzene. 1,2,4,6-Fluorotrini-trobenzene (picryl fluoride) was prepared by Olah, Pavlath, J. Kuhn and Varsanyi [49] by acting on 1,2,4-fluorodinitrobenzene with a nitrating mixture composed of fuming nitric acid and 60% oleum. The yield was 36% of theoretical. 

Glycosylfluorides. The anomeric hydroxyl or acetoxy group of monosaccharides is converted into a fluoro group by reaction with Olah s reagent in 70-90% yield. This reaction is useful for preparation of the thermodynamically more stable P-glycosyl fluoride (p/a >95 5). 

Influence of the Catalyst. Several different types of aromatic reactions are catalyzed by Lewis acids, including alkylation, polymerization, isomerization, acylation, and halogenation. The dependence of these reactions on various Lewis acids is shown in Table 12.11. This table shows a few common Lewis acids and the type of reaction(s) for which each is best suited. The relative strength of Lewis acids was discussed in Section 2.3. Olah gives a comprehensive list of Lewis acid catalysts, and includes several typical synthetic applications. Metal alkyl catalysts are also effective catalysts, but the aromatic substrate is usually converted to a mono-, di-, or trialkyl derivative. Both metal halides and their alkyl derivatives are effective Friedel-Crafts catalysts, as shown in Table 12.11,m as are common inorganic and organic acids. Triflate derivatives are trifluorosulfonate ester (—S02CF3 OTf) can be prepared with various metal counterions. Triflates are very effective catalyst in Friedel Crafts reactions. Some of the more common catalysts are B(OTf)3, Al(OTf)3, and Ga(OTf)3.ll3... 

Bausch J W, Prakash G K S, Olah G A, Tse D S, Lorents D C, Bae Y K and Malhotra R 1991 Considered novel aromatic systems. 11. Diamagnetic polyanions of the Cgg and C g fullerenes. preparation, 13-C and 7-Li NMR spectroscopic observation, and alkylation with methyliodide to polymethylated fullerenes J. Am. 

Olah s original preparative nitrations were carried out with mixtures of the aromatic compound and nitronium salt alone or in ether, and later with sulpholan as the solvent. High yields of nitro-compounds were obtained from a wide range of aromatic compounds, and the anhydrous conditions have obvious advantages when functional groups such as cyano, alkoxycarbonyl, or halogenocarbonyl are present. The presence of basic fimctions raises difficulties with pyridine no C-nitration occurs, i-nitropyridinium being formed. ... 

Deng, Y., Wu, J., Lloyd, T.L., Chi, C.L., Olah, T.V., Unger, S.E. (2002). High-speed gradient parallel liquid chromatography/tandem mass spectrometry with fully automated sample preparation for hioanalysis 30 seconds per sample from plasma. Rapid Commun. Mass Spectrom. 16, 1116-1123. 

Our success in super-stabilization of cation 6 led us to the preparation of a higher homologue, that is, cyclooctatetraene (COT), fully annelated with BCO units 9 (9). As compared with a large number of studies on its radical anion or dianions, the studies on the cationic species of COT have been quite limited. There have been only one study by Olah and Paquette on the substituted COT dication (70), which is a typical 6n Hiickel aromatic system, and few sporadic studies on radical cations, which involve indirect spectral observations, such as electronic spectra in Freon matrix at low temperature (77,72) and constant-flow ESR study (13). 

Carbocations having more than four cationic centers are rare species, and very few have been isolated as isolable salts. A tetrahedrally-arrayed tetracation, which was stable only at low temperature was generated by G. A. Olah et al. in 1995 (22). Recently, R. Rathore et al. prepared isolable tetra- and hexatrityl cations utilizing tetraphenylmethane and hexaphenylbenzene as platforms (25). Tetracation 254 is one of the new multi-charged methylium compounds with considerable high stability. 

Olah et al. (1979) reinvestigated the preparation of [47] (and some alkyl and aryl substituted analogues) from the superacid treatment of alcohol [54] or chloride [55], In contrast with earlier studies, the alcohol [54] clearly gave the desired trishomocyclopropenyl cation [47] and not the previously observed cyclopentyl ion [56], Olah et al. (1979) attributed this difference to the highly purified (freshly distilled) SbF5 used in their experiments. These new data and the 13C NMR spectrum of [47] provide strong support for its classification as a trishomoaromatic. 

Materials. A series of a,to-bis(hydroxyphenyl)PSU oligomers with different molecular weights were synthesized and characterized as was previously reported (12). Two samples of PPO (one from Aldrich and one from General Electric Co.) were both purified by precipitation from chloroform solution into methanol. A commercial sample (Dow Chemical) of an isomeric mixture of chloromethylstyrenes (C1MS, 40% para, 60% meta) was used as received. 1-Chloromethoxy-4-chlorobu-tane (CMCB) was prepared according to a procedure developed by Olah et al. (14) and modified by Daly et al. (15), i.e., from paraformaldehyde, tetrahydrofuran and anhydrous HC1. 

C. L. Olah, T. V. et al. High-speed gradient parallel liquid chromatography/tandem mass spectrometry with fully automated sample preparation for bioanalysis ... 

Olah and co-workers ° conducted a comprehensive study into the use of N-nitropyridinium salts for nitration. Such salts are easily prepared from the slow addition of the appropriate heterocyclic base to an equimolar suspension of nitronium tetrafluoroborate in acetonitrile. Olah studied the effect on nitration of changing both the structure of the heterocyclic base and the counter ion. Three of these salts (20, 21, 22) illustrated above have been synthesized and used for the 0-nitration of alcohols with success. Transfer nitrations with Al-nitropyridinium salts are particularly useful for the preparation of nitrate esters from acid-sensitive alcohols and polyols because conditions are essentially neutral. 

Olah and Lin reported obtaining pure TNB (2) in 50 % yield from the nitration of m-dinitrobenzene (32) with nitronium tetrafluoroborate in fluorosulfuric acid at 150 °C higher yields of TNB can be obtained by reducing reaction time but the product then contains some unreacted m-dinitrobenzene. A solution of dinitrogen pentoxide in sulfuric acid at 160 °C is also reported to effect the conversion of m-dinitrobenzene to TNB. TNB is rarely prepared via these routes and is best obtained from TNT via an indirect route (Section 4.9). 

A convenient method for the preparation of nitronium tetrafluoroborate involves treating a mixture of absolute nitric acid or an alkyl nitrate " with anhydrous hydrogen fluoride and an excess of boron trifluoride. Pure nitronium triflate can be synthesized by treating triflic anhydride or triflic acid with dinitrogen pentoxide in an inert solvent. Other methods for nitronium salt synthesis are discussed by Olah. ... 

---