Fluoro acidity

Fluoroacetate can also be detected in extracts from the seeds of D. toxicarium (ratsbane). Unlike the South African D. cymosum, the main toxicity of ratsbane seems, however, to be due to a long-chain fluoro acid, which has not yet been thoroughly characterized.3... 

This method is mainly illustrated by the fluorodediazoniation of a-amino acids which provides one of the best accesses to a-fluoro acids. Except for the preparation of /1-fluoroaspartic acid from 2,3-diaminosuccinic acid,304 little work has been performed in anhydrous hydrogen... 

Fluoroheptanoic acid required no more than the usual precautions accorded organic compounds, for it and its precursors have LD50>100 mg /kg in mice The relatively low toxicity of this and other 2-fluoroalkanoic acids is in contrast to the high toxicity of the w-fluoro acids F(CH2)KCOOH with n an odd number (if n = 5, LD50 =1.3 mg./kg in mice).4... 

The solubility of the fluoro acid in water is sufficient to require thorough ether extraction. 

On the pages which follow, general methods are illustrated for the synthesis of a wide variety of classes of organic compounds including acyl isocyanates (from amides and oxalyl chloride p. 16), epoxides (from reductive coupling of aromatic aldehydes by hexamethylphosphorous triamide p. 31), a-fluoro acids (from 1-alkenes p. 37), 0-lactams (from olefins and chlorosulfonyl isocyanate p. 51), 1 y3,5-triketones (from dianions of 1,3-diketones and esters p. 57), sulfinate esters (from disulfides, alcohols, and lead tetraacetate p. 62), carboxylic acids (from carbonylation of alcohols or olefins via carbonium-ion intermediates p. 72), sulfoxides (from sulfides and sodium periodate p. 78), carbazoles... 

Aldehydes. Fluorinated aldehydes are unknown. It has been observed that the reduction of a fluoro acid yields the alcohol directly, and also that the oxidation of a fluoro alcohol does not stop short of the acid.88... 

Ag3F8, silver(III) resides in an electron rich species close in character to [AgF ]. The salt formation Ag(II)[Ag(III)F4]2 fits the known fluoro base properties of AgF2 and the fluoro acid character of AgF3. 

Stronger fluoro acids AsF5, SbF5 and BiF5 (A) are sufficiently good F acceptors to cause AgF3 to enter into solution in aHF first as Ag(III)(solv) and finally as Ag v) with liberation of fluorine. 

Cationic Ag(II) in aHF oxidizes xenon at ordinary temperatures and pressures [11]. As long as there is enough fluoro acid AsF5 present in aHF to generate the cationic blue Ag(II) species that solution will oxidize Xe to XeF2, or its derivatives. 

When all of cationic Ag(II) has been displaced, the oxidation of xenon ceases. Therefore fluoro acid must be supplied to neutralize the XeF2, if oxidation of Xe is to continue ... 

Additional acid ensures that Ag(II) remains in solution as cationic species (i.e. AgF2, which is insoluble in aHF, is not precipitated) and the xenon oxidation continues. Removal of aHF from a solution where additional fluoro acid was not provided for the neutralization of XeF2 gave a mixture of AgF2, Xe2F3AsF6 and [Ag(XeF2)2]AsF6 [39],... 

NiF4 [44] was precipitated from the solution of (Xe2F) 1)2NiF6 [45] or (XeF5)2NiFg [46] in aHF at 208 K by the fluoro acid AsFs or BF3. 

Reaction of excess of fluoro acid with R— or H—NiF3 in aHF give cationic species which are most probably cationic Ni(IV)solv and not cationic Ni(III)SO V. 

The three fluoro-acids HF, HS03F and CF3S03H have proved to be fruitful and essential media for preparation of many compounds of ionic species of transition metals in unusually high or low oxidation states and of cations of non-metallic elements in fractional oxidation states. 

Pure H2SO4 is an extremely viscous liquid, melting at 10.371 °C and boiling with decomposition at about 300°C. It can be manipulated in glass apparatus but, for purposes of inorganic syntheses, it presents experimental problems not associated with the fluoro-acids in that it is difficult to remove from a reaction by distillation because of its high boiling point and, further, decantation and filtration of solids are made very difficult because of its viscosity. 

The shapes of the H0 plots in Fig. 1 reflect, of course, the nature and extent of ionisation processes in the four superacids themselves. The three fluoro-acids undergo simple autoprotolysis which can be represented as ... 

The simple autoprotolysis reactions for the three fluoro-acids contrast markedly with the complexity of ionisation processes in H2S04 which include the self-ionisation equilibria in Eqns (2) and (3) ... 

If H2S04 were to be used as a superacidic medium in which tight control of acidity or basicity was necessary, the interrelated ionic equilibria, complicated still further by the formation of ionic species resulting from the addition of reactants, could lead to a buffered system which would militate against adequate acidity/basicity control. However the simple and relatively small autoprotolyses allow quite precise control of levels of acidity or basicity in the three fluoro-acids, as will be discussed in Sec. 11.2. 

The low freezing points of the fluoro-acids have been used to advantage to obtain vastly improved resolution of NMR spectra resulting from the slowing of exchange reactions at temperatures near the freezing point. It will be shown in Sec. 11.3.5 that use of reduced reaction temperatures can allow successful synthesis of compounds expected to be thermally unstable at higher reaction temperatures or even at ambient temperature. 

As Fig. 1 shows, CF3SO3H, HSO3F and HF provide progressively more acidic media than H2S04, particularly as their acidity is increased by addition of Lewis acids. Control of acidity and basicity is far superior, as will be indicated in Secs 11.2 and 11.3. Also, it will be shown in Secs. 11.3.4 and 11.3.5 that highly reduced or oxidised species which would disproportionate in H20 or reduce it to H2 or oxidise it to 02 can be generated and form stable solutions in the fluoro-acids, particularly HF. 

It will be seen in the examples given in Sec. 11.3 that a much broader range of binary and complex compounds in a wide range of oxidation states has been synthesised in HF than in the other two fluoro-acids. However, it can be assumed that, with appropriate modifications and with account taken of the differences in acidity levels of the three acids, many of the strategies developed for synthesis of compounds... 

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